Commit | Line | Data |
---|---|---|
a0d0e21e | 1 | =head1 NAME |
d74e8afc | 2 | X<function> |
a0d0e21e LW |
3 | |
4 | perlfunc - Perl builtin functions | |
5 | ||
6 | =head1 DESCRIPTION | |
7 | ||
8 | The functions in this section can serve as terms in an expression. | |
9 | They fall into two major categories: list operators and named unary | |
10 | operators. These differ in their precedence relationship with a | |
11 | following comma. (See the precedence table in L<perlop>.) List | |
12 | operators take more than one argument, while unary operators can never | |
13 | take more than one argument. Thus, a comma terminates the argument of | |
14 | a unary operator, but merely separates the arguments of a list | |
8f1da26d | 15 | operator. A unary operator generally provides scalar context to its |
2b5ab1e7 | 16 | argument, while a list operator may provide either scalar or list |
3b10bc60 | 17 | contexts for its arguments. If it does both, scalar arguments |
18 | come first and list argument follow, and there can only ever | |
19 | be one such list argument. For instance, splice() has three scalar | |
2b5ab1e7 TC |
20 | arguments followed by a list, whereas gethostbyname() has four scalar |
21 | arguments. | |
a0d0e21e LW |
22 | |
23 | In the syntax descriptions that follow, list operators that expect a | |
3b10bc60 | 24 | list (and provide list context for elements of the list) are shown |
a0d0e21e LW |
25 | with LIST as an argument. Such a list may consist of any combination |
26 | of scalar arguments or list values; the list values will be included | |
27 | in the list as if each individual element were interpolated at that | |
28 | point in the list, forming a longer single-dimensional list value. | |
8bdbc703 | 29 | Commas should separate literal elements of the LIST. |
a0d0e21e LW |
30 | |
31 | Any function in the list below may be used either with or without | |
32 | parentheses around its arguments. (The syntax descriptions omit the | |
3b10bc60 | 33 | parentheses.) If you use parentheses, the simple but occasionally |
34 | surprising rule is this: It I<looks> like a function, therefore it I<is> a | |
a0d0e21e | 35 | function, and precedence doesn't matter. Otherwise it's a list |
3b10bc60 | 36 | operator or unary operator, and precedence does matter. Whitespace |
37 | between the function and left parenthesis doesn't count, so sometimes | |
38 | you need to be careful: | |
a0d0e21e | 39 | |
5ed4f2ec | 40 | print 1+2+4; # Prints 7. |
41 | print(1+2) + 4; # Prints 3. | |
42 | print (1+2)+4; # Also prints 3! | |
43 | print +(1+2)+4; # Prints 7. | |
44 | print ((1+2)+4); # Prints 7. | |
a0d0e21e LW |
45 | |
46 | If you run Perl with the B<-w> switch it can warn you about this. For | |
47 | example, the third line above produces: | |
48 | ||
49 | print (...) interpreted as function at - line 1. | |
50 | Useless use of integer addition in void context at - line 1. | |
51 | ||
2b5ab1e7 TC |
52 | A few functions take no arguments at all, and therefore work as neither |
53 | unary nor list operators. These include such functions as C<time> | |
54 | and C<endpwent>. For example, C<time+86_400> always means | |
55 | C<time() + 86_400>. | |
56 | ||
a0d0e21e | 57 | For functions that can be used in either a scalar or list context, |
8f1da26d TC |
58 | nonabortive failure is generally indicated in scalar context by |
59 | returning the undefined value, and in list context by returning the | |
3b10bc60 | 60 | empty list. |
a0d0e21e | 61 | |
5a964f20 TC |
62 | Remember the following important rule: There is B<no rule> that relates |
63 | the behavior of an expression in list context to its behavior in scalar | |
64 | context, or vice versa. It might do two totally different things. | |
80d38338 | 65 | Each operator and function decides which sort of value would be most |
2b5ab1e7 | 66 | appropriate to return in scalar context. Some operators return the |
5a964f20 | 67 | length of the list that would have been returned in list context. Some |
a0d0e21e LW |
68 | operators return the first value in the list. Some operators return the |
69 | last value in the list. Some operators return a count of successful | |
70 | operations. In general, they do what you want, unless you want | |
71 | consistency. | |
d74e8afc | 72 | X<context> |
a0d0e21e | 73 | |
d1be9408 | 74 | A named array in scalar context is quite different from what would at |
5a964f20 TC |
75 | first glance appear to be a list in scalar context. You can't get a list |
76 | like C<(1,2,3)> into being in scalar context, because the compiler knows | |
77 | the context at compile time. It would generate the scalar comma operator | |
78 | there, not the list construction version of the comma. That means it | |
79 | was never a list to start with. | |
80 | ||
3b10bc60 | 81 | In general, functions in Perl that serve as wrappers for system calls ("syscalls") |
5dac7880 | 82 | of the same name (like chown(2), fork(2), closedir(2), etc.) return |
5a964f20 TC |
83 | true when they succeed and C<undef> otherwise, as is usually mentioned |
84 | in the descriptions below. This is different from the C interfaces, | |
5dac7880 | 85 | which return C<-1> on failure. Exceptions to this rule include C<wait>, |
19799a22 | 86 | C<waitpid>, and C<syscall>. System calls also set the special C<$!> |
5a964f20 TC |
87 | variable on failure. Other functions do not, except accidentally. |
88 | ||
88e1f1a2 JV |
89 | Extension modules can also hook into the Perl parser to define new |
90 | kinds of keyword-headed expression. These may look like functions, but | |
91 | may also look completely different. The syntax following the keyword | |
92 | is defined entirely by the extension. If you are an implementor, see | |
93 | L<perlapi/PL_keyword_plugin> for the mechanism. If you are using such | |
94 | a module, see the module's documentation for details of the syntax that | |
95 | it defines. | |
96 | ||
cb1a09d0 | 97 | =head2 Perl Functions by Category |
d74e8afc | 98 | X<function> |
cb1a09d0 AD |
99 | |
100 | Here are Perl's functions (including things that look like | |
5a964f20 | 101 | functions, like some keywords and named operators) |
cb1a09d0 AD |
102 | arranged by category. Some functions appear in more |
103 | than one place. | |
104 | ||
13a2d996 | 105 | =over 4 |
cb1a09d0 AD |
106 | |
107 | =item Functions for SCALARs or strings | |
d74e8afc | 108 | X<scalar> X<string> X<character> |
cb1a09d0 | 109 | |
c17cdb72 NC |
110 | =for Pod::Functions =String |
111 | ||
628253b8 BF |
112 | C<chomp>, C<chop>, C<chr>, C<crypt>, C<fc>, C<hex>, C<index>, C<lc>, |
113 | C<lcfirst>, C<length>, C<oct>, C<ord>, C<pack>, C<q//>, C<qq//>, C<reverse>, | |
945c54fd | 114 | C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///> |
cb1a09d0 | 115 | |
4fe70ef9 NC |
116 | C<fc> is available only if the C<"fc"> feature is enabled or if it is |
117 | prefixed with C<CORE::>. The C<"fc"> feature is enabled automatically | |
3dd9a840 | 118 | with a C<use v5.16> (or higher) declaration in the current scope. |
4fe70ef9 NC |
119 | |
120 | ||
cb1a09d0 | 121 | =item Regular expressions and pattern matching |
d74e8afc | 122 | X<regular expression> X<regex> X<regexp> |
cb1a09d0 | 123 | |
c17cdb72 NC |
124 | =for Pod::Functions =Regexp |
125 | ||
f5fa2679 | 126 | C<m//>, C<pos>, C<qr//>, C<quotemeta>, C<s///>, C<split>, C<study> |
cb1a09d0 AD |
127 | |
128 | =item Numeric functions | |
d74e8afc | 129 | X<numeric> X<number> X<trigonometric> X<trigonometry> |
cb1a09d0 | 130 | |
c17cdb72 NC |
131 | =for Pod::Functions =Math |
132 | ||
22fae026 TM |
133 | C<abs>, C<atan2>, C<cos>, C<exp>, C<hex>, C<int>, C<log>, C<oct>, C<rand>, |
134 | C<sin>, C<sqrt>, C<srand> | |
cb1a09d0 AD |
135 | |
136 | =item Functions for real @ARRAYs | |
d74e8afc | 137 | X<array> |
cb1a09d0 | 138 | |
c17cdb72 NC |
139 | =for Pod::Functions =ARRAY |
140 | ||
a5ce339c | 141 | C<each>, C<keys>, C<pop>, C<push>, C<shift>, C<splice>, C<unshift>, C<values> |
cb1a09d0 AD |
142 | |
143 | =item Functions for list data | |
d74e8afc | 144 | X<list> |
cb1a09d0 | 145 | |
c17cdb72 NC |
146 | =for Pod::Functions =LIST |
147 | ||
1dc8ecb8 | 148 | C<grep>, C<join>, C<map>, C<qw//>, C<reverse>, C<sort>, C<unpack> |
cb1a09d0 AD |
149 | |
150 | =item Functions for real %HASHes | |
d74e8afc | 151 | X<hash> |
cb1a09d0 | 152 | |
c17cdb72 NC |
153 | =for Pod::Functions =HASH |
154 | ||
22fae026 | 155 | C<delete>, C<each>, C<exists>, C<keys>, C<values> |
cb1a09d0 AD |
156 | |
157 | =item Input and output functions | |
d74e8afc | 158 | X<I/O> X<input> X<output> X<dbm> |
cb1a09d0 | 159 | |
c17cdb72 NC |
160 | =for Pod::Functions =I/O |
161 | ||
22fae026 TM |
162 | C<binmode>, C<close>, C<closedir>, C<dbmclose>, C<dbmopen>, C<die>, C<eof>, |
163 | C<fileno>, C<flock>, C<format>, C<getc>, C<print>, C<printf>, C<read>, | |
7c919445 NC |
164 | C<readdir>, C<readline> C<rewinddir>, C<say>, C<seek>, C<seekdir>, C<select>, |
165 | C<syscall>, C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>, | |
166 | C<truncate>, C<warn>, C<write> | |
cb1a09d0 | 167 | |
4fe70ef9 NC |
168 | C<say> is available only if the C<"say"> feature is enabled or if it is |
169 | prefixed with C<CORE::>. The C<"say"> feature is enabled automatically | |
170 | with a C<use v5.10> (or higher) declaration in the current scope. | |
171 | ||
5dac7880 | 172 | =item Functions for fixed-length data or records |
cb1a09d0 | 173 | |
c17cdb72 NC |
174 | =for Pod::Functions =Binary |
175 | ||
7c919445 NC |
176 | C<pack>, C<read>, C<syscall>, C<sysread>, C<sysseek>, C<syswrite>, C<unpack>, |
177 | C<vec> | |
cb1a09d0 AD |
178 | |
179 | =item Functions for filehandles, files, or directories | |
d74e8afc | 180 | X<file> X<filehandle> X<directory> X<pipe> X<link> X<symlink> |
cb1a09d0 | 181 | |
c17cdb72 NC |
182 | =for Pod::Functions =File |
183 | ||
22fae026 | 184 | C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>, |
5ff3f7a4 | 185 | C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>, |
1e278fd9 JH |
186 | C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<sysopen>, |
187 | C<umask>, C<unlink>, C<utime> | |
cb1a09d0 | 188 | |
cf264981 | 189 | =item Keywords related to the control flow of your Perl program |
d74e8afc | 190 | X<control flow> |
cb1a09d0 | 191 | |
c17cdb72 NC |
192 | =for Pod::Functions =Flow |
193 | ||
dba7b065 | 194 | C<break>, C<caller>, C<continue>, C<die>, C<do>, |
7289c5e6 | 195 | C<dump>, C<eval>, C<evalbytes> C<exit>, |
cfa52385 | 196 | C<__FILE__>, C<goto>, C<last>, C<__LINE__>, C<next>, C<__PACKAGE__>, |
17d15541 | 197 | C<redo>, C<return>, C<sub>, C<__SUB__>, C<wantarray> |
84ed0108 | 198 | |
dba7b065 | 199 | C<break> is available only if you enable the experimental C<"switch"> |
7161e5c2 | 200 | feature or use the C<CORE::> prefix. The C<"switch"> feature also enables |
dba7b065 | 201 | the C<default>, C<given> and C<when> statements, which are documented in |
7161e5c2 | 202 | L<perlsyn/"Switch Statements">. The C<"switch"> feature is enabled |
dba7b065 | 203 | automatically with a C<use v5.10> (or higher) declaration in the current |
7161e5c2 | 204 | scope. In Perl v5.14 and earlier, C<continue> required the C<"switch"> |
dba7b065 NC |
205 | feature, like the other keywords. |
206 | ||
e3f68f70 | 207 | C<evalbytes> is only available with the C<"evalbytes"> feature (see |
4fe70ef9 | 208 | L<feature>) or if prefixed with C<CORE::>. C<__SUB__> is only available |
7161e5c2 | 209 | with the C<"current_sub"> feature or if prefixed with C<CORE::>. Both |
4fe70ef9 NC |
210 | the C<"evalbytes"> and C<"current_sub"> features are enabled automatically |
211 | with a C<use v5.16> (or higher) declaration in the current scope. | |
cb1a09d0 | 212 | |
54310121 | 213 | =item Keywords related to scoping |
cb1a09d0 | 214 | |
c17cdb72 NC |
215 | =for Pod::Functions =Namespace |
216 | ||
8f1da26d | 217 | C<caller>, C<import>, C<local>, C<my>, C<our>, C<package>, C<state>, C<use> |
36fb85f3 | 218 | |
4fe70ef9 NC |
219 | C<state> is available only if the C<"state"> feature is enabled or if it is |
220 | prefixed with C<CORE::>. The C<"state"> feature is enabled automatically | |
221 | with a C<use v5.10> (or higher) declaration in the current scope. | |
cb1a09d0 AD |
222 | |
223 | =item Miscellaneous functions | |
224 | ||
c17cdb72 NC |
225 | =for Pod::Functions =Misc |
226 | ||
17d15541 | 227 | C<defined>, C<formline>, C<lock>, C<prototype>, C<reset>, C<scalar>, C<undef> |
cb1a09d0 AD |
228 | |
229 | =item Functions for processes and process groups | |
d74e8afc | 230 | X<process> X<pid> X<process id> |
cb1a09d0 | 231 | |
c17cdb72 NC |
232 | =for Pod::Functions =Process |
233 | ||
22fae026 | 234 | C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>, |
4319b00c FC |
235 | C<pipe>, C<qx//>, C<readpipe>, C<setpgrp>, |
236 | C<setpriority>, C<sleep>, C<system>, | |
22fae026 | 237 | C<times>, C<wait>, C<waitpid> |
cb1a09d0 | 238 | |
3b10bc60 | 239 | =item Keywords related to Perl modules |
d74e8afc | 240 | X<module> |
cb1a09d0 | 241 | |
c17cdb72 NC |
242 | =for Pod::Functions =Modules |
243 | ||
22fae026 | 244 | C<do>, C<import>, C<no>, C<package>, C<require>, C<use> |
cb1a09d0 | 245 | |
353c6505 | 246 | =item Keywords related to classes and object-orientation |
d74e8afc | 247 | X<object> X<class> X<package> |
cb1a09d0 | 248 | |
c17cdb72 NC |
249 | =for Pod::Functions =Objects |
250 | ||
22fae026 TM |
251 | C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>, |
252 | C<untie>, C<use> | |
cb1a09d0 AD |
253 | |
254 | =item Low-level socket functions | |
d74e8afc | 255 | X<socket> X<sock> |
cb1a09d0 | 256 | |
c17cdb72 NC |
257 | =for Pod::Functions =Socket |
258 | ||
22fae026 TM |
259 | C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>, |
260 | C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>, | |
737dd4b4 | 261 | C<socket>, C<socketpair> |
cb1a09d0 AD |
262 | |
263 | =item System V interprocess communication functions | |
d74e8afc | 264 | X<IPC> X<System V> X<semaphore> X<shared memory> X<memory> X<message> |
cb1a09d0 | 265 | |
c17cdb72 NC |
266 | =for Pod::Functions =SysV |
267 | ||
22fae026 TM |
268 | C<msgctl>, C<msgget>, C<msgrcv>, C<msgsnd>, C<semctl>, C<semget>, C<semop>, |
269 | C<shmctl>, C<shmget>, C<shmread>, C<shmwrite> | |
cb1a09d0 AD |
270 | |
271 | =item Fetching user and group info | |
d74e8afc | 272 | X<user> X<group> X<password> X<uid> X<gid> X<passwd> X</etc/passwd> |
cb1a09d0 | 273 | |
c17cdb72 NC |
274 | =for Pod::Functions =User |
275 | ||
22fae026 TM |
276 | C<endgrent>, C<endhostent>, C<endnetent>, C<endpwent>, C<getgrent>, |
277 | C<getgrgid>, C<getgrnam>, C<getlogin>, C<getpwent>, C<getpwnam>, | |
278 | C<getpwuid>, C<setgrent>, C<setpwent> | |
cb1a09d0 AD |
279 | |
280 | =item Fetching network info | |
d74e8afc | 281 | X<network> X<protocol> X<host> X<hostname> X<IP> X<address> X<service> |
cb1a09d0 | 282 | |
c17cdb72 NC |
283 | =for Pod::Functions =Network |
284 | ||
22fae026 TM |
285 | C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>, |
286 | C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>, | |
287 | C<getprotobyname>, C<getprotobynumber>, C<getprotoent>, | |
288 | C<getservbyname>, C<getservbyport>, C<getservent>, C<sethostent>, | |
289 | C<setnetent>, C<setprotoent>, C<setservent> | |
cb1a09d0 AD |
290 | |
291 | =item Time-related functions | |
d74e8afc | 292 | X<time> X<date> |
cb1a09d0 | 293 | |
c17cdb72 NC |
294 | =for Pod::Functions =Time |
295 | ||
22fae026 | 296 | C<gmtime>, C<localtime>, C<time>, C<times> |
cb1a09d0 | 297 | |
8f0d6a61 RS |
298 | =item Non-function keywords |
299 | ||
c17cdb72 NC |
300 | =for Pod::Functions =!Non-functions |
301 | ||
f5fa2679 | 302 | C<and>, C<AUTOLOAD>, C<BEGIN>, C<CHECK>, C<cmp>, C<CORE>, C<__DATA__>, |
dba7b065 NC |
303 | C<default>, C<DESTROY>, C<else>, C<elseif>, C<elsif>, C<END>, C<__END__>, |
304 | C<eq>, C<for>, C<foreach>, C<ge>, C<given>, C<gt>, C<if>, C<INIT>, C<le>, | |
305 | C<lt>, C<ne>, C<not>, C<or>, C<UNITCHECK>, C<unless>, C<until>, C<when>, | |
306 | C<while>, C<x>, C<xor> | |
8f0d6a61 | 307 | |
cb1a09d0 AD |
308 | =back |
309 | ||
60f9f73c | 310 | =head2 Portability |
d74e8afc | 311 | X<portability> X<Unix> X<portable> |
60f9f73c | 312 | |
2b5ab1e7 TC |
313 | Perl was born in Unix and can therefore access all common Unix |
314 | system calls. In non-Unix environments, the functionality of some | |
8f1da26d | 315 | Unix system calls may not be available or details of the available |
2b5ab1e7 | 316 | functionality may differ slightly. The Perl functions affected |
60f9f73c JH |
317 | by this are: |
318 | ||
319 | C<-X>, C<binmode>, C<chmod>, C<chown>, C<chroot>, C<crypt>, | |
320 | C<dbmclose>, C<dbmopen>, C<dump>, C<endgrent>, C<endhostent>, | |
321 | C<endnetent>, C<endprotoent>, C<endpwent>, C<endservent>, C<exec>, | |
ef5a6dd7 JH |
322 | C<fcntl>, C<flock>, C<fork>, C<getgrent>, C<getgrgid>, C<gethostbyname>, |
323 | C<gethostent>, C<getlogin>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>, | |
54d7b083 | 324 | C<getppid>, C<getpgrp>, C<getpriority>, C<getprotobynumber>, |
60f9f73c JH |
325 | C<getprotoent>, C<getpwent>, C<getpwnam>, C<getpwuid>, |
326 | C<getservbyport>, C<getservent>, C<getsockopt>, C<glob>, C<ioctl>, | |
327 | C<kill>, C<link>, C<lstat>, C<msgctl>, C<msgget>, C<msgrcv>, | |
2b5ab1e7 | 328 | C<msgsnd>, C<open>, C<pipe>, C<readlink>, C<rename>, C<select>, C<semctl>, |
60f9f73c JH |
329 | C<semget>, C<semop>, C<setgrent>, C<sethostent>, C<setnetent>, |
330 | C<setpgrp>, C<setpriority>, C<setprotoent>, C<setpwent>, | |
331 | C<setservent>, C<setsockopt>, C<shmctl>, C<shmget>, C<shmread>, | |
737dd4b4 | 332 | C<shmwrite>, C<socket>, C<socketpair>, |
80cbd5ad JH |
333 | C<stat>, C<symlink>, C<syscall>, C<sysopen>, C<system>, |
334 | C<times>, C<truncate>, C<umask>, C<unlink>, | |
2b5ab1e7 | 335 | C<utime>, C<wait>, C<waitpid> |
60f9f73c JH |
336 | |
337 | For more information about the portability of these functions, see | |
338 | L<perlport> and other available platform-specific documentation. | |
339 | ||
cb1a09d0 AD |
340 | =head2 Alphabetical Listing of Perl Functions |
341 | ||
3b10bc60 | 342 | =over |
a0d0e21e | 343 | |
5b3c99c0 | 344 | =item -X FILEHANDLE |
d74e8afc ITB |
345 | X<-r>X<-w>X<-x>X<-o>X<-R>X<-W>X<-X>X<-O>X<-e>X<-z>X<-s>X<-f>X<-d>X<-l>X<-p> |
346 | X<-S>X<-b>X<-c>X<-t>X<-u>X<-g>X<-k>X<-T>X<-B>X<-M>X<-A>X<-C> | |
a0d0e21e | 347 | |
5b3c99c0 | 348 | =item -X EXPR |
a0d0e21e | 349 | |
5228a96c SP |
350 | =item -X DIRHANDLE |
351 | ||
5b3c99c0 | 352 | =item -X |
a0d0e21e | 353 | |
c17cdb72 NC |
354 | =for Pod::Functions a file test (-r, -x, etc) |
355 | ||
a0d0e21e | 356 | A file test, where X is one of the letters listed below. This unary |
5228a96c SP |
357 | operator takes one argument, either a filename, a filehandle, or a dirhandle, |
358 | and tests the associated file to see if something is true about it. If the | |
7660c0ab | 359 | argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN. |
139c8d14 DG |
360 | Unless otherwise documented, it returns C<1> for true and C<''> for false. |
361 | If the file doesn't exist or can't be examined, it returns C<undef> and | |
362 | sets C<$!> (errno). Despite the funny names, precedence is the same as any | |
363 | other named unary operator. The operator may be any of: | |
a0d0e21e | 364 | |
5ed4f2ec | 365 | -r File is readable by effective uid/gid. |
366 | -w File is writable by effective uid/gid. | |
367 | -x File is executable by effective uid/gid. | |
368 | -o File is owned by effective uid. | |
a0d0e21e | 369 | |
5ed4f2ec | 370 | -R File is readable by real uid/gid. |
371 | -W File is writable by real uid/gid. | |
372 | -X File is executable by real uid/gid. | |
373 | -O File is owned by real uid. | |
a0d0e21e | 374 | |
5ed4f2ec | 375 | -e File exists. |
376 | -z File has zero size (is empty). | |
377 | -s File has nonzero size (returns size in bytes). | |
a0d0e21e | 378 | |
5ed4f2ec | 379 | -f File is a plain file. |
380 | -d File is a directory. | |
ae07d0f9 S |
381 | -l File is a symbolic link (false if symlinks aren't |
382 | supported by the file system). | |
5ed4f2ec | 383 | -p File is a named pipe (FIFO), or Filehandle is a pipe. |
384 | -S File is a socket. | |
385 | -b File is a block special file. | |
386 | -c File is a character special file. | |
387 | -t Filehandle is opened to a tty. | |
a0d0e21e | 388 | |
5ed4f2ec | 389 | -u File has setuid bit set. |
390 | -g File has setgid bit set. | |
391 | -k File has sticky bit set. | |
a0d0e21e | 392 | |
65cc07c9 | 393 | -T File is an ASCII or UTF-8 text file (heuristic guess). |
5ed4f2ec | 394 | -B File is a "binary" file (opposite of -T). |
a0d0e21e | 395 | |
5ed4f2ec | 396 | -M Script start time minus file modification time, in days. |
397 | -A Same for access time. | |
f7051f2c FC |
398 | -C Same for inode change time (Unix, may differ for other |
399 | platforms) | |
a0d0e21e | 400 | |
a0d0e21e LW |
401 | Example: |
402 | ||
403 | while (<>) { | |
a9a5a0dc VP |
404 | chomp; |
405 | next unless -f $_; # ignore specials | |
406 | #... | |
a0d0e21e LW |
407 | } |
408 | ||
4fb67938 FC |
409 | Note that C<-s/a/b/> does not do a negated substitution. Saying |
410 | C<-exp($foo)> still works as expected, however: only single letters | |
411 | following a minus are interpreted as file tests. | |
412 | ||
413 | These operators are exempt from the "looks like a function rule" described | |
4d0444a3 FC |
414 | above. That is, an opening parenthesis after the operator does not affect |
415 | how much of the following code constitutes the argument. Put the opening | |
4fb67938 FC |
416 | parentheses before the operator to separate it from code that follows (this |
417 | applies only to operators with higher precedence than unary operators, of | |
418 | course): | |
419 | ||
420 | -s($file) + 1024 # probably wrong; same as -s($file + 1024) | |
421 | (-s $file) + 1024 # correct | |
422 | ||
5ff3f7a4 GS |
423 | The interpretation of the file permission operators C<-r>, C<-R>, |
424 | C<-w>, C<-W>, C<-x>, and C<-X> is by default based solely on the mode | |
425 | of the file and the uids and gids of the user. There may be other | |
ecae030f MO |
426 | reasons you can't actually read, write, or execute the file: for |
427 | example network filesystem access controls, ACLs (access control lists), | |
428 | read-only filesystems, and unrecognized executable formats. Note | |
429 | that the use of these six specific operators to verify if some operation | |
430 | is possible is usually a mistake, because it may be open to race | |
431 | conditions. | |
5ff3f7a4 | 432 | |
2b5ab1e7 TC |
433 | Also note that, for the superuser on the local filesystems, the C<-r>, |
434 | C<-R>, C<-w>, and C<-W> tests always return 1, and C<-x> and C<-X> return 1 | |
5ff3f7a4 GS |
435 | if any execute bit is set in the mode. Scripts run by the superuser |
436 | may thus need to do a stat() to determine the actual mode of the file, | |
2b5ab1e7 | 437 | or temporarily set their effective uid to something else. |
5ff3f7a4 GS |
438 | |
439 | If you are using ACLs, there is a pragma called C<filetest> that may | |
440 | produce more accurate results than the bare stat() mode bits. | |
5dac7880 FC |
441 | When under C<use filetest 'access'> the above-mentioned filetests |
442 | test whether the permission can(not) be granted using the | |
3b10bc60 | 443 | access(2) family of system calls. Also note that the C<-x> and C<-X> may |
5ff3f7a4 GS |
444 | under this pragma return true even if there are no execute permission |
445 | bits set (nor any extra execute permission ACLs). This strangeness is | |
391b733c | 446 | due to the underlying system calls' definitions. Note also that, due to |
ecae030f MO |
447 | the implementation of C<use filetest 'access'>, the C<_> special |
448 | filehandle won't cache the results of the file tests when this pragma is | |
449 | in effect. Read the documentation for the C<filetest> pragma for more | |
450 | information. | |
5ff3f7a4 | 451 | |
65cc07c9 KW |
452 | The C<-T> and C<-B> switches work as follows. The first block or so of |
453 | the file is examined to see if it is valid UTF-8 that includes non-ASCII | |
454 | characters. If, so it's a C<-T> file. Otherwise, that same portion of | |
455 | the file is examined for odd characters such as strange control codes or | |
456 | characters with the high bit set. If more than a third of the | |
457 | characters are strange, it's a C<-B> file; otherwise it's a C<-T> file. | |
458 | Also, any file containing a zero byte in the examined portion is | |
459 | considered a binary file. (If executed within the scope of a L<S<use | |
460 | locale>|perllocale> which includes C<LC_CTYPE>, odd characters are | |
444d4f5c | 461 | anything that isn't a printable nor space in the current locale.) If |
65cc07c9 KW |
462 | C<-T> or C<-B> is used on a filehandle, the current IO buffer is |
463 | examined | |
3b10bc60 | 464 | rather than the first block. Both C<-T> and C<-B> return true on an empty |
54310121 | 465 | file, or a file at EOF when testing a filehandle. Because you have to |
4633a7c4 LW |
466 | read a file to do the C<-T> test, on most occasions you want to use a C<-f> |
467 | against the file first, as in C<next unless -f $file && -T $file>. | |
a0d0e21e | 468 | |
5dac7880 | 469 | If any of the file tests (or either the C<stat> or C<lstat> operator) is given |
28757baa | 470 | the special filehandle consisting of a solitary underline, then the stat |
a0d0e21e LW |
471 | structure of the previous file test (or stat operator) is used, saving |
472 | a system call. (This doesn't work with C<-t>, and you need to remember | |
3b10bc60 | 473 | that lstat() and C<-l> leave values in the stat structure for the |
5c9aa243 | 474 | symbolic link, not the real file.) (Also, if the stat buffer was filled by |
cf264981 | 475 | an C<lstat> call, C<-T> and C<-B> will reset it with the results of C<stat _>). |
5c9aa243 | 476 | Example: |
a0d0e21e LW |
477 | |
478 | print "Can do.\n" if -r $a || -w _ || -x _; | |
479 | ||
480 | stat($filename); | |
481 | print "Readable\n" if -r _; | |
482 | print "Writable\n" if -w _; | |
483 | print "Executable\n" if -x _; | |
484 | print "Setuid\n" if -u _; | |
485 | print "Setgid\n" if -g _; | |
486 | print "Sticky\n" if -k _; | |
487 | print "Text\n" if -T _; | |
488 | print "Binary\n" if -B _; | |
489 | ||
e9fa405d | 490 | As of Perl 5.10.0, as a form of purely syntactic sugar, you can stack file |
fbb0b3b3 | 491 | test operators, in a way that C<-f -w -x $file> is equivalent to |
a5840dee | 492 | C<-x $file && -w _ && -f _>. (This is only fancy syntax: if you use |
fbb0b3b3 RGS |
493 | the return value of C<-f $file> as an argument to another filetest |
494 | operator, no special magic will happen.) | |
495 | ||
bee96257 | 496 | Portability issues: L<perlport/-X>. |
ea9eb35a | 497 | |
bade7fbc TC |
498 | To avoid confusing would-be users of your code with mysterious |
499 | syntax errors, put something like this at the top of your script: | |
500 | ||
501 | use 5.010; # so filetest ops can stack | |
502 | ||
a0d0e21e | 503 | =item abs VALUE |
d74e8afc | 504 | X<abs> X<absolute> |
a0d0e21e | 505 | |
54310121 | 506 | =item abs |
bbce6d69 | 507 | |
c17cdb72 NC |
508 | =for Pod::Functions absolute value function |
509 | ||
a0d0e21e | 510 | Returns the absolute value of its argument. |
7660c0ab | 511 | If VALUE is omitted, uses C<$_>. |
a0d0e21e LW |
512 | |
513 | =item accept NEWSOCKET,GENERICSOCKET | |
d74e8afc | 514 | X<accept> |
a0d0e21e | 515 | |
c17cdb72 NC |
516 | =for Pod::Functions accept an incoming socket connect |
517 | ||
3b10bc60 | 518 | Accepts an incoming socket connect, just as accept(2) |
19799a22 | 519 | does. Returns the packed address if it succeeded, false otherwise. |
2b5ab1e7 | 520 | See the example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e | 521 | |
8d2a6795 GS |
522 | On systems that support a close-on-exec flag on files, the flag will |
523 | be set for the newly opened file descriptor, as determined by the | |
524 | value of $^F. See L<perlvar/$^F>. | |
525 | ||
a0d0e21e | 526 | =item alarm SECONDS |
d74e8afc ITB |
527 | X<alarm> |
528 | X<SIGALRM> | |
529 | X<timer> | |
a0d0e21e | 530 | |
54310121 | 531 | =item alarm |
bbce6d69 | 532 | |
c17cdb72 NC |
533 | =for Pod::Functions schedule a SIGALRM |
534 | ||
a0d0e21e | 535 | Arranges to have a SIGALRM delivered to this process after the |
cf264981 | 536 | specified number of wallclock seconds has elapsed. If SECONDS is not |
391b733c | 537 | specified, the value stored in C<$_> is used. (On some machines, |
d400eac8 JH |
538 | unfortunately, the elapsed time may be up to one second less or more |
539 | than you specified because of how seconds are counted, and process | |
540 | scheduling may delay the delivery of the signal even further.) | |
541 | ||
542 | Only one timer may be counting at once. Each call disables the | |
543 | previous timer, and an argument of C<0> may be supplied to cancel the | |
544 | previous timer without starting a new one. The returned value is the | |
545 | amount of time remaining on the previous timer. | |
a0d0e21e | 546 | |
2bc69794 BS |
547 | For delays of finer granularity than one second, the Time::HiRes module |
548 | (from CPAN, and starting from Perl 5.8 part of the standard | |
549 | distribution) provides ualarm(). You may also use Perl's four-argument | |
550 | version of select() leaving the first three arguments undefined, or you | |
551 | might be able to use the C<syscall> interface to access setitimer(2) if | |
391b733c | 552 | your system supports it. See L<perlfaq8> for details. |
2b5ab1e7 | 553 | |
80d38338 TC |
554 | It is usually a mistake to intermix C<alarm> and C<sleep> calls, because |
555 | C<sleep> may be internally implemented on your system with C<alarm>. | |
a0d0e21e | 556 | |
19799a22 GS |
557 | If you want to use C<alarm> to time out a system call you need to use an |
558 | C<eval>/C<die> pair. You can't rely on the alarm causing the system call to | |
f86cebdf | 559 | fail with C<$!> set to C<EINTR> because Perl sets up signal handlers to |
19799a22 | 560 | restart system calls on some systems. Using C<eval>/C<die> always works, |
5a964f20 | 561 | modulo the caveats given in L<perlipc/"Signals">. |
ff68c719 | 562 | |
563 | eval { | |
a9a5a0dc VP |
564 | local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required |
565 | alarm $timeout; | |
566 | $nread = sysread SOCKET, $buffer, $size; | |
567 | alarm 0; | |
ff68c719 | 568 | }; |
ff68c719 | 569 | if ($@) { |
a9a5a0dc | 570 | die unless $@ eq "alarm\n"; # propagate unexpected errors |
5ed4f2ec | 571 | # timed out |
ff68c719 | 572 | } |
573 | else { | |
5ed4f2ec | 574 | # didn't |
ff68c719 | 575 | } |
576 | ||
91d81acc JH |
577 | For more information see L<perlipc>. |
578 | ||
ea9eb35a BJ |
579 | Portability issues: L<perlport/alarm>. |
580 | ||
a0d0e21e | 581 | =item atan2 Y,X |
d74e8afc | 582 | X<atan2> X<arctangent> X<tan> X<tangent> |
a0d0e21e | 583 | |
c17cdb72 NC |
584 | =for Pod::Functions arctangent of Y/X in the range -PI to PI |
585 | ||
a0d0e21e LW |
586 | Returns the arctangent of Y/X in the range -PI to PI. |
587 | ||
ca6e1c26 | 588 | For the tangent operation, you may use the C<Math::Trig::tan> |
28757baa | 589 | function, or use the familiar relation: |
590 | ||
591 | sub tan { sin($_[0]) / cos($_[0]) } | |
592 | ||
a1021d57 RGS |
593 | The return value for C<atan2(0,0)> is implementation-defined; consult |
594 | your atan2(3) manpage for more information. | |
bf5f1b4c | 595 | |
ea9eb35a BJ |
596 | Portability issues: L<perlport/atan2>. |
597 | ||
a0d0e21e | 598 | =item bind SOCKET,NAME |
d74e8afc | 599 | X<bind> |
a0d0e21e | 600 | |
c17cdb72 NC |
601 | =for Pod::Functions binds an address to a socket |
602 | ||
3b10bc60 | 603 | Binds a network address to a socket, just as bind(2) |
19799a22 | 604 | does. Returns true if it succeeded, false otherwise. NAME should be a |
4633a7c4 LW |
605 | packed address of the appropriate type for the socket. See the examples in |
606 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 607 | |
fae2c0fb | 608 | =item binmode FILEHANDLE, LAYER |
d74e8afc | 609 | X<binmode> X<binary> X<text> X<DOS> X<Windows> |
1c1fc3ea | 610 | |
a0d0e21e LW |
611 | =item binmode FILEHANDLE |
612 | ||
c17cdb72 NC |
613 | =for Pod::Functions prepare binary files for I/O |
614 | ||
1cbfc93d NIS |
615 | Arranges for FILEHANDLE to be read or written in "binary" or "text" |
616 | mode on systems where the run-time libraries distinguish between | |
617 | binary and text files. If FILEHANDLE is an expression, the value is | |
618 | taken as the name of the filehandle. Returns true on success, | |
b5fe5ca2 | 619 | otherwise it returns C<undef> and sets C<$!> (errno). |
1cbfc93d | 620 | |
8f1da26d | 621 | On some systems (in general, DOS- and Windows-based systems) binmode() |
d807c6f4 | 622 | is necessary when you're not working with a text file. For the sake |
d7a0d798 FC |
623 | of portability it is a good idea always to use it when appropriate, |
624 | and never to use it when it isn't appropriate. Also, people can | |
8f1da26d | 625 | set their I/O to be by default UTF8-encoded Unicode, not bytes. |
d807c6f4 JH |
626 | |
627 | In other words: regardless of platform, use binmode() on binary data, | |
d7a0d798 | 628 | like images, for example. |
d807c6f4 JH |
629 | |
630 | If LAYER is present it is a single string, but may contain multiple | |
391b733c | 631 | directives. The directives alter the behaviour of the filehandle. |
d7a0d798 | 632 | When LAYER is present, using binmode on a text file makes sense. |
d807c6f4 | 633 | |
fae2c0fb | 634 | If LAYER is omitted or specified as C<:raw> the filehandle is made |
391b733c | 635 | suitable for passing binary data. This includes turning off possible CRLF |
0226bbdb | 636 | translation and marking it as bytes (as opposed to Unicode characters). |
749683d2 | 637 | Note that, despite what may be implied in I<"Programming Perl"> (the |
3b10bc60 | 638 | Camel, 3rd edition) or elsewhere, C<:raw> is I<not> simply the inverse of C<:crlf>. |
639 | Other layers that would affect the binary nature of the stream are | |
391b733c | 640 | I<also> disabled. See L<PerlIO>, L<perlrun>, and the discussion about the |
0226bbdb | 641 | PERLIO environment variable. |
01e6739c | 642 | |
3b10bc60 | 643 | The C<:bytes>, C<:crlf>, C<:utf8>, and any other directives of the |
d807c6f4 JH |
644 | form C<:...>, are called I/O I<layers>. The C<open> pragma can be used to |
645 | establish default I/O layers. See L<open>. | |
646 | ||
fae2c0fb RGS |
647 | I<The LAYER parameter of the binmode() function is described as "DISCIPLINE" |
648 | in "Programming Perl, 3rd Edition". However, since the publishing of this | |
649 | book, by many known as "Camel III", the consensus of the naming of this | |
650 | functionality has moved from "discipline" to "layer". All documentation | |
651 | of this version of Perl therefore refers to "layers" rather than to | |
652 | "disciplines". Now back to the regularly scheduled documentation...> | |
653 | ||
8f1da26d | 654 | To mark FILEHANDLE as UTF-8, use C<:utf8> or C<:encoding(UTF-8)>. |
6902c96a | 655 | C<:utf8> just marks the data as UTF-8 without further checking, |
8f1da26d | 656 | while C<:encoding(UTF-8)> checks the data for actually being valid |
391b733c | 657 | UTF-8. More details can be found in L<PerlIO::encoding>. |
1cbfc93d | 658 | |
ed53a2bb | 659 | In general, binmode() should be called after open() but before any I/O |
3b10bc60 | 660 | is done on the filehandle. Calling binmode() normally flushes any |
01e6739c | 661 | pending buffered output data (and perhaps pending input data) on the |
fae2c0fb | 662 | handle. An exception to this is the C<:encoding> layer that |
d7a0d798 | 663 | changes the default character encoding of the handle; see L</open>. |
fae2c0fb | 664 | The C<:encoding> layer sometimes needs to be called in |
3874323d JH |
665 | mid-stream, and it doesn't flush the stream. The C<:encoding> |
666 | also implicitly pushes on top of itself the C<:utf8> layer because | |
3b10bc60 | 667 | internally Perl operates on UTF8-encoded Unicode characters. |
16fe6d59 | 668 | |
19799a22 | 669 | The operating system, device drivers, C libraries, and Perl run-time |
8f1da26d TC |
670 | system all conspire to let the programmer treat a single |
671 | character (C<\n>) as the line terminator, irrespective of external | |
30168b04 GS |
672 | representation. On many operating systems, the native text file |
673 | representation matches the internal representation, but on some | |
674 | platforms the external representation of C<\n> is made up of more than | |
675 | one character. | |
676 | ||
8f1da26d TC |
677 | All variants of Unix, Mac OS (old and new), and Stream_LF files on VMS use |
678 | a single character to end each line in the external representation of text | |
679 | (even though that single character is CARRIAGE RETURN on old, pre-Darwin | |
391b733c | 680 | flavors of Mac OS, and is LINE FEED on Unix and most VMS files). In other |
8f1da26d TC |
681 | systems like OS/2, DOS, and the various flavors of MS-Windows, your program |
682 | sees a C<\n> as a simple C<\cJ>, but what's stored in text files are the | |
683 | two characters C<\cM\cJ>. That means that if you don't use binmode() on | |
684 | these systems, C<\cM\cJ> sequences on disk will be converted to C<\n> on | |
685 | input, and any C<\n> in your program will be converted back to C<\cM\cJ> on | |
686 | output. This is what you want for text files, but it can be disastrous for | |
687 | binary files. | |
30168b04 GS |
688 | |
689 | Another consequence of using binmode() (on some systems) is that | |
690 | special end-of-file markers will be seen as part of the data stream. | |
d7a0d798 FC |
691 | For systems from the Microsoft family this means that, if your binary |
692 | data contain C<\cZ>, the I/O subsystem will regard it as the end of | |
30168b04 GS |
693 | the file, unless you use binmode(). |
694 | ||
3b10bc60 | 695 | binmode() is important not only for readline() and print() operations, |
30168b04 GS |
696 | but also when using read(), seek(), sysread(), syswrite() and tell() |
697 | (see L<perlport> for more details). See the C<$/> and C<$\> variables | |
698 | in L<perlvar> for how to manually set your input and output | |
699 | line-termination sequences. | |
a0d0e21e | 700 | |
ea9eb35a BJ |
701 | Portability issues: L<perlport/binmode>. |
702 | ||
4633a7c4 | 703 | =item bless REF,CLASSNAME |
d74e8afc | 704 | X<bless> |
a0d0e21e LW |
705 | |
706 | =item bless REF | |
707 | ||
c17cdb72 NC |
708 | =for Pod::Functions create an object |
709 | ||
2b5ab1e7 TC |
710 | This function tells the thingy referenced by REF that it is now an object |
711 | in the CLASSNAME package. If CLASSNAME is omitted, the current package | |
19799a22 | 712 | is used. Because a C<bless> is often the last thing in a constructor, |
2b5ab1e7 | 713 | it returns the reference for convenience. Always use the two-argument |
cf264981 | 714 | version if a derived class might inherit the function doing the blessing. |
e54e4959 | 715 | See L<perlobj> for more about the blessing (and blessings) of objects. |
a0d0e21e | 716 | |
57668c4d | 717 | Consider always blessing objects in CLASSNAMEs that are mixed case. |
2b5ab1e7 | 718 | Namespaces with all lowercase names are considered reserved for |
391b733c | 719 | Perl pragmata. Builtin types have all uppercase names. To prevent |
2b5ab1e7 TC |
720 | confusion, you may wish to avoid such package names as well. Make sure |
721 | that CLASSNAME is a true value. | |
60ad88b8 GS |
722 | |
723 | See L<perlmod/"Perl Modules">. | |
724 | ||
0d863452 RH |
725 | =item break |
726 | ||
d9b04284 | 727 | =for Pod::Functions +switch break out of a C<given> block |
c17cdb72 | 728 | |
0d863452 RH |
729 | Break out of a C<given()> block. |
730 | ||
a8a26e52 JK |
731 | This keyword is enabled by the C<"switch"> feature; see L<feature> for |
732 | more information on C<"switch">. You can also access it by prefixing it | |
733 | with C<CORE::>. Alternatively, include a C<use v5.10> or later to the | |
734 | current scope. | |
0d863452 | 735 | |
a0d0e21e | 736 | =item caller EXPR |
d74e8afc | 737 | X<caller> X<call stack> X<stack> X<stack trace> |
a0d0e21e LW |
738 | |
739 | =item caller | |
740 | ||
c17cdb72 NC |
741 | =for Pod::Functions get context of the current subroutine call |
742 | ||
1d56df50 DD |
743 | Returns the context of the current pure perl subroutine call. In scalar |
744 | context, returns the caller's package name if there I<is> a caller (that is, if | |
80d38338 | 745 | we're in a subroutine or C<eval> or C<require>) and the undefined value |
1d56df50 | 746 | otherwise. caller never returns XS subs and they are skipped. The next pure |
444d4f5c FC |
747 | perl sub will appear instead of the XS |
748 | sub in caller's return values. In list | |
1d56df50 | 749 | context, caller returns |
a0d0e21e | 750 | |
ee6b43cc | 751 | # 0 1 2 |
748a9306 | 752 | ($package, $filename, $line) = caller; |
a0d0e21e LW |
753 | |
754 | With EXPR, it returns some extra information that the debugger uses to | |
755 | print a stack trace. The value of EXPR indicates how many call frames | |
756 | to go back before the current one. | |
757 | ||
ee6b43cc | 758 | # 0 1 2 3 4 |
f3aa04c2 | 759 | ($package, $filename, $line, $subroutine, $hasargs, |
ee6b43cc | 760 | |
761 | # 5 6 7 8 9 10 | |
b3ca2e83 | 762 | $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash) |
ee6b43cc | 763 | = caller($i); |
e7ea3e70 | 764 | |
02729fef | 765 | Here, $subroutine is the function that the caller called (rather than the |
444d4f5c | 766 | function containing the caller). Note that $subroutine may be C<(eval)> if |
02729fef DM |
767 | the frame is not a subroutine call, but an C<eval>. In such a case |
768 | additional elements $evaltext and | |
7660c0ab | 769 | C<$is_require> are set: C<$is_require> is true if the frame is created by a |
19799a22 | 770 | C<require> or C<use> statement, $evaltext contains the text of the |
277ddfaf | 771 | C<eval EXPR> statement. In particular, for an C<eval BLOCK> statement, |
cc1c2e42 | 772 | $subroutine is C<(eval)>, but $evaltext is undefined. (Note also that |
0fc9dec4 RGS |
773 | each C<use> statement creates a C<require> frame inside an C<eval EXPR> |
774 | frame.) $subroutine may also be C<(unknown)> if this particular | |
775 | subroutine happens to have been deleted from the symbol table. | |
776 | C<$hasargs> is true if a new instance of C<@_> was set up for the frame. | |
777 | C<$hints> and C<$bitmask> contain pragmatic hints that the caller was | |
585d73c3 | 778 | compiled with. C<$hints> corresponds to C<$^H>, and C<$bitmask> |
1adb05cd FC |
779 | corresponds to C<${^WARNING_BITS}>. The |
780 | C<$hints> and C<$bitmask> values are subject | |
585d73c3 | 781 | to change between versions of Perl, and are not meant for external use. |
748a9306 | 782 | |
b3ca2e83 | 783 | C<$hinthash> is a reference to a hash containing the value of C<%^H> when the |
391b733c | 784 | caller was compiled, or C<undef> if C<%^H> was empty. Do not modify the values |
b3ca2e83 NC |
785 | of this hash, as they are the actual values stored in the optree. |
786 | ||
ffe0c19d FC |
787 | Furthermore, when called from within the DB package in |
788 | list context, and with an argument, caller returns more | |
7660c0ab | 789 | detailed information: it sets the list variable C<@DB::args> to be the |
54310121 | 790 | arguments with which the subroutine was invoked. |
748a9306 | 791 | |
7660c0ab | 792 | Be aware that the optimizer might have optimized call frames away before |
19799a22 | 793 | C<caller> had a chance to get the information. That means that C<caller(N)> |
80d38338 | 794 | might not return information about the call frame you expect it to, for |
b76cc8ba | 795 | C<< N > 1 >>. In particular, C<@DB::args> might have information from the |
19799a22 | 796 | previous time C<caller> was called. |
7660c0ab | 797 | |
8f1da26d | 798 | Be aware that setting C<@DB::args> is I<best effort>, intended for |
391b733c | 799 | debugging or generating backtraces, and should not be relied upon. In |
ca9f0cb5 NC |
800 | particular, as C<@_> contains aliases to the caller's arguments, Perl does |
801 | not take a copy of C<@_>, so C<@DB::args> will contain modifications the | |
802 | subroutine makes to C<@_> or its contents, not the original values at call | |
391b733c | 803 | time. C<@DB::args>, like C<@_>, does not hold explicit references to its |
ca9f0cb5 | 804 | elements, so under certain cases its elements may have become freed and |
391b733c | 805 | reallocated for other variables or temporary values. Finally, a side effect |
d7a0d798 | 806 | of the current implementation is that the effects of C<shift @_> can |
8f1da26d TC |
807 | I<normally> be undone (but not C<pop @_> or other splicing, I<and> not if a |
808 | reference to C<@_> has been taken, I<and> subject to the caveat about reallocated | |
ca9f0cb5 | 809 | elements), so C<@DB::args> is actually a hybrid of the current state and |
391b733c | 810 | initial state of C<@_>. Buyer beware. |
ca9f0cb5 | 811 | |
a0d0e21e | 812 | =item chdir EXPR |
d74e8afc ITB |
813 | X<chdir> |
814 | X<cd> | |
f723aae1 | 815 | X<directory, change> |
a0d0e21e | 816 | |
c4aca7d0 GA |
817 | =item chdir FILEHANDLE |
818 | ||
819 | =item chdir DIRHANDLE | |
820 | ||
ce2984c3 PF |
821 | =item chdir |
822 | ||
c17cdb72 NC |
823 | =for Pod::Functions change your current working directory |
824 | ||
391b733c | 825 | Changes the working directory to EXPR, if possible. If EXPR is omitted, |
0bfc1ec4 | 826 | changes to the directory specified by C<$ENV{HOME}>, if set; if not, |
391b733c FC |
827 | changes to the directory specified by C<$ENV{LOGDIR}>. (Under VMS, the |
828 | variable C<$ENV{SYS$LOGIN}> is also checked, and used if it is set.) If | |
829 | neither is set, C<chdir> does nothing. It returns true on success, | |
830 | false otherwise. See the example under C<die>. | |
a0d0e21e | 831 | |
3b10bc60 | 832 | On systems that support fchdir(2), you may pass a filehandle or |
34169887 | 833 | directory handle as the argument. On systems that don't support fchdir(2), |
3b10bc60 | 834 | passing handles raises an exception. |
c4aca7d0 | 835 | |
a0d0e21e | 836 | =item chmod LIST |
d74e8afc | 837 | X<chmod> X<permission> X<mode> |
a0d0e21e | 838 | |
c17cdb72 NC |
839 | =for Pod::Functions changes the permissions on a list of files |
840 | ||
a0d0e21e | 841 | Changes the permissions of a list of files. The first element of the |
8f1da26d | 842 | list must be the numeric mode, which should probably be an octal |
4ad40acf | 843 | number, and which definitely should I<not> be a string of octal digits: |
3b10bc60 | 844 | C<0644> is okay, but C<"0644"> is not. Returns the number of files |
8f1da26d | 845 | successfully changed. See also L</oct> if all you have is a string. |
a0d0e21e | 846 | |
3b10bc60 | 847 | $cnt = chmod 0755, "foo", "bar"; |
a0d0e21e | 848 | chmod 0755, @executables; |
3b10bc60 | 849 | $mode = "0644"; chmod $mode, "foo"; # !!! sets mode to |
f86cebdf | 850 | # --w----r-T |
3b10bc60 | 851 | $mode = "0644"; chmod oct($mode), "foo"; # this is better |
852 | $mode = 0644; chmod $mode, "foo"; # this is best | |
a0d0e21e | 853 | |
3b10bc60 | 854 | On systems that support fchmod(2), you may pass filehandles among the |
855 | files. On systems that don't support fchmod(2), passing filehandles raises | |
856 | an exception. Filehandles must be passed as globs or glob references to be | |
857 | recognized; barewords are considered filenames. | |
c4aca7d0 GA |
858 | |
859 | open(my $fh, "<", "foo"); | |
860 | my $perm = (stat $fh)[2] & 07777; | |
861 | chmod($perm | 0600, $fh); | |
862 | ||
3b10bc60 | 863 | You can also import the symbolic C<S_I*> constants from the C<Fcntl> |
ca6e1c26 JH |
864 | module: |
865 | ||
3b10bc60 | 866 | use Fcntl qw( :mode ); |
ca6e1c26 | 867 | chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables; |
3b10bc60 | 868 | # Identical to the chmod 0755 of the example above. |
ca6e1c26 | 869 | |
ea9eb35a BJ |
870 | Portability issues: L<perlport/chmod>. |
871 | ||
a0d0e21e | 872 | =item chomp VARIABLE |
d74e8afc | 873 | X<chomp> X<INPUT_RECORD_SEPARATOR> X<$/> X<newline> X<eol> |
a0d0e21e | 874 | |
313c9f5c | 875 | =item chomp( LIST ) |
a0d0e21e LW |
876 | |
877 | =item chomp | |
878 | ||
c17cdb72 NC |
879 | =for Pod::Functions remove a trailing record separator from a string |
880 | ||
2b5ab1e7 TC |
881 | This safer version of L</chop> removes any trailing string |
882 | that corresponds to the current value of C<$/> (also known as | |
28757baa | 883 | $INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total |
884 | number of characters removed from all its arguments. It's often used to | |
885 | remove the newline from the end of an input record when you're worried | |
2b5ab1e7 TC |
886 | that the final record may be missing its newline. When in paragraph |
887 | mode (C<$/ = "">), it removes all trailing newlines from the string. | |
4c5a6083 | 888 | When in slurp mode (C<$/ = undef>) or fixed-length record mode (C<$/> is |
34169887 | 889 | a reference to an integer or the like; see L<perlvar>) chomp() won't |
b76cc8ba | 890 | remove anything. |
19799a22 | 891 | If VARIABLE is omitted, it chomps C<$_>. Example: |
a0d0e21e LW |
892 | |
893 | while (<>) { | |
a9a5a0dc VP |
894 | chomp; # avoid \n on last field |
895 | @array = split(/:/); | |
896 | # ... | |
a0d0e21e LW |
897 | } |
898 | ||
feef49c9 FC |
899 | If VARIABLE is a hash, it chomps the hash's values, but not its keys, |
900 | resetting the C<each> iterator in the process. | |
4bf21a6d | 901 | |
a0d0e21e LW |
902 | You can actually chomp anything that's an lvalue, including an assignment: |
903 | ||
904 | chomp($cwd = `pwd`); | |
905 | chomp($answer = <STDIN>); | |
906 | ||
907 | If you chomp a list, each element is chomped, and the total number of | |
908 | characters removed is returned. | |
909 | ||
15e44fd8 RGS |
910 | Note that parentheses are necessary when you're chomping anything |
911 | that is not a simple variable. This is because C<chomp $cwd = `pwd`;> | |
912 | is interpreted as C<(chomp $cwd) = `pwd`;>, rather than as | |
913 | C<chomp( $cwd = `pwd` )> which you might expect. Similarly, | |
914 | C<chomp $a, $b> is interpreted as C<chomp($a), $b> rather than | |
915 | as C<chomp($a, $b)>. | |
916 | ||
a0d0e21e | 917 | =item chop VARIABLE |
d74e8afc | 918 | X<chop> |
a0d0e21e | 919 | |
313c9f5c | 920 | =item chop( LIST ) |
a0d0e21e LW |
921 | |
922 | =item chop | |
923 | ||
c17cdb72 NC |
924 | =for Pod::Functions remove the last character from a string |
925 | ||
a0d0e21e | 926 | Chops off the last character of a string and returns the character |
5b3eff12 | 927 | chopped. It is much more efficient than C<s/.$//s> because it neither |
7660c0ab | 928 | scans nor copies the string. If VARIABLE is omitted, chops C<$_>. |
feef49c9 FC |
929 | If VARIABLE is a hash, it chops the hash's values, but not its keys, |
930 | resetting the C<each> iterator in the process. | |
4bf21a6d | 931 | |
5b3eff12 | 932 | You can actually chop anything that's an lvalue, including an assignment. |
a0d0e21e LW |
933 | |
934 | If you chop a list, each element is chopped. Only the value of the | |
19799a22 | 935 | last C<chop> is returned. |
a0d0e21e | 936 | |
19799a22 | 937 | Note that C<chop> returns the last character. To return all but the last |
748a9306 LW |
938 | character, use C<substr($string, 0, -1)>. |
939 | ||
15e44fd8 RGS |
940 | See also L</chomp>. |
941 | ||
a0d0e21e | 942 | =item chown LIST |
d74e8afc | 943 | X<chown> X<owner> X<user> X<group> |
a0d0e21e | 944 | |
c17cdb72 NC |
945 | =for Pod::Functions change the ownership on a list of files |
946 | ||
a0d0e21e | 947 | Changes the owner (and group) of a list of files. The first two |
19799a22 GS |
948 | elements of the list must be the I<numeric> uid and gid, in that |
949 | order. A value of -1 in either position is interpreted by most | |
950 | systems to leave that value unchanged. Returns the number of files | |
951 | successfully changed. | |
a0d0e21e LW |
952 | |
953 | $cnt = chown $uid, $gid, 'foo', 'bar'; | |
954 | chown $uid, $gid, @filenames; | |
955 | ||
3b10bc60 | 956 | On systems that support fchown(2), you may pass filehandles among the |
957 | files. On systems that don't support fchown(2), passing filehandles raises | |
958 | an exception. Filehandles must be passed as globs or glob references to be | |
959 | recognized; barewords are considered filenames. | |
c4aca7d0 | 960 | |
54310121 | 961 | Here's an example that looks up nonnumeric uids in the passwd file: |
a0d0e21e LW |
962 | |
963 | print "User: "; | |
19799a22 | 964 | chomp($user = <STDIN>); |
5a964f20 | 965 | print "Files: "; |
19799a22 | 966 | chomp($pattern = <STDIN>); |
a0d0e21e LW |
967 | |
968 | ($login,$pass,$uid,$gid) = getpwnam($user) | |
a9a5a0dc | 969 | or die "$user not in passwd file"; |
a0d0e21e | 970 | |
5ed4f2ec | 971 | @ary = glob($pattern); # expand filenames |
a0d0e21e LW |
972 | chown $uid, $gid, @ary; |
973 | ||
54310121 | 974 | On most systems, you are not allowed to change the ownership of the |
4633a7c4 LW |
975 | file unless you're the superuser, although you should be able to change |
976 | the group to any of your secondary groups. On insecure systems, these | |
977 | restrictions may be relaxed, but this is not a portable assumption. | |
19799a22 GS |
978 | On POSIX systems, you can detect this condition this way: |
979 | ||
980 | use POSIX qw(sysconf _PC_CHOWN_RESTRICTED); | |
981 | $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED); | |
4633a7c4 | 982 | |
f48496b1 | 983 | Portability issues: L<perlport/chown>. |
ea9eb35a | 984 | |
a0d0e21e | 985 | =item chr NUMBER |
d74e8afc | 986 | X<chr> X<character> X<ASCII> X<Unicode> |
a0d0e21e | 987 | |
54310121 | 988 | =item chr |
bbce6d69 | 989 | |
c17cdb72 NC |
990 | =for Pod::Functions get character this number represents |
991 | ||
a0d0e21e | 992 | Returns the character represented by that NUMBER in the character set. |
a0ed51b3 | 993 | For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and |
2575c402 | 994 | chr(0x263a) is a Unicode smiley face. |
aaa68c4a | 995 | |
8a064bd6 | 996 | Negative values give the Unicode replacement character (chr(0xfffd)), |
80d38338 | 997 | except under the L<bytes> pragma, where the low eight bits of the value |
8a064bd6 JH |
998 | (truncated to an integer) are used. |
999 | ||
974da8e5 JH |
1000 | If NUMBER is omitted, uses C<$_>. |
1001 | ||
b76cc8ba | 1002 | For the reverse, use L</ord>. |
a0d0e21e | 1003 | |
2575c402 JW |
1004 | Note that characters from 128 to 255 (inclusive) are by default |
1005 | internally not encoded as UTF-8 for backward compatibility reasons. | |
974da8e5 | 1006 | |
2575c402 | 1007 | See L<perlunicode> for more about Unicode. |
bbce6d69 | 1008 | |
a0d0e21e | 1009 | =item chroot FILENAME |
d74e8afc | 1010 | X<chroot> X<root> |
a0d0e21e | 1011 | |
54310121 | 1012 | =item chroot |
bbce6d69 | 1013 | |
c17cdb72 NC |
1014 | =for Pod::Functions make directory new root for path lookups |
1015 | ||
5a964f20 | 1016 | This function works like the system call by the same name: it makes the |
4633a7c4 | 1017 | named directory the new root directory for all further pathnames that |
951ba7fe | 1018 | begin with a C</> by your process and all its children. (It doesn't |
28757baa | 1019 | change your current working directory, which is unaffected.) For security |
4633a7c4 | 1020 | reasons, this call is restricted to the superuser. If FILENAME is |
19799a22 | 1021 | omitted, does a C<chroot> to C<$_>. |
a0d0e21e | 1022 | |
b00d10dc JH |
1023 | B<NOTE:> It is good security practice to do C<chdir("/")> (to the root |
1024 | directory) immediately after a C<chroot()>. | |
1025 | ||
ea9eb35a BJ |
1026 | Portability issues: L<perlport/chroot>. |
1027 | ||
a0d0e21e | 1028 | =item close FILEHANDLE |
d74e8afc | 1029 | X<close> |
a0d0e21e | 1030 | |
6a518fbc TP |
1031 | =item close |
1032 | ||
c17cdb72 NC |
1033 | =for Pod::Functions close file (or pipe or socket) handle |
1034 | ||
3b10bc60 | 1035 | Closes the file or pipe associated with the filehandle, flushes the IO |
e0f13c26 | 1036 | buffers, and closes the system file descriptor. Returns true if those |
8f1da26d | 1037 | operations succeed and if no error was reported by any PerlIO |
e0f13c26 RGS |
1038 | layer. Closes the currently selected filehandle if the argument is |
1039 | omitted. | |
fb73857a | 1040 | |
1041 | You don't have to close FILEHANDLE if you are immediately going to do | |
3b10bc60 | 1042 | another C<open> on it, because C<open> closes it for you. (See |
01aa884e | 1043 | L<open|/open FILEHANDLE>.) However, an explicit C<close> on an input file resets the line |
19799a22 | 1044 | counter (C<$.>), while the implicit close done by C<open> does not. |
fb73857a | 1045 | |
3b10bc60 | 1046 | If the filehandle came from a piped open, C<close> returns false if one of |
1047 | the other syscalls involved fails or if its program exits with non-zero | |
1048 | status. If the only problem was that the program exited non-zero, C<$!> | |
1049 | will be set to C<0>. Closing a pipe also waits for the process executing | |
1050 | on the pipe to exit--in case you wish to look at the output of the pipe | |
1051 | afterwards--and implicitly puts the exit status value of that command into | |
1052 | C<$?> and C<${^CHILD_ERROR_NATIVE}>. | |
5a964f20 | 1053 | |
2e0cfa16 FC |
1054 | If there are multiple threads running, C<close> on a filehandle from a |
1055 | piped open returns true without waiting for the child process to terminate, | |
1056 | if the filehandle is still open in another thread. | |
1057 | ||
80d38338 TC |
1058 | Closing the read end of a pipe before the process writing to it at the |
1059 | other end is done writing results in the writer receiving a SIGPIPE. If | |
1060 | the other end can't handle that, be sure to read all the data before | |
1061 | closing the pipe. | |
73689b13 | 1062 | |
fb73857a | 1063 | Example: |
a0d0e21e | 1064 | |
fb73857a | 1065 | open(OUTPUT, '|sort >foo') # pipe to sort |
1066 | or die "Can't start sort: $!"; | |
5ed4f2ec | 1067 | #... # print stuff to output |
1068 | close OUTPUT # wait for sort to finish | |
fb73857a | 1069 | or warn $! ? "Error closing sort pipe: $!" |
1070 | : "Exit status $? from sort"; | |
5ed4f2ec | 1071 | open(INPUT, 'foo') # get sort's results |
fb73857a | 1072 | or die "Can't open 'foo' for input: $!"; |
a0d0e21e | 1073 | |
5a964f20 | 1074 | FILEHANDLE may be an expression whose value can be used as an indirect |
8f1da26d | 1075 | filehandle, usually the real filehandle name or an autovivified handle. |
a0d0e21e LW |
1076 | |
1077 | =item closedir DIRHANDLE | |
d74e8afc | 1078 | X<closedir> |
a0d0e21e | 1079 | |
c17cdb72 NC |
1080 | =for Pod::Functions close directory handle |
1081 | ||
19799a22 | 1082 | Closes a directory opened by C<opendir> and returns the success of that |
5a964f20 TC |
1083 | system call. |
1084 | ||
a0d0e21e | 1085 | =item connect SOCKET,NAME |
d74e8afc | 1086 | X<connect> |
a0d0e21e | 1087 | |
c17cdb72 NC |
1088 | =for Pod::Functions connect to a remote socket |
1089 | ||
80d38338 TC |
1090 | Attempts to connect to a remote socket, just like connect(2). |
1091 | Returns true if it succeeded, false otherwise. NAME should be a | |
4633a7c4 LW |
1092 | packed address of the appropriate type for the socket. See the examples in |
1093 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 1094 | |
cb1a09d0 | 1095 | =item continue BLOCK |
d74e8afc | 1096 | X<continue> |
cb1a09d0 | 1097 | |
0d863452 RH |
1098 | =item continue |
1099 | ||
c17cdb72 NC |
1100 | =for Pod::Functions optional trailing block in a while or foreach |
1101 | ||
4a904372 FC |
1102 | When followed by a BLOCK, C<continue> is actually a |
1103 | flow control statement rather than a function. If | |
cf264981 | 1104 | there is a C<continue> BLOCK attached to a BLOCK (typically in a C<while> or |
98293880 JH |
1105 | C<foreach>), it is always executed just before the conditional is about to |
1106 | be evaluated again, just like the third part of a C<for> loop in C. Thus | |
cb1a09d0 AD |
1107 | it can be used to increment a loop variable, even when the loop has been |
1108 | continued via the C<next> statement (which is similar to the C C<continue> | |
1109 | statement). | |
1110 | ||
98293880 | 1111 | C<last>, C<next>, or C<redo> may appear within a C<continue> |
3b10bc60 | 1112 | block; C<last> and C<redo> behave as if they had been executed within |
19799a22 | 1113 | the main block. So will C<next>, but since it will execute a C<continue> |
1d2dff63 GS |
1114 | block, it may be more entertaining. |
1115 | ||
1116 | while (EXPR) { | |
a9a5a0dc VP |
1117 | ### redo always comes here |
1118 | do_something; | |
1d2dff63 | 1119 | } continue { |
a9a5a0dc VP |
1120 | ### next always comes here |
1121 | do_something_else; | |
1122 | # then back the top to re-check EXPR | |
1d2dff63 GS |
1123 | } |
1124 | ### last always comes here | |
1125 | ||
3b10bc60 | 1126 | Omitting the C<continue> section is equivalent to using an |
1127 | empty one, logically enough, so C<next> goes directly back | |
1d2dff63 GS |
1128 | to check the condition at the top of the loop. |
1129 | ||
4a904372 | 1130 | When there is no BLOCK, C<continue> is a function that |
8f1da26d TC |
1131 | falls through the current C<when> or C<default> block instead of iterating |
1132 | a dynamically enclosing C<foreach> or exiting a lexically enclosing C<given>. | |
4a904372 FC |
1133 | In Perl 5.14 and earlier, this form of C<continue> was |
1134 | only available when the C<"switch"> feature was enabled. | |
48238296 | 1135 | See L<feature> and L<perlsyn/"Switch Statements"> for more |
8f1da26d | 1136 | information. |
0d863452 | 1137 | |
a0d0e21e | 1138 | =item cos EXPR |
d74e8afc | 1139 | X<cos> X<cosine> X<acos> X<arccosine> |
a0d0e21e | 1140 | |
d6217f1e GS |
1141 | =item cos |
1142 | ||
c17cdb72 NC |
1143 | =for Pod::Functions cosine function |
1144 | ||
5a964f20 | 1145 | Returns the cosine of EXPR (expressed in radians). If EXPR is omitted, |
34169887 | 1146 | takes the cosine of C<$_>. |
a0d0e21e | 1147 | |
ca6e1c26 | 1148 | For the inverse cosine operation, you may use the C<Math::Trig::acos()> |
28757baa | 1149 | function, or use this relation: |
1150 | ||
1151 | sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) } | |
1152 | ||
a0d0e21e | 1153 | =item crypt PLAINTEXT,SALT |
d74e8afc | 1154 | X<crypt> X<digest> X<hash> X<salt> X<plaintext> X<password> |
f723aae1 | 1155 | X<decrypt> X<cryptography> X<passwd> X<encrypt> |
a0d0e21e | 1156 | |
c17cdb72 NC |
1157 | =for Pod::Functions one-way passwd-style encryption |
1158 | ||
ef2e6798 MS |
1159 | Creates a digest string exactly like the crypt(3) function in the C |
1160 | library (assuming that you actually have a version there that has not | |
bb23f8d1 | 1161 | been extirpated as a potential munition). |
ef2e6798 | 1162 | |
34169887 | 1163 | crypt() is a one-way hash function. The PLAINTEXT and SALT are turned |
ef2e6798 MS |
1164 | into a short string, called a digest, which is returned. The same |
1165 | PLAINTEXT and SALT will always return the same string, but there is no | |
1166 | (known) way to get the original PLAINTEXT from the hash. Small | |
1167 | changes in the PLAINTEXT or SALT will result in large changes in the | |
1168 | digest. | |
1169 | ||
1170 | There is no decrypt function. This function isn't all that useful for | |
1171 | cryptography (for that, look for F<Crypt> modules on your nearby CPAN | |
1172 | mirror) and the name "crypt" is a bit of a misnomer. Instead it is | |
1173 | primarily used to check if two pieces of text are the same without | |
1174 | having to transmit or store the text itself. An example is checking | |
1175 | if a correct password is given. The digest of the password is stored, | |
cf264981 | 1176 | not the password itself. The user types in a password that is |
ef2e6798 | 1177 | crypt()'d with the same salt as the stored digest. If the two digests |
34169887 | 1178 | match, the password is correct. |
ef2e6798 MS |
1179 | |
1180 | When verifying an existing digest string you should use the digest as | |
1181 | the salt (like C<crypt($plain, $digest) eq $digest>). The SALT used | |
cf264981 | 1182 | to create the digest is visible as part of the digest. This ensures |
ef2e6798 MS |
1183 | crypt() will hash the new string with the same salt as the digest. |
1184 | This allows your code to work with the standard L<crypt|/crypt> and | |
8f1da26d TC |
1185 | with more exotic implementations. In other words, assume |
1186 | nothing about the returned string itself nor about how many bytes | |
1187 | of SALT may matter. | |
85c16d83 JH |
1188 | |
1189 | Traditionally the result is a string of 13 bytes: two first bytes of | |
1190 | the salt, followed by 11 bytes from the set C<[./0-9A-Za-z]>, and only | |
391b733c | 1191 | the first eight bytes of PLAINTEXT mattered. But alternative |
ef2e6798 | 1192 | hashing schemes (like MD5), higher level security schemes (like C2), |
e1020413 | 1193 | and implementations on non-Unix platforms may produce different |
ef2e6798 | 1194 | strings. |
85c16d83 JH |
1195 | |
1196 | When choosing a new salt create a random two character string whose | |
1197 | characters come from the set C<[./0-9A-Za-z]> (like C<join '', ('.', | |
d3989d75 CW |
1198 | '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]>). This set of |
1199 | characters is just a recommendation; the characters allowed in | |
1200 | the salt depend solely on your system's crypt library, and Perl can't | |
1201 | restrict what salts C<crypt()> accepts. | |
e71965be | 1202 | |
a0d0e21e | 1203 | Here's an example that makes sure that whoever runs this program knows |
cf264981 | 1204 | their password: |
a0d0e21e LW |
1205 | |
1206 | $pwd = (getpwuid($<))[1]; | |
a0d0e21e LW |
1207 | |
1208 | system "stty -echo"; | |
1209 | print "Password: "; | |
e71965be | 1210 | chomp($word = <STDIN>); |
a0d0e21e LW |
1211 | print "\n"; |
1212 | system "stty echo"; | |
1213 | ||
e71965be | 1214 | if (crypt($word, $pwd) ne $pwd) { |
a9a5a0dc | 1215 | die "Sorry...\n"; |
a0d0e21e | 1216 | } else { |
a9a5a0dc | 1217 | print "ok\n"; |
54310121 | 1218 | } |
a0d0e21e | 1219 | |
9f8f0c9d | 1220 | Of course, typing in your own password to whoever asks you |
748a9306 | 1221 | for it is unwise. |
a0d0e21e | 1222 | |
ef2e6798 | 1223 | The L<crypt|/crypt> function is unsuitable for hashing large quantities |
19799a22 | 1224 | of data, not least of all because you can't get the information |
ef2e6798 | 1225 | back. Look at the L<Digest> module for more robust algorithms. |
19799a22 | 1226 | |
f2791508 JH |
1227 | If using crypt() on a Unicode string (which I<potentially> has |
1228 | characters with codepoints above 255), Perl tries to make sense | |
34169887 | 1229 | of the situation by trying to downgrade (a copy of) |
f2791508 JH |
1230 | the string back to an eight-bit byte string before calling crypt() |
1231 | (on that copy). If that works, good. If not, crypt() dies with | |
1232 | C<Wide character in crypt>. | |
85c16d83 | 1233 | |
ea9eb35a BJ |
1234 | Portability issues: L<perlport/crypt>. |
1235 | ||
aa689395 | 1236 | =item dbmclose HASH |
d74e8afc | 1237 | X<dbmclose> |
a0d0e21e | 1238 | |
c17cdb72 NC |
1239 | =for Pod::Functions breaks binding on a tied dbm file |
1240 | ||
19799a22 | 1241 | [This function has been largely superseded by the C<untie> function.] |
a0d0e21e | 1242 | |
aa689395 | 1243 | Breaks the binding between a DBM file and a hash. |
a0d0e21e | 1244 | |
ea9eb35a BJ |
1245 | Portability issues: L<perlport/dbmclose>. |
1246 | ||
19799a22 | 1247 | =item dbmopen HASH,DBNAME,MASK |
d74e8afc | 1248 | X<dbmopen> X<dbm> X<ndbm> X<sdbm> X<gdbm> |
a0d0e21e | 1249 | |
c17cdb72 NC |
1250 | =for Pod::Functions create binding on a tied dbm file |
1251 | ||
01aa884e KW |
1252 | [This function has been largely superseded by the |
1253 | L<tie|/tie VARIABLE,CLASSNAME,LIST> function.] | |
a0d0e21e | 1254 | |
7b8d334a | 1255 | This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a |
19799a22 GS |
1256 | hash. HASH is the name of the hash. (Unlike normal C<open>, the first |
1257 | argument is I<not> a filehandle, even though it looks like one). DBNAME | |
aa689395 | 1258 | is the name of the database (without the F<.dir> or F<.pag> extension if |
1259 | any). If the database does not exist, it is created with protection | |
1b3a6178 FC |
1260 | specified by MASK (as modified by the C<umask>). To prevent creation of |
1261 | the database if it doesn't exist, you may specify a MODE | |
1262 | of 0, and the function will return a false value if it | |
1263 | can't find an existing database. If your system supports | |
80d38338 | 1264 | only the older DBM functions, you may make only one C<dbmopen> call in your |
aa689395 | 1265 | program. In older versions of Perl, if your system had neither DBM nor |
19799a22 | 1266 | ndbm, calling C<dbmopen> produced a fatal error; it now falls back to |
aa689395 | 1267 | sdbm(3). |
1268 | ||
1269 | If you don't have write access to the DBM file, you can only read hash | |
1270 | variables, not set them. If you want to test whether you can write, | |
3b10bc60 | 1271 | either use file tests or try setting a dummy hash entry inside an C<eval> |
1272 | to trap the error. | |
a0d0e21e | 1273 | |
19799a22 GS |
1274 | Note that functions such as C<keys> and C<values> may return huge lists |
1275 | when used on large DBM files. You may prefer to use the C<each> | |
a0d0e21e LW |
1276 | function to iterate over large DBM files. Example: |
1277 | ||
1278 | # print out history file offsets | |
1279 | dbmopen(%HIST,'/usr/lib/news/history',0666); | |
1280 | while (($key,$val) = each %HIST) { | |
a9a5a0dc | 1281 | print $key, ' = ', unpack('L',$val), "\n"; |
a0d0e21e LW |
1282 | } |
1283 | dbmclose(%HIST); | |
1284 | ||
cb1a09d0 | 1285 | See also L<AnyDBM_File> for a more general description of the pros and |
184e9718 | 1286 | cons of the various dbm approaches, as well as L<DB_File> for a particularly |
cb1a09d0 | 1287 | rich implementation. |
4633a7c4 | 1288 | |
2b5ab1e7 TC |
1289 | You can control which DBM library you use by loading that library |
1290 | before you call dbmopen(): | |
1291 | ||
1292 | use DB_File; | |
1293 | dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db") | |
a9a5a0dc | 1294 | or die "Can't open netscape history file: $!"; |
2b5ab1e7 | 1295 | |
ea9eb35a BJ |
1296 | Portability issues: L<perlport/dbmopen>. |
1297 | ||
a0d0e21e | 1298 | =item defined EXPR |
d74e8afc | 1299 | X<defined> X<undef> X<undefined> |
a0d0e21e | 1300 | |
54310121 | 1301 | =item defined |
bbce6d69 | 1302 | |
c17cdb72 NC |
1303 | =for Pod::Functions test whether a value, variable, or function is defined |
1304 | ||
2f9daede | 1305 | Returns a Boolean value telling whether EXPR has a value other than |
3b10bc60 | 1306 | the undefined value C<undef>. If EXPR is not present, C<$_> is |
2f9daede TP |
1307 | checked. |
1308 | ||
1309 | Many operations return C<undef> to indicate failure, end of file, | |
1310 | system error, uninitialized variable, and other exceptional | |
1311 | conditions. This function allows you to distinguish C<undef> from | |
1312 | other values. (A simple Boolean test will not distinguish among | |
7660c0ab | 1313 | C<undef>, zero, the empty string, and C<"0">, which are all equally |
2f9daede | 1314 | false.) Note that since C<undef> is a valid scalar, its presence |
19799a22 | 1315 | doesn't I<necessarily> indicate an exceptional condition: C<pop> |
2f9daede TP |
1316 | returns C<undef> when its argument is an empty array, I<or> when the |
1317 | element to return happens to be C<undef>. | |
1318 | ||
f10b0346 GS |
1319 | You may also use C<defined(&func)> to check whether subroutine C<&func> |
1320 | has ever been defined. The return value is unaffected by any forward | |
80d38338 | 1321 | declarations of C<&func>. A subroutine that is not defined |
847c7ebe | 1322 | may still be callable: its package may have an C<AUTOLOAD> method that |
3b10bc60 | 1323 | makes it spring into existence the first time that it is called; see |
847c7ebe | 1324 | L<perlsub>. |
f10b0346 GS |
1325 | |
1326 | Use of C<defined> on aggregates (hashes and arrays) is deprecated. It | |
34169887 | 1327 | used to report whether memory for that aggregate had ever been |
f10b0346 GS |
1328 | allocated. This behavior may disappear in future versions of Perl. |
1329 | You should instead use a simple test for size: | |
1330 | ||
1331 | if (@an_array) { print "has array elements\n" } | |
1332 | if (%a_hash) { print "has hash members\n" } | |
2f9daede TP |
1333 | |
1334 | When used on a hash element, it tells you whether the value is defined, | |
dc848c6f | 1335 | not whether the key exists in the hash. Use L</exists> for the latter |
2f9daede | 1336 | purpose. |
a0d0e21e LW |
1337 | |
1338 | Examples: | |
1339 | ||
8f1da26d | 1340 | print if defined $switch{D}; |
a0d0e21e LW |
1341 | print "$val\n" while defined($val = pop(@ary)); |
1342 | die "Can't readlink $sym: $!" | |
a9a5a0dc | 1343 | unless defined($value = readlink $sym); |
a0d0e21e | 1344 | sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } |
2f9daede | 1345 | $debugging = 0 unless defined $debugging; |
a0d0e21e | 1346 | |
8f1da26d | 1347 | Note: Many folks tend to overuse C<defined> and are then surprised to |
7660c0ab | 1348 | discover that the number C<0> and C<""> (the zero-length string) are, in fact, |
2f9daede | 1349 | defined values. For example, if you say |
a5f75d66 AD |
1350 | |
1351 | "ab" =~ /a(.*)b/; | |
1352 | ||
80d38338 | 1353 | The pattern match succeeds and C<$1> is defined, although it |
cf264981 | 1354 | matched "nothing". It didn't really fail to match anything. Rather, it |
2b5ab1e7 | 1355 | matched something that happened to be zero characters long. This is all |
a5f75d66 | 1356 | very above-board and honest. When a function returns an undefined value, |
2f9daede | 1357 | it's an admission that it couldn't give you an honest answer. So you |
3b10bc60 | 1358 | should use C<defined> only when questioning the integrity of what |
7660c0ab | 1359 | you're trying to do. At other times, a simple comparison to C<0> or C<""> is |
2f9daede TP |
1360 | what you want. |
1361 | ||
dc848c6f | 1362 | See also L</undef>, L</exists>, L</ref>. |
2f9daede | 1363 | |
a0d0e21e | 1364 | =item delete EXPR |
d74e8afc | 1365 | X<delete> |
a0d0e21e | 1366 | |
c17cdb72 NC |
1367 | =for Pod::Functions deletes a value from a hash |
1368 | ||
d0a76353 RS |
1369 | Given an expression that specifies an element or slice of a hash, C<delete> |
1370 | deletes the specified elements from that hash so that exists() on that element | |
1371 | no longer returns true. Setting a hash element to the undefined value does | |
1372 | not remove its key, but deleting it does; see L</exists>. | |
80d38338 | 1373 | |
8f1da26d | 1374 | In list context, returns the value or values deleted, or the last such |
80d38338 | 1375 | element in scalar context. The return list's length always matches that of |
d0a76353 RS |
1376 | the argument list: deleting non-existent elements returns the undefined value |
1377 | in their corresponding positions. | |
80d38338 | 1378 | |
d0a76353 RS |
1379 | delete() may also be used on arrays and array slices, but its behavior is less |
1380 | straightforward. Although exists() will return false for deleted entries, | |
1381 | deleting array elements never changes indices of existing values; use shift() | |
deaf6ad3 | 1382 | or splice() for that. However, if any deleted elements fall at the end of an |
d0a76353 | 1383 | array, the array's size shrinks to the position of the highest element that |
444d4f5c | 1384 | still tests true for exists(), or to 0 if none do. In other words, an |
deaf6ad3 | 1385 | array won't have trailing nonexistent elements after a delete. |
d0a76353 | 1386 | |
2fbadc08 RS |
1387 | B<WARNING:> Calling C<delete> on array values is strongly discouraged. The |
1388 | notion of deleting or checking the existence of Perl array elements is not | |
1389 | conceptually coherent, and can lead to surprising behavior. | |
80d38338 TC |
1390 | |
1391 | Deleting from C<%ENV> modifies the environment. Deleting from a hash tied to | |
1392 | a DBM file deletes the entry from the DBM file. Deleting from a C<tied> hash | |
1393 | or array may not necessarily return anything; it depends on the implementation | |
1394 | of the C<tied> package's DELETE method, which may do whatever it pleases. | |
a0d0e21e | 1395 | |
80d38338 TC |
1396 | The C<delete local EXPR> construct localizes the deletion to the current |
1397 | block at run time. Until the block exits, elements locally deleted | |
1398 | temporarily no longer exist. See L<perlsub/"Localized deletion of elements | |
1399 | of composite types">. | |
eba0920a EM |
1400 | |
1401 | %hash = (foo => 11, bar => 22, baz => 33); | |
f7051f2c FC |
1402 | $scalar = delete $hash{foo}; # $scalar is 11 |
1403 | $scalar = delete @hash{qw(foo bar)}; # $scalar is 22 | |
1404 | @array = delete @hash{qw(foo baz)}; # @array is (undef,33) | |
eba0920a | 1405 | |
01020589 | 1406 | The following (inefficiently) deletes all the values of %HASH and @ARRAY: |
a0d0e21e | 1407 | |
5f05dabc | 1408 | foreach $key (keys %HASH) { |
a9a5a0dc | 1409 | delete $HASH{$key}; |
a0d0e21e LW |
1410 | } |
1411 | ||
01020589 | 1412 | foreach $index (0 .. $#ARRAY) { |
a9a5a0dc | 1413 | delete $ARRAY[$index]; |
01020589 GS |
1414 | } |
1415 | ||
1416 | And so do these: | |
5f05dabc | 1417 | |
01020589 GS |
1418 | delete @HASH{keys %HASH}; |
1419 | ||
9740c838 | 1420 | delete @ARRAY[0 .. $#ARRAY]; |
5f05dabc | 1421 | |
80d38338 TC |
1422 | But both are slower than assigning the empty list |
1423 | or undefining %HASH or @ARRAY, which is the customary | |
1424 | way to empty out an aggregate: | |
01020589 | 1425 | |
5ed4f2ec | 1426 | %HASH = (); # completely empty %HASH |
1427 | undef %HASH; # forget %HASH ever existed | |
2b5ab1e7 | 1428 | |
5ed4f2ec | 1429 | @ARRAY = (); # completely empty @ARRAY |
1430 | undef @ARRAY; # forget @ARRAY ever existed | |
2b5ab1e7 | 1431 | |
80d38338 TC |
1432 | The EXPR can be arbitrarily complicated provided its |
1433 | final operation is an element or slice of an aggregate: | |
a0d0e21e LW |
1434 | |
1435 | delete $ref->[$x][$y]{$key}; | |
5f05dabc | 1436 | delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys}; |
a0d0e21e | 1437 | |
01020589 GS |
1438 | delete $ref->[$x][$y][$index]; |
1439 | delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices]; | |
1440 | ||
a0d0e21e | 1441 | =item die LIST |
d74e8afc | 1442 | X<die> X<throw> X<exception> X<raise> X<$@> X<abort> |
a0d0e21e | 1443 | |
c17cdb72 NC |
1444 | =for Pod::Functions raise an exception or bail out |
1445 | ||
391b733c | 1446 | C<die> raises an exception. Inside an C<eval> the error message is stuffed |
4c050ad5 NC |
1447 | into C<$@> and the C<eval> is terminated with the undefined value. |
1448 | If the exception is outside of all enclosing C<eval>s, then the uncaught | |
391b733c | 1449 | exception prints LIST to C<STDERR> and exits with a non-zero value. If you |
96090e4f | 1450 | need to exit the process with a specific exit code, see L</exit>. |
a0d0e21e LW |
1451 | |
1452 | Equivalent examples: | |
1453 | ||
1454 | die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; | |
54310121 | 1455 | chdir '/usr/spool/news' or die "Can't cd to spool: $!\n" |
a0d0e21e | 1456 | |
ccac6780 | 1457 | If the last element of LIST does not end in a newline, the current |
df37ec69 WW |
1458 | script line number and input line number (if any) are also printed, |
1459 | and a newline is supplied. Note that the "input line number" (also | |
1460 | known as "chunk") is subject to whatever notion of "line" happens to | |
1461 | be currently in effect, and is also available as the special variable | |
1462 | C<$.>. See L<perlvar/"$/"> and L<perlvar/"$.">. | |
1463 | ||
1464 | Hint: sometimes appending C<", stopped"> to your message will cause it | |
1465 | to make better sense when the string C<"at foo line 123"> is appended. | |
1466 | Suppose you are running script "canasta". | |
a0d0e21e LW |
1467 | |
1468 | die "/etc/games is no good"; | |
1469 | die "/etc/games is no good, stopped"; | |
1470 | ||
1471 | produce, respectively | |
1472 | ||
1473 | /etc/games is no good at canasta line 123. | |
1474 | /etc/games is no good, stopped at canasta line 123. | |
1475 | ||
a96d0188 | 1476 | If the output is empty and C<$@> already contains a value (typically from a |
7660c0ab | 1477 | previous eval) that value is reused after appending C<"\t...propagated">. |
fb73857a | 1478 | This is useful for propagating exceptions: |
1479 | ||
1480 | eval { ... }; | |
1481 | die unless $@ =~ /Expected exception/; | |
1482 | ||
a96d0188 | 1483 | If the output is empty and C<$@> contains an object reference that has a |
ad216e65 JH |
1484 | C<PROPAGATE> method, that method will be called with additional file |
1485 | and line number parameters. The return value replaces the value in | |
34169887 | 1486 | C<$@>; i.e., as if C<< $@ = eval { $@->PROPAGATE(__FILE__, __LINE__) }; >> |
ad216e65 JH |
1487 | were called. |
1488 | ||
7660c0ab | 1489 | If C<$@> is empty then the string C<"Died"> is used. |
fb73857a | 1490 | |
4c050ad5 NC |
1491 | If an uncaught exception results in interpreter exit, the exit code is |
1492 | determined from the values of C<$!> and C<$?> with this pseudocode: | |
1493 | ||
1494 | exit $! if $!; # errno | |
1495 | exit $? >> 8 if $? >> 8; # child exit status | |
1496 | exit 255; # last resort | |
1497 | ||
1498 | The intent is to squeeze as much possible information about the likely cause | |
391b733c FC |
1499 | into the limited space of the system exit |
1500 | code. However, as C<$!> is the value | |
4c050ad5 NC |
1501 | of C's C<errno>, which can be set by any system call, this means that the value |
1502 | of the exit code used by C<die> can be non-predictable, so should not be relied | |
1503 | upon, other than to be non-zero. | |
1504 | ||
80d38338 TC |
1505 | You can also call C<die> with a reference argument, and if this is trapped |
1506 | within an C<eval>, C<$@> contains that reference. This permits more | |
1507 | elaborate exception handling using objects that maintain arbitrary state | |
1508 | about the exception. Such a scheme is sometimes preferable to matching | |
1509 | particular string values of C<$@> with regular expressions. Because C<$@> | |
1510 | is a global variable and C<eval> may be used within object implementations, | |
1511 | be careful that analyzing the error object doesn't replace the reference in | |
1512 | the global variable. It's easiest to make a local copy of the reference | |
1513 | before any manipulations. Here's an example: | |
52531d10 | 1514 | |
80d38338 | 1515 | use Scalar::Util "blessed"; |
da279afe | 1516 | |
52531d10 | 1517 | eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) }; |
746d7dd7 | 1518 | if (my $ev_err = $@) { |
f7051f2c FC |
1519 | if (blessed($ev_err) |
1520 | && $ev_err->isa("Some::Module::Exception")) { | |
52531d10 GS |
1521 | # handle Some::Module::Exception |
1522 | } | |
1523 | else { | |
1524 | # handle all other possible exceptions | |
1525 | } | |
1526 | } | |
1527 | ||
3b10bc60 | 1528 | Because Perl stringifies uncaught exception messages before display, |
80d38338 | 1529 | you'll probably want to overload stringification operations on |
52531d10 GS |
1530 | exception objects. See L<overload> for details about that. |
1531 | ||
19799a22 GS |
1532 | You can arrange for a callback to be run just before the C<die> |
1533 | does its deed, by setting the C<$SIG{__DIE__}> hook. The associated | |
3b10bc60 | 1534 | handler is called with the error text and can change the error |
19799a22 | 1535 | message, if it sees fit, by calling C<die> again. See |
96090e4f | 1536 | L<perlvar/%SIG> for details on setting C<%SIG> entries, and |
cf264981 | 1537 | L<"eval BLOCK"> for some examples. Although this feature was |
19799a22 | 1538 | to be run only right before your program was to exit, this is not |
3b10bc60 | 1539 | currently so: the C<$SIG{__DIE__}> hook is currently called |
19799a22 GS |
1540 | even inside eval()ed blocks/strings! If one wants the hook to do |
1541 | nothing in such situations, put | |
fb73857a | 1542 | |
5ed4f2ec | 1543 | die @_ if $^S; |
fb73857a | 1544 | |
19799a22 GS |
1545 | as the first line of the handler (see L<perlvar/$^S>). Because |
1546 | this promotes strange action at a distance, this counterintuitive | |
b76cc8ba | 1547 | behavior may be fixed in a future release. |
774d564b | 1548 | |
4c050ad5 NC |
1549 | See also exit(), warn(), and the Carp module. |
1550 | ||
a0d0e21e | 1551 | =item do BLOCK |
d74e8afc | 1552 | X<do> X<block> |
a0d0e21e | 1553 | |
c17cdb72 NC |
1554 | =for Pod::Functions turn a BLOCK into a TERM |
1555 | ||
a0d0e21e | 1556 | Not really a function. Returns the value of the last command in the |
6b275a1f RGS |
1557 | sequence of commands indicated by BLOCK. When modified by the C<while> or |
1558 | C<until> loop modifier, executes the BLOCK once before testing the loop | |
391b733c | 1559 | condition. (On other statements the loop modifiers test the conditional |
6b275a1f | 1560 | first.) |
a0d0e21e | 1561 | |
4968c1e4 | 1562 | C<do BLOCK> does I<not> count as a loop, so the loop control statements |
2b5ab1e7 TC |
1563 | C<next>, C<last>, or C<redo> cannot be used to leave or restart the block. |
1564 | See L<perlsyn> for alternative strategies. | |
4968c1e4 | 1565 | |
a0d0e21e | 1566 | =item do EXPR |
d74e8afc | 1567 | X<do> |
a0d0e21e LW |
1568 | |
1569 | Uses the value of EXPR as a filename and executes the contents of the | |
ea63ef19 | 1570 | file as a Perl script. |
a0d0e21e LW |
1571 | |
1572 | do 'stat.pl'; | |
1573 | ||
c319391a | 1574 | is largely like |
a0d0e21e | 1575 | |
986b19de | 1576 | eval `cat stat.pl`; |
a0d0e21e | 1577 | |
c319391a AC |
1578 | except that it's more concise, runs no external processes, keeps track of |
1579 | the current | |
96090e4f LB |
1580 | filename for error messages, searches the C<@INC> directories, and updates |
1581 | C<%INC> if the file is found. See L<perlvar/@INC> and L<perlvar/%INC> for | |
1582 | these variables. It also differs in that code evaluated with C<do FILENAME> | |
2b5ab1e7 TC |
1583 | cannot see lexicals in the enclosing scope; C<eval STRING> does. It's the |
1584 | same, however, in that it does reparse the file every time you call it, | |
1585 | so you probably don't want to do this inside a loop. | |
a0d0e21e | 1586 | |
8f1da26d | 1587 | If C<do> can read the file but cannot compile it, it returns C<undef> and sets |
9dc513c5 DG |
1588 | an error message in C<$@>. If C<do> cannot read the file, it returns undef |
1589 | and sets C<$!> to the error. Always check C<$@> first, as compilation | |
1590 | could fail in a way that also sets C<$!>. If the file is successfully | |
1591 | compiled, C<do> returns the value of the last expression evaluated. | |
8e30cc93 | 1592 | |
80d38338 | 1593 | Inclusion of library modules is better done with the |
19799a22 | 1594 | C<use> and C<require> operators, which also do automatic error checking |
4633a7c4 | 1595 | and raise an exception if there's a problem. |
a0d0e21e | 1596 | |
5a964f20 TC |
1597 | You might like to use C<do> to read in a program configuration |
1598 | file. Manual error checking can be done this way: | |
1599 | ||
b76cc8ba | 1600 | # read in config files: system first, then user |
f86cebdf | 1601 | for $file ("/share/prog/defaults.rc", |
b76cc8ba | 1602 | "$ENV{HOME}/.someprogrc") |
a9a5a0dc VP |
1603 | { |
1604 | unless ($return = do $file) { | |
1605 | warn "couldn't parse $file: $@" if $@; | |
1606 | warn "couldn't do $file: $!" unless defined $return; | |
1607 | warn "couldn't run $file" unless $return; | |
1608 | } | |
5a964f20 TC |
1609 | } |
1610 | ||
a0d0e21e | 1611 | =item dump LABEL |
d74e8afc | 1612 | X<dump> X<core> X<undump> |
a0d0e21e | 1613 | |
8a7e748e FC |
1614 | =item dump EXPR |
1615 | ||
1614b0e3 JD |
1616 | =item dump |
1617 | ||
c17cdb72 NC |
1618 | =for Pod::Functions create an immediate core dump |
1619 | ||
19799a22 GS |
1620 | This function causes an immediate core dump. See also the B<-u> |
1621 | command-line switch in L<perlrun>, which does the same thing. | |
1622 | Primarily this is so that you can use the B<undump> program (not | |
1623 | supplied) to turn your core dump into an executable binary after | |
1624 | having initialized all your variables at the beginning of the | |
1625 | program. When the new binary is executed it will begin by executing | |
1626 | a C<goto LABEL> (with all the restrictions that C<goto> suffers). | |
1627 | Think of it as a goto with an intervening core dump and reincarnation. | |
8a7e748e FC |
1628 | If C<LABEL> is omitted, restarts the program from the top. The |
1629 | C<dump EXPR> form, available starting in Perl 5.18.0, allows a name to be | |
1630 | computed at run time, being otherwise identical to C<dump LABEL>. | |
19799a22 GS |
1631 | |
1632 | B<WARNING>: Any files opened at the time of the dump will I<not> | |
1633 | be open any more when the program is reincarnated, with possible | |
80d38338 | 1634 | resulting confusion by Perl. |
19799a22 | 1635 | |
59f521f4 | 1636 | This function is now largely obsolete, mostly because it's very hard to |
391b733c | 1637 | convert a core file into an executable. That's why you should now invoke |
59f521f4 | 1638 | it as C<CORE::dump()>, if you don't want to be warned against a possible |
ac206dc8 | 1639 | typo. |
19799a22 | 1640 | |
2ba1f20a FC |
1641 | Unlike most named operators, this has the same precedence as assignment. |
1642 | It is also exempt from the looks-like-a-function rule, so | |
1643 | C<dump ("foo")."bar"> will cause "bar" to be part of the argument to | |
1644 | C<dump>. | |
1645 | ||
ea9eb35a BJ |
1646 | Portability issues: L<perlport/dump>. |
1647 | ||
532eee96 | 1648 | =item each HASH |
d74e8afc | 1649 | X<each> X<hash, iterator> |
aa689395 | 1650 | |
532eee96 | 1651 | =item each ARRAY |
aeedbbed NC |
1652 | X<array, iterator> |
1653 | ||
f5a93a43 TC |
1654 | =item each EXPR |
1655 | ||
c17cdb72 NC |
1656 | =for Pod::Functions retrieve the next key/value pair from a hash |
1657 | ||
bade7fbc TC |
1658 | When called on a hash in list context, returns a 2-element list |
1659 | consisting of the key and value for the next element of a hash. In Perl | |
1660 | 5.12 and later only, it will also return the index and value for the next | |
1661 | element of an array so that you can iterate over it; older Perls consider | |
1662 | this a syntax error. When called in scalar context, returns only the key | |
1663 | (not the value) in a hash, or the index in an array. | |
2f9daede | 1664 | |
aeedbbed | 1665 | Hash entries are returned in an apparently random order. The actual random |
7bf59113 | 1666 | order is specific to a given hash; the exact same series of operations |
7161e5c2 | 1667 | on two hashes may result in a different order for each hash. Any insertion |
7bf59113 YO |
1668 | into the hash may change the order, as will any deletion, with the exception |
1669 | that the most recent key returned by C<each> or C<keys> may be deleted | |
7161e5c2 | 1670 | without changing the order. So long as a given hash is unmodified you may |
7bf59113 | 1671 | rely on C<keys>, C<values> and C<each> to repeatedly return the same order |
7161e5c2 FC |
1672 | as each other. See L<perlsec/"Algorithmic Complexity Attacks"> for |
1673 | details on why hash order is randomized. Aside from the guarantees | |
7bf59113 YO |
1674 | provided here the exact details of Perl's hash algorithm and the hash |
1675 | traversal order are subject to change in any release of Perl. | |
ab192400 | 1676 | |
80d38338 TC |
1677 | After C<each> has returned all entries from the hash or array, the next |
1678 | call to C<each> returns the empty list in list context and C<undef> in | |
bade7fbc TC |
1679 | scalar context; the next call following I<that> one restarts iteration. |
1680 | Each hash or array has its own internal iterator, accessed by C<each>, | |
1681 | C<keys>, and C<values>. The iterator is implicitly reset when C<each> has | |
1682 | reached the end as just described; it can be explicitly reset by calling | |
1683 | C<keys> or C<values> on the hash or array. If you add or delete a hash's | |
49daec89 DM |
1684 | elements while iterating over it, the effect on the iterator is |
1685 | unspecified; for example, entries may be skipped or duplicated--so don't | |
d8021140 PJ |
1686 | do that. Exception: It is always safe to delete the item most recently |
1687 | returned by C<each()>, so the following code works properly: | |
74fc8b5f MJD |
1688 | |
1689 | while (($key, $value) = each %hash) { | |
1690 | print $key, "\n"; | |
1691 | delete $hash{$key}; # This is safe | |
1692 | } | |
aa689395 | 1693 | |
883f220b TC |
1694 | Tied hashes may have a different ordering behaviour to perl's hash |
1695 | implementation. | |
1696 | ||
80d38338 | 1697 | This prints out your environment like the printenv(1) program, |
3b10bc60 | 1698 | but in a different order: |
a0d0e21e LW |
1699 | |
1700 | while (($key,$value) = each %ENV) { | |
a9a5a0dc | 1701 | print "$key=$value\n"; |
a0d0e21e LW |
1702 | } |
1703 | ||
f5a93a43 TC |
1704 | Starting with Perl 5.14, C<each> can take a scalar EXPR, which must hold |
1705 | reference to an unblessed hash or array. The argument will be dereferenced | |
1706 | automatically. This aspect of C<each> is considered highly experimental. | |
1707 | The exact behaviour may change in a future version of Perl. | |
cba5a3b0 DG |
1708 | |
1709 | while (($key,$value) = each $hashref) { ... } | |
1710 | ||
e6a0db3e FC |
1711 | As of Perl 5.18 you can use a bare C<each> in a C<while> loop, |
1712 | which will set C<$_> on every iteration. | |
1713 | ||
1714 | while(each %ENV) { | |
1715 | print "$_=$ENV{$_}\n"; | |
1716 | } | |
1717 | ||
bade7fbc TC |
1718 | To avoid confusing would-be users of your code who are running earlier |
1719 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
1720 | the top of your file to signal that your code will work I<only> on Perls of | |
1721 | a recent vintage: | |
1722 | ||
1723 | use 5.012; # so keys/values/each work on arrays | |
1724 | use 5.014; # so keys/values/each work on scalars (experimental) | |
e6a0db3e | 1725 | use 5.018; # so each assigns to $_ in a lone while test |
bade7fbc | 1726 | |
8f1da26d | 1727 | See also C<keys>, C<values>, and C<sort>. |
a0d0e21e LW |
1728 | |
1729 | =item eof FILEHANDLE | |
d74e8afc ITB |
1730 | X<eof> |
1731 | X<end of file> | |
1732 | X<end-of-file> | |
a0d0e21e | 1733 | |
4633a7c4 LW |
1734 | =item eof () |
1735 | ||
a0d0e21e LW |
1736 | =item eof |
1737 | ||
c17cdb72 NC |
1738 | =for Pod::Functions test a filehandle for its end |
1739 | ||
8f1da26d | 1740 | Returns 1 if the next read on FILEHANDLE will return end of file I<or> if |
a0d0e21e | 1741 | FILEHANDLE is not open. FILEHANDLE may be an expression whose value |
5a964f20 | 1742 | gives the real filehandle. (Note that this function actually |
80d38338 | 1743 | reads a character and then C<ungetc>s it, so isn't useful in an |
748a9306 | 1744 | interactive context.) Do not read from a terminal file (or call |
19799a22 | 1745 | C<eof(FILEHANDLE)> on it) after end-of-file is reached. File types such |
748a9306 LW |
1746 | as terminals may lose the end-of-file condition if you do. |
1747 | ||
820475bd | 1748 | An C<eof> without an argument uses the last file read. Using C<eof()> |
80d38338 | 1749 | with empty parentheses is different. It refers to the pseudo file |
820475bd | 1750 | formed from the files listed on the command line and accessed via the |
61eff3bc JH |
1751 | C<< <> >> operator. Since C<< <> >> isn't explicitly opened, |
1752 | as a normal filehandle is, an C<eof()> before C<< <> >> has been | |
820475bd | 1753 | used will cause C<@ARGV> to be examined to determine if input is |
67408cae | 1754 | available. Similarly, an C<eof()> after C<< <> >> has returned |
efdd0218 RB |
1755 | end-of-file will assume you are processing another C<@ARGV> list, |
1756 | and if you haven't set C<@ARGV>, will read input from C<STDIN>; | |
1757 | see L<perlop/"I/O Operators">. | |
820475bd | 1758 | |
61eff3bc | 1759 | In a C<< while (<>) >> loop, C<eof> or C<eof(ARGV)> can be used to |
8f1da26d TC |
1760 | detect the end of each file, whereas C<eof()> will detect the end |
1761 | of the very last file only. Examples: | |
a0d0e21e | 1762 | |
748a9306 LW |
1763 | # reset line numbering on each input file |
1764 | while (<>) { | |
a9a5a0dc VP |
1765 | next if /^\s*#/; # skip comments |
1766 | print "$.\t$_"; | |
5a964f20 | 1767 | } continue { |
a9a5a0dc | 1768 | close ARGV if eof; # Not eof()! |
748a9306 LW |
1769 | } |
1770 | ||
a0d0e21e LW |
1771 | # insert dashes just before last line of last file |
1772 | while (<>) { | |
a9a5a0dc VP |
1773 | if (eof()) { # check for end of last file |
1774 | print "--------------\n"; | |
1775 | } | |
1776 | print; | |
f7051f2c | 1777 | last if eof(); # needed if we're reading from a terminal |
a0d0e21e LW |
1778 | } |
1779 | ||
a0d0e21e | 1780 | Practical hint: you almost never need to use C<eof> in Perl, because the |
8f1da26d TC |
1781 | input operators typically return C<undef> when they run out of data or |
1782 | encounter an error. | |
a0d0e21e LW |
1783 | |
1784 | =item eval EXPR | |
d74e8afc | 1785 | X<eval> X<try> X<catch> X<evaluate> X<parse> X<execute> |
f723aae1 | 1786 | X<error, handling> X<exception, handling> |
a0d0e21e LW |
1787 | |
1788 | =item eval BLOCK | |
1789 | ||
ce2984c3 PF |
1790 | =item eval |
1791 | ||
c17cdb72 NC |
1792 | =for Pod::Functions catch exceptions or compile and run code |
1793 | ||
798dc914 KW |
1794 | In the first form, often referred to as a "string eval", the return |
1795 | value of EXPR is parsed and executed as if it | |
c7cc6f1c | 1796 | were a little Perl program. The value of the expression (which is itself |
8f1da26d | 1797 | determined within scalar context) is first parsed, and if there were no |
2341804c | 1798 | errors, executed as a block within the lexical context of the current Perl |
df4833a8 | 1799 | program. This means, that in particular, any outer lexical variables are |
2341804c DM |
1800 | visible to it, and any package variable settings or subroutine and format |
1801 | definitions remain afterwards. | |
1802 | ||
1803 | Note that the value is parsed every time the C<eval> executes. | |
be3174d2 GS |
1804 | If EXPR is omitted, evaluates C<$_>. This form is typically used to |
1805 | delay parsing and subsequent execution of the text of EXPR until run time. | |
c7cc6f1c | 1806 | |
7289c5e6 FC |
1807 | If the C<unicode_eval> feature is enabled (which is the default under a |
1808 | C<use 5.16> or higher declaration), EXPR or C<$_> is treated as a string of | |
1809 | characters, so C<use utf8> declarations have no effect, and source filters | |
1810 | are forbidden. In the absence of the C<unicode_eval> feature, the string | |
1811 | will sometimes be treated as characters and sometimes as bytes, depending | |
1812 | on the internal encoding, and source filters activated within the C<eval> | |
1813 | exhibit the erratic, but historical, behaviour of affecting some outer file | |
1814 | scope that is still compiling. See also the L</evalbytes> keyword, which | |
1815 | always treats its input as a byte stream and works properly with source | |
1816 | filters, and the L<feature> pragma. | |
1817 | ||
798dc914 KW |
1818 | Problems can arise if the string expands a scalar containing a floating |
1819 | point number. That scalar can expand to letters, such as C<"NaN"> or | |
1820 | C<"Infinity">; or, within the scope of a C<use locale>, the decimal | |
1821 | point character may be something other than a dot (such as a comma). | |
1822 | None of these are likely to parse as you are likely expecting. | |
1823 | ||
c7cc6f1c | 1824 | In the second form, the code within the BLOCK is parsed only once--at the |
cf264981 | 1825 | same time the code surrounding the C<eval> itself was parsed--and executed |
c7cc6f1c GS |
1826 | within the context of the current Perl program. This form is typically |
1827 | used to trap exceptions more efficiently than the first (see below), while | |
1828 | also providing the benefit of checking the code within BLOCK at compile | |
1829 | time. | |
1830 | ||
1831 | The final semicolon, if any, may be omitted from the value of EXPR or within | |
1832 | the BLOCK. | |
1833 | ||
1834 | In both forms, the value returned is the value of the last expression | |
5a964f20 | 1835 | evaluated inside the mini-program; a return statement may be also used, just |
c7cc6f1c | 1836 | as with subroutines. The expression providing the return value is evaluated |
cf264981 SP |
1837 | in void, scalar, or list context, depending on the context of the C<eval> |
1838 | itself. See L</wantarray> for more on how the evaluation context can be | |
1839 | determined. | |
a0d0e21e | 1840 | |
19799a22 | 1841 | If there is a syntax error or runtime error, or a C<die> statement is |
8f1da26d | 1842 | executed, C<eval> returns C<undef> in scalar context |
774b80e8 FC |
1843 | or an empty list in list context, and C<$@> is set to the error |
1844 | message. (Prior to 5.16, a bug caused C<undef> to be returned | |
1845 | in list context for syntax errors, but not for runtime errors.) | |
1846 | If there was no error, C<$@> is set to the empty string. A | |
9cc672d4 FC |
1847 | control flow operator like C<last> or C<goto> can bypass the setting of |
1848 | C<$@>. Beware that using C<eval> neither silences Perl from printing | |
c7cc6f1c | 1849 | warnings to STDERR, nor does it stuff the text of warning messages into C<$@>. |
d9984052 A |
1850 | To do either of those, you have to use the C<$SIG{__WARN__}> facility, or |
1851 | turn off warnings inside the BLOCK or EXPR using S<C<no warnings 'all'>>. | |
44ecbbd8 | 1852 | See L</warn>, L<perlvar>, and L<warnings>. |
a0d0e21e | 1853 | |
19799a22 GS |
1854 | Note that, because C<eval> traps otherwise-fatal errors, it is useful for |
1855 | determining whether a particular feature (such as C<socket> or C<symlink>) | |
82bcec1b | 1856 | is implemented. It is also Perl's exception-trapping mechanism, where |
a0d0e21e LW |
1857 | the die operator is used to raise exceptions. |
1858 | ||
5f1da31c NT |
1859 | If you want to trap errors when loading an XS module, some problems with |
1860 | the binary interface (such as Perl version skew) may be fatal even with | |
df4833a8 | 1861 | C<eval> unless C<$ENV{PERL_DL_NONLAZY}> is set. See L<perlrun>. |
5f1da31c | 1862 | |
a0d0e21e LW |
1863 | If the code to be executed doesn't vary, you may use the eval-BLOCK |
1864 | form to trap run-time errors without incurring the penalty of | |
1865 | recompiling each time. The error, if any, is still returned in C<$@>. | |
1866 | Examples: | |
1867 | ||
54310121 | 1868 | # make divide-by-zero nonfatal |
a0d0e21e LW |
1869 | eval { $answer = $a / $b; }; warn $@ if $@; |
1870 | ||
1871 | # same thing, but less efficient | |
1872 | eval '$answer = $a / $b'; warn $@ if $@; | |
1873 | ||
1874 | # a compile-time error | |
5ed4f2ec | 1875 | eval { $answer = }; # WRONG |
a0d0e21e LW |
1876 | |
1877 | # a run-time error | |
5ed4f2ec | 1878 | eval '$answer ='; # sets $@ |
a0d0e21e | 1879 | |
cf264981 SP |
1880 | Using the C<eval{}> form as an exception trap in libraries does have some |
1881 | issues. Due to the current arguably broken state of C<__DIE__> hooks, you | |
1882 | may wish not to trigger any C<__DIE__> hooks that user code may have installed. | |
2b5ab1e7 | 1883 | You can use the C<local $SIG{__DIE__}> construct for this purpose, |
80d38338 | 1884 | as this example shows: |
774d564b | 1885 | |
80d38338 | 1886 | # a private exception trap for divide-by-zero |
f86cebdf GS |
1887 | eval { local $SIG{'__DIE__'}; $answer = $a / $b; }; |
1888 | warn $@ if $@; | |
774d564b | 1889 | |
1890 | This is especially significant, given that C<__DIE__> hooks can call | |
19799a22 | 1891 | C<die> again, which has the effect of changing their error messages: |
774d564b | 1892 | |
1893 | # __DIE__ hooks may modify error messages | |
1894 | { | |
f86cebdf GS |
1895 | local $SIG{'__DIE__'} = |
1896 | sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x }; | |
c7cc6f1c GS |
1897 | eval { die "foo lives here" }; |
1898 | print $@ if $@; # prints "bar lives here" | |
774d564b | 1899 | } |
1900 | ||
19799a22 | 1901 | Because this promotes action at a distance, this counterintuitive behavior |
2b5ab1e7 TC |
1902 | may be fixed in a future release. |
1903 | ||
19799a22 | 1904 | With an C<eval>, you should be especially careful to remember what's |
a0d0e21e LW |
1905 | being looked at when: |
1906 | ||
5ed4f2ec | 1907 | eval $x; # CASE 1 |
1908 | eval "$x"; # CASE 2 | |
a0d0e21e | 1909 | |
5ed4f2ec | 1910 | eval '$x'; # CASE 3 |
1911 | eval { $x }; # CASE 4 | |
a0d0e21e | 1912 | |
5ed4f2ec | 1913 | eval "\$$x++"; # CASE 5 |
1914 | $$x++; # CASE 6 | |
a0d0e21e | 1915 | |
2f9daede | 1916 | Cases 1 and 2 above behave identically: they run the code contained in |
19799a22 | 1917 | the variable $x. (Although case 2 has misleading double quotes making |
2f9daede | 1918 | the reader wonder what else might be happening (nothing is).) Cases 3 |
7660c0ab | 1919 | and 4 likewise behave in the same way: they run the code C<'$x'>, which |
19799a22 | 1920 | does nothing but return the value of $x. (Case 4 is preferred for |
2f9daede TP |
1921 | purely visual reasons, but it also has the advantage of compiling at |
1922 | compile-time instead of at run-time.) Case 5 is a place where | |
19799a22 | 1923 | normally you I<would> like to use double quotes, except that in this |
2f9daede TP |
1924 | particular situation, you can just use symbolic references instead, as |
1925 | in case 6. | |
a0d0e21e | 1926 | |
b6538e4f | 1927 | Before Perl 5.14, the assignment to C<$@> occurred before restoration |
bade7fbc | 1928 | of localized variables, which means that for your code to run on older |
b208c909 | 1929 | versions, a temporary is required if you want to mask some but not all |
8a5a710d DN |
1930 | errors: |
1931 | ||
1932 | # alter $@ on nefarious repugnancy only | |
1933 | { | |
1934 | my $e; | |
1935 | { | |
f7051f2c FC |
1936 | local $@; # protect existing $@ |
1937 | eval { test_repugnancy() }; | |
1938 | # $@ =~ /nefarious/ and die $@; # Perl 5.14 and higher only | |
1939 | $@ =~ /nefarious/ and $e = $@; | |
8a5a710d DN |
1940 | } |
1941 | die $e if defined $e | |
1942 | } | |
1943 | ||
4968c1e4 | 1944 | C<eval BLOCK> does I<not> count as a loop, so the loop control statements |
2b5ab1e7 | 1945 | C<next>, C<last>, or C<redo> cannot be used to leave or restart the block. |
4968c1e4 | 1946 | |
4f00fc7e FC |
1947 | An C<eval ''> executed within a subroutine defined |
1948 | in the C<DB> package doesn't see the usual | |
3b10bc60 | 1949 | surrounding lexical scope, but rather the scope of the first non-DB piece |
df4833a8 | 1950 | of code that called it. You don't normally need to worry about this unless |
3b10bc60 | 1951 | you are writing a Perl debugger. |
d819b83a | 1952 | |
7289c5e6 FC |
1953 | =item evalbytes EXPR |
1954 | X<evalbytes> | |
1955 | ||
1956 | =item evalbytes | |
1957 | ||
d9b04284 | 1958 | =for Pod::Functions +evalbytes similar to string eval, but intend to parse a bytestream |
c17cdb72 | 1959 | |
7289c5e6 FC |
1960 | This function is like L</eval> with a string argument, except it always |
1961 | parses its argument, or C<$_> if EXPR is omitted, as a string of bytes. A | |
1962 | string containing characters whose ordinal value exceeds 255 results in an | |
1963 | error. Source filters activated within the evaluated code apply to the | |
1964 | code itself. | |
1965 | ||
1966 | This function is only available under the C<evalbytes> feature, a | |
1967 | C<use v5.16> (or higher) declaration, or with a C<CORE::> prefix. See | |
1968 | L<feature> for more information. | |
1969 | ||
a0d0e21e | 1970 | =item exec LIST |
d74e8afc | 1971 | X<exec> X<execute> |
a0d0e21e | 1972 | |
8bf3b016 GS |
1973 | =item exec PROGRAM LIST |
1974 | ||
c17cdb72 NC |
1975 | =for Pod::Functions abandon this program to run another |
1976 | ||
3b10bc60 | 1977 | The C<exec> function executes a system command I<and never returns>; |
19799a22 GS |
1978 | use C<system> instead of C<exec> if you want it to return. It fails and |
1979 | returns false only if the command does not exist I<and> it is executed | |
fb73857a | 1980 | directly instead of via your system's command shell (see below). |
a0d0e21e | 1981 | |
19799a22 | 1982 | Since it's a common mistake to use C<exec> instead of C<system>, Perl |
4642e50d EB |
1983 | warns you if C<exec> is called in void context and if there is a following |
1984 | statement that isn't C<die>, C<warn>, or C<exit> (if C<-w> is set--but | |
1985 | you always do that, right?). If you I<really> want to follow an C<exec> | |
1986 | with some other statement, you can use one of these styles to avoid the warning: | |
55d729e4 | 1987 | |
5a964f20 TC |
1988 | exec ('foo') or print STDERR "couldn't exec foo: $!"; |
1989 | { exec ('foo') }; print STDERR "couldn't exec foo: $!"; | |
55d729e4 | 1990 | |
667eac0c RS |
1991 | If there is more than one argument in LIST, this calls execvp(3) with the |
1992 | arguments in LIST. If there is only one element in LIST, the argument is | |
1993 | checked for shell metacharacters, and if there are any, the entire | |
1994 | argument is passed to the system's command shell for parsing (this is | |
1995 | C</bin/sh -c> on Unix platforms, but varies on other platforms). If | |
1996 | there are no shell metacharacters in the argument, it is split into words | |
1997 | and passed directly to C<execvp>, which is more efficient. Examples: | |
a0d0e21e | 1998 | |
19799a22 GS |
1999 | exec '/bin/echo', 'Your arguments are: ', @ARGV; |
2000 | exec "sort $outfile | uniq"; | |
a0d0e21e LW |
2001 | |
2002 | If you don't really want to execute the first argument, but want to lie | |
2003 | to the program you are executing about its own name, you can specify | |
2004 | the program you actually want to run as an "indirect object" (without a | |
94d4006a TS |
2005 | comma) in front of the LIST, as in C<exec PROGRAM LIST>. (This always |
2006 | forces interpretation of the LIST as a multivalued list, even if there | |
2007 | is only a single scalar in the list.) Example: | |
a0d0e21e LW |
2008 | |
2009 | $shell = '/bin/csh'; | |
5ed4f2ec | 2010 | exec $shell '-sh'; # pretend it's a login shell |
a0d0e21e LW |
2011 | |
2012 | or, more directly, | |
2013 | ||
5ed4f2ec | 2014 | exec {'/bin/csh'} '-sh'; # pretend it's a login shell |
a0d0e21e | 2015 | |
3b10bc60 | 2016 | When the arguments get executed via the system shell, results are |
2017 | subject to its quirks and capabilities. See L<perlop/"`STRING`"> | |
bb32b41a GS |
2018 | for details. |
2019 | ||
19799a22 GS |
2020 | Using an indirect object with C<exec> or C<system> is also more |
2021 | secure. This usage (which also works fine with system()) forces | |
2022 | interpretation of the arguments as a multivalued list, even if the | |
2023 | list had just one argument. That way you're safe from the shell | |
2024 | expanding wildcards or splitting up words with whitespace in them. | |
5a964f20 TC |
2025 | |
2026 | @args = ( "echo surprise" ); | |
2027 | ||
2b5ab1e7 | 2028 | exec @args; # subject to shell escapes |
f86cebdf | 2029 | # if @args == 1 |
2b5ab1e7 | 2030 | exec { $args[0] } @args; # safe even with one-arg list |
5a964f20 TC |
2031 | |
2032 | The first version, the one without the indirect object, ran the I<echo> | |
80d38338 TC |
2033 | program, passing it C<"surprise"> an argument. The second version didn't; |
2034 | it tried to run a program named I<"echo surprise">, didn't find it, and set | |
2035 | C<$?> to a non-zero value indicating failure. | |
5a964f20 | 2036 | |
94d4006a TS |
2037 | On Windows, only the C<exec PROGRAM LIST> indirect object syntax will |
2038 | reliably avoid using the shell; C<exec LIST>, even with more than one | |
2039 | element, will fall back to the shell if the first spawn fails. | |
2040 | ||
e9fa405d BF |
2041 | Perl attempts to flush all files opened for output before the exec, |
2042 | but this may not be supported on some platforms (see L<perlport>). | |
2043 | To be safe, you may need to set C<$|> ($AUTOFLUSH in English) or | |
2044 | call the C<autoflush()> method of C<IO::Handle> on any open handles | |
2045 | to avoid lost output. | |
0f897271 | 2046 | |
80d38338 TC |
2047 | Note that C<exec> will not call your C<END> blocks, nor will it invoke |
2048 | C<DESTROY> methods on your objects. | |
7660c0ab | 2049 | |
ea9eb35a BJ |
2050 | Portability issues: L<perlport/exec>. |
2051 | ||
a0d0e21e | 2052 | =item exists EXPR |
d74e8afc | 2053 | X<exists> X<autovivification> |
a0d0e21e | 2054 | |
c17cdb72 NC |
2055 | =for Pod::Functions test whether a hash key is present |
2056 | ||
d0a76353 RS |
2057 | Given an expression that specifies an element of a hash, returns true if the |
2058 | specified element in the hash has ever been initialized, even if the | |
2059 | corresponding value is undefined. | |
a0d0e21e | 2060 | |
5ed4f2ec | 2061 | print "Exists\n" if exists $hash{$key}; |
2062 | print "Defined\n" if defined $hash{$key}; | |
01020589 GS |
2063 | print "True\n" if $hash{$key}; |
2064 | ||
d0a76353 | 2065 | exists may also be called on array elements, but its behavior is much less |
2fbadc08 RS |
2066 | obvious and is strongly tied to the use of L</delete> on arrays. |
2067 | ||
2068 | B<WARNING:> Calling C<exists> on array values is strongly discouraged. The | |
2069 | notion of deleting or checking the existence of Perl array elements is not | |
2070 | conceptually coherent, and can lead to surprising behavior. | |
d0a76353 | 2071 | |
5ed4f2ec | 2072 | print "Exists\n" if exists $array[$index]; |
2073 | print "Defined\n" if defined $array[$index]; | |
01020589 | 2074 | print "True\n" if $array[$index]; |
a0d0e21e | 2075 | |
8f1da26d | 2076 | A hash or array element can be true only if it's defined and defined only if |
a0d0e21e LW |
2077 | it exists, but the reverse doesn't necessarily hold true. |
2078 | ||
afebc493 GS |
2079 | Given an expression that specifies the name of a subroutine, |
2080 | returns true if the specified subroutine has ever been declared, even | |
2081 | if it is undefined. Mentioning a subroutine name for exists or defined | |
80d38338 | 2082 | does not count as declaring it. Note that a subroutine that does not |
847c7ebe DD |
2083 | exist may still be callable: its package may have an C<AUTOLOAD> |
2084 | method that makes it spring into existence the first time that it is | |
3b10bc60 | 2085 | called; see L<perlsub>. |
afebc493 | 2086 | |
5ed4f2ec | 2087 | print "Exists\n" if exists &subroutine; |
2088 | print "Defined\n" if defined &subroutine; | |
afebc493 | 2089 | |
a0d0e21e | 2090 | Note that the EXPR can be arbitrarily complicated as long as the final |
afebc493 | 2091 | operation is a hash or array key lookup or subroutine name: |
a0d0e21e | 2092 | |
5ed4f2ec | 2093 | if (exists $ref->{A}->{B}->{$key}) { } |
2094 | if (exists $hash{A}{B}{$key}) { } | |
2b5ab1e7 | 2095 | |
5ed4f2ec | 2096 | if (exists $ref->{A}->{B}->[$ix]) { } |
2097 | if (exists $hash{A}{B}[$ix]) { } | |
01020589 | 2098 | |
afebc493 GS |
2099 | if (exists &{$ref->{A}{B}{$key}}) { } |
2100 | ||
9590a7cd | 2101 | Although the most deeply nested array or hash element will not spring into |
3b10bc60 | 2102 | existence just because its existence was tested, any intervening ones will. |
61eff3bc | 2103 | Thus C<< $ref->{"A"} >> and C<< $ref->{"A"}->{"B"} >> will spring |
01020589 | 2104 | into existence due to the existence test for the $key element above. |
3b10bc60 | 2105 | This happens anywhere the arrow operator is used, including even here: |
5a964f20 | 2106 | |
2b5ab1e7 | 2107 | undef $ref; |
5ed4f2ec | 2108 | if (exists $ref->{"Some key"}) { } |
2109 | print $ref; # prints HASH(0x80d3d5c) | |
2b5ab1e7 TC |
2110 | |
2111 | This surprising autovivification in what does not at first--or even | |
2112 | second--glance appear to be an lvalue context may be fixed in a future | |
5a964f20 | 2113 | release. |
a0d0e21e | 2114 | |
afebc493 GS |
2115 | Use of a subroutine call, rather than a subroutine name, as an argument |
2116 | to exists() is an error. | |
2117 | ||
5ed4f2ec | 2118 | exists ⊂ # OK |
2119 | exists &sub(); # Error | |
afebc493 | 2120 | |
a0d0e21e | 2121 | =item exit EXPR |
d74e8afc | 2122 | X<exit> X<terminate> X<abort> |
a0d0e21e | 2123 | |
ce2984c3 PF |
2124 | =item exit |
2125 | ||
c17cdb72 NC |
2126 | =for Pod::Functions terminate this program |
2127 | ||
2b5ab1e7 | 2128 | Evaluates EXPR and exits immediately with that value. Example: |
a0d0e21e LW |
2129 | |
2130 | $ans = <STDIN>; | |
2131 | exit 0 if $ans =~ /^[Xx]/; | |
2132 | ||
19799a22 | 2133 | See also C<die>. If EXPR is omitted, exits with C<0> status. The only |
2b5ab1e7 TC |
2134 | universally recognized values for EXPR are C<0> for success and C<1> |
2135 | for error; other values are subject to interpretation depending on the | |
2136 | environment in which the Perl program is running. For example, exiting | |
2137 | 69 (EX_UNAVAILABLE) from a I<sendmail> incoming-mail filter will cause | |
2138 | the mailer to return the item undelivered, but that's not true everywhere. | |
a0d0e21e | 2139 | |
19799a22 GS |
2140 | Don't use C<exit> to abort a subroutine if there's any chance that |
2141 | someone might want to trap whatever error happened. Use C<die> instead, | |
2142 | which can be trapped by an C<eval>. | |
28757baa | 2143 | |
19799a22 | 2144 | The exit() function does not always exit immediately. It calls any |
2b5ab1e7 | 2145 | defined C<END> routines first, but these C<END> routines may not |
19799a22 | 2146 | themselves abort the exit. Likewise any object destructors that need to |
60275626 | 2147 | be called are called before the real exit. C<END> routines and destructors |
391b733c | 2148 | can change the exit status by modifying C<$?>. If this is a problem, you |
fae6f8fa | 2149 | can call C<POSIX::_exit($status)> to avoid END and destructor processing. |
87275199 | 2150 | See L<perlmod> for details. |
5a964f20 | 2151 | |
ea9eb35a BJ |
2152 | Portability issues: L<perlport/exit>. |
2153 | ||
a0d0e21e | 2154 | =item exp EXPR |
d74e8afc | 2155 | X<exp> X<exponential> X<antilog> X<antilogarithm> X<e> |
a0d0e21e | 2156 | |
54310121 | 2157 | =item exp |
bbce6d69 | 2158 | |
c17cdb72 NC |
2159 | =for Pod::Functions raise I<e> to a power |
2160 | ||
b76cc8ba | 2161 | Returns I<e> (the natural logarithm base) to the power of EXPR. |
a0d0e21e LW |
2162 | If EXPR is omitted, gives C<exp($_)>. |
2163 | ||
628253b8 BF |
2164 | =item fc EXPR |
2165 | X<fc> X<foldcase> X<casefold> X<fold-case> X<case-fold> | |
2166 | ||
2167 | =item fc | |
2168 | ||
d9b04284 | 2169 | =for Pod::Functions +fc return casefolded version of a string |
c17cdb72 | 2170 | |
628253b8 BF |
2171 | Returns the casefolded version of EXPR. This is the internal function |
2172 | implementing the C<\F> escape in double-quoted strings. | |
2173 | ||
2174 | Casefolding is the process of mapping strings to a form where case | |
2175 | differences are erased; comparing two strings in their casefolded | |
2176 | form is effectively a way of asking if two strings are equal, | |
2177 | regardless of case. | |
2178 | ||
2179 | Roughly, if you ever found yourself writing this | |
2180 | ||
f6c6dcb6 | 2181 | lc($this) eq lc($that) # Wrong! |
628253b8 | 2182 | # or |
f6c6dcb6 | 2183 | uc($this) eq uc($that) # Also wrong! |
628253b8 | 2184 | # or |
f6c6dcb6 | 2185 | $this =~ /^\Q$that\E\z/i # Right! |
628253b8 BF |
2186 | |
2187 | Now you can write | |
2188 | ||
2189 | fc($this) eq fc($that) | |
2190 | ||
2191 | And get the correct results. | |
2192 | ||
fc39a31f KW |
2193 | Perl only implements the full form of casefolding, |
2194 | but you can access the simple folds using L<Unicode::UCD/casefold()> and | |
2195 | L<Unicode::UCD/prop_invmap()>. | |
628253b8 BF |
2196 | For further information on casefolding, refer to |
2197 | the Unicode Standard, specifically sections 3.13 C<Default Case Operations>, | |
2198 | 4.2 C<Case-Normative>, and 5.18 C<Case Mappings>, | |
2199 | available at L<http://www.unicode.org/versions/latest/>, as well as the | |
2200 | Case Charts available at L<http://www.unicode.org/charts/case/>. | |
2201 | ||
2202 | If EXPR is omitted, uses C<$_>. | |
2203 | ||
1ca267a5 KW |
2204 | This function behaves the same way under various pragma, such as within |
2205 | S<C<"use feature 'unicode_strings">>, as L</lc> does, with the single | |
2206 | exception of C<fc> of LATIN CAPITAL LETTER SHARP S (U+1E9E) within the | |
2207 | scope of S<C<use locale>>. The foldcase of this character would | |
2208 | normally be C<"ss">, but as explained in the L</lc> section, case | |
2209 | changes that cross the 255/256 boundary are problematic under locales, | |
2210 | and are hence prohibited. Therefore, this function under locale returns | |
2211 | instead the string C<"\x{17F}\x{17F}">, which is the LATIN SMALL LETTER | |
2212 | LONG S. Since that character itself folds to C<"s">, the string of two | |
2213 | of them together should be equivalent to a single U+1E9E when foldcased. | |
628253b8 BF |
2214 | |
2215 | While the Unicode Standard defines two additional forms of casefolding, | |
2216 | one for Turkic languages and one that never maps one character into multiple | |
2217 | characters, these are not provided by the Perl core; However, the CPAN module | |
2218 | C<Unicode::Casing> may be used to provide an implementation. | |
2219 | ||
2220 | This keyword is available only when the C<"fc"> feature is enabled, | |
7161e5c2 | 2221 | or when prefixed with C<CORE::>; See L<feature>. Alternately, |
628253b8 BF |
2222 | include a C<use v5.16> or later to the current scope. |
2223 | ||
a0d0e21e | 2224 | =item fcntl FILEHANDLE,FUNCTION,SCALAR |
d74e8afc | 2225 | X<fcntl> |
a0d0e21e | 2226 | |
c17cdb72 NC |
2227 | =for Pod::Functions file control system call |
2228 | ||
f86cebdf | 2229 | Implements the fcntl(2) function. You'll probably have to say |
a0d0e21e LW |
2230 | |
2231 | use Fcntl; | |
2232 | ||
0ade1984 | 2233 | first to get the correct constant definitions. Argument processing and |
3b10bc60 | 2234 | value returned work just like C<ioctl> below. |
a0d0e21e LW |
2235 | For example: |
2236 | ||
2237 | use Fcntl; | |
5a964f20 | 2238 | fcntl($filehandle, F_GETFL, $packed_return_buffer) |
a9a5a0dc | 2239 | or die "can't fcntl F_GETFL: $!"; |
5a964f20 | 2240 | |
554ad1fc | 2241 | You don't have to check for C<defined> on the return from C<fcntl>. |
951ba7fe GS |
2242 | Like C<ioctl>, it maps a C<0> return from the system call into |
2243 | C<"0 but true"> in Perl. This string is true in boolean context and C<0> | |
2b5ab1e7 TC |
2244 | in numeric context. It is also exempt from the normal B<-w> warnings |
2245 | on improper numeric conversions. | |
5a964f20 | 2246 | |
3b10bc60 | 2247 | Note that C<fcntl> raises an exception if used on a machine that |
2b5ab1e7 TC |
2248 | doesn't implement fcntl(2). See the Fcntl module or your fcntl(2) |
2249 | manpage to learn what functions are available on your system. | |
a0d0e21e | 2250 | |
be2f7487 TH |
2251 | Here's an example of setting a filehandle named C<REMOTE> to be |
2252 | non-blocking at the system level. You'll have to negotiate C<$|> | |
2253 | on your own, though. | |
2254 | ||
2255 | use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK); | |
2256 | ||
2257 | $flags = fcntl(REMOTE, F_GETFL, 0) | |
2258 | or die "Can't get flags for the socket: $!\n"; | |
2259 | ||
2260 | $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK) | |
2261 | or die "Can't set flags for the socket: $!\n"; | |
2262 | ||
ea9eb35a BJ |
2263 | Portability issues: L<perlport/fcntl>. |
2264 | ||
cfa52385 FC |
2265 | =item __FILE__ |
2266 | X<__FILE__> | |
2267 | ||
c17cdb72 NC |
2268 | =for Pod::Functions the name of the current source file |
2269 | ||
cfa52385 FC |
2270 | A special token that returns the name of the file in which it occurs. |
2271 | ||
a0d0e21e | 2272 | =item fileno FILEHANDLE |
d74e8afc | 2273 | X<fileno> |
a0d0e21e | 2274 | |
c17cdb72 NC |
2275 | =for Pod::Functions return file descriptor from filehandle |
2276 | ||
2b5ab1e7 | 2277 | Returns the file descriptor for a filehandle, or undefined if the |
a7c1632d FC |
2278 | filehandle is not open. If there is no real file descriptor at the OS |
2279 | level, as can happen with filehandles connected to memory objects via | |
2280 | C<open> with a reference for the third argument, -1 is returned. | |
2281 | ||
2282 | This is mainly useful for constructing | |
19799a22 | 2283 | bitmaps for C<select> and low-level POSIX tty-handling operations. |
2b5ab1e7 TC |
2284 | If FILEHANDLE is an expression, the value is taken as an indirect |
2285 | filehandle, generally its name. | |
5a964f20 | 2286 | |
b76cc8ba | 2287 | You can use this to find out whether two handles refer to the |
5a964f20 TC |
2288 | same underlying descriptor: |
2289 | ||
3231d257 | 2290 | if (fileno(THIS) != -1 && fileno(THIS) == fileno(THAT)) { |
a9a5a0dc | 2291 | print "THIS and THAT are dups\n"; |
3231d257 | 2292 | } elsif (fileno(THIS) != -1 && fileno(THAT) != -1) { |
555bd962 BG |
2293 | print "THIS and THAT have different " . |
2294 | "underlying file descriptors\n"; | |
3231d257 | 2295 | } else { |
555bd962 BG |
2296 | print "At least one of THIS and THAT does " . |
2297 | "not have a real file descriptor\n"; | |
b76cc8ba NIS |
2298 | } |
2299 | ||
a0d0e21e | 2300 | =item flock FILEHANDLE,OPERATION |
d74e8afc | 2301 | X<flock> X<lock> X<locking> |
a0d0e21e | 2302 | |
c17cdb72 NC |
2303 | =for Pod::Functions lock an entire file with an advisory lock |
2304 | ||
19799a22 GS |
2305 | Calls flock(2), or an emulation of it, on FILEHANDLE. Returns true |
2306 | for success, false on failure. Produces a fatal error if used on a | |
2b5ab1e7 | 2307 | machine that doesn't implement flock(2), fcntl(2) locking, or lockf(3). |
dbfe1e81 | 2308 | C<flock> is Perl's portable file-locking interface, although it locks |
3b10bc60 | 2309 | entire files only, not records. |
2b5ab1e7 TC |
2310 | |
2311 | Two potentially non-obvious but traditional C<flock> semantics are | |
2312 | that it waits indefinitely until the lock is granted, and that its locks | |
dbfe1e81 FC |
2313 | are B<merely advisory>. Such discretionary locks are more flexible, but |
2314 | offer fewer guarantees. This means that programs that do not also use | |
2315 | C<flock> may modify files locked with C<flock>. See L<perlport>, | |
8f1da26d | 2316 | your port's specific documentation, and your system-specific local manpages |
2b5ab1e7 TC |
2317 | for details. It's best to assume traditional behavior if you're writing |
2318 | portable programs. (But if you're not, you should as always feel perfectly | |
2319 | free to write for your own system's idiosyncrasies (sometimes called | |
2320 | "features"). Slavish adherence to portability concerns shouldn't get | |
2321 | in the way of your getting your job done.) | |
a3cb178b | 2322 | |
8ebc5c01 | 2323 | OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with |
2324 | LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but | |
8f1da26d TC |
2325 | you can use the symbolic names if you import them from the L<Fcntl> module, |
2326 | either individually, or as a group using the C<:flock> tag. LOCK_SH | |
68dc0745 | 2327 | requests a shared lock, LOCK_EX requests an exclusive lock, and LOCK_UN |
ea3105be | 2328 | releases a previously requested lock. If LOCK_NB is bitwise-or'ed with |
8f1da26d | 2329 | LOCK_SH or LOCK_EX, then C<flock> returns immediately rather than blocking |
3b10bc60 | 2330 | waiting for the lock; check the return status to see if you got it. |
68dc0745 | 2331 | |
2b5ab1e7 TC |
2332 | To avoid the possibility of miscoordination, Perl now flushes FILEHANDLE |
2333 | before locking or unlocking it. | |
8ebc5c01 | 2334 | |
f86cebdf | 2335 | Note that the emulation built with lockf(3) doesn't provide shared |
8ebc5c01 | 2336 | locks, and it requires that FILEHANDLE be open with write intent. These |
2b5ab1e7 | 2337 | are the semantics that lockf(3) implements. Most if not all systems |
f86cebdf | 2338 | implement lockf(3) in terms of fcntl(2) locking, though, so the |
8ebc5c01 | 2339 | differing semantics shouldn't bite too many people. |
2340 | ||
becacb53 TM |
2341 | Note that the fcntl(2) emulation of flock(3) requires that FILEHANDLE |
2342 | be open with read intent to use LOCK_SH and requires that it be open | |
2343 | with write intent to use LOCK_EX. | |
2344 | ||
19799a22 GS |
2345 | Note also that some versions of C<flock> cannot lock things over the |
2346 | network; you would need to use the more system-specific C<fcntl> for | |
f86cebdf GS |
2347 | that. If you like you can force Perl to ignore your system's flock(2) |
2348 | function, and so provide its own fcntl(2)-based emulation, by passing | |
8ebc5c01 | 2349 | the switch C<-Ud_flock> to the F<Configure> program when you configure |
8f1da26d | 2350 | and build a new Perl. |
4633a7c4 LW |
2351 | |
2352 | Here's a mailbox appender for BSD systems. | |
a0d0e21e | 2353 | |
f7051f2c FC |
2354 | # import LOCK_* and SEEK_END constants |
2355 | use Fcntl qw(:flock SEEK_END); | |
a0d0e21e LW |
2356 | |
2357 | sub lock { | |
a9a5a0dc VP |
2358 | my ($fh) = @_; |
2359 | flock($fh, LOCK_EX) or die "Cannot lock mailbox - $!\n"; | |
7ed5353d | 2360 | |
a9a5a0dc VP |
2361 | # and, in case someone appended while we were waiting... |
2362 | seek($fh, 0, SEEK_END) or die "Cannot seek - $!\n"; | |
a0d0e21e LW |
2363 | } |
2364 | ||
2365 | sub unlock { | |
a9a5a0dc VP |
2366 | my ($fh) = @_; |
2367 | flock($fh, LOCK_UN) or die "Cannot unlock mailbox - $!\n"; | |
a0d0e21e LW |
2368 | } |
2369 | ||
b0169937 | 2370 | open(my $mbox, ">>", "/usr/spool/mail/$ENV{'USER'}") |
5ed4f2ec | 2371 | or die "Can't open mailbox: $!"; |
a0d0e21e | 2372 | |
7ed5353d | 2373 | lock($mbox); |
b0169937 | 2374 | print $mbox $msg,"\n\n"; |
7ed5353d | 2375 | unlock($mbox); |
a0d0e21e | 2376 | |
3b10bc60 | 2377 | On systems that support a real flock(2), locks are inherited across fork() |
2378 | calls, whereas those that must resort to the more capricious fcntl(2) | |
2379 | function lose their locks, making it seriously harder to write servers. | |
2b5ab1e7 | 2380 | |
cb1a09d0 | 2381 | See also L<DB_File> for other flock() examples. |
a0d0e21e | 2382 | |
ea9eb35a BJ |
2383 | Portability issues: L<perlport/flock>. |
2384 | ||
a0d0e21e | 2385 | =item fork |
d74e8afc | 2386 | X<fork> X<child> X<parent> |
a0d0e21e | 2387 | |
c17cdb72 NC |
2388 | =for Pod::Functions create a new process just like this one |
2389 | ||
2b5ab1e7 TC |
2390 | Does a fork(2) system call to create a new process running the |
2391 | same program at the same point. It returns the child pid to the | |
2392 | parent process, C<0> to the child process, or C<undef> if the fork is | |
2393 | unsuccessful. File descriptors (and sometimes locks on those descriptors) | |
2394 | are shared, while everything else is copied. On most systems supporting | |
2395 | fork(), great care has gone into making it extremely efficient (for | |
2396 | example, using copy-on-write technology on data pages), making it the | |
2397 | dominant paradigm for multitasking over the last few decades. | |
5a964f20 | 2398 | |
e9fa405d | 2399 | Perl attempts to flush all files opened for |
0f897271 GS |
2400 | output before forking the child process, but this may not be supported |
2401 | on some platforms (see L<perlport>). To be safe, you may need to set | |
2402 | C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method of | |
80d38338 | 2403 | C<IO::Handle> on any open handles to avoid duplicate output. |
a0d0e21e | 2404 | |
19799a22 | 2405 | If you C<fork> without ever waiting on your children, you will |
2b5ab1e7 TC |
2406 | accumulate zombies. On some systems, you can avoid this by setting |
2407 | C<$SIG{CHLD}> to C<"IGNORE">. See also L<perlipc> for more examples of | |
2408 | forking and reaping moribund children. | |
cb1a09d0 | 2409 | |
28757baa | 2410 | Note that if your forked child inherits system file descriptors like |
2411 | STDIN and STDOUT that are actually connected by a pipe or socket, even | |
2b5ab1e7 | 2412 | if you exit, then the remote server (such as, say, a CGI script or a |
19799a22 | 2413 | backgrounded job launched from a remote shell) won't think you're done. |
2b5ab1e7 | 2414 | You should reopen those to F</dev/null> if it's any issue. |
28757baa | 2415 | |
ea9eb35a | 2416 | On some platforms such as Windows, where the fork() system call is not available, |
391b733c FC |
2417 | Perl can be built to emulate fork() in the Perl interpreter. |
2418 | The emulation is designed, at the level of the Perl program, | |
2419 | to be as compatible as possible with the "Unix" fork(). | |
6d17f725 | 2420 | However it has limitations that have to be considered in code intended to be portable. |
ea9eb35a BJ |
2421 | See L<perlfork> for more details. |
2422 | ||
2423 | Portability issues: L<perlport/fork>. | |
2424 | ||
cb1a09d0 | 2425 | =item format |
d74e8afc | 2426 | X<format> |
cb1a09d0 | 2427 | |
c17cdb72 NC |
2428 | =for Pod::Functions declare a picture format with use by the write() function |
2429 | ||
19799a22 | 2430 | Declare a picture format for use by the C<write> function. For |
cb1a09d0 AD |
2431 | example: |
2432 | ||
54310121 | 2433 | format Something = |
a9a5a0dc VP |
2434 | Test: @<<<<<<<< @||||| @>>>>> |
2435 | $str, $%, '$' . int($num) | |
cb1a09d0 AD |
2436 | . |
2437 | ||
2438 | $str = "widget"; | |
184e9718 | 2439 | $num = $cost/$quantity; |
cb1a09d0 AD |
2440 | $~ = 'Something'; |
2441 | write; | |
2442 | ||
2443 | See L<perlform> for many details and examples. | |
2444 | ||
8903cb82 | 2445 | =item formline PICTURE,LIST |
d74e8afc | 2446 | X<formline> |
a0d0e21e | 2447 | |
c17cdb72 NC |
2448 | =for Pod::Functions internal function used for formats |
2449 | ||
5a964f20 | 2450 | This is an internal function used by C<format>s, though you may call it, |
a0d0e21e LW |
2451 | too. It formats (see L<perlform>) a list of values according to the |
2452 | contents of PICTURE, placing the output into the format output | |
7660c0ab | 2453 | accumulator, C<$^A> (or C<$ACCUMULATOR> in English). |
19799a22 | 2454 | Eventually, when a C<write> is done, the contents of |
cf264981 SP |
2455 | C<$^A> are written to some filehandle. You could also read C<$^A> |
2456 | and then set C<$^A> back to C<"">. Note that a format typically | |
19799a22 | 2457 | does one C<formline> per line of form, but the C<formline> function itself |
748a9306 | 2458 | doesn't care how many newlines are embedded in the PICTURE. This means |
3b10bc60 | 2459 | that the C<~> and C<~~> tokens treat the entire PICTURE as a single line. |
748a9306 | 2460 | You may therefore need to use multiple formlines to implement a single |
3b10bc60 | 2461 | record format, just like the C<format> compiler. |
748a9306 | 2462 | |
19799a22 | 2463 | Be careful if you put double quotes around the picture, because an C<@> |
748a9306 | 2464 | character may be taken to mean the beginning of an array name. |
19799a22 | 2465 | C<formline> always returns true. See L<perlform> for other examples. |
a0d0e21e | 2466 | |
445b09e5 FC |
2467 | If you are trying to use this instead of C<write> to capture the output, |
2468 | you may find it easier to open a filehandle to a scalar | |
2469 | (C<< open $fh, ">", \$output >>) and write to that instead. | |
2470 | ||
a0d0e21e | 2471 | =item getc FILEHANDLE |
f723aae1 | 2472 | X<getc> X<getchar> X<character> X<file, read> |
a0d0e21e LW |
2473 | |
2474 | =item getc | |
2475 | ||
c17cdb72 NC |
2476 | =for Pod::Functions get the next character from the filehandle |
2477 | ||
a0d0e21e | 2478 | Returns the next character from the input file attached to FILEHANDLE, |
3b10bc60 | 2479 | or the undefined value at end of file or if there was an error (in |
b5fe5ca2 SR |
2480 | the latter case C<$!> is set). If FILEHANDLE is omitted, reads from |
2481 | STDIN. This is not particularly efficient. However, it cannot be | |
2482 | used by itself to fetch single characters without waiting for the user | |
2483 | to hit enter. For that, try something more like: | |
4633a7c4 LW |
2484 | |
2485 | if ($BSD_STYLE) { | |
a9a5a0dc | 2486 | system "stty cbreak </dev/tty >/dev/tty 2>&1"; |
4633a7c4 LW |
2487 | } |
2488 | else { | |
a9a5a0dc | 2489 | system "stty", '-icanon', 'eol', "\001"; |
4633a7c4 LW |
2490 | } |
2491 | ||
2492 | $key = getc(STDIN); | |
2493 | ||
2494 | if ($BSD_STYLE) { | |
a9a5a0dc | 2495 | system "stty -cbreak </dev/tty >/dev/tty 2>&1"; |
4633a7c4 LW |
2496 | } |
2497 | else { | |
3b10bc60 | 2498 | system 'stty', 'icanon', 'eol', '^@'; # ASCII NUL |
4633a7c4 LW |
2499 | } |
2500 | print "\n"; | |
2501 | ||
54310121 | 2502 | Determination of whether $BSD_STYLE should be set |
2503 | is left as an exercise to the reader. | |
cb1a09d0 | 2504 | |
19799a22 | 2505 | The C<POSIX::getattr> function can do this more portably on |
2b5ab1e7 | 2506 | systems purporting POSIX compliance. See also the C<Term::ReadKey> |
3d6c5fec | 2507 | module from your nearest L<CPAN|http://www.cpan.org> site. |
a0d0e21e LW |
2508 | |
2509 | =item getlogin | |
d74e8afc | 2510 | X<getlogin> X<login> |
a0d0e21e | 2511 | |
c17cdb72 NC |
2512 | =for Pod::Functions return who logged in at this tty |
2513 | ||
cf264981 | 2514 | This implements the C library function of the same name, which on most |
3b10bc60 | 2515 | systems returns the current login from F</etc/utmp>, if any. If it |
2516 | returns the empty string, use C<getpwuid>. | |
a0d0e21e | 2517 | |
f86702cc | 2518 | $login = getlogin || getpwuid($<) || "Kilroy"; |
a0d0e21e | 2519 | |
19799a22 GS |
2520 | Do not consider C<getlogin> for authentication: it is not as |
2521 | secure as C<getpwuid>. | |
4633a7c4 | 2522 | |
ea9eb35a BJ |
2523 | Portability issues: L<perlport/getlogin>. |
2524 | ||
a0d0e21e | 2525 | =item getpeername SOCKET |
d74e8afc | 2526 | X<getpeername> X<peer> |
a0d0e21e | 2527 | |
c17cdb72 NC |
2528 | =for Pod::Functions find the other end of a socket connection |
2529 | ||
a3390c9f FC |
2530 | Returns the packed sockaddr address of the other end of the SOCKET |
2531 | connection. | |
a0d0e21e | 2532 | |
4633a7c4 LW |
2533 | use Socket; |
2534 | $hersockaddr = getpeername(SOCK); | |
19799a22 | 2535 | ($port, $iaddr) = sockaddr_in($hersockaddr); |
4633a7c4 LW |
2536 | $herhostname = gethostbyaddr($iaddr, AF_INET); |
2537 | $herstraddr = inet_ntoa($iaddr); | |
a0d0e21e LW |
2538 | |
2539 | =item getpgrp PID | |
d74e8afc | 2540 | X<getpgrp> X<group> |
a0d0e21e | 2541 | |
c17cdb72 NC |
2542 | =for Pod::Functions get process group |
2543 | ||
47e29363 | 2544 | Returns the current process group for the specified PID. Use |
7660c0ab | 2545 | a PID of C<0> to get the current process group for the |
4633a7c4 | 2546 | current process. Will raise an exception if used on a machine that |
a3390c9f FC |
2547 | doesn't implement getpgrp(2). If PID is omitted, returns the process |
2548 | group of the current process. Note that the POSIX version of C<getpgrp> | |
7660c0ab | 2549 | does not accept a PID argument, so only C<PID==0> is truly portable. |
a0d0e21e | 2550 | |
ea9eb35a BJ |
2551 | Portability issues: L<perlport/getpgrp>. |
2552 | ||
a0d0e21e | 2553 | =item getppid |
d74e8afc | 2554 | X<getppid> X<parent> X<pid> |
a0d0e21e | 2555 | |
c17cdb72 NC |
2556 | =for Pod::Functions get parent process ID |
2557 | ||
a0d0e21e LW |
2558 | Returns the process id of the parent process. |
2559 | ||
d7c042c9 AB |
2560 | Note for Linux users: Between v5.8.1 and v5.16.0 Perl would work |
2561 | around non-POSIX thread semantics the minority of Linux systems (and | |
2562 | Debian GNU/kFreeBSD systems) that used LinuxThreads, this emulation | |
7161e5c2 | 2563 | has since been removed. See the documentation for L<$$|perlvar/$$> for |
d7c042c9 | 2564 | details. |
4d76a344 | 2565 | |
ea9eb35a BJ |
2566 | Portability issues: L<perlport/getppid>. |
2567 | ||
a0d0e21e | 2568 | =item getpriority WHICH,WHO |
d74e8afc | 2569 | X<getpriority> X<priority> X<nice> |
a0d0e21e | 2570 | |
c17cdb72 NC |
2571 | =for Pod::Functions get current nice value |
2572 | ||
4633a7c4 | 2573 | Returns the current priority for a process, a process group, or a user. |
01aa884e | 2574 | (See L<getpriority(2)>.) Will raise a fatal exception if used on a |
f86cebdf | 2575 | machine that doesn't implement getpriority(2). |
a0d0e21e | 2576 | |
ea9eb35a BJ |
2577 | Portability issues: L<perlport/getpriority>. |
2578 | ||
a0d0e21e | 2579 | =item getpwnam NAME |
d74e8afc ITB |
2580 | X<getpwnam> X<getgrnam> X<gethostbyname> X<getnetbyname> X<getprotobyname> |
2581 | X<getpwuid> X<getgrgid> X<getservbyname> X<gethostbyaddr> X<getnetbyaddr> | |
2582 | X<getprotobynumber> X<getservbyport> X<getpwent> X<getgrent> X<gethostent> | |
2583 | X<getnetent> X<getprotoent> X<getservent> X<setpwent> X<setgrent> X<sethostent> | |
2584 | X<setnetent> X<setprotoent> X<setservent> X<endpwent> X<endgrent> X<endhostent> | |
2585 | X<endnetent> X<endprotoent> X<endservent> | |
a0d0e21e | 2586 | |
c17cdb72 NC |
2587 | =for Pod::Functions get passwd record given user login name |
2588 | ||
a0d0e21e LW |
2589 | =item getgrnam NAME |
2590 | ||
c17cdb72 NC |
2591 | =for Pod::Functions get group record given group name |
2592 | ||
a0d0e21e LW |
2593 | =item gethostbyname NAME |
2594 | ||
c17cdb72 NC |
2595 | =for Pod::Functions get host record given name |
2596 | ||
a0d0e21e LW |
2597 | =item getnetbyname NAME |
2598 | ||
c17cdb72 NC |
2599 | =for Pod::Functions get networks record given name |
2600 | ||
a0d0e21e LW |
2601 | =item getprotobyname NAME |
2602 | ||
c17cdb72 NC |
2603 | =for Pod::Functions get protocol record given name |
2604 | ||
a0d0e21e LW |
2605 | =item getpwuid UID |
2606 | ||
c17cdb72 NC |
2607 | =for Pod::Functions get passwd record given user ID |
2608 | ||
a0d0e21e LW |
2609 | =item getgrgid GID |
2610 | ||
c17cdb72 NC |
2611 | =for Pod::Functions get group record given group user ID |
2612 | ||
a0d0e21e LW |
2613 | =item getservbyname NAME,PROTO |
2614 | ||
c17cdb72 NC |
2615 | =for Pod::Functions get services record given its name |
2616 | ||
a0d0e21e LW |
2617 | =item gethostbyaddr ADDR,ADDRTYPE |
2618 | ||
c17cdb72 NC |
2619 | =for Pod::Functions get host record given its address |
2620 | ||
a0d0e21e LW |
2621 | =item getnetbyaddr ADDR,ADDRTYPE |
2622 | ||
c17cdb72 NC |
2623 | =for Pod::Functions get network record given its address |
2624 | ||
a0d0e21e LW |
2625 | =item getprotobynumber NUMBER |
2626 | ||
c17cdb72 NC |
2627 | =for Pod::Functions get protocol record numeric protocol |
2628 | ||
a0d0e21e LW |
2629 | =item getservbyport PORT,PROTO |
2630 | ||
c17cdb72 NC |
2631 | =for Pod::Functions get services record given numeric port |
2632 | ||
a0d0e21e LW |
2633 | =item getpwent |
2634 | ||
c17cdb72 NC |
2635 | =for Pod::Functions get next passwd record |
2636 | ||
a0d0e21e LW |
2637 | =item getgrent |
2638 | ||
c17cdb72 NC |
2639 | =for Pod::Functions get next group record |
2640 | ||
a0d0e21e LW |
2641 | =item gethostent |
2642 | ||
c17cdb72 NC |
2643 | =for Pod::Functions get next hosts record |
2644 | ||
a0d0e21e LW |
2645 | =item getnetent |
2646 | ||
c17cdb72 NC |
2647 | =for Pod::Functions get next networks record |
2648 | ||
a0d0e21e LW |
2649 | =item getprotoent |
2650 | ||
c17cdb72 NC |
2651 | =for Pod::Functions get next protocols record |
2652 | ||
a0d0e21e LW |
2653 | =item getservent |
2654 | ||
c17cdb72 NC |
2655 | =for Pod::Functions get next services record |
2656 | ||
a0d0e21e LW |
2657 | =item setpwent |
2658 | ||
c17cdb72 NC |
2659 | =for Pod::Functions prepare passwd file for use |
2660 | ||
a0d0e21e LW |
2661 | =item setgrent |
2662 | ||
c17cdb72 NC |
2663 | =for Pod::Functions prepare group file for use |
2664 | ||
a0d0e21e LW |
2665 | =item sethostent STAYOPEN |
2666 | ||
c17cdb72 NC |
2667 | =for Pod::Functions prepare hosts file for use |
2668 | ||
a0d0e21e LW |
2669 | =item setnetent STAYOPEN |
2670 | ||
c17cdb72 NC |
2671 | =for Pod::Functions prepare networks file for use |
2672 | ||
a0d0e21e LW |
2673 | =item setprotoent STAYOPEN |
2674 | ||
c17cdb72 NC |
2675 | =for Pod::Functions prepare protocols file for use |
2676 | ||
a0d0e21e LW |
2677 | =item setservent STAYOPEN |
2678 | ||
c17cdb72 NC |
2679 | =for Pod::Functions prepare services file for use |
2680 | ||
a0d0e21e LW |
2681 | =item endpwent |
2682 | ||
c17cdb72 NC |
2683 | =for Pod::Functions be done using passwd file |
2684 | ||
a0d0e21e LW |
2685 | =item endgrent |
2686 | ||
c17cdb72 NC |
2687 | =for Pod::Functions be done using group file |
2688 | ||
a0d0e21e LW |
2689 | =item endhostent |
2690 | ||
c17cdb72 NC |
2691 | =for Pod::Functions be done using hosts file |
2692 | ||
a0d0e21e LW |
2693 | =item endnetent |
2694 | ||
c17cdb72 NC |
2695 | =for Pod::Functions be done using networks file |
2696 | ||
a0d0e21e LW |
2697 | =item endprotoent |
2698 | ||
c17cdb72 NC |
2699 | =for Pod::Functions be done using protocols file |
2700 | ||
a0d0e21e LW |
2701 | =item endservent |
2702 | ||
c17cdb72 NC |
2703 | =for Pod::Functions be done using services file |
2704 | ||
80d38338 TC |
2705 | These routines are the same as their counterparts in the |
2706 | system C library. In list context, the return values from the | |
a0d0e21e LW |
2707 | various get routines are as follows: |
2708 | ||
f0081f64 AP |
2709 | # 0 1 2 3 4 |
2710 | ( $name, $passwd, $gid, $members ) = getgr* | |
2711 | ( $name, $aliases, $addrtype, $net ) = getnet* | |
2712 | ( $name, $aliases, $port, $proto ) = getserv* | |
2713 | ( $name, $aliases, $proto ) = getproto* | |
2714 | ( $name, $aliases, $addrtype, $length, @addrs ) = gethost* | |
2715 | ( $name, $passwd, $uid, $gid, $quota, | |
2716 | $comment, $gcos, $dir, $shell, $expire ) = getpw* | |
2717 | # 5 6 7 8 9 | |
a0d0e21e | 2718 | |
3b10bc60 | 2719 | (If the entry doesn't exist you get an empty list.) |
a0d0e21e | 2720 | |
4602f195 JH |
2721 | The exact meaning of the $gcos field varies but it usually contains |
2722 | the real name of the user (as opposed to the login name) and other | |
2723 | information pertaining to the user. Beware, however, that in many | |
2724 | system users are able to change this information and therefore it | |
106325ad | 2725 | cannot be trusted and therefore the $gcos is tainted (see |
2959b6e3 | 2726 | L<perlsec>). The $passwd and $shell, user's encrypted password and |
a3390c9f | 2727 | login shell, are also tainted, for the same reason. |
4602f195 | 2728 | |
5a964f20 | 2729 | In scalar context, you get the name, unless the function was a |
a0d0e21e LW |
2730 | lookup by name, in which case you get the other thing, whatever it is. |
2731 | (If the entry doesn't exist you get the undefined value.) For example: | |
2732 | ||
5a964f20 TC |
2733 | $uid = getpwnam($name); |
2734 | $name = getpwuid($num); | |
2735 | $name = getpwent(); | |
2736 | $gid = getgrnam($name); | |
08a33e13 | 2737 | $name = getgrgid($num); |
5a964f20 TC |
2738 | $name = getgrent(); |
2739 | #etc. | |
a0d0e21e | 2740 | |
4602f195 | 2741 | In I<getpw*()> the fields $quota, $comment, and $expire are special |
80d38338 | 2742 | in that they are unsupported on many systems. If the |
4602f195 JH |
2743 | $quota is unsupported, it is an empty scalar. If it is supported, it |
2744 | usually encodes the disk quota. If the $comment field is unsupported, | |
2745 | it is an empty scalar. If it is supported it usually encodes some | |
2746 | administrative comment about the user. In some systems the $quota | |
2747 | field may be $change or $age, fields that have to do with password | |
2748 | aging. In some systems the $comment field may be $class. The $expire | |
2749 | field, if present, encodes the expiration period of the account or the | |
2750 | password. For the availability and the exact meaning of these fields | |
8f1da26d | 2751 | in your system, please consult getpwnam(3) and your system's |
4602f195 JH |
2752 | F<pwd.h> file. You can also find out from within Perl what your |
2753 | $quota and $comment fields mean and whether you have the $expire field | |
2754 | by using the C<Config> module and the values C<d_pwquota>, C<d_pwage>, | |
2755 | C<d_pwchange>, C<d_pwcomment>, and C<d_pwexpire>. Shadow password | |
3b10bc60 | 2756 | files are supported only if your vendor has implemented them in the |
4602f195 | 2757 | intuitive fashion that calling the regular C library routines gets the |
5d3a0a3b | 2758 | shadow versions if you're running under privilege or if there exists |
cf264981 | 2759 | the shadow(3) functions as found in System V (this includes Solaris |
a3390c9f | 2760 | and Linux). Those systems that implement a proprietary shadow password |
5d3a0a3b | 2761 | facility are unlikely to be supported. |
6ee623d5 | 2762 | |
a3390c9f | 2763 | The $members value returned by I<getgr*()> is a space-separated list of |
a0d0e21e LW |
2764 | the login names of the members of the group. |
2765 | ||
2766 | For the I<gethost*()> functions, if the C<h_errno> variable is supported in | |
2767 | C, it will be returned to you via C<$?> if the function call fails. The | |
3b10bc60 | 2768 | C<@addrs> value returned by a successful call is a list of raw |
2769 | addresses returned by the corresponding library call. In the | |
2770 | Internet domain, each address is four bytes long; you can unpack it | |
a0d0e21e LW |
2771 | by saying something like: |
2772 | ||
f337b084 | 2773 | ($a,$b,$c,$d) = unpack('W4',$addr[0]); |
a0d0e21e | 2774 | |
2b5ab1e7 TC |
2775 | The Socket library makes this slightly easier: |
2776 | ||
2777 | use Socket; | |
2778 | $iaddr = inet_aton("127.1"); # or whatever address | |
2779 | $name = gethostbyaddr($iaddr, AF_INET); | |
2780 | ||
2781 | # or going the other way | |
19799a22 | 2782 | $straddr = inet_ntoa($iaddr); |
2b5ab1e7 | 2783 | |
d760c846 GS |
2784 | In the opposite way, to resolve a hostname to the IP address |
2785 | you can write this: | |
2786 | ||
2787 | use Socket; | |
2788 | $packed_ip = gethostbyname("www.perl.org"); | |
2789 | if (defined $packed_ip) { | |
2790 | $ip_address = inet_ntoa($packed_ip); | |
2791 | } | |
2792 | ||
b018eaf1 | 2793 | Make sure C<gethostbyname()> is called in SCALAR context and that |
d760c846 GS |
2794 | its return value is checked for definedness. |
2795 | ||
0d043efa FC |
2796 | The C<getprotobynumber> function, even though it only takes one argument, |
2797 | has the precedence of a list operator, so beware: | |
2798 | ||
2799 | getprotobynumber $number eq 'icmp' # WRONG | |
2800 | getprotobynumber($number eq 'icmp') # actually means this | |
2801 | getprotobynumber($number) eq 'icmp' # better this way | |
2802 | ||
19799a22 GS |
2803 | If you get tired of remembering which element of the return list |
2804 | contains which return value, by-name interfaces are provided | |
2805 | in standard modules: C<File::stat>, C<Net::hostent>, C<Net::netent>, | |
2806 | C<Net::protoent>, C<Net::servent>, C<Time::gmtime>, C<Time::localtime>, | |
2807 | and C<User::grent>. These override the normal built-ins, supplying | |
2808 | versions that return objects with the appropriate names | |
2809 | for each field. For example: | |
5a964f20 TC |
2810 | |
2811 | use File::stat; | |
2812 | use User::pwent; | |
2813 | $is_his = (stat($filename)->uid == pwent($whoever)->uid); | |
2814 | ||
a3390c9f | 2815 | Even though it looks as though they're the same method calls (uid), |
b76cc8ba | 2816 | they aren't, because a C<File::stat> object is different from |
19799a22 | 2817 | a C<User::pwent> object. |
5a964f20 | 2818 | |
ea9eb35a BJ |
2819 | Portability issues: L<perlport/getpwnam> to L<perlport/endservent>. |
2820 | ||
a0d0e21e | 2821 | =item getsockname SOCKET |
d74e8afc | 2822 | X<getsockname> |
a0d0e21e | 2823 | |
c17cdb72 NC |
2824 | =for Pod::Functions retrieve the sockaddr for a given socket |
2825 | ||
19799a22 GS |
2826 | Returns the packed sockaddr address of this end of the SOCKET connection, |
2827 | in case you don't know the address because you have several different | |
2828 | IPs that the connection might have come in on. | |
a0d0e21e | 2829 | |
4633a7c4 LW |
2830 | use Socket; |
2831 | $mysockaddr = getsockname(SOCK); | |
19799a22 | 2832 | ($port, $myaddr) = sockaddr_in($mysockaddr); |
b76cc8ba | 2833 | printf "Connect to %s [%s]\n", |
19799a22 GS |
2834 | scalar gethostbyaddr($myaddr, AF_INET), |
2835 | inet_ntoa($myaddr); | |
a0d0e21e LW |
2836 | |
2837 | =item getsockopt SOCKET,LEVEL,OPTNAME | |
d74e8afc | 2838 | X<getsockopt> |
a0d0e21e | 2839 | |
c17cdb72 NC |
2840 | =for Pod::Functions get socket options on a given socket |
2841 | ||
636e6b1f TH |
2842 | Queries the option named OPTNAME associated with SOCKET at a given LEVEL. |
2843 | Options may exist at multiple protocol levels depending on the socket | |
2844 | type, but at least the uppermost socket level SOL_SOCKET (defined in the | |
391b733c | 2845 | C<Socket> module) will exist. To query options at another level the |
636e6b1f | 2846 | protocol number of the appropriate protocol controlling the option |
391b733c | 2847 | should be supplied. For example, to indicate that an option is to be |
636e6b1f | 2848 | interpreted by the TCP protocol, LEVEL should be set to the protocol |
80d38338 | 2849 | number of TCP, which you can get using C<getprotobyname>. |
636e6b1f | 2850 | |
80d38338 | 2851 | The function returns a packed string representing the requested socket |
3b10bc60 | 2852 | option, or C<undef> on error, with the reason for the error placed in |
391b733c | 2853 | C<$!>. Just what is in the packed string depends on LEVEL and OPTNAME; |
80d38338 TC |
2854 | consult getsockopt(2) for details. A common case is that the option is an |
2855 | integer, in which case the result is a packed integer, which you can decode | |
2856 | using C<unpack> with the C<i> (or C<I>) format. | |
636e6b1f | 2857 | |
8f1da26d | 2858 | Here's an example to test whether Nagle's algorithm is enabled on a socket: |
636e6b1f | 2859 | |
4852725b | 2860 | use Socket qw(:all); |
636e6b1f TH |
2861 | |
2862 | defined(my $tcp = getprotobyname("tcp")) | |
a9a5a0dc | 2863 | or die "Could not determine the protocol number for tcp"; |
4852725b DD |
2864 | # my $tcp = IPPROTO_TCP; # Alternative |
2865 | my $packed = getsockopt($socket, $tcp, TCP_NODELAY) | |
80d38338 | 2866 | or die "getsockopt TCP_NODELAY: $!"; |
636e6b1f | 2867 | my $nodelay = unpack("I", $packed); |
f7051f2c FC |
2868 | print "Nagle's algorithm is turned ", |
2869 | $nodelay ? "off\n" : "on\n"; | |
636e6b1f | 2870 | |
ea9eb35a | 2871 | Portability issues: L<perlport/getsockopt>. |
a0d0e21e LW |
2872 | |
2873 | =item glob EXPR | |
d74e8afc | 2874 | X<glob> X<wildcard> X<filename, expansion> X<expand> |
a0d0e21e | 2875 | |
0a753a76 | 2876 | =item glob |
2877 | ||
c17cdb72 NC |
2878 | =for Pod::Functions expand filenames using wildcards |
2879 | ||
d9a9d457 | 2880 | In list context, returns a (possibly empty) list of filename expansions on |
391b733c | 2881 | the value of EXPR such as the standard Unix shell F</bin/csh> would do. In |
d9a9d457 | 2882 | scalar context, glob iterates through such filename expansions, returning |
391b733c FC |
2883 | undef when the list is exhausted. This is the internal function |
2884 | implementing the C<< <*.c> >> operator, but you can use it directly. If | |
d9a9d457 JL |
2885 | EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is discussed in |
2886 | more detail in L<perlop/"I/O Operators">. | |
a0d0e21e | 2887 | |
80d38338 TC |
2888 | Note that C<glob> splits its arguments on whitespace and treats |
2889 | each segment as separate pattern. As such, C<glob("*.c *.h")> | |
2890 | matches all files with a F<.c> or F<.h> extension. The expression | |
b474a1b1 | 2891 | C<glob(".* *")> matches all files in the current working directory. |
a91bb7b1 TC |
2892 | If you want to glob filenames that might contain whitespace, you'll |
2893 | have to use extra quotes around the spacey filename to protect it. | |
2894 | For example, to glob filenames that have an C<e> followed by a space | |
2895 | followed by an C<f>, use either of: | |
2896 | ||
2897 | @spacies = <"*e f*">; | |
2898 | @spacies = glob '"*e f*"'; | |
2899 | @spacies = glob q("*e f*"); | |
2900 | ||
2901 | If you had to get a variable through, you could do this: | |
2902 | ||
2903 | @spacies = glob "'*${var}e f*'"; | |
2904 | @spacies = glob qq("*${var}e f*"); | |
80d38338 TC |
2905 | |
2906 | If non-empty braces are the only wildcard characters used in the | |
2907 | C<glob>, no filenames are matched, but potentially many strings | |
2908 | are returned. For example, this produces nine strings, one for | |
2909 | each pairing of fruits and colors: | |
2910 | ||
2911 | @many = glob "{apple,tomato,cherry}={green,yellow,red}"; | |
5c0c9249 | 2912 | |
e9fa405d | 2913 | This operator is implemented using the standard |
5c0c9249 PF |
2914 | C<File::Glob> extension. See L<File::Glob> for details, including |
2915 | C<bsd_glob> which does not treat whitespace as a pattern separator. | |
3a4b19e4 | 2916 | |
ea9eb35a BJ |
2917 | Portability issues: L<perlport/glob>. |
2918 | ||
a0d0e21e | 2919 | =item gmtime EXPR |
d74e8afc | 2920 | X<gmtime> X<UTC> X<Greenwich> |
a0d0e21e | 2921 | |
ce2984c3 PF |
2922 | =item gmtime |
2923 | ||
c17cdb72 NC |
2924 | =for Pod::Functions convert UNIX time into record or string using Greenwich time |
2925 | ||
4509d391 | 2926 | Works just like L</localtime> but the returned values are |
435fbc73 | 2927 | localized for the standard Greenwich time zone. |
a0d0e21e | 2928 | |
a3390c9f FC |
2929 | Note: When called in list context, $isdst, the last value |
2930 | returned by gmtime, is always C<0>. There is no | |
435fbc73 | 2931 | Daylight Saving Time in GMT. |
0a753a76 | 2932 | |
ea9eb35a | 2933 | Portability issues: L<perlport/gmtime>. |
62aa5637 | 2934 | |
a0d0e21e | 2935 | =item goto LABEL |
d74e8afc | 2936 | X<goto> X<jump> X<jmp> |
a0d0e21e | 2937 | |
748a9306 LW |
2938 | =item goto EXPR |
2939 | ||
a0d0e21e LW |
2940 | =item goto &NAME |
2941 | ||
c17cdb72 NC |
2942 | =for Pod::Functions create spaghetti code |
2943 | ||
5a5b79a3 | 2944 | The C<goto LABEL> form finds the statement labeled with LABEL and |
391b733c | 2945 | resumes execution there. It can't be used to get out of a block or |
b500e03b GG |
2946 | subroutine given to C<sort>. It can be used to go almost anywhere |
2947 | else within the dynamic scope, including out of subroutines, but it's | |
2948 | usually better to use some other construct such as C<last> or C<die>. | |
2949 | The author of Perl has never felt the need to use this form of C<goto> | |
3b10bc60 | 2950 | (in Perl, that is; C is another matter). (The difference is that C |
b500e03b GG |
2951 | does not offer named loops combined with loop control. Perl does, and |
2952 | this replaces most structured uses of C<goto> in other languages.) | |
a0d0e21e | 2953 | |
5a5b79a3 | 2954 | The C<goto EXPR> form expects to evaluate C<EXPR> to a code reference or |
3e8a6370 | 2955 | a label name. If it evaluates to a code reference, it will be handled |
5a5b79a3 | 2956 | like C<goto &NAME>, below. This is especially useful for implementing |
3e8a6370 RS |
2957 | tail recursion via C<goto __SUB__>. |
2958 | ||
2959 | If the expression evaluates to a label name, its scope will be resolved | |
7660c0ab | 2960 | dynamically. This allows for computed C<goto>s per FORTRAN, but isn't |
748a9306 LW |
2961 | necessarily recommended if you're optimizing for maintainability: |
2962 | ||
2963 | goto ("FOO", "BAR", "GLARCH")[$i]; | |
2964 | ||
5a5b79a3 | 2965 | As shown in this example, C<goto EXPR> is exempt from the "looks like a |
391b733c FC |
2966 | function" rule. A pair of parentheses following it does not (necessarily) |
2967 | delimit its argument. C<goto("NE")."XT"> is equivalent to C<goto NEXT>. | |
8a7e748e FC |
2968 | Also, unlike most named operators, this has the same precedence as |
2969 | assignment. | |
887d89fd | 2970 | |
5a5b79a3 | 2971 | Use of C<goto LABEL> or C<goto EXPR> to jump into a construct is |
0b98bec9 | 2972 | deprecated and will issue a warning. Even then, it may not be used to |
b500e03b GG |
2973 | go into any construct that requires initialization, such as a |
2974 | subroutine or a C<foreach> loop. It also can't be used to go into a | |
0b98bec9 | 2975 | construct that is optimized away. |
b500e03b | 2976 | |
5a5b79a3 | 2977 | The C<goto &NAME> form is quite different from the other forms of |
1b6921cb BT |
2978 | C<goto>. In fact, it isn't a goto in the normal sense at all, and |
2979 | doesn't have the stigma associated with other gotos. Instead, it | |
2980 | exits the current subroutine (losing any changes set by local()) and | |
2981 | immediately calls in its place the named subroutine using the current | |
2982 | value of @_. This is used by C<AUTOLOAD> subroutines that wish to | |
2983 | load another subroutine and then pretend that the other subroutine had | |
2984 | been called in the first place (except that any modifications to C<@_> | |
6cb9131c GS |
2985 | in the current subroutine are propagated to the other subroutine.) |
2986 | After the C<goto>, not even C<caller> will be able to tell that this | |
2987 | routine was called first. | |
2988 | ||
2989 | NAME needn't be the name of a subroutine; it can be a scalar variable | |
8f1da26d | 2990 | containing a code reference or a block that evaluates to a code |
6cb9131c | 2991 | reference. |
a0d0e21e LW |
2992 | |
2993 | =item grep BLOCK LIST | |
d74e8afc | 2994 | X<grep> |
a0d0e21e LW |
2995 | |
2996 | =item grep EXPR,LIST | |
2997 | ||
c17cdb72 NC |
2998 | =for Pod::Functions locate elements in a list test true against a given criterion |
2999 | ||
2b5ab1e7 TC |
3000 | This is similar in spirit to, but not the same as, grep(1) and its |
3001 | relatives. In particular, it is not limited to using regular expressions. | |
2f9daede | 3002 | |
a0d0e21e | 3003 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
7660c0ab | 3004 | C<$_> to each element) and returns the list value consisting of those |
19799a22 GS |
3005 | elements for which the expression evaluated to true. In scalar |
3006 | context, returns the number of times the expression was true. | |
a0d0e21e LW |
3007 | |
3008 | @foo = grep(!/^#/, @bar); # weed out comments | |
3009 | ||
3010 | or equivalently, | |
3011 | ||
3012 | @foo = grep {!/^#/} @bar; # weed out comments | |
3013 | ||
be3174d2 GS |
3014 | Note that C<$_> is an alias to the list value, so it can be used to |
3015 | modify the elements of the LIST. While this is useful and supported, | |
3016 | it can cause bizarre results if the elements of LIST are not variables. | |
2b5ab1e7 TC |
3017 | Similarly, grep returns aliases into the original list, much as a for |
3018 | loop's index variable aliases the list elements. That is, modifying an | |
19799a22 GS |
3019 | element of a list returned by grep (for example, in a C<foreach>, C<map> |
3020 | or another C<grep>) actually modifies the element in the original list. | |
2b5ab1e7 | 3021 | This is usually something to be avoided when writing clear code. |
a0d0e21e | 3022 | |
a4fb8298 | 3023 | If C<$_> is lexical in the scope where the C<grep> appears (because it has |
c071e214 FC |
3024 | been declared with the deprecated C<my $_> construct) |
3025 | then, in addition to being locally aliased to | |
80d38338 | 3026 | the list elements, C<$_> keeps being lexical inside the block; i.e., it |
a4fb8298 RGS |
3027 | can't be seen from the outside, avoiding any potential side-effects. |
3028 | ||
19799a22 | 3029 | See also L</map> for a list composed of the results of the BLOCK or EXPR. |
38325410 | 3030 | |
a0d0e21e | 3031 | =item hex EXPR |
d74e8afc | 3032 | X<hex> X<hexadecimal> |
a0d0e21e | 3033 | |
54310121 | 3034 | =item hex |
bbce6d69 | 3035 | |
c17cdb72 NC |
3036 | =for Pod::Functions convert a string to a hexadecimal number |
3037 | ||
2b5ab1e7 | 3038 | Interprets EXPR as a hex string and returns the corresponding value. |
38366c11 | 3039 | (To convert strings that might start with either C<0>, C<0x>, or C<0b>, see |
2b5ab1e7 | 3040 | L</oct>.) If EXPR is omitted, uses C<$_>. |
2f9daede TP |
3041 | |
3042 | print hex '0xAf'; # prints '175' | |
3043 | print hex 'aF'; # same | |
a0d0e21e | 3044 | |
19799a22 | 3045 | Hex strings may only represent integers. Strings that would cause |
53305cf1 | 3046 | integer overflow trigger a warning. Leading whitespace is not stripped, |
391b733c | 3047 | unlike oct(). To present something as hex, look into L</printf>, |
8f1da26d | 3048 | L</sprintf>, and L</unpack>. |
19799a22 | 3049 | |
ce2984c3 | 3050 | =item import LIST |
d74e8afc | 3051 | X<import> |
a0d0e21e | 3052 | |
c17cdb72 NC |
3053 | =for Pod::Functions patch a module's namespace into your own |
3054 | ||
19799a22 | 3055 | There is no builtin C<import> function. It is just an ordinary |
4633a7c4 | 3056 | method (subroutine) defined (or inherited) by modules that wish to export |
19799a22 | 3057 | names to another module. The C<use> function calls the C<import> method |
cea6626f | 3058 | for the package used. See also L</use>, L<perlmod>, and L<Exporter>. |
a0d0e21e LW |
3059 | |
3060 | =item index STR,SUBSTR,POSITION | |
d74e8afc | 3061 | X<index> X<indexOf> X<InStr> |
a0d0e21e LW |
3062 | |
3063 | =item index STR,SUBSTR | |
3064 | ||
c17cdb72 NC |
3065 | =for Pod::Functions find a substring within a string |
3066 | ||
2b5ab1e7 TC |
3067 | The index function searches for one string within another, but without |
3068 | the wildcard-like behavior of a full regular-expression pattern match. | |
3069 | It returns the position of the first occurrence of SUBSTR in STR at | |
3070 | or after POSITION. If POSITION is omitted, starts searching from the | |
26f149de YST |
3071 | beginning of the string. POSITION before the beginning of the string |
3072 | or after its end is treated as if it were the beginning or the end, | |
e1dccc0d Z |
3073 | respectively. POSITION and the return value are based at zero. |
3074 | If the substring is not found, C<index> returns -1. | |
a0d0e21e LW |
3075 | |
3076 | =item int EXPR | |
f723aae1 | 3077 | X<int> X<integer> X<truncate> X<trunc> X<floor> |
a0d0e21e | 3078 | |
54310121 | 3079 | =item int |
bbce6d69 | 3080 | |
c17cdb72 NC |
3081 | =for Pod::Functions get the integer portion of a number |
3082 | ||
7660c0ab | 3083 | Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>. |
2b5ab1e7 | 3084 | You should not use this function for rounding: one because it truncates |
3b10bc60 | 3085 | towards C<0>, and two because machine representations of floating-point |
2b5ab1e7 TC |
3086 | numbers can sometimes produce counterintuitive results. For example, |
3087 | C<int(-6.725/0.025)> produces -268 rather than the correct -269; that's | |
3088 | because it's really more like -268.99999999999994315658 instead. Usually, | |
19799a22 | 3089 | the C<sprintf>, C<printf>, or the C<POSIX::floor> and C<POSIX::ceil> |
2b5ab1e7 | 3090 | functions will serve you better than will int(). |
a0d0e21e LW |
3091 | |
3092 | =item ioctl FILEHANDLE,FUNCTION,SCALAR | |
d74e8afc | 3093 | X<ioctl> |
a0d0e21e | 3094 | |
c17cdb72 NC |
3095 | =for Pod::Functions system-dependent device control system call |
3096 | ||
2b5ab1e7 | 3097 | Implements the ioctl(2) function. You'll probably first have to say |
a0d0e21e | 3098 | |
f7051f2c FC |
3099 | require "sys/ioctl.ph"; # probably in |
3100 | # $Config{archlib}/sys/ioctl.ph | |
a0d0e21e | 3101 | |
a11c483f | 3102 | to get the correct function definitions. If F<sys/ioctl.ph> doesn't |
a0d0e21e | 3103 | exist or doesn't have the correct definitions you'll have to roll your |
61eff3bc | 3104 | own, based on your C header files such as F<< <sys/ioctl.h> >>. |
5a964f20 | 3105 | (There is a Perl script called B<h2ph> that comes with the Perl kit that |
54310121 | 3106 | may help you in this, but it's nontrivial.) SCALAR will be read and/or |
3b10bc60 | 3107 | written depending on the FUNCTION; a C pointer to the string value of SCALAR |
19799a22 | 3108 | will be passed as the third argument of the actual C<ioctl> call. (If SCALAR |
4633a7c4 LW |
3109 | has no string value but does have a numeric value, that value will be |
3110 | passed rather than a pointer to the string value. To guarantee this to be | |
19799a22 GS |
3111 | true, add a C<0> to the scalar before using it.) The C<pack> and C<unpack> |
3112 | functions may be needed to manipulate the values of structures used by | |
b76cc8ba | 3113 | C<ioctl>. |
a0d0e21e | 3114 | |
19799a22 | 3115 | The return value of C<ioctl> (and C<fcntl>) is as follows: |
a0d0e21e | 3116 | |
5ed4f2ec | 3117 | if OS returns: then Perl returns: |
3118 | -1 undefined value | |
3119 | 0 string "0 but true" | |
3120 | anything else that number | |
a0d0e21e | 3121 | |
19799a22 | 3122 | Thus Perl returns true on success and false on failure, yet you can |
a0d0e21e LW |
3123 | still easily determine the actual value returned by the operating |
3124 | system: | |
3125 | ||
2b5ab1e7 | 3126 | $retval = ioctl(...) || -1; |
a0d0e21e LW |
3127 | printf "System returned %d\n", $retval; |
3128 | ||
be2f7487 | 3129 | The special string C<"0 but true"> is exempt from B<-w> complaints |
5a964f20 TC |
3130 | about improper numeric conversions. |
3131 | ||
ea9eb35a BJ |
3132 | Portability issues: L<perlport/ioctl>. |
3133 | ||
a0d0e21e | 3134 | =item join EXPR,LIST |
d74e8afc | 3135 | X<join> |
a0d0e21e | 3136 | |
c17cdb72 NC |
3137 | =for Pod::Functions join a list into a string using a separator |
3138 | ||
2b5ab1e7 TC |
3139 | Joins the separate strings of LIST into a single string with fields |
3140 | separated by the value of EXPR, and returns that new string. Example: | |
a0d0e21e | 3141 | |
2b5ab1e7 | 3142 | $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); |
a0d0e21e | 3143 | |
eb6e2d6f GS |
3144 | Beware that unlike C<split>, C<join> doesn't take a pattern as its |
3145 | first argument. Compare L</split>. | |
a0d0e21e | 3146 | |
532eee96 | 3147 | =item keys HASH |
d74e8afc | 3148 | X<keys> X<key> |
aa689395 | 3149 | |
532eee96 | 3150 | =item keys ARRAY |
aeedbbed | 3151 | |
f5a93a43 TC |
3152 | =item keys EXPR |
3153 | ||
c17cdb72 NC |
3154 | =for Pod::Functions retrieve list of indices from a hash |
3155 | ||
bade7fbc TC |
3156 | Called in list context, returns a list consisting of all the keys of the |
3157 | named hash, or in Perl 5.12 or later only, the indices of an array. Perl | |
3158 | releases prior to 5.12 will produce a syntax error if you try to use an | |
3159 | array argument. In scalar context, returns the number of keys or indices. | |
504f80c1 | 3160 | |
7bf59113 YO |
3161 | Hash entries are returned in an apparently random order. The actual random |
3162 | order is specific to a given hash; the exact same series of operations | |
7161e5c2 | 3163 | on two hashes may result in a different order for each hash. Any insertion |
7bf59113 YO |
3164 | into the hash may change the order, as will any deletion, with the exception |
3165 | that the most recent key returned by C<each> or C<keys> may be deleted | |
7161e5c2 | 3166 | without changing the order. So long as a given hash is unmodified you may |
7bf59113 | 3167 | rely on C<keys>, C<values> and C<each> to repeatedly return the same order |
7161e5c2 FC |
3168 | as each other. See L<perlsec/"Algorithmic Complexity Attacks"> for |
3169 | details on why hash order is randomized. Aside from the guarantees | |
7bf59113 | 3170 | provided here the exact details of Perl's hash algorithm and the hash |
883f220b TC |
3171 | traversal order are subject to change in any release of Perl. Tied hashes |
3172 | may behave differently to Perl's hashes with respect to changes in order on | |
3173 | insertion and deletion of items. | |
504f80c1 | 3174 | |
a02807f8 JK |
3175 | As a side effect, calling keys() resets the internal iterator of the HASH or |
3176 | ARRAY (see L</each>). In particular, calling keys() in void context resets | |
cf264981 | 3177 | the iterator with no other overhead. |
a0d0e21e | 3178 | |
aa689395 | 3179 | Here is yet another way to print your environment: |
a0d0e21e LW |
3180 | |
3181 | @keys = keys %ENV; | |
3182 | @values = values %ENV; | |
b76cc8ba | 3183 | while (@keys) { |
a9a5a0dc | 3184 | print pop(@keys), '=', pop(@values), "\n"; |
a0d0e21e LW |
3185 | } |
3186 | ||
3187 | or how about sorted by key: | |
3188 | ||
3189 | foreach $key (sort(keys %ENV)) { | |
a9a5a0dc | 3190 | print $key, '=', $ENV{$key}, "\n"; |
a0d0e21e LW |
3191 | } |
3192 | ||
8ea1e5d4 GS |
3193 | The returned values are copies of the original keys in the hash, so |
3194 | modifying them will not affect the original hash. Compare L</values>. | |
3195 | ||
19799a22 | 3196 | To sort a hash by value, you'll need to use a C<sort> function. |
aa689395 | 3197 | Here's a descending numeric sort of a hash by its values: |
4633a7c4 | 3198 | |
5a964f20 | 3199 | foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) { |
a9a5a0dc | 3200 | printf "%4d %s\n", $hash{$key}, $key; |
4633a7c4 LW |
3201 | } |
3202 | ||
3b10bc60 | 3203 | Used as an lvalue, C<keys> allows you to increase the number of hash buckets |
aa689395 | 3204 | allocated for the given hash. This can gain you a measure of efficiency if |
3205 | you know the hash is going to get big. (This is similar to pre-extending | |
3206 | an array by assigning a larger number to $#array.) If you say | |
55497cff | 3207 | |
3208 | keys %hash = 200; | |
3209 | ||
ab192400 GS |
3210 | then C<%hash> will have at least 200 buckets allocated for it--256 of them, |
3211 | in fact, since it rounds up to the next power of two. These | |
55497cff | 3212 | buckets will be retained even if you do C<%hash = ()>, use C<undef |
3213 | %hash> if you want to free the storage while C<%hash> is still in scope. | |
3214 | You can't shrink the number of buckets allocated for the hash using | |
19799a22 | 3215 | C<keys> in this way (but you needn't worry about doing this by accident, |
0d3e3823 | 3216 | as trying has no effect). C<keys @array> in an lvalue context is a syntax |
aeedbbed | 3217 | error. |
55497cff | 3218 | |
f5a93a43 TC |
3219 | Starting with Perl 5.14, C<keys> can take a scalar EXPR, which must contain |
3220 | a reference to an unblessed hash or array. The argument will be | |
3221 | dereferenced automatically. This aspect of C<keys> is considered highly | |
3222 | experimental. The exact behaviour may change in a future version of Perl. | |
cba5a3b0 DG |
3223 | |
3224 | for (keys $hashref) { ... } | |
3225 | for (keys $obj->get_arrayref) { ... } | |
3226 | ||
bade7fbc TC |
3227 | To avoid confusing would-be users of your code who are running earlier |
3228 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
3229 | the top of your file to signal that your code will work I<only> on Perls of | |
3230 | a recent vintage: | |
3231 | ||
3232 | use 5.012; # so keys/values/each work on arrays | |
3233 | use 5.014; # so keys/values/each work on scalars (experimental) | |
3234 | ||
8f1da26d | 3235 | See also C<each>, C<values>, and C<sort>. |
ab192400 | 3236 | |
b350dd2f | 3237 | =item kill SIGNAL, LIST |
9c7e4b76 KW |
3238 | |
3239 | =item kill SIGNAL | |
d74e8afc | 3240 | X<kill> X<signal> |
a0d0e21e | 3241 | |
c17cdb72 NC |
3242 | =for Pod::Functions send a signal to a process or process group |
3243 | ||
12733a03 DM |
3244 | Sends a signal to a list of processes. Returns the number of arguments |
3245 | that were successfully used to signal (which is not necessarily the same | |
3246 | as the number of processes actually killed, e.g. where a process group is | |
3247 | killed). | |
a0d0e21e | 3248 | |
1ac81c06 LM |
3249 | $cnt = kill 'HUP', $child1, $child2; |
3250 | kill 'KILL', @goners; | |
3251 | ||
3252 | SIGNAL may be either a signal name (a string) or a signal number. A signal | |
16bf540f | 3253 | name may start with a C<SIG> prefix, thus C<FOO> and C<SIGFOO> refer to the |
1ac81c06 LM |
3254 | same signal. The string form of SIGNAL is recommended for portability because |
3255 | the same signal may have different numbers in different operating systems. | |
3256 | ||
3257 | A list of signal names supported by the current platform can be found in | |
7161e5c2 | 3258 | C<$Config{sig_name}>, which is provided by the C<Config> module. See L<Config> |
1ac81c06 LM |
3259 | for more details. |
3260 | ||
3261 | A negative signal name is the same as a negative signal number, killing process | |
3262 | groups instead of processes. For example, C<kill '-KILL', $pgrp> and | |
7161e5c2 FC |
3263 | C<kill -9, $pgrp> will send C<SIGKILL> to |
3264 | the entire process group specified. That | |
1ac81c06 LM |
3265 | means you usually want to use positive not negative signals. |
3266 | ||
3875f14c | 3267 | If SIGNAL is either the number 0 or the string C<ZERO> (or C<SIGZERO>), |
16bf540f | 3268 | no signal is sent to |
1ac81c06 LM |
3269 | the process, but C<kill> checks whether it's I<possible> to send a signal to it |
3270 | (that means, to be brief, that the process is owned by the same user, or we are | |
3b10bc60 | 3271 | the super-user). This is useful to check that a child process is still |
81fd35db DN |
3272 | alive (even if only as a zombie) and hasn't changed its UID. See |
3273 | L<perlport> for notes on the portability of this construct. | |
b350dd2f | 3274 | |
e2c0f81f DG |
3275 | The behavior of kill when a I<PROCESS> number is zero or negative depends on |
3276 | the operating system. For example, on POSIX-conforming systems, zero will | |
c2fd40cb DM |
3277 | signal the current process group, -1 will signal all processes, and any |
3278 | other negative PROCESS number will act as a negative signal number and | |
3279 | kill the entire process group specified. | |
3280 | ||
3281 | If both the SIGNAL and the PROCESS are negative, the results are undefined. | |
3282 | A warning may be produced in a future version. | |
1e9c1022 JL |
3283 | |
3284 | See L<perlipc/"Signals"> for more details. | |
a0d0e21e | 3285 | |
4a70680a SK |
3286 | On some platforms such as Windows where the fork() system call is not |
3287 | available, Perl can be built to emulate fork() at the interpreter level. | |
6d17f725 | 3288 | This emulation has limitations related to kill that have to be considered, |
ea9eb35a BJ |
3289 | for code running on Windows and in code intended to be portable. |
3290 | ||
3291 | See L<perlfork> for more details. | |
3292 | ||
9c7e4b76 KW |
3293 | If there is no I<LIST> of processes, no signal is sent, and the return |
3294 | value is 0. This form is sometimes used, however, because it causes | |
3295 | tainting checks to be run. But see | |
3296 | L<perlsec/Laundering and Detecting Tainted Data>. | |
3297 | ||
ea9eb35a BJ |
3298 | Portability issues: L<perlport/kill>. |
3299 | ||
a0d0e21e | 3300 | =item last LABEL |
d74e8afc | 3301 | X<last> X<break> |
a0d0e21e | 3302 | |
8a7e748e FC |
3303 | =item last EXPR |
3304 | ||
a0d0e21e LW |
3305 | =item last |
3306 | ||
c17cdb72 NC |
3307 | =for Pod::Functions exit a block prematurely |
3308 | ||
a0d0e21e LW |
3309 | The C<last> command is like the C<break> statement in C (as used in |
3310 | loops); it immediately exits the loop in question. If the LABEL is | |
8a7e748e FC |
3311 | omitted, the command refers to the innermost enclosing |
3312 | loop. The C<last EXPR> form, available starting in Perl | |
3313 | 5.18.0, allows a label name to be computed at run time, | |
3314 | and is otherwise identical to C<last LABEL>. The | |
a0d0e21e LW |
3315 | C<continue> block, if any, is not executed: |
3316 | ||
4633a7c4 | 3317 | LINE: while (<STDIN>) { |
a9a5a0dc VP |
3318 | last LINE if /^$/; # exit when done with header |
3319 | #... | |
a0d0e21e LW |
3320 | } |
3321 | ||
80d38338 | 3322 | C<last> cannot be used to exit a block that returns a value such as |
8f1da26d | 3323 | C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit |
2b5ab1e7 | 3324 | a grep() or map() operation. |
4968c1e4 | 3325 | |
6c1372ed GS |
3326 | Note that a block by itself is semantically identical to a loop |
3327 | that executes once. Thus C<last> can be used to effect an early | |
3328 | exit out of such a block. | |
3329 | ||
98293880 JH |
3330 | See also L</continue> for an illustration of how C<last>, C<next>, and |
3331 | C<redo> work. | |
1d2dff63 | 3332 | |
2ba1f20a FC |
3333 | Unlike most named operators, this has the same precedence as assignment. |
3334 | It is also exempt from the looks-like-a-function rule, so | |
3335 | C<last ("foo")."bar"> will cause "bar" to be part of the argument to | |
3336 | C<last>. | |
3337 | ||
a0d0e21e | 3338 | =item lc EXPR |
d74e8afc | 3339 | X<lc> X<lowercase> |
a0d0e21e | 3340 | |
54310121 | 3341 | =item lc |
bbce6d69 | 3342 | |
c17cdb72 NC |
3343 | =for Pod::Functions return lower-case version of a string |
3344 | ||
d1be9408 | 3345 | Returns a lowercased version of EXPR. This is the internal function |
3980dc9c | 3346 | implementing the C<\L> escape in double-quoted strings. |
a0d0e21e | 3347 | |
7660c0ab | 3348 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 3349 | |
3980dc9c KW |
3350 | What gets returned depends on several factors: |
3351 | ||
3352 | =over | |
3353 | ||
3354 | =item If C<use bytes> is in effect: | |
3355 | ||
850b7ec9 | 3356 | The results follow ASCII rules. Only the characters C<A-Z> change, |
a93e23f1 | 3357 | to C<a-z> respectively. |
3980dc9c | 3358 | |
d6ded950 | 3359 | =item Otherwise, if C<use locale> for C<LC_CTYPE> is in effect: |
3980dc9c | 3360 | |
d6ded950 | 3361 | Respects current C<LC_CTYPE> locale for code points < 256; and uses Unicode |
850b7ec9 | 3362 | rules for the remaining code points (this last can only happen if |
094a2f8c | 3363 | the UTF8 flag is also set). See L<perllocale>. |
3980dc9c | 3364 | |
86ceb7c6 | 3365 | Starting in v5.20, Perl uses full Unicode rules if the locale is |
31f05a37 KW |
3366 | UTF-8. Otherwise, there is a deficiency in this scheme, which is that |
3367 | case changes that cross the 255/256 | |
094a2f8c | 3368 | boundary are not well-defined. For example, the lower case of LATIN CAPITAL |
850b7ec9 | 3369 | LETTER SHARP S (U+1E9E) in Unicode rules is U+00DF (on ASCII |
31f05a37 KW |
3370 | platforms). But under C<use locale> (prior to v5.20 or not a UTF-8 |
3371 | locale), the lower case of U+1E9E is | |
094a2f8c KW |
3372 | itself, because 0xDF may not be LATIN SMALL LETTER SHARP S in the |
3373 | current locale, and Perl has no way of knowing if that character even | |
3374 | exists in the locale, much less what code point it is. Perl returns | |
ab0b796c KW |
3375 | a result that is above 255 (almost always the input character unchanged, |
3376 | for all instances (and there aren't many) where the 255/256 boundary | |
3377 | would otherwise be crossed; and starting in v5.22, it raises a | |
3378 | L<locale|perldiag/Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".> warning. | |
3980dc9c | 3379 | |
66cbab2c | 3380 | =item Otherwise, If EXPR has the UTF8 flag set: |
094a2f8c | 3381 | |
850b7ec9 | 3382 | Unicode rules are used for the case change. |
3980dc9c | 3383 | |
48cbae4f | 3384 | =item Otherwise, if C<use feature 'unicode_strings'> or C<use locale ':not_characters'> is in effect: |
3980dc9c | 3385 | |
850b7ec9 | 3386 | Unicode rules are used for the case change. |
3980dc9c KW |
3387 | |
3388 | =item Otherwise: | |
3389 | ||
850b7ec9 | 3390 | ASCII rules are used for the case change. The lowercase of any character |
3980dc9c KW |
3391 | outside the ASCII range is the character itself. |
3392 | ||
3393 | =back | |
3394 | ||
a0d0e21e | 3395 | =item lcfirst EXPR |
d74e8afc | 3396 | X<lcfirst> X<lowercase> |
a0d0e21e | 3397 | |
54310121 | 3398 | =item lcfirst |
bbce6d69 | 3399 | |
c17cdb72 NC |
3400 | =for Pod::Functions return a string with just the next letter in lower case |
3401 | ||
ad0029c4 JH |
3402 | Returns the value of EXPR with the first character lowercased. This |
3403 | is the internal function implementing the C<\l> escape in | |
3980dc9c | 3404 | double-quoted strings. |
a0d0e21e | 3405 | |
7660c0ab | 3406 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 3407 | |
15dbbbab | 3408 | This function behaves the same way under various pragmata, such as in a locale, |
3980dc9c KW |
3409 | as L</lc> does. |
3410 | ||
a0d0e21e | 3411 | =item length EXPR |
d74e8afc | 3412 | X<length> X<size> |
a0d0e21e | 3413 | |
54310121 | 3414 | =item length |
bbce6d69 | 3415 | |
c52f983f | 3416 | =for Pod::Functions return the number of characters in a string |
c17cdb72 | 3417 | |
974da8e5 | 3418 | Returns the length in I<characters> of the value of EXPR. If EXPR is |
15dbbbab FC |
3419 | omitted, returns the length of C<$_>. If EXPR is undefined, returns |
3420 | C<undef>. | |
3b10bc60 | 3421 | |
3422 | This function cannot be used on an entire array or hash to find out how | |
3423 | many elements these have. For that, use C<scalar @array> and C<scalar keys | |
3424 | %hash>, respectively. | |
3425 | ||
3426 | Like all Perl character operations, length() normally deals in logical | |
3427 | characters, not physical bytes. For how many bytes a string encoded as | |
3428 | UTF-8 would take up, use C<length(Encode::encode_utf8(EXPR))> (you'll have | |
3429 | to C<use Encode> first). See L<Encode> and L<perlunicode>. | |
974da8e5 | 3430 | |
cfa52385 FC |
3431 | =item __LINE__ |
3432 | X<__LINE__> | |
3433 | ||
c17cdb72 NC |
3434 | =for Pod::Functions the current source line number |
3435 | ||
cfa52385 FC |
3436 | A special token that compiles to the current line number. |
3437 | ||
a0d0e21e | 3438 | =item link OLDFILE,NEWFILE |
d74e8afc | 3439 | X<link> |
a0d0e21e | 3440 | |
c17cdb72 NC |
3441 | =for Pod::Functions create a hard link in the filesystem |
3442 | ||
19799a22 | 3443 | Creates a new filename linked to the old filename. Returns true for |
b76cc8ba | 3444 | success, false otherwise. |
a0d0e21e | 3445 | |
ea9eb35a BJ |
3446 | Portability issues: L<perlport/link>. |
3447 | ||
a0d0e21e | 3448 | =item listen SOCKET,QUEUESIZE |
d74e8afc | 3449 | X<listen> |
a0d0e21e | 3450 | |
c17cdb72 NC |
3451 | =for Pod::Functions register your socket as a server |
3452 | ||
3b10bc60 | 3453 | Does the same thing that the listen(2) system call does. Returns true if |
b76cc8ba | 3454 | it succeeded, false otherwise. See the example in |
cea6626f | 3455 | L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
3456 | |
3457 | =item local EXPR | |
d74e8afc | 3458 | X<local> |
a0d0e21e | 3459 | |
c17cdb72 NC |
3460 | =for Pod::Functions create a temporary value for a global variable (dynamic scoping) |
3461 | ||
19799a22 | 3462 | You really probably want to be using C<my> instead, because C<local> isn't |
b76cc8ba | 3463 | what most people think of as "local". See |
13a2d996 | 3464 | L<perlsub/"Private Variables via my()"> for details. |
2b5ab1e7 | 3465 | |
5a964f20 TC |
3466 | A local modifies the listed variables to be local to the enclosing |
3467 | block, file, or eval. If more than one value is listed, the list must | |
3468 | be placed in parentheses. See L<perlsub/"Temporary Values via local()"> | |
3469 | for details, including issues with tied arrays and hashes. | |
a0d0e21e | 3470 | |
d361fafa VP |
3471 | The C<delete local EXPR> construct can also be used to localize the deletion |
3472 | of array/hash elements to the current block. | |
3473 | See L<perlsub/"Localized deletion of elements of composite types">. | |
3474 | ||
a0d0e21e | 3475 | =item localtime EXPR |
435fbc73 | 3476 | X<localtime> X<ctime> |
a0d0e21e | 3477 | |
ba053783 AL |
3478 | =item localtime |
3479 | ||
c17cdb72 NC |
3480 | =for Pod::Functions convert UNIX time into record or string using local time |
3481 | ||
19799a22 | 3482 | Converts a time as returned by the time function to a 9-element list |
5f05dabc | 3483 | with the time analyzed for the local time zone. Typically used as |
a0d0e21e LW |
3484 | follows: |
3485 | ||
54310121 | 3486 | # 0 1 2 3 4 5 6 7 8 |
a0d0e21e | 3487 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
ba053783 | 3488 | localtime(time); |
a0d0e21e | 3489 | |
8f1da26d | 3490 | All list elements are numeric and come straight out of the C `struct |
ba053783 AL |
3491 | tm'. C<$sec>, C<$min>, and C<$hour> are the seconds, minutes, and hours |
3492 | of the specified time. | |
48a26b3a | 3493 | |
8f1da26d TC |
3494 | C<$mday> is the day of the month and C<$mon> the month in |
3495 | the range C<0..11>, with 0 indicating January and 11 indicating December. | |
ba053783 | 3496 | This makes it easy to get a month name from a list: |
54310121 | 3497 | |
f7051f2c | 3498 | my @abbr = qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec); |
ba053783 AL |
3499 | print "$abbr[$mon] $mday"; |
3500 | # $mon=9, $mday=18 gives "Oct 18" | |
abd75f24 | 3501 | |
0d3e3823 | 3502 | C<$year> contains the number of years since 1900. To get a 4-digit |
570b1bb1 | 3503 | year write: |
abd75f24 | 3504 | |
ba053783 | 3505 | $year += 1900; |
abd75f24 | 3506 | |
8f1da26d | 3507 | To get the last two digits of the year (e.g., "01" in 2001) do: |
ba053783 AL |
3508 | |
3509 | $year = sprintf("%02d", $year % 100); | |
3510 | ||
3511 | C<$wday> is the day of the week, with 0 indicating Sunday and 3 indicating | |
3512 | Wednesday. C<$yday> is the day of the year, in the range C<0..364> | |
3513 | (or C<0..365> in leap years.) | |
3514 | ||
3515 | C<$isdst> is true if the specified time occurs during Daylight Saving | |
3516 | Time, false otherwise. | |
abd75f24 | 3517 | |
e1998452 | 3518 | If EXPR is omitted, C<localtime()> uses the current time (as returned |
e3176d09 | 3519 | by time(3)). |
a0d0e21e | 3520 | |
48a26b3a | 3521 | In scalar context, C<localtime()> returns the ctime(3) value: |
a0d0e21e | 3522 | |
5f05dabc | 3523 | $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994" |
a0d0e21e | 3524 | |
391b733c FC |
3525 | The format of this scalar value is B<not> locale-dependent |
3526 | but built into Perl. For GMT instead of local | |
3527 | time use the L</gmtime> builtin. See also the | |
8f1da26d | 3528 | C<Time::Local> module (for converting seconds, minutes, hours, and such back to |
fe86afc2 NC |
3529 | the integer value returned by time()), and the L<POSIX> module's strftime(3) |
3530 | and mktime(3) functions. | |
3531 | ||
15dbbbab | 3532 | To get somewhat similar but locale-dependent date strings, set up your |
fe86afc2 NC |
3533 | locale environment variables appropriately (please see L<perllocale>) and |
3534 | try for example: | |
a3cb178b | 3535 | |
5a964f20 | 3536 | use POSIX qw(strftime); |
2b5ab1e7 | 3537 | $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime; |
fe86afc2 NC |
3538 | # or for GMT formatted appropriately for your locale: |
3539 | $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime; | |
a3cb178b GS |
3540 | |
3541 | Note that the C<%a> and C<%b>, the short forms of the day of the week | |
3542 | and the month of the year, may not necessarily be three characters wide. | |
a0d0e21e | 3543 | |
15dbbbab | 3544 | The L<Time::gmtime> and L<Time::localtime> modules provide a convenient, |
435fbc73 GS |
3545 | by-name access mechanism to the gmtime() and localtime() functions, |
3546 | respectively. | |
3547 | ||
3548 | For a comprehensive date and time representation look at the | |
3549 | L<DateTime> module on CPAN. | |
3550 | ||
ea9eb35a BJ |
3551 | Portability issues: L<perlport/localtime>. |
3552 | ||
07698885 | 3553 | =item lock THING |
d74e8afc | 3554 | X<lock> |
19799a22 | 3555 | |
d9b04284 | 3556 | =for Pod::Functions +5.005 get a thread lock on a variable, subroutine, or method |
c17cdb72 | 3557 | |
15dbbbab | 3558 | This function places an advisory lock on a shared variable or referenced |
03730085 | 3559 | object contained in I<THING> until the lock goes out of scope. |
a6d5524e | 3560 | |
904028df | 3561 | The value returned is the scalar itself, if the argument is a scalar, or a |
f79aa60b | 3562 | reference, if the argument is a hash, array or subroutine. |
904028df | 3563 | |
f3a23afb | 3564 | lock() is a "weak keyword" : this means that if you've defined a function |
67408cae | 3565 | by this name (before any calls to it), that function will be called |
7b043ca5 RGS |
3566 | instead. If you are not under C<use threads::shared> this does nothing. |
3567 | See L<threads::shared>. | |
19799a22 | 3568 | |
a0d0e21e | 3569 | =item log EXPR |
d74e8afc | 3570 | X<log> X<logarithm> X<e> X<ln> X<base> |
a0d0e21e | 3571 | |
54310121 | 3572 | =item log |
bbce6d69 | 3573 | |
c17cdb72 NC |
3574 | =for Pod::Functions retrieve the natural logarithm for a number |
3575 | ||
2b5ab1e7 | 3576 | Returns the natural logarithm (base I<e>) of EXPR. If EXPR is omitted, |
15dbbbab FC |
3577 | returns the log of C<$_>. To get the |
3578 | log of another base, use basic algebra: | |
19799a22 | 3579 | The base-N log of a number is equal to the natural log of that number |
2b5ab1e7 TC |
3580 | divided by the natural log of N. For example: |
3581 | ||
3582 | sub log10 { | |
a9a5a0dc VP |
3583 | my $n = shift; |
3584 | return log($n)/log(10); | |
b76cc8ba | 3585 | } |
2b5ab1e7 TC |
3586 | |
3587 | See also L</exp> for the inverse operation. | |
a0d0e21e | 3588 | |
7ded94be | 3589 | =item lstat FILEHANDLE |
d74e8afc | 3590 | X<lstat> |
a0d0e21e | 3591 | |
7ded94be FC |
3592 | =item lstat EXPR |
3593 | ||
3594 | =item lstat DIRHANDLE | |
3595 | ||
54310121 | 3596 | =item lstat |
bbce6d69 | 3597 | |
c17cdb72 NC |
3598 | =for Pod::Functions stat a symbolic link |
3599 | ||
19799a22 | 3600 | Does the same thing as the C<stat> function (including setting the |
5a964f20 TC |
3601 | special C<_> filehandle) but stats a symbolic link instead of the file |
3602 | the symbolic link points to. If symbolic links are unimplemented on | |
c837d5b4 DP |
3603 | your system, a normal C<stat> is done. For much more detailed |
3604 | information, please see the documentation for C<stat>. | |
a0d0e21e | 3605 | |
7660c0ab | 3606 | If EXPR is omitted, stats C<$_>. |
bbce6d69 | 3607 | |
ea9eb35a BJ |
3608 | Portability issues: L<perlport/lstat>. |
3609 | ||
a0d0e21e LW |
3610 | =item m// |
3611 | ||
c17cdb72 NC |
3612 | =for Pod::Functions match a string with a regular expression pattern |
3613 | ||
9f4b9cd0 | 3614 | The match operator. See L<perlop/"Regexp Quote-Like Operators">. |
a0d0e21e LW |
3615 | |
3616 | =item map BLOCK LIST | |
d74e8afc | 3617 | X<map> |
a0d0e21e LW |
3618 | |
3619 | =item map EXPR,LIST | |
3620 | ||
c17cdb72 NC |
3621 | =for Pod::Functions apply a change to a list to get back a new list with the changes |
3622 | ||
19799a22 GS |
3623 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
3624 | C<$_> to each element) and returns the list value composed of the | |
3625 | results of each such evaluation. In scalar context, returns the | |
3626 | total number of elements so generated. Evaluates BLOCK or EXPR in | |
3627 | list context, so each element of LIST may produce zero, one, or | |
3628 | more elements in the returned value. | |
dd99ebda | 3629 | |
f9476272 | 3630 | @chars = map(chr, @numbers); |
a0d0e21e | 3631 | |
f9476272 AH |
3632 | translates a list of numbers to the corresponding characters. |
3633 | ||
3634 | my @squares = map { $_ * $_ } @numbers; | |
3635 | ||
3636 | translates a list of numbers to their squared values. | |
3637 | ||
3638 | my @squares = map { $_ > 5 ? ($_ * $_) : () } @numbers; | |
3639 | ||
3640 | shows that number of returned elements can differ from the number of | |
391b733c | 3641 | input elements. To omit an element, return an empty list (). |
f9476272 AH |
3642 | This could also be achieved by writing |
3643 | ||
3644 | my @squares = map { $_ * $_ } grep { $_ > 5 } @numbers; | |
3645 | ||
3646 | which makes the intention more clear. | |
3647 | ||
15dbbbab FC |
3648 | Map always returns a list, which can be |
3649 | assigned to a hash such that the elements | |
391b733c | 3650 | become key/value pairs. See L<perldata> for more details. |
a0d0e21e | 3651 | |
d8216f19 | 3652 | %hash = map { get_a_key_for($_) => $_ } @array; |
a0d0e21e LW |
3653 | |
3654 | is just a funny way to write | |
3655 | ||
3656 | %hash = (); | |
d8216f19 | 3657 | foreach (@array) { |
a9a5a0dc | 3658 | $hash{get_a_key_for($_)} = $_; |
a0d0e21e LW |
3659 | } |
3660 | ||
be3174d2 GS |
3661 | Note that C<$_> is an alias to the list value, so it can be used to |
3662 | modify the elements of the LIST. While this is useful and supported, | |
3663 | it can cause bizarre results if the elements of LIST are not variables. | |
2b5ab1e7 TC |
3664 | Using a regular C<foreach> loop for this purpose would be clearer in |
3665 | most cases. See also L</grep> for an array composed of those items of | |
3666 | the original list for which the BLOCK or EXPR evaluates to true. | |
fb73857a | 3667 | |
a4fb8298 | 3668 | If C<$_> is lexical in the scope where the C<map> appears (because it has |
c071e214 FC |
3669 | been declared with the deprecated C<my $_> construct), |
3670 | then, in addition to being locally aliased to | |
d8216f19 | 3671 | the list elements, C<$_> keeps being lexical inside the block; that is, it |
a4fb8298 RGS |
3672 | can't be seen from the outside, avoiding any potential side-effects. |
3673 | ||
205fdb4d | 3674 | C<{> starts both hash references and blocks, so C<map { ...> could be either |
391b733c | 3675 | the start of map BLOCK LIST or map EXPR, LIST. Because Perl doesn't look |
80d38338 | 3676 | ahead for the closing C<}> it has to take a guess at which it's dealing with |
391b733c FC |
3677 | based on what it finds just after the |
3678 | C<{>. Usually it gets it right, but if it | |
205fdb4d | 3679 | doesn't it won't realize something is wrong until it gets to the C<}> and |
391b733c | 3680 | encounters the missing (or unexpected) comma. The syntax error will be |
80d38338 | 3681 | reported close to the C<}>, but you'll need to change something near the C<{> |
24fe90a1 | 3682 | such as using a unary C<+> or semicolon to give Perl some help: |
205fdb4d | 3683 | |
f7051f2c FC |
3684 | %hash = map { "\L$_" => 1 } @array # perl guesses EXPR. wrong |
3685 | %hash = map { +"\L$_" => 1 } @array # perl guesses BLOCK. right | |
24fe90a1 FC |
3686 | %hash = map {; "\L$_" => 1 } @array # this also works |
3687 | %hash = map { ("\L$_" => 1) } @array # as does this | |
3688 | %hash = map { lc($_) => 1 } @array # and this. | |
f7051f2c | 3689 | %hash = map +( lc($_) => 1 ), @array # this is EXPR and works! |
cea6626f | 3690 | |
f7051f2c | 3691 | %hash = map ( lc($_), 1 ), @array # evaluates to (1, @array) |
205fdb4d | 3692 | |
d8216f19 | 3693 | or to force an anon hash constructor use C<+{>: |
205fdb4d | 3694 | |
f7051f2c FC |
3695 | @hashes = map +{ lc($_) => 1 }, @array # EXPR, so needs |
3696 | # comma at end | |
205fdb4d | 3697 | |
3b10bc60 | 3698 | to get a list of anonymous hashes each with only one entry apiece. |
205fdb4d | 3699 | |
19799a22 | 3700 | =item mkdir FILENAME,MASK |
d74e8afc | 3701 | X<mkdir> X<md> X<directory, create> |
a0d0e21e | 3702 | |
5a211162 GS |
3703 | =item mkdir FILENAME |
3704 | ||
491873e5 RGS |
3705 | =item mkdir |
3706 | ||
c17cdb72 NC |
3707 | =for Pod::Functions create a directory |
3708 | ||
0591cd52 | 3709 | Creates the directory specified by FILENAME, with permissions |
19799a22 | 3710 | specified by MASK (as modified by C<umask>). If it succeeds it |
8f1da26d TC |
3711 | returns true; otherwise it returns false and sets C<$!> (errno). |
3712 | MASK defaults to 0777 if omitted, and FILENAME defaults | |
3713 | to C<$_> if omitted. | |
0591cd52 | 3714 | |
8f1da26d TC |
3715 | In general, it is better to create directories with a permissive MASK |
3716 | and let the user modify that with their C<umask> than it is to supply | |
19799a22 | 3717 | a restrictive MASK and give the user no way to be more permissive. |
0591cd52 NT |
3718 | The exceptions to this rule are when the file or directory should be |
3719 | kept private (mail files, for instance). The perlfunc(1) entry on | |
19799a22 | 3720 | C<umask> discusses the choice of MASK in more detail. |
a0d0e21e | 3721 | |
cc1852e8 JH |
3722 | Note that according to the POSIX 1003.1-1996 the FILENAME may have any |
3723 | number of trailing slashes. Some operating and filesystems do not get | |
3724 | this right, so Perl automatically removes all trailing slashes to keep | |
3725 | everyone happy. | |
3726 | ||
80d38338 | 3727 | To recursively create a directory structure, look at |
a22ececd | 3728 | the C<make_path> function of the L<File::Path> module. |
dd184578 | 3729 | |
a0d0e21e | 3730 | =item msgctl ID,CMD,ARG |
d74e8afc | 3731 | X<msgctl> |
a0d0e21e | 3732 | |
c17cdb72 NC |
3733 | =for Pod::Functions SysV IPC message control operations |
3734 | ||
f86cebdf | 3735 | Calls the System V IPC function msgctl(2). You'll probably have to say |
0ade1984 JH |
3736 | |
3737 | use IPC::SysV; | |
3738 | ||
7660c0ab | 3739 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
cf264981 | 3740 | then ARG must be a variable that will hold the returned C<msqid_ds> |
951ba7fe GS |
3741 | structure. Returns like C<ioctl>: the undefined value for error, |
3742 | C<"0 but true"> for zero, or the actual return value otherwise. See also | |
15dbbbab FC |
3743 | L<perlipc/"SysV IPC"> and the documentation for C<IPC::SysV> and |
3744 | C<IPC::Semaphore>. | |
a0d0e21e | 3745 | |
ea9eb35a BJ |
3746 | Portability issues: L<perlport/msgctl>. |
3747 | ||
a0d0e21e | 3748 | =item msgget KEY,FLAGS |
d74e8afc | 3749 | X<msgget> |
a0d0e21e | 3750 | |
c17cdb72 NC |
3751 | =for Pod::Functions get SysV IPC message queue |
3752 | ||
f86cebdf | 3753 | Calls the System V IPC function msgget(2). Returns the message queue |
8f1da26d | 3754 | id, or C<undef> on error. See also |
15dbbbab FC |
3755 | L<perlipc/"SysV IPC"> and the documentation for C<IPC::SysV> and |
3756 | C<IPC::Msg>. | |
a0d0e21e | 3757 | |
ea9eb35a BJ |
3758 | Portability issues: L<perlport/msgget>. |
3759 | ||
a0d0e21e | 3760 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS |
d74e8afc | 3761 | X<msgrcv> |
a0d0e21e | 3762 | |
c17cdb72 NC |
3763 | =for Pod::Functions receive a SysV IPC message from a message queue |
3764 | ||
a0d0e21e LW |
3765 | Calls the System V IPC function msgrcv to receive a message from |
3766 | message queue ID into variable VAR with a maximum message size of | |
41d6edb2 JH |
3767 | SIZE. Note that when a message is received, the message type as a |
3768 | native long integer will be the first thing in VAR, followed by the | |
3769 | actual message. This packing may be opened with C<unpack("l! a*")>. | |
8f1da26d TC |
3770 | Taints the variable. Returns true if successful, false |
3771 | on error. See also L<perlipc/"SysV IPC"> and the documentation for | |
15dbbbab | 3772 | C<IPC::SysV> and C<IPC::SysV::Msg>. |
41d6edb2 | 3773 | |
ea9eb35a BJ |
3774 | Portability issues: L<perlport/msgrcv>. |
3775 | ||
41d6edb2 | 3776 | =item msgsnd ID,MSG,FLAGS |
d74e8afc | 3777 | X<msgsnd> |
41d6edb2 | 3778 | |
c17cdb72 NC |
3779 | =for Pod::Functions send a SysV IPC message to a message queue |
3780 | ||
41d6edb2 JH |
3781 | Calls the System V IPC function msgsnd to send the message MSG to the |
3782 | message queue ID. MSG must begin with the native long integer message | |
8f1da26d | 3783 | type, be followed by the length of the actual message, and then finally |
41d6edb2 JH |
3784 | the message itself. This kind of packing can be achieved with |
3785 | C<pack("l! a*", $type, $message)>. Returns true if successful, | |
8f1da26d | 3786 | false on error. See also the C<IPC::SysV> |
41d6edb2 | 3787 | and C<IPC::SysV::Msg> documentation. |
a0d0e21e | 3788 | |
ea9eb35a BJ |
3789 | Portability issues: L<perlport/msgsnd>. |
3790 | ||
672208d2 | 3791 | =item my VARLIST |
d74e8afc | 3792 | X<my> |
a0d0e21e | 3793 | |
672208d2 | 3794 | =item my TYPE VARLIST |
307ea6df | 3795 | |
672208d2 | 3796 | =item my VARLIST : ATTRS |
09bef843 | 3797 | |
672208d2 | 3798 | =item my TYPE VARLIST : ATTRS |
307ea6df | 3799 | |
c17cdb72 NC |
3800 | =for Pod::Functions declare and assign a local variable (lexical scoping) |
3801 | ||
19799a22 | 3802 | A C<my> declares the listed variables to be local (lexically) to the |
672208d2 | 3803 | enclosing block, file, or C<eval>. If more than one variable is listed, |
1d2de774 | 3804 | the list must be placed in parentheses. |
307ea6df | 3805 | |
1d2de774 | 3806 | The exact semantics and interface of TYPE and ATTRS are still |
ab461de4 FC |
3807 | evolving. TYPE may be a bareword, a constant declared |
3808 | with C<use constant>, or C<__PACKAGE__>. It is | |
3809 | currently bound to the use of the C<fields> pragma, | |
307ea6df JH |
3810 | and attributes are handled using the C<attributes> pragma, or starting |
3811 | from Perl 5.8.0 also via the C<Attribute::Handlers> module. See | |
3812 | L<perlsub/"Private Variables via my()"> for details, and L<fields>, | |
3813 | L<attributes>, and L<Attribute::Handlers>. | |
4633a7c4 | 3814 | |
672208d2 JV |
3815 | Note that with a parenthesised list, C<undef> can be used as a dummy |
3816 | placeholder, for example to skip assignment of initial values: | |
3817 | ||
3818 | my ( undef, $min, $hour ) = localtime; | |
3819 | ||
a0d0e21e | 3820 | =item next LABEL |
d74e8afc | 3821 | X<next> X<continue> |
a0d0e21e | 3822 | |
8a7e748e FC |
3823 | =item next EXPR |
3824 | ||
a0d0e21e LW |
3825 | =item next |
3826 | ||
c17cdb72 NC |
3827 | =for Pod::Functions iterate a block prematurely |
3828 | ||
a0d0e21e LW |
3829 | The C<next> command is like the C<continue> statement in C; it starts |
3830 | the next iteration of the loop: | |
3831 | ||
4633a7c4 | 3832 | LINE: while (<STDIN>) { |
a9a5a0dc VP |
3833 | next LINE if /^#/; # discard comments |
3834 | #... | |
a0d0e21e LW |
3835 | } |
3836 | ||
3837 | Note that if there were a C<continue> block on the above, it would get | |
3b10bc60 | 3838 | executed even on discarded lines. If LABEL is omitted, the command |
8a7e748e FC |
3839 | refers to the innermost enclosing loop. The C<next EXPR> form, available |
3840 | as of Perl 5.18.0, allows a label name to be computed at run time, being | |
3841 | otherwise identical to C<next LABEL>. | |
a0d0e21e | 3842 | |
4968c1e4 | 3843 | C<next> cannot be used to exit a block which returns a value such as |
8f1da26d | 3844 | C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit |
2b5ab1e7 | 3845 | a grep() or map() operation. |
4968c1e4 | 3846 | |
6c1372ed GS |
3847 | Note that a block by itself is semantically identical to a loop |
3848 | that executes once. Thus C<next> will exit such a block early. | |
3849 | ||
98293880 JH |
3850 | See also L</continue> for an illustration of how C<last>, C<next>, and |
3851 | C<redo> work. | |
1d2dff63 | 3852 | |
2ba1f20a FC |
3853 | Unlike most named operators, this has the same precedence as assignment. |
3854 | It is also exempt from the looks-like-a-function rule, so | |
3855 | C<next ("foo")."bar"> will cause "bar" to be part of the argument to | |
3856 | C<next>. | |
3857 | ||
3b10bc60 | 3858 | =item no MODULE VERSION LIST |
3859 | X<no declarations> | |
3860 | X<unimporting> | |
4a66ea5a | 3861 | |
3b10bc60 | 3862 | =item no MODULE VERSION |
4a66ea5a | 3863 | |
3b10bc60 | 3864 | =item no MODULE LIST |
a0d0e21e | 3865 | |
3b10bc60 | 3866 | =item no MODULE |
4a66ea5a | 3867 | |
c986422f RGS |
3868 | =item no VERSION |
3869 | ||
c17cdb72 NC |
3870 | =for Pod::Functions unimport some module symbols or semantics at compile time |
3871 | ||
593b9c14 | 3872 | See the C<use> function, of which C<no> is the opposite. |
a0d0e21e LW |
3873 | |
3874 | =item oct EXPR | |
d74e8afc | 3875 | X<oct> X<octal> X<hex> X<hexadecimal> X<binary> X<bin> |
a0d0e21e | 3876 | |
54310121 | 3877 | =item oct |
bbce6d69 | 3878 | |
c17cdb72 NC |
3879 | =for Pod::Functions convert a string to an octal number |
3880 | ||
4633a7c4 | 3881 | Interprets EXPR as an octal string and returns the corresponding |
4f19785b WSI |
3882 | value. (If EXPR happens to start off with C<0x>, interprets it as a |
3883 | hex string. If EXPR starts off with C<0b>, it is interpreted as a | |
53305cf1 | 3884 | binary string. Leading whitespace is ignored in all three cases.) |
3b10bc60 | 3885 | The following will handle decimal, binary, octal, and hex in standard |
3886 | Perl notation: | |
a0d0e21e LW |
3887 | |
3888 | $val = oct($val) if $val =~ /^0/; | |
3889 | ||
19799a22 GS |
3890 | If EXPR is omitted, uses C<$_>. To go the other way (produce a number |
3891 | in octal), use sprintf() or printf(): | |
3892 | ||
3b10bc60 | 3893 | $dec_perms = (stat("filename"))[2] & 07777; |
3894 | $oct_perm_str = sprintf "%o", $perms; | |
19799a22 GS |
3895 | |
3896 | The oct() function is commonly used when a string such as C<644> needs | |
3b10bc60 | 3897 | to be converted into a file mode, for example. Although Perl |
3898 | automatically converts strings into numbers as needed, this automatic | |
3899 | conversion assumes base 10. | |
3900 | ||
3901 | Leading white space is ignored without warning, as too are any trailing | |
3902 | non-digits, such as a decimal point (C<oct> only handles non-negative | |
3903 | integers, not negative integers or floating point). | |
a0d0e21e LW |
3904 | |
3905 | =item open FILEHANDLE,EXPR | |
d74e8afc | 3906 | X<open> X<pipe> X<file, open> X<fopen> |
a0d0e21e | 3907 | |
68bd7414 NIS |
3908 | =item open FILEHANDLE,MODE,EXPR |
3909 | ||
3910 | =item open FILEHANDLE,MODE,EXPR,LIST | |
3911 | ||
ba964c95 T |
3912 | =item open FILEHANDLE,MODE,REFERENCE |
3913 | ||
a0d0e21e LW |
3914 | =item open FILEHANDLE |
3915 | ||
c17cdb72 NC |
3916 | =for Pod::Functions open a file, pipe, or descriptor |
3917 | ||
a0d0e21e | 3918 | Opens the file whose filename is given by EXPR, and associates it with |
ed53a2bb JH |
3919 | FILEHANDLE. |
3920 | ||
460b70c2 GS |
3921 | Simple examples to open a file for reading: |
3922 | ||
8f1da26d TC |
3923 | open(my $fh, "<", "input.txt") |
3924 | or die "cannot open < input.txt: $!"; | |
460b70c2 GS |
3925 | |
3926 | and for writing: | |
3927 | ||
8f1da26d TC |
3928 | open(my $fh, ">", "output.txt") |
3929 | or die "cannot open > output.txt: $!"; | |
460b70c2 | 3930 | |
ed53a2bb JH |
3931 | (The following is a comprehensive reference to open(): for a gentler |
3932 | introduction you may consider L<perlopentut>.) | |
3933 | ||
8f1da26d TC |
3934 | If FILEHANDLE is an undefined scalar variable (or array or hash element), a |
3935 | new filehandle is autovivified, meaning that the variable is assigned a | |
3936 | reference to a newly allocated anonymous filehandle. Otherwise if | |
3937 | FILEHANDLE is an expression, its value is the real filehandle. (This is | |
3938 | considered a symbolic reference, so C<use strict "refs"> should I<not> be | |
3939 | in effect.) | |
3940 | ||
8f1da26d TC |
3941 | If three (or more) arguments are specified, the open mode (including |
3942 | optional encoding) in the second argument are distinct from the filename in | |
3943 | the third. If MODE is C<< < >> or nothing, the file is opened for input. | |
3944 | If MODE is C<< > >>, the file is opened for output, with existing files | |
3945 | first being truncated ("clobbered") and nonexisting files newly created. | |
3946 | If MODE is C<<< >> >>>, the file is opened for appending, again being | |
3947 | created if necessary. | |
3948 | ||
3949 | You can put a C<+> in front of the C<< > >> or C<< < >> to | |
ed53a2bb | 3950 | indicate that you want both read and write access to the file; thus |
8f1da26d | 3951 | C<< +< >> is almost always preferred for read/write updates--the |
1dfd3418 | 3952 | C<< +> >> mode would clobber the file first. You can't usually use |
ed53a2bb | 3953 | either read-write mode for updating textfiles, since they have |
bea6df1c | 3954 | variable-length records. See the B<-i> switch in L<perlrun> for a |
ed53a2bb | 3955 | better approach. The file is created with permissions of C<0666> |
e1020413 | 3956 | modified by the process's C<umask> value. |
ed53a2bb | 3957 | |
8f1da26d TC |
3958 | These various prefixes correspond to the fopen(3) modes of C<r>, |
3959 | C<r+>, C<w>, C<w+>, C<a>, and C<a+>. | |
5f05dabc | 3960 | |
8f1da26d TC |
3961 | In the one- and two-argument forms of the call, the mode and filename |
3962 | should be concatenated (in that order), preferably separated by white | |
3963 | space. You can--but shouldn't--omit the mode in these forms when that mode | |
3964 | is C<< < >>. It is always safe to use the two-argument form of C<open> if | |
3965 | the filename argument is a known literal. | |
6170680b | 3966 | |
8f1da26d | 3967 | For three or more arguments if MODE is C<|->, the filename is |
ed53a2bb | 3968 | interpreted as a command to which output is to be piped, and if MODE |
8f1da26d | 3969 | is C<-|>, the filename is interpreted as a command that pipes |
3b10bc60 | 3970 | output to us. In the two-argument (and one-argument) form, one should |
8f1da26d | 3971 | replace dash (C<->) with the command. |
ed53a2bb JH |
3972 | See L<perlipc/"Using open() for IPC"> for more examples of this. |
3973 | (You are not allowed to C<open> to a command that pipes both in I<and> | |
3974 | out, but see L<IPC::Open2>, L<IPC::Open3>, and | |
96090e4f LB |
3975 | L<perlipc/"Bidirectional Communication with Another Process"> for |
3976 | alternatives.) | |
ed53a2bb | 3977 | |
3b10bc60 | 3978 | In the form of pipe opens taking three or more arguments, if LIST is specified |
ed53a2bb JH |
3979 | (extra arguments after the command name) then LIST becomes arguments |
3980 | to the command invoked if the platform supports it. The meaning of | |
3981 | C<open> with more than three arguments for non-pipe modes is not yet | |
3b10bc60 | 3982 | defined, but experimental "layers" may give extra LIST arguments |
ed53a2bb | 3983 | meaning. |
6170680b | 3984 | |
8f1da26d TC |
3985 | In the two-argument (and one-argument) form, opening C<< <- >> |
3986 | or C<-> opens STDIN and opening C<< >- >> opens STDOUT. | |
6170680b | 3987 | |
8f1da26d TC |
3988 | You may (and usually should) use the three-argument form of open to specify |
3989 | I/O layers (sometimes referred to as "disciplines") to apply to the handle | |
fae2c0fb | 3990 | that affect how the input and output are processed (see L<open> and |
391b733c | 3991 | L<PerlIO> for more details). For example: |
7207e29d | 3992 | |
3b10bc60 | 3993 | open(my $fh, "<:encoding(UTF-8)", "filename") |
3994 | || die "can't open UTF-8 encoded filename: $!"; | |
9124316e | 3995 | |
8f1da26d | 3996 | opens the UTF8-encoded file containing Unicode characters; |
391b733c | 3997 | see L<perluniintro>. Note that if layers are specified in the |
3b10bc60 | 3998 | three-argument form, then default layers stored in ${^OPEN} (see L<perlvar>; |
6d5e88a0 | 3999 | usually set by the B<open> pragma or the switch B<-CioD>) are ignored. |
c0fd9d21 FC |
4000 | Those layers will also be ignored if you specifying a colon with no name |
4001 | following it. In that case the default layer for the operating system | |
4002 | (:raw on Unix, :crlf on Windows) is used. | |
ed53a2bb | 4003 | |
80d38338 | 4004 | Open returns nonzero on success, the undefined value otherwise. If |
ed53a2bb JH |
4005 | the C<open> involved a pipe, the return value happens to be the pid of |
4006 | the subprocess. | |
cb1a09d0 | 4007 | |
ed53a2bb JH |
4008 | If you're running Perl on a system that distinguishes between text |
4009 | files and binary files, then you should check out L</binmode> for tips | |
4010 | for dealing with this. The key distinction between systems that need | |
4011 | C<binmode> and those that don't is their text file formats. Systems | |
80d38338 TC |
4012 | like Unix, Mac OS, and Plan 9, that end lines with a single |
4013 | character and encode that character in C as C<"\n"> do not | |
ed53a2bb | 4014 | need C<binmode>. The rest need it. |
cb1a09d0 | 4015 | |
80d38338 TC |
4016 | When opening a file, it's seldom a good idea to continue |
4017 | if the request failed, so C<open> is frequently used with | |
19799a22 | 4018 | C<die>. Even if C<die> won't do what you want (say, in a CGI script, |
80d38338 TC |
4019 | where you want to format a suitable error message (but there are |
4020 | modules that can help with that problem)) always check | |
4021 | the return value from opening a file. | |
fb73857a | 4022 | |
1578dcc9 EA |
4023 | The filehandle will be closed when its reference count reaches zero. |
4024 | If it is a lexically scoped variable declared with C<my>, that usually | |
4025 | means the end of the enclosing scope. However, this automatic close | |
4026 | does not check for errors, so it is better to explicitly close | |
4027 | filehandles, especially those used for writing: | |
4028 | ||
4029 | close($handle) | |
4030 | || warn "close failed: $!"; | |
4031 | ||
4032 | An older style is to use a bareword as the filehandle, as | |
4033 | ||
4034 | open(FH, "<", "input.txt") | |
4035 | or die "cannot open < input.txt: $!"; | |
4036 | ||
4037 | Then you can use C<FH> as the filehandle, in C<< close FH >> and C<< | |
4038 | <FH> >> and so on. Note that it's a global variable, so this form is | |
4039 | not recommended in new code. | |
4040 | ||
4041 | As a shortcut a one-argument call takes the filename from the global | |
4042 | scalar variable of the same name as the filehandle: | |
4043 | ||
4044 | $ARTICLE = 100; | |
4045 | open(ARTICLE) or die "Can't find article $ARTICLE: $!\n"; | |
4046 | ||
4047 | Here C<$ARTICLE> must be a global (package) scalar variable - not one | |
4048 | declared with C<my> or C<state>. | |
4049 | ||
8f1da26d | 4050 | As a special case the three-argument form with a read/write mode and the third |
ed53a2bb | 4051 | argument being C<undef>: |
b76cc8ba | 4052 | |
460b70c2 | 4053 | open(my $tmp, "+>", undef) or die ... |
b76cc8ba | 4054 | |
8f1da26d | 4055 | opens a filehandle to an anonymous temporary file. Also using C<< +< >> |
f253e835 JH |
4056 | works for symmetry, but you really should consider writing something |
4057 | to the temporary file first. You will need to seek() to do the | |
4058 | reading. | |
b76cc8ba | 4059 | |
e9fa405d | 4060 | Perl is built using PerlIO by default; Unless you've |
8f1da26d TC |
4061 | changed this (such as building Perl with C<Configure -Uuseperlio>), you can |
4062 | open filehandles directly to Perl scalars via: | |
ba964c95 | 4063 | |
8f1da26d | 4064 | open($fh, ">", \$variable) || .. |
b996200f | 4065 | |
3b10bc60 | 4066 | To (re)open C<STDOUT> or C<STDERR> as an in-memory file, close it first: |
b996200f SB |
4067 | |
4068 | close STDOUT; | |
8f1da26d TC |
4069 | open(STDOUT, ">", \$variable) |
4070 | or die "Can't open STDOUT: $!"; | |
ba964c95 | 4071 | |
3b10bc60 | 4072 | General examples: |
a0d0e21e | 4073 | |
8f1da26d | 4074 | open(LOG, ">>/usr/spool/news/twitlog"); # (log is reserved) |
fb73857a | 4075 | # if the open fails, output is discarded |
a0d0e21e | 4076 | |
8f1da26d | 4077 | open(my $dbase, "+<", "dbase.mine") # open for update |
a9a5a0dc | 4078 | or die "Can't open 'dbase.mine' for update: $!"; |
cb1a09d0 | 4079 | |
8f1da26d | 4080 | open(my $dbase, "+<dbase.mine") # ditto |
a9a5a0dc | 4081 | or die "Can't open 'dbase.mine' for update: $!"; |
6170680b | 4082 | |
8f1da26d | 4083 | open(ARTICLE, "-|", "caesar <$article") # decrypt article |
a9a5a0dc | 4084 | or die "Can't start caesar: $!"; |
a0d0e21e | 4085 | |
5ed4f2ec | 4086 | open(ARTICLE, "caesar <$article |") # ditto |
a9a5a0dc | 4087 | or die "Can't start caesar: $!"; |
6170680b | 4088 | |
5ed4f2ec | 4089 | open(EXTRACT, "|sort >Tmp$$") # $$ is our process id |
a9a5a0dc | 4090 | or die "Can't start sort: $!"; |
a0d0e21e | 4091 | |
3b10bc60 | 4092 | # in-memory files |
8f1da26d | 4093 | open(MEMORY, ">", \$var) |
a9a5a0dc | 4094 | or die "Can't open memory file: $!"; |
f7051f2c | 4095 | print MEMORY "foo!\n"; # output will appear in $var |
ba964c95 | 4096 | |
a0d0e21e LW |
4097 | # process argument list of files along with any includes |
4098 | ||
4099 | foreach $file (@ARGV) { | |
8f1da26d | 4100 | process($file, "fh00"); |
a0d0e21e LW |
4101 | } |
4102 | ||
4103 | sub process { | |
a9a5a0dc VP |
4104 | my($filename, $input) = @_; |
4105 | $input++; # this is a string increment | |
8f1da26d | 4106 | unless (open($input, "<", $filename)) { |
a9a5a0dc VP |
4107 | print STDERR "Can't open $filename: $!\n"; |
4108 | return; | |
4109 | } | |
5ed4f2ec | 4110 | |
a9a5a0dc VP |
4111 | local $_; |
4112 | while (<$input>) { # note use of indirection | |
4113 | if (/^#include "(.*)"/) { | |
4114 | process($1, $input); | |
4115 | next; | |
4116 | } | |
4117 | #... # whatever | |
5ed4f2ec | 4118 | } |
a0d0e21e LW |
4119 | } |
4120 | ||
ae4c5402 | 4121 | See L<perliol> for detailed info on PerlIO. |
2ce64696 | 4122 | |
a0d0e21e | 4123 | You may also, in the Bourne shell tradition, specify an EXPR beginning |
8f1da26d | 4124 | with C<< >& >>, in which case the rest of the string is interpreted |
00cafafa | 4125 | as the name of a filehandle (or file descriptor, if numeric) to be |
f4084e39 | 4126 | duped (as C<dup(2)>) and opened. You may use C<&> after C<< > >>, |
00cafafa JH |
4127 | C<<< >> >>>, C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>. |
4128 | The mode you specify should match the mode of the original filehandle. | |
4129 | (Duping a filehandle does not take into account any existing contents | |
391b733c FC |
4130 | of IO buffers.) If you use the three-argument |
4131 | form, then you can pass either a | |
8f1da26d | 4132 | number, the name of a filehandle, or the normal "reference to a glob". |
6170680b | 4133 | |
eae1b76b SB |
4134 | Here is a script that saves, redirects, and restores C<STDOUT> and |
4135 | C<STDERR> using various methods: | |
a0d0e21e LW |
4136 | |
4137 | #!/usr/bin/perl | |
8f1da26d TC |
4138 | open(my $oldout, ">&STDOUT") or die "Can't dup STDOUT: $!"; |
4139 | open(OLDERR, ">&", \*STDERR) or die "Can't dup STDERR: $!"; | |
818c4caa | 4140 | |
8f1da26d TC |
4141 | open(STDOUT, '>', "foo.out") or die "Can't redirect STDOUT: $!"; |
4142 | open(STDERR, ">&STDOUT") or die "Can't dup STDOUT: $!"; | |
a0d0e21e | 4143 | |
5ed4f2ec | 4144 | select STDERR; $| = 1; # make unbuffered |
4145 | select STDOUT; $| = 1; # make unbuffered | |
a0d0e21e | 4146 | |
5ed4f2ec | 4147 | print STDOUT "stdout 1\n"; # this works for |
4148 | print STDERR "stderr 1\n"; # subprocesses too | |
a0d0e21e | 4149 | |
8f1da26d TC |
4150 | open(STDOUT, ">&", $oldout) or die "Can't dup \$oldout: $!"; |
4151 | open(STDERR, ">&OLDERR") or die "Can't dup OLDERR: $!"; | |
a0d0e21e LW |
4152 | |
4153 | print STDOUT "stdout 2\n"; | |
4154 | print STDERR "stderr 2\n"; | |
4155 | ||
ef8b303f JH |
4156 | If you specify C<< '<&=X' >>, where C<X> is a file descriptor number |
4157 | or a filehandle, then Perl will do an equivalent of C's C<fdopen> of | |
f4084e39 | 4158 | that file descriptor (and not call C<dup(2)>); this is more |
ef8b303f | 4159 | parsimonious of file descriptors. For example: |
a0d0e21e | 4160 | |
00cafafa | 4161 | # open for input, reusing the fileno of $fd |
a0d0e21e | 4162 | open(FILEHANDLE, "<&=$fd") |
df632fdf | 4163 | |
b76cc8ba | 4164 | or |
df632fdf | 4165 | |
b76cc8ba | 4166 | open(FILEHANDLE, "<&=", $fd) |
a0d0e21e | 4167 | |
00cafafa JH |
4168 | or |
4169 | ||
4170 | # open for append, using the fileno of OLDFH | |
4171 | open(FH, ">>&=", OLDFH) | |
4172 | ||
4173 | or | |
4174 | ||
4175 | open(FH, ">>&=OLDFH") | |
4176 | ||
ef8b303f JH |
4177 | Being parsimonious on filehandles is also useful (besides being |
4178 | parsimonious) for example when something is dependent on file | |
4179 | descriptors, like for example locking using flock(). If you do just | |
8f1da26d TC |
4180 | C<< open(A, ">>&B") >>, the filehandle A will not have the same file |
4181 | descriptor as B, and therefore flock(A) will not flock(B) nor vice | |
4182 | versa. But with C<< open(A, ">>&=B") >>, the filehandles will share | |
4183 | the same underlying system file descriptor. | |
4184 | ||
4185 | Note that under Perls older than 5.8.0, Perl uses the standard C library's' | |
4186 | fdopen() to implement the C<=> functionality. On many Unix systems, | |
4187 | fdopen() fails when file descriptors exceed a certain value, typically 255. | |
4188 | For Perls 5.8.0 and later, PerlIO is (most often) the default. | |
4189 | ||
4190 | You can see whether your Perl was built with PerlIO by running C<perl -V> | |
4191 | and looking for the C<useperlio=> line. If C<useperlio> is C<define>, you | |
4192 | have PerlIO; otherwise you don't. | |
4193 | ||
4194 | If you open a pipe on the command C<-> (that is, specify either C<|-> or C<-|> | |
4195 | with the one- or two-argument forms of C<open>), | |
4196 | an implicit C<fork> is done, so C<open> returns twice: in the parent | |
4197 | process it returns the pid | |
4198 | of the child process, and in the child process it returns (a defined) C<0>. | |
4199 | Use C<defined($pid)> or C<//> to determine whether the open was successful. | |
4200 | ||
4201 | For example, use either | |
4202 | ||
5f64ea7a | 4203 | $child_pid = open(FROM_KID, "-|") // die "can't fork: $!"; |
8f1da26d TC |
4204 | |
4205 | or | |
d18fc9db | 4206 | |
8f1da26d TC |
4207 | $child_pid = open(TO_KID, "|-") // die "can't fork: $!"; |
4208 | ||
4209 | followed by | |
4210 | ||
4211 | if ($child_pid) { | |
4212 | # am the parent: | |
4213 | # either write TO_KID or else read FROM_KID | |
4214 | ... | |
237f7097 | 4215 | waitpid $child_pid, 0; |
8f1da26d TC |
4216 | } else { |
4217 | # am the child; use STDIN/STDOUT normally | |
4218 | ... | |
4219 | exit; | |
4220 | } | |
4221 | ||
3b10bc60 | 4222 | The filehandle behaves normally for the parent, but I/O to that |
a0d0e21e | 4223 | filehandle is piped from/to the STDOUT/STDIN of the child process. |
3b10bc60 | 4224 | In the child process, the filehandle isn't opened--I/O happens from/to |
4225 | the new STDOUT/STDIN. Typically this is used like the normal | |
a0d0e21e | 4226 | piped open when you want to exercise more control over just how the |
3b10bc60 | 4227 | pipe command gets executed, such as when running setuid and |
4228 | you don't want to have to scan shell commands for metacharacters. | |
4229 | ||
5b867647 | 4230 | The following blocks are more or less equivalent: |
a0d0e21e LW |
4231 | |
4232 | open(FOO, "|tr '[a-z]' '[A-Z]'"); | |
8f1da26d TC |
4233 | open(FOO, "|-", "tr '[a-z]' '[A-Z]'"); |
4234 | open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]'; | |
4235 | open(FOO, "|-", "tr", '[a-z]', '[A-Z]'); | |
a0d0e21e LW |
4236 | |
4237 | open(FOO, "cat -n '$file'|"); | |
8f1da26d TC |
4238 | open(FOO, "-|", "cat -n '$file'"); |
4239 | open(FOO, "-|") || exec "cat", "-n", $file; | |
4240 | open(FOO, "-|", "cat", "-n", $file); | |
b76cc8ba | 4241 | |
8f1da26d | 4242 | The last two examples in each block show the pipe as "list form", which is |
64da03b2 | 4243 | not yet supported on all platforms. A good rule of thumb is that if |
8f1da26d TC |
4244 | your platform has a real C<fork()> (in other words, if your platform is |
4245 | Unix, including Linux and MacOS X), you can use the list form. You would | |
4246 | want to use the list form of the pipe so you can pass literal arguments | |
4247 | to the command without risk of the shell interpreting any shell metacharacters | |
4248 | in them. However, this also bars you from opening pipes to commands | |
4249 | that intentionally contain shell metacharacters, such as: | |
4250 | ||
4251 | open(FOO, "|cat -n | expand -4 | lpr") | |
4252 | // die "Can't open pipeline to lpr: $!"; | |
a0d0e21e | 4253 | |
4633a7c4 LW |
4254 | See L<perlipc/"Safe Pipe Opens"> for more examples of this. |
4255 | ||
e9fa405d | 4256 | Perl will attempt to flush all files opened for |
0f897271 GS |
4257 | output before any operation that may do a fork, but this may not be |
4258 | supported on some platforms (see L<perlport>). To be safe, you may need | |
4259 | to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method | |
4260 | of C<IO::Handle> on any open handles. | |
4261 | ||
ed53a2bb JH |
4262 | On systems that support a close-on-exec flag on files, the flag will |
4263 | be set for the newly opened file descriptor as determined by the value | |
8f1da26d | 4264 | of C<$^F>. See L<perlvar/$^F>. |
a0d0e21e | 4265 | |
0dccf244 | 4266 | Closing any piped filehandle causes the parent process to wait for the |
8f1da26d | 4267 | child to finish, then returns the status value in C<$?> and |
e5218da5 | 4268 | C<${^CHILD_ERROR_NATIVE}>. |
0dccf244 | 4269 | |
8f1da26d TC |
4270 | The filename passed to the one- and two-argument forms of open() will |
4271 | have leading and trailing whitespace deleted and normal | |
ed53a2bb | 4272 | redirection characters honored. This property, known as "magic open", |
5a964f20 | 4273 | can often be used to good effect. A user could specify a filename of |
7660c0ab | 4274 | F<"rsh cat file |">, or you could change certain filenames as needed: |
5a964f20 TC |
4275 | |
4276 | $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/; | |
4277 | open(FH, $filename) or die "Can't open $filename: $!"; | |
4278 | ||
8f1da26d | 4279 | Use the three-argument form to open a file with arbitrary weird characters in it, |
6170680b | 4280 | |
8f1da26d TC |
4281 | open(FOO, "<", $file) |
4282 | || die "can't open < $file: $!"; | |
6170680b IZ |
4283 | |
4284 | otherwise it's necessary to protect any leading and trailing whitespace: | |
5a964f20 TC |
4285 | |
4286 | $file =~ s#^(\s)#./$1#; | |
8f1da26d TC |
4287 | open(FOO, "< $file\0") |
4288 | || die "open failed: $!"; | |
5a964f20 | 4289 | |
a31a806a | 4290 | (this may not work on some bizarre filesystems). One should |
8f1da26d | 4291 | conscientiously choose between the I<magic> and I<three-argument> form |
6170680b IZ |
4292 | of open(): |
4293 | ||
8f1da26d | 4294 | open(IN, $ARGV[0]) || die "can't open $ARGV[0]: $!"; |
6170680b IZ |
4295 | |
4296 | will allow the user to specify an argument of the form C<"rsh cat file |">, | |
80d38338 | 4297 | but will not work on a filename that happens to have a trailing space, while |
6170680b | 4298 | |
8f1da26d TC |
4299 | open(IN, "<", $ARGV[0]) |
4300 | || die "can't open < $ARGV[0]: $!"; | |
6170680b IZ |
4301 | |
4302 | will have exactly the opposite restrictions. | |
4303 | ||
01aa884e | 4304 | If you want a "real" C C<open> (see L<open(2)> on your system), then you |
8f1da26d TC |
4305 | should use the C<sysopen> function, which involves no such magic (but may |
4306 | use subtly different filemodes than Perl open(), which is mapped to C | |
4307 | fopen()). This is another way to protect your filenames from | |
4308 | interpretation. For example: | |
5a964f20 TC |
4309 | |
4310 | use IO::Handle; | |
4311 | sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL) | |
a9a5a0dc | 4312 | or die "sysopen $path: $!"; |
5a964f20 | 4313 | $oldfh = select(HANDLE); $| = 1; select($oldfh); |
38762f02 | 4314 | print HANDLE "stuff $$\n"; |
5a964f20 TC |
4315 | seek(HANDLE, 0, 0); |
4316 | print "File contains: ", <HANDLE>; | |
4317 | ||
b687b08b | 4318 | See L</seek> for some details about mixing reading and writing. |
a0d0e21e | 4319 | |
ea9eb35a BJ |
4320 | Portability issues: L<perlport/open>. |
4321 | ||
a0d0e21e | 4322 | =item opendir DIRHANDLE,EXPR |
d74e8afc | 4323 | X<opendir> |
a0d0e21e | 4324 | |
c17cdb72 NC |
4325 | =for Pod::Functions open a directory |
4326 | ||
19799a22 GS |
4327 | Opens a directory named EXPR for processing by C<readdir>, C<telldir>, |
4328 | C<seekdir>, C<rewinddir>, and C<closedir>. Returns true if successful. | |
a28cd5c9 NT |
4329 | DIRHANDLE may be an expression whose value can be used as an indirect |
4330 | dirhandle, usually the real dirhandle name. If DIRHANDLE is an undefined | |
4331 | scalar variable (or array or hash element), the variable is assigned a | |
8f1da26d | 4332 | reference to a new anonymous dirhandle; that is, it's autovivified. |
a0d0e21e LW |
4333 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
4334 | ||
bea6df1c | 4335 | See the example at C<readdir>. |
b0169937 | 4336 | |
a0d0e21e | 4337 | =item ord EXPR |
d74e8afc | 4338 | X<ord> X<encoding> |
a0d0e21e | 4339 | |
54310121 | 4340 | =item ord |
bbce6d69 | 4341 | |
c17cdb72 NC |
4342 | =for Pod::Functions find a character's numeric representation |
4343 | ||
c9b06361 | 4344 | Returns the numeric value of the first character of EXPR. |
8f1da26d TC |
4345 | If EXPR is an empty string, returns 0. If EXPR is omitted, uses C<$_>. |
4346 | (Note I<character>, not byte.) | |
121910a4 JH |
4347 | |
4348 | For the reverse, see L</chr>. | |
2575c402 | 4349 | See L<perlunicode> for more about Unicode. |
a0d0e21e | 4350 | |
672208d2 | 4351 | =item our VARLIST |
d74e8afc | 4352 | X<our> X<global> |
77ca0c92 | 4353 | |
672208d2 | 4354 | =item our TYPE VARLIST |
307ea6df | 4355 | |
672208d2 | 4356 | =item our VARLIST : ATTRS |
9969eac4 | 4357 | |
672208d2 | 4358 | =item our TYPE VARLIST : ATTRS |
307ea6df | 4359 | |
d9b04284 | 4360 | =for Pod::Functions +5.6.0 declare and assign a package variable (lexical scoping) |
c17cdb72 | 4361 | |
0195d767 DG |
4362 | C<our> makes a lexical alias to a package (i.e. global) variable of the |
4363 | same name in the current package for use within the current lexical scope. | |
66b30015 | 4364 | |
0195d767 DG |
4365 | C<our> has the same scoping rules as C<my> or C<state>, meaning that it is |
4366 | only valid within a lexical scope. Unlike C<my> and C<state>, which both | |
4367 | declare new (lexical) variables, C<our> only creates an alias to an | |
4368 | existing variable: a package variable of the same name. | |
66b30015 DG |
4369 | |
4370 | This means that when C<use strict 'vars'> is in effect, C<our> lets you use | |
4371 | a package variable without qualifying it with the package name, but only within | |
0195d767 DG |
4372 | the lexical scope of the C<our> declaration. |
4373 | ||
4374 | package Foo; | |
4375 | use strict; | |
4376 | ||
4377 | $Foo::foo = 23; | |
4378 | ||
4379 | { | |
4380 | our $foo; # alias to $Foo::foo | |
4381 | print $foo; # prints 23 | |
4382 | } | |
4383 | ||
4384 | print $Foo::foo; # prints 23 | |
4385 | ||
4386 | print $foo; # ERROR: requires explicit package name | |
4387 | ||
4388 | This works even if the package variable has not been used before, as | |
4389 | package variables spring into existence when first used. | |
4390 | ||
4391 | package Foo; | |
4392 | use strict; | |
4393 | ||
4394 | our $foo = 23; # just like $Foo::foo = 23 | |
4395 | ||
4396 | print $Foo::foo; # prints 23 | |
65c680eb | 4397 | |
672208d2 | 4398 | If more than one variable is listed, the list must be placed |
65c680eb | 4399 | in parentheses. |
85d8b7d5 | 4400 | |
85d8b7d5 | 4401 | our($bar, $baz); |
77ca0c92 | 4402 | |
66b30015 | 4403 | An C<our> declaration declares an alias for a package variable that will be visible |
f472eb5c GS |
4404 | across its entire lexical scope, even across package boundaries. The |
4405 | package in which the variable is entered is determined at the point | |
4406 | of the declaration, not at the point of use. This means the following | |
4407 | behavior holds: | |
4408 | ||
4409 | package Foo; | |
5ed4f2ec | 4410 | our $bar; # declares $Foo::bar for rest of lexical scope |
f472eb5c GS |
4411 | $bar = 20; |
4412 | ||
4413 | package Bar; | |
5ed4f2ec | 4414 | print $bar; # prints 20, as it refers to $Foo::bar |
f472eb5c | 4415 | |
65c680eb MS |
4416 | Multiple C<our> declarations with the same name in the same lexical |
4417 | scope are allowed if they are in different packages. If they happen | |
4418 | to be in the same package, Perl will emit warnings if you have asked | |
4419 | for them, just like multiple C<my> declarations. Unlike a second | |
4420 | C<my> declaration, which will bind the name to a fresh variable, a | |
4421 | second C<our> declaration in the same package, in the same scope, is | |
4422 | merely redundant. | |
f472eb5c GS |
4423 | |
4424 | use warnings; | |
4425 | package Foo; | |
5ed4f2ec | 4426 | our $bar; # declares $Foo::bar for rest of lexical scope |
f472eb5c GS |
4427 | $bar = 20; |
4428 | ||
4429 | package Bar; | |
5ed4f2ec | 4430 | our $bar = 30; # declares $Bar::bar for rest of lexical scope |
4431 | print $bar; # prints 30 | |
f472eb5c | 4432 | |
5ed4f2ec | 4433 | our $bar; # emits warning but has no other effect |
4434 | print $bar; # still prints 30 | |
f472eb5c | 4435 | |
9969eac4 | 4436 | An C<our> declaration may also have a list of attributes associated |
307ea6df JH |
4437 | with it. |
4438 | ||
1d2de774 | 4439 | The exact semantics and interface of TYPE and ATTRS are still |
bade7fbc TC |
4440 | evolving. TYPE is currently bound to the use of the C<fields> pragma, |
4441 | and attributes are handled using the C<attributes> pragma, or, starting | |
4442 | from Perl 5.8.0, also via the C<Attribute::Handlers> module. See | |
307ea6df JH |
4443 | L<perlsub/"Private Variables via my()"> for details, and L<fields>, |
4444 | L<attributes>, and L<Attribute::Handlers>. | |
4445 | ||
672208d2 JV |
4446 | Note that with a parenthesised list, C<undef> can be used as a dummy |
4447 | placeholder, for example to skip assignment of initial values: | |
4448 | ||
4449 | our ( undef, $min, $hour ) = localtime; | |
4450 | ||
0195d767 DG |
4451 | C<our> differs from C<use vars>, which allows use of an unqualified name |
4452 | I<only> within the affected package, but across scopes. | |
4453 | ||
a0d0e21e | 4454 | =item pack TEMPLATE,LIST |
d74e8afc | 4455 | X<pack> |
a0d0e21e | 4456 | |
c17cdb72 NC |
4457 | =for Pod::Functions convert a list into a binary representation |
4458 | ||
2b6c5635 GS |
4459 | Takes a LIST of values and converts it into a string using the rules |
4460 | given by the TEMPLATE. The resulting string is the concatenation of | |
4461 | the converted values. Typically, each converted value looks | |
4462 | like its machine-level representation. For example, on 32-bit machines | |
3980dc9c KW |
4463 | an integer may be represented by a sequence of 4 bytes, which will in |
4464 | Perl be presented as a string that's 4 characters long. | |
4465 | ||
4466 | See L<perlpacktut> for an introduction to this function. | |
e1b711da | 4467 | |
18529408 IZ |
4468 | The TEMPLATE is a sequence of characters that give the order and type |
4469 | of values, as follows: | |
a0d0e21e | 4470 | |
5ed4f2ec | 4471 | a A string with arbitrary binary data, will be null padded. |
4472 | A A text (ASCII) string, will be space padded. | |
3b10bc60 | 4473 | Z A null-terminated (ASCIZ) string, will be null padded. |
5a929a98 | 4474 | |
4d0444a3 FC |
4475 | b A bit string (ascending bit order inside each byte, |
4476 | like vec()). | |
5ed4f2ec | 4477 | B A bit string (descending bit order inside each byte). |
4478 | h A hex string (low nybble first). | |
4479 | H A hex string (high nybble first). | |
a0d0e21e | 4480 | |
5ed4f2ec | 4481 | c A signed char (8-bit) value. |
4482 | C An unsigned char (octet) value. | |
3b10bc60 | 4483 | W An unsigned char value (can be greater than 255). |
96e4d5b1 | 4484 | |
5ed4f2ec | 4485 | s A signed short (16-bit) value. |
4486 | S An unsigned short value. | |
96e4d5b1 | 4487 | |
5ed4f2ec | 4488 | l A signed long (32-bit) value. |
4489 | L An unsigned long value. | |
a0d0e21e | 4490 | |
5ed4f2ec | 4491 | q A signed quad (64-bit) value. |
4492 | Q An unsigned quad value. | |
4d0444a3 FC |
4493 | (Quads are available only if your system supports 64-bit |
4494 | integer values _and_ if Perl has been compiled to support | |
4495 | those. Raises an exception otherwise.) | |
dae0da7a | 4496 | |
5ed4f2ec | 4497 | i A signed integer value. |
4498 | I A unsigned integer value. | |
4d0444a3 FC |
4499 | (This 'integer' is _at_least_ 32 bits wide. Its exact |
4500 | size depends on what a local C compiler calls 'int'.) | |
2b191d53 | 4501 | |
5ed4f2ec | 4502 | n An unsigned short (16-bit) in "network" (big-endian) order. |
4503 | N An unsigned long (32-bit) in "network" (big-endian) order. | |
4504 | v An unsigned short (16-bit) in "VAX" (little-endian) order. | |
4505 | V An unsigned long (32-bit) in "VAX" (little-endian) order. | |
1109a392 | 4506 | |
4d0444a3 FC |
4507 | j A Perl internal signed integer value (IV). |
4508 | J A Perl internal unsigned integer value (UV). | |
92d41999 | 4509 | |
3b10bc60 | 4510 | f A single-precision float in native format. |
4511 | d A double-precision float in native format. | |
a0d0e21e | 4512 | |
3b10bc60 | 4513 | F A Perl internal floating-point value (NV) in native format |
4514 | D A float of long-double precision in native format. | |
4d0444a3 FC |
4515 | (Long doubles are available only if your system supports |
4516 | long double values _and_ if Perl has been compiled to | |
aacf4ea2 JH |
4517 | support those. Raises an exception otherwise. |
4518 | Note that there are different long double formats.) | |
92d41999 | 4519 | |
5ed4f2ec | 4520 | p A pointer to a null-terminated string. |
4521 | P A pointer to a structure (fixed-length string). | |
a0d0e21e | 4522 | |
5ed4f2ec | 4523 | u A uuencoded string. |
4d0444a3 FC |
4524 | U A Unicode character number. Encodes to a character in char- |
4525 | acter mode and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in | |
4526 | byte mode. | |
a0d0e21e | 4527 | |
4d0444a3 FC |
4528 | w A BER compressed integer (not an ASN.1 BER, see perlpacktut |
4529 | for details). Its bytes represent an unsigned integer in | |
4530 | base 128, most significant digit first, with as few digits | |
4531 | as possible. Bit eight (the high bit) is set on each byte | |
4532 | except the last. | |
def98dd4 | 4533 | |
3b10bc60 | 4534 | x A null byte (a.k.a ASCII NUL, "\000", chr(0)) |
5ed4f2ec | 4535 | X Back up a byte. |
3b10bc60 | 4536 | @ Null-fill or truncate to absolute position, counted from the |
4537 | start of the innermost ()-group. | |
4d0444a3 FC |
4538 | . Null-fill or truncate to absolute position specified by |
4539 | the value. | |
5ed4f2ec | 4540 | ( Start of a ()-group. |
a0d0e21e | 4541 | |
3b10bc60 | 4542 | One or more modifiers below may optionally follow certain letters in the |
4543 | TEMPLATE (the second column lists letters for which the modifier is valid): | |
1109a392 MHM |
4544 | |
4545 | ! sSlLiI Forces native (short, long, int) sizes instead | |
4546 | of fixed (16-/32-bit) sizes. | |
4547 | ||
c584250a | 4548 | ! xX Make x and X act as alignment commands. |
1109a392 | 4549 | |
c584250a | 4550 | ! nNvV Treat integers as signed instead of unsigned. |
1109a392 | 4551 | |
c584250a | 4552 | ! @. Specify position as byte offset in the internal |
391b733c FC |
4553 | representation of the packed string. Efficient |
4554 | but dangerous. | |
28be1210 | 4555 | |
1109a392 MHM |
4556 | > sSiIlLqQ Force big-endian byte-order on the type. |
4557 | jJfFdDpP (The "big end" touches the construct.) | |
4558 | ||
4559 | < sSiIlLqQ Force little-endian byte-order on the type. | |
4560 | jJfFdDpP (The "little end" touches the construct.) | |
4561 | ||
3b10bc60 | 4562 | The C<< > >> and C<< < >> modifiers can also be used on C<()> groups |
4563 | to force a particular byte-order on all components in that group, | |
4564 | including all its subgroups. | |
66c611c5 | 4565 | |
24f4b7da NC |
4566 | =begin comment |
4567 | ||
4568 | Larry recalls that the hex and bit string formats (H, h, B, b) were added to | |
7161e5c2 | 4569 | pack for processing data from NASA's Magellan probe. Magellan was in an |
24f4b7da NC |
4570 | elliptical orbit, using the antenna for the radar mapping when close to |
4571 | Venus and for communicating data back to Earth for the rest of the orbit. | |
4572 | There were two transmission units, but one of these failed, and then the | |
4573 | other developed a fault whereby it would randomly flip the sense of all the | |
4574 | bits. It was easy to automatically detect complete records with the correct | |
4575 | sense, and complete records with all the bits flipped. However, this didn't | |
4576 | recover the records where the sense flipped midway. A colleague of Larry's | |
4577 | was able to pretty much eyeball where the records flipped, so they wrote an | |
4578 | editor named kybble (a pun on the dog food Kibbles 'n Bits) to enable him to | |
4579 | manually correct the records and recover the data. For this purpose pack | |
4580 | gained the hex and bit string format specifiers. | |
4581 | ||
4582 | git shows that they were added to perl 3.0 in patch #44 (Jan 1991, commit | |
4583 | 27e2fb84680b9cc1), but the patch description makes no mention of their | |
4584 | addition, let alone the story behind them. | |
4585 | ||
4586 | =end comment | |
4587 | ||
5a929a98 VU |
4588 | The following rules apply: |
4589 | ||
3b10bc60 | 4590 | =over |
5a929a98 VU |
4591 | |
4592 | =item * | |
4593 | ||
3b10bc60 | 4594 | Each letter may optionally be followed by a number indicating the repeat |
4595 | count. A numeric repeat count may optionally be enclosed in brackets, as | |
4596 | in C<pack("C[80]", @arr)>. The repeat count gobbles that many values from | |
4597 | the LIST when used with all format types other than C<a>, C<A>, C<Z>, C<b>, | |
4598 | C<B>, C<h>, C<H>, C<@>, C<.>, C<x>, C<X>, and C<P>, where it means | |
7698aede | 4599 | something else, described below. Supplying a C<*> for the repeat count |
3b10bc60 | 4600 | instead of a number means to use however many items are left, except for: |
4601 | ||
4602 | =over | |
4603 | ||
4604 | =item * | |
4605 | ||
4606 | C<@>, C<x>, and C<X>, where it is equivalent to C<0>. | |
4607 | ||
4608 | =item * | |
4609 | ||
4610 | <.>, where it means relative to the start of the string. | |
4611 | ||
4612 | =item * | |
4613 | ||
4614 | C<u>, where it is equivalent to 1 (or 45, which here is equivalent). | |
4615 | ||
4616 | =back | |
4617 | ||
4618 | One can replace a numeric repeat count with a template letter enclosed in | |
4619 | brackets to use the packed byte length of the bracketed template for the | |
4620 | repeat count. | |
4621 | ||
4622 | For example, the template C<x[L]> skips as many bytes as in a packed long, | |
4623 | and the template C<"$t X[$t] $t"> unpacks twice whatever $t (when | |
4624 | variable-expanded) unpacks. If the template in brackets contains alignment | |
4625 | commands (such as C<x![d]>), its packed length is calculated as if the | |
4626 | start of the template had the maximal possible alignment. | |
4627 | ||
4628 | When used with C<Z>, a C<*> as the repeat count is guaranteed to add a | |
4629 | trailing null byte, so the resulting string is always one byte longer than | |
4630 | the byte length of the item itself. | |
2b6c5635 | 4631 | |
28be1210 | 4632 | When used with C<@>, the repeat count represents an offset from the start |
3b10bc60 | 4633 | of the innermost C<()> group. |
4634 | ||
4635 | When used with C<.>, the repeat count determines the starting position to | |
4636 | calculate the value offset as follows: | |
4637 | ||
4638 | =over | |
4639 | ||
4640 | =item * | |
4641 | ||
4642 | If the repeat count is C<0>, it's relative to the current position. | |
28be1210 | 4643 | |
3b10bc60 | 4644 | =item * |
4645 | ||
4646 | If the repeat count is C<*>, the offset is relative to the start of the | |
4647 | packed string. | |
4648 | ||
4649 | =item * | |
4650 | ||
4651 | And if it's an integer I<n>, the offset is relative to the start of the | |
8f1da26d | 4652 | I<n>th innermost C<( )> group, or to the start of the string if I<n> is |
3b10bc60 | 4653 | bigger then the group level. |
4654 | ||
4655 | =back | |
28be1210 | 4656 | |
951ba7fe | 4657 | The repeat count for C<u> is interpreted as the maximal number of bytes |
391b733c | 4658 | to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat |
f337b084 | 4659 | count should not be more than 65. |
5a929a98 VU |
4660 | |
4661 | =item * | |
4662 | ||
951ba7fe | 4663 | The C<a>, C<A>, and C<Z> types gobble just one value, but pack it as a |
3b10bc60 | 4664 | string of length count, padding with nulls or spaces as needed. When |
18bdf90a | 4665 | unpacking, C<A> strips trailing whitespace and nulls, C<Z> strips everything |
8f1da26d | 4666 | after the first null, and C<a> returns data with no stripping at all. |
2b6c5635 | 4667 | |
3b10bc60 | 4668 | If the value to pack is too long, the result is truncated. If it's too |
4669 | long and an explicit count is provided, C<Z> packs only C<$count-1> bytes, | |
4670 | followed by a null byte. Thus C<Z> always packs a trailing null, except | |
8f1da26d | 4671 | when the count is 0. |
5a929a98 VU |
4672 | |
4673 | =item * | |
4674 | ||
3b10bc60 | 4675 | Likewise, the C<b> and C<B> formats pack a string that's that many bits long. |
8f1da26d TC |
4676 | Each such format generates 1 bit of the result. These are typically followed |
4677 | by a repeat count like C<B8> or C<B64>. | |
3b10bc60 | 4678 | |
c73032f5 | 4679 | Each result bit is based on the least-significant bit of the corresponding |
f337b084 | 4680 | input character, i.e., on C<ord($char)%2>. In particular, characters C<"0"> |
3b10bc60 | 4681 | and C<"1"> generate bits 0 and 1, as do characters C<"\000"> and C<"\001">. |
c73032f5 | 4682 | |
3b10bc60 | 4683 | Starting from the beginning of the input string, each 8-tuple |
4684 | of characters is converted to 1 character of output. With format C<b>, | |
f337b084 | 4685 | the first character of the 8-tuple determines the least-significant bit of a |
3b10bc60 | 4686 | character; with format C<B>, it determines the most-significant bit of |
f337b084 | 4687 | a character. |
c73032f5 | 4688 | |
3b10bc60 | 4689 | If the length of the input string is not evenly divisible by 8, the |
f337b084 | 4690 | remainder is packed as if the input string were padded by null characters |
3b10bc60 | 4691 | at the end. Similarly during unpacking, "extra" bits are ignored. |
c73032f5 | 4692 | |
3b10bc60 | 4693 | If the input string is longer than needed, remaining characters are ignored. |
4694 | ||
4695 | A C<*> for the repeat count uses all characters of the input field. | |
8f1da26d | 4696 | On unpacking, bits are converted to a string of C<0>s and C<1>s. |
5a929a98 VU |
4697 | |
4698 | =item * | |
4699 | ||
3b10bc60 | 4700 | The C<h> and C<H> formats pack a string that many nybbles (4-bit groups, |
4701 | representable as hexadecimal digits, C<"0".."9"> C<"a".."f">) long. | |
5a929a98 | 4702 | |
8f1da26d | 4703 | For each such format, pack() generates 4 bits of result. |
3b10bc60 | 4704 | With non-alphabetical characters, the result is based on the 4 least-significant |
f337b084 TH |
4705 | bits of the input character, i.e., on C<ord($char)%16>. In particular, |
4706 | characters C<"0"> and C<"1"> generate nybbles 0 and 1, as do bytes | |
ce7b6f06 | 4707 | C<"\000"> and C<"\001">. For characters C<"a".."f"> and C<"A".."F">, the result |
c73032f5 | 4708 | is compatible with the usual hexadecimal digits, so that C<"a"> and |
8f1da26d TC |
4709 | C<"A"> both generate the nybble C<0xA==10>. Use only these specific hex |
4710 | characters with this format. | |
c73032f5 | 4711 | |
3b10bc60 | 4712 | Starting from the beginning of the template to pack(), each pair |
4713 | of characters is converted to 1 character of output. With format C<h>, the | |
f337b084 | 4714 | first character of the pair determines the least-significant nybble of the |
3b10bc60 | 4715 | output character; with format C<H>, it determines the most-significant |
c73032f5 IZ |
4716 | nybble. |
4717 | ||
3b10bc60 | 4718 | If the length of the input string is not even, it behaves as if padded by |
4719 | a null character at the end. Similarly, "extra" nybbles are ignored during | |
4720 | unpacking. | |
4721 | ||
4722 | If the input string is longer than needed, extra characters are ignored. | |
c73032f5 | 4723 | |
3b10bc60 | 4724 | A C<*> for the repeat count uses all characters of the input field. For |
4725 | unpack(), nybbles are converted to a string of hexadecimal digits. | |
c73032f5 | 4726 | |
5a929a98 VU |
4727 | =item * |
4728 | ||
3b10bc60 | 4729 | The C<p> format packs a pointer to a null-terminated string. You are |
4730 | responsible for ensuring that the string is not a temporary value, as that | |
4731 | could potentially get deallocated before you got around to using the packed | |
4732 | result. The C<P> format packs a pointer to a structure of the size indicated | |
4733 | by the length. A null pointer is created if the corresponding value for | |
4734 | C<p> or C<P> is C<undef>; similarly with unpack(), where a null pointer | |
4735 | unpacks into C<undef>. | |
5a929a98 | 4736 | |
3b10bc60 | 4737 | If your system has a strange pointer size--meaning a pointer is neither as |
4738 | big as an int nor as big as a long--it may not be possible to pack or | |
1109a392 | 4739 | unpack pointers in big- or little-endian byte order. Attempting to do |
3b10bc60 | 4740 | so raises an exception. |
1109a392 | 4741 | |
5a929a98 VU |
4742 | =item * |
4743 | ||
246f24af | 4744 | The C</> template character allows packing and unpacking of a sequence of |
3b10bc60 | 4745 | items where the packed structure contains a packed item count followed by |
4746 | the packed items themselves. This is useful when the structure you're | |
4747 | unpacking has encoded the sizes or repeat counts for some of its fields | |
4748 | within the structure itself as separate fields. | |
4749 | ||
4750 | For C<pack>, you write I<length-item>C</>I<sequence-item>, and the | |
391b733c | 4751 | I<length-item> describes how the length value is packed. Formats likely |
3b10bc60 | 4752 | to be of most use are integer-packing ones like C<n> for Java strings, |
4753 | C<w> for ASN.1 or SNMP, and C<N> for Sun XDR. | |
4754 | ||
4755 | For C<pack>, I<sequence-item> may have a repeat count, in which case | |
4756 | the minimum of that and the number of available items is used as the argument | |
391b733c | 4757 | for I<length-item>. If it has no repeat count or uses a '*', the number |
54f961c9 PD |
4758 | of available items is used. |
4759 | ||
3b10bc60 | 4760 | For C<unpack>, an internal stack of integer arguments unpacked so far is |
391b733c FC |
4761 | used. You write C</>I<sequence-item> and the repeat count is obtained by |
4762 | popping off the last element from the stack. The I<sequence-item> must not | |
54f961c9 | 4763 | have a repeat count. |
246f24af | 4764 | |
3b10bc60 | 4765 | If I<sequence-item> refers to a string type (C<"A">, C<"a">, or C<"Z">), |
4766 | the I<length-item> is the string length, not the number of strings. With | |
4767 | an explicit repeat count for pack, the packed string is adjusted to that | |
4768 | length. For example: | |
246f24af | 4769 | |
f7051f2c | 4770 | This code: gives this result: |
f703fc96 | 4771 | |
f7051f2c FC |
4772 | unpack("W/a", "\004Gurusamy") ("Guru") |
4773 | unpack("a3/A A*", "007 Bond J ") (" Bond", "J") | |
4774 | unpack("a3 x2 /A A*", "007: Bond, J.") ("Bond, J", ".") | |
3b10bc60 | 4775 | |
f7051f2c FC |
4776 | pack("n/a* w/a","hello,","world") "\000\006hello,\005world" |
4777 | pack("a/W2", ord("a") .. ord("z")) "2ab" | |
43192e07 IP |
4778 | |
4779 | The I<length-item> is not returned explicitly from C<unpack>. | |
4780 | ||
3b10bc60 | 4781 | Supplying a count to the I<length-item> format letter is only useful with |
4782 | C<A>, C<a>, or C<Z>. Packing with a I<length-item> of C<a> or C<Z> may | |
4783 | introduce C<"\000"> characters, which Perl does not regard as legal in | |
4784 | numeric strings. | |
43192e07 IP |
4785 | |
4786 | =item * | |
4787 | ||
951ba7fe | 4788 | The integer types C<s>, C<S>, C<l>, and C<L> may be |
3b10bc60 | 4789 | followed by a C<!> modifier to specify native shorts or |
4790 | longs. As shown in the example above, a bare C<l> means | |
4791 | exactly 32 bits, although the native C<long> as seen by the local C compiler | |
4792 | may be larger. This is mainly an issue on 64-bit platforms. You can | |
4793 | see whether using C<!> makes any difference this way: | |
4794 | ||
4795 | printf "format s is %d, s! is %d\n", | |
4796 | length pack("s"), length pack("s!"); | |
726ea183 | 4797 | |
3b10bc60 | 4798 | printf "format l is %d, l! is %d\n", |
4799 | length pack("l"), length pack("l!"); | |
ef54e1a4 | 4800 | |
3b10bc60 | 4801 | |
4802 | C<i!> and C<I!> are also allowed, but only for completeness' sake: | |
951ba7fe | 4803 | they are identical to C<i> and C<I>. |
ef54e1a4 | 4804 | |
19799a22 | 4805 | The actual sizes (in bytes) of native shorts, ints, longs, and long |
3b10bc60 | 4806 | longs on the platform where Perl was built are also available from |
4807 | the command line: | |
4808 | ||
4809 | $ perl -V:{short,int,long{,long}}size | |
4810 | shortsize='2'; | |
4811 | intsize='4'; | |
4812 | longsize='4'; | |
4813 | longlongsize='8'; | |
4814 | ||
4815 | or programmatically via the C<Config> module: | |
19799a22 GS |
4816 | |
4817 | use Config; | |
4818 | print $Config{shortsize}, "\n"; | |
4819 | print $Config{intsize}, "\n"; | |
4820 | print $Config{longsize}, "\n"; | |
4821 | print $Config{longlongsize}, "\n"; | |
ef54e1a4 | 4822 | |
3b10bc60 | 4823 | C<$Config{longlongsize}> is undefined on systems without |
4824 | long long support. | |
851646ae | 4825 | |
ef54e1a4 JH |
4826 | =item * |
4827 | ||
3b10bc60 | 4828 | The integer formats C<s>, C<S>, C<i>, C<I>, C<l>, C<L>, C<j>, and C<J> are |
4829 | inherently non-portable between processors and operating systems because | |
4830 | they obey native byteorder and endianness. For example, a 4-byte integer | |
4831 | 0x12345678 (305419896 decimal) would be ordered natively (arranged in and | |
4832 | handled by the CPU registers) into bytes as | |
61eff3bc | 4833 | |
5ed4f2ec | 4834 | 0x12 0x34 0x56 0x78 # big-endian |
4835 | 0x78 0x56 0x34 0x12 # little-endian | |
61eff3bc | 4836 | |
3b10bc60 | 4837 | Basically, Intel and VAX CPUs are little-endian, while everybody else, |
4838 | including Motorola m68k/88k, PPC, Sparc, HP PA, Power, and Cray, are | |
8f1da26d TC |
4839 | big-endian. Alpha and MIPS can be either: Digital/Compaq uses (well, used) |
4840 | them in little-endian mode, but SGI/Cray uses them in big-endian mode. | |
719a3cf5 | 4841 | |
3b10bc60 | 4842 | The names I<big-endian> and I<little-endian> are comic references to the |
4843 | egg-eating habits of the little-endian Lilliputians and the big-endian | |
4844 | Blefuscudians from the classic Jonathan Swift satire, I<Gulliver's Travels>. | |
4845 | This entered computer lingo via the paper "On Holy Wars and a Plea for | |
4846 | Peace" by Danny Cohen, USC/ISI IEN 137, April 1, 1980. | |
61eff3bc | 4847 | |
140cb37e | 4848 | Some systems may have even weirder byte orders such as |
61eff3bc | 4849 | |
5ed4f2ec | 4850 | 0x56 0x78 0x12 0x34 |
4851 | 0x34 0x12 0x78 0x56 | |
61eff3bc | 4852 | |
c34cc94d JH |
4853 | These are called mid-endian, middle-endian, mixed-endian, or just weird. |
4854 | ||
3b10bc60 | 4855 | You can determine your system endianness with this incantation: |
ef54e1a4 | 4856 | |
3b10bc60 | 4857 | printf("%#02x ", $_) for unpack("W*", pack L=>0x12345678); |
ef54e1a4 | 4858 | |
d99ad34e | 4859 | The byteorder on the platform where Perl was built is also available |
726ea183 | 4860 | via L<Config>: |
ef54e1a4 | 4861 | |
5ed4f2ec | 4862 | use Config; |
3b10bc60 | 4863 | print "$Config{byteorder}\n"; |
4864 | ||
4865 | or from the command line: | |
ef54e1a4 | 4866 | |
3b10bc60 | 4867 | $ perl -V:byteorder |
719a3cf5 | 4868 | |
3b10bc60 | 4869 | Byteorders C<"1234"> and C<"12345678"> are little-endian; C<"4321"> |
c34cc94d JH |
4870 | and C<"87654321"> are big-endian. Systems with multiarchitecture binaries |
4871 | will have C<"ffff">, signifying that static information doesn't work, | |
4872 | one must use runtime probing. | |
3b10bc60 | 4873 | |
4874 | For portably packed integers, either use the formats C<n>, C<N>, C<v>, | |
4875 | and C<V> or else use the C<< > >> and C<< < >> modifiers described | |
4876 | immediately below. See also L<perlport>. | |
ef54e1a4 JH |
4877 | |
4878 | =item * | |
4879 | ||
e8944635 JH |
4880 | Also floating point numbers have endianness. Usually (but not always) |
4881 | this agrees with the integer endianness. Even though most platforms | |
4882 | these days use the IEEE 754 binary format, there are differences, | |
4883 | especially if the long doubles are involved. You can see the | |
4884 | C<Config> variables C<doublekind> and C<longdblkind> (also C<doublesize>, | |
4885 | C<longdblsize>): the "kind" values are enums, unlike C<byteorder>. | |
4886 | ||
4887 | Portability-wise the best option is probably to keep to the IEEE 754 | |
4888 | 64-bit doubles, and of agreed-upon endianness. Another possibility | |
4889 | is the C<"%a">) format of C<printf>. | |
4890 | ||
4891 | =item * | |
4892 | ||
e9fa405d | 4893 | Starting with Perl 5.10.0, integer and floating-point formats, along with |
3b10bc60 | 4894 | the C<p> and C<P> formats and C<()> groups, may all be followed by the |
4895 | C<< > >> or C<< < >> endianness modifiers to respectively enforce big- | |
4896 | or little-endian byte-order. These modifiers are especially useful | |
8f1da26d | 4897 | given how C<n>, C<N>, C<v>, and C<V> don't cover signed integers, |
3b10bc60 | 4898 | 64-bit integers, or floating-point values. |
4899 | ||
bea6df1c | 4900 | Here are some concerns to keep in mind when using an endianness modifier: |
3b10bc60 | 4901 | |
4902 | =over | |
4903 | ||
4904 | =item * | |
4905 | ||
4906 | Exchanging signed integers between different platforms works only | |
4907 | when all platforms store them in the same format. Most platforms store | |
4908 | signed integers in two's-complement notation, so usually this is not an issue. | |
1109a392 | 4909 | |
3b10bc60 | 4910 | =item * |
1109a392 | 4911 | |
3b10bc60 | 4912 | The C<< > >> or C<< < >> modifiers can only be used on floating-point |
1109a392 | 4913 | formats on big- or little-endian machines. Otherwise, attempting to |
3b10bc60 | 4914 | use them raises an exception. |
1109a392 | 4915 | |
3b10bc60 | 4916 | =item * |
4917 | ||
4918 | Forcing big- or little-endian byte-order on floating-point values for | |
4919 | data exchange can work only if all platforms use the same | |
4920 | binary representation such as IEEE floating-point. Even if all | |
4921 | platforms are using IEEE, there may still be subtle differences. Being able | |
4922 | to use C<< > >> or C<< < >> on floating-point values can be useful, | |
80d38338 | 4923 | but also dangerous if you don't know exactly what you're doing. |
3b10bc60 | 4924 | It is not a general way to portably store floating-point values. |
4925 | ||
4926 | =item * | |
1109a392 | 4927 | |
3b10bc60 | 4928 | When using C<< > >> or C<< < >> on a C<()> group, this affects |
4929 | all types inside the group that accept byte-order modifiers, | |
4930 | including all subgroups. It is silently ignored for all other | |
66c611c5 MHM |
4931 | types. You are not allowed to override the byte-order within a group |
4932 | that already has a byte-order modifier suffix. | |
4933 | ||
3b10bc60 | 4934 | =back |
4935 | ||
1109a392 MHM |
4936 | =item * |
4937 | ||
3b10bc60 | 4938 | Real numbers (floats and doubles) are in native machine format only. |
4939 | Due to the multiplicity of floating-point formats and the lack of a | |
4940 | standard "network" representation for them, no facility for interchange has been | |
4941 | made. This means that packed floating-point data written on one machine | |
4942 | may not be readable on another, even if both use IEEE floating-point | |
4943 | arithmetic (because the endianness of the memory representation is not part | |
851646ae | 4944 | of the IEEE spec). See also L<perlport>. |
5a929a98 | 4945 | |
3b10bc60 | 4946 | If you know I<exactly> what you're doing, you can use the C<< > >> or C<< < >> |
4947 | modifiers to force big- or little-endian byte-order on floating-point values. | |
1109a392 | 4948 | |
3b10bc60 | 4949 | Because Perl uses doubles (or long doubles, if configured) internally for |
4950 | all numeric calculation, converting from double into float and thence | |
4951 | to double again loses precision, so C<unpack("f", pack("f", $foo)>) | |
4952 | will not in general equal $foo. | |
5a929a98 | 4953 | |
851646ae JH |
4954 | =item * |
4955 | ||
3b10bc60 | 4956 | Pack and unpack can operate in two modes: character mode (C<C0> mode) where |
4957 | the packed string is processed per character, and UTF-8 mode (C<U0> mode) | |
f337b084 | 4958 | where the packed string is processed in its UTF-8-encoded Unicode form on |
391b733c FC |
4959 | a byte-by-byte basis. Character mode is the default |
4960 | unless the format string starts with C<U>. You | |
4961 | can always switch mode mid-format with an explicit | |
3b10bc60 | 4962 | C<C0> or C<U0> in the format. This mode remains in effect until the next |
4963 | mode change, or until the end of the C<()> group it (directly) applies to. | |
036b4402 | 4964 | |
8f1da26d TC |
4965 | Using C<C0> to get Unicode characters while using C<U0> to get I<non>-Unicode |
4966 | bytes is not necessarily obvious. Probably only the first of these | |
4967 | is what you want: | |
4968 | ||
4969 | $ perl -CS -E 'say "\x{3B1}\x{3C9}"' | | |
4970 | perl -CS -ne 'printf "%v04X\n", $_ for unpack("C0A*", $_)' | |
4971 | 03B1.03C9 | |
4972 | $ perl -CS -E 'say "\x{3B1}\x{3C9}"' | | |
4973 | perl -CS -ne 'printf "%v02X\n", $_ for unpack("U0A*", $_)' | |
4974 | CE.B1.CF.89 | |
4975 | $ perl -CS -E 'say "\x{3B1}\x{3C9}"' | | |
4976 | perl -C0 -ne 'printf "%v02X\n", $_ for unpack("C0A*", $_)' | |
4977 | CE.B1.CF.89 | |
4978 | $ perl -CS -E 'say "\x{3B1}\x{3C9}"' | | |
4979 | perl -C0 -ne 'printf "%v02X\n", $_ for unpack("U0A*", $_)' | |
4980 | C3.8E.C2.B1.C3.8F.C2.89 | |
4981 | ||
4982 | Those examples also illustrate that you should not try to use | |
4983 | C<pack>/C<unpack> as a substitute for the L<Encode> module. | |
4984 | ||
036b4402 GS |
4985 | =item * |
4986 | ||
3b10bc60 | 4987 | You must yourself do any alignment or padding by inserting, for example, |
4988 | enough C<"x">es while packing. There is no way for pack() and unpack() | |
4989 | to know where characters are going to or coming from, so they | |
4990 | handle their output and input as flat sequences of characters. | |
851646ae | 4991 | |
17f4a12d IZ |
4992 | =item * |
4993 | ||
3b10bc60 | 4994 | A C<()> group is a sub-TEMPLATE enclosed in parentheses. A group may |
4995 | take a repeat count either as postfix, or for unpack(), also via the C</> | |
4996 | template character. Within each repetition of a group, positioning with | |
391b733c | 4997 | C<@> starts over at 0. Therefore, the result of |
49704364 | 4998 | |
3b10bc60 | 4999 | pack("@1A((@2A)@3A)", qw[X Y Z]) |
49704364 | 5000 | |
3b10bc60 | 5001 | is the string C<"\0X\0\0YZ">. |
49704364 | 5002 | |
18529408 IZ |
5003 | =item * |
5004 | ||
3b10bc60 | 5005 | C<x> and C<X> accept the C<!> modifier to act as alignment commands: they |
5006 | jump forward or back to the closest position aligned at a multiple of C<count> | |
391b733c | 5007 | characters. For example, to pack() or unpack() a C structure like |
666f95b9 | 5008 | |
3b10bc60 | 5009 | struct { |
5010 | char c; /* one signed, 8-bit character */ | |
5011 | double d; | |
5012 | char cc[2]; | |
5013 | } | |
5014 | ||
5015 | one may need to use the template C<c x![d] d c[2]>. This assumes that | |
5016 | doubles must be aligned to the size of double. | |
5017 | ||
5018 | For alignment commands, a C<count> of 0 is equivalent to a C<count> of 1; | |
5019 | both are no-ops. | |
666f95b9 | 5020 | |
62f95557 IZ |
5021 | =item * |
5022 | ||
3b10bc60 | 5023 | C<n>, C<N>, C<v> and C<V> accept the C<!> modifier to |
5024 | represent signed 16-/32-bit integers in big-/little-endian order. | |
5025 | This is portable only when all platforms sharing packed data use the | |
5026 | same binary representation for signed integers; for example, when all | |
5027 | platforms use two's-complement representation. | |
068bd2e7 MHM |
5028 | |
5029 | =item * | |
5030 | ||
3b10bc60 | 5031 | Comments can be embedded in a TEMPLATE using C<#> through the end of line. |
5032 | White space can separate pack codes from each other, but modifiers and | |
5033 | repeat counts must follow immediately. Breaking complex templates into | |
5034 | individual line-by-line components, suitably annotated, can do as much to | |
5035 | improve legibility and maintainability of pack/unpack formats as C</x> can | |
5036 | for complicated pattern matches. | |
17f4a12d | 5037 | |
2b6c5635 GS |
5038 | =item * |
5039 | ||
bea6df1c | 5040 | If TEMPLATE requires more arguments than pack() is given, pack() |
cf264981 | 5041 | assumes additional C<""> arguments. If TEMPLATE requires fewer arguments |
3b10bc60 | 5042 | than given, extra arguments are ignored. |
2b6c5635 | 5043 | |
ad93219c JH |
5044 | =item * |
5045 | ||
5046 | Attempting to pack the special floating point values C<Inf> and C<NaN> | |
5047 | (infinity, also in negative, and not-a-number) into packed integer values | |
5048 | (like C<"L">) is a fatal error. The reason for this is that there simply | |
5049 | isn't any sensible mapping for these special values into integers. | |
5050 | ||
5a929a98 | 5051 | =back |
a0d0e21e LW |
5052 | |
5053 | Examples: | |
5054 | ||
f337b084 | 5055 | $foo = pack("WWWW",65,66,67,68); |
a0d0e21e | 5056 | # foo eq "ABCD" |
f337b084 | 5057 | $foo = pack("W4",65,66,67,68); |
a0d0e21e | 5058 | # same thing |
f337b084 TH |
5059 | $foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9); |
5060 | # same thing with Unicode circled letters. | |
a0ed51b3 | 5061 | $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9); |
391b733c | 5062 | # same thing with Unicode circled letters. You don't get the |
4d0444a3 FC |
5063 | # UTF-8 bytes because the U at the start of the format caused |
5064 | # a switch to U0-mode, so the UTF-8 bytes get joined into | |
5065 | # characters | |
f337b084 TH |
5066 | $foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9); |
5067 | # foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9" | |
4d0444a3 FC |
5068 | # This is the UTF-8 encoding of the string in the |
5069 | # previous example | |
a0d0e21e LW |
5070 | |
5071 | $foo = pack("ccxxcc",65,66,67,68); | |
5072 | # foo eq "AB\0\0CD" | |
5073 | ||
3b10bc60 | 5074 | # NOTE: The examples above featuring "W" and "c" are true |
9ccd05c0 | 5075 | # only on ASCII and ASCII-derived systems such as ISO Latin 1 |
3b10bc60 | 5076 | # and UTF-8. On EBCDIC systems, the first example would be |
5077 | # $foo = pack("WWWW",193,194,195,196); | |
9ccd05c0 | 5078 | |
a0d0e21e | 5079 | $foo = pack("s2",1,2); |
ce7b6f06 KW |
5080 | # "\001\000\002\000" on little-endian |
5081 | # "\000\001\000\002" on big-endian | |
a0d0e21e LW |
5082 | |
5083 | $foo = pack("a4","abcd","x","y","z"); | |
5084 | # "abcd" | |
5085 | ||
5086 | $foo = pack("aaaa","abcd","x","y","z"); | |
5087 | # "axyz" | |
5088 | ||
5089 | $foo = pack("a14","abcdefg"); | |
5090 | # "abcdefg\0\0\0\0\0\0\0" | |
5091 | ||
5092 | $foo = pack("i9pl", gmtime); | |
5093 | # a real struct tm (on my system anyway) | |
5094 | ||
5a929a98 VU |
5095 | $utmp_template = "Z8 Z8 Z16 L"; |
5096 | $utmp = pack($utmp_template, @utmp1); | |
5097 | # a struct utmp (BSDish) | |
5098 | ||
5099 | @utmp2 = unpack($utmp_template, $utmp); | |
5100 | # "@utmp1" eq "@utmp2" | |
5101 | ||
a0d0e21e | 5102 | sub bintodec { |
a9a5a0dc | 5103 | unpack("N", pack("B32", substr("0" x 32 . shift, -32))); |
a0d0e21e LW |
5104 | } |
5105 | ||
851646ae JH |
5106 | $foo = pack('sx2l', 12, 34); |
5107 | # short 12, two zero bytes padding, long 34 | |
5108 | $bar = pack('s@4l', 12, 34); | |
5109 | # short 12, zero fill to position 4, long 34 | |
5110 | # $foo eq $bar | |
28be1210 TH |
5111 | $baz = pack('s.l', 12, 4, 34); |
5112 | # short 12, zero fill to position 4, long 34 | |
851646ae | 5113 | |
1109a392 MHM |
5114 | $foo = pack('nN', 42, 4711); |
5115 | # pack big-endian 16- and 32-bit unsigned integers | |
5116 | $foo = pack('S>L>', 42, 4711); | |
5117 | # exactly the same | |
5118 | $foo = pack('s<l<', -42, 4711); | |
5119 | # pack little-endian 16- and 32-bit signed integers | |
66c611c5 MHM |
5120 | $foo = pack('(sl)<', -42, 4711); |
5121 | # exactly the same | |
1109a392 | 5122 | |
5a929a98 | 5123 | The same template may generally also be used in unpack(). |
a0d0e21e | 5124 | |
8f1da26d TC |
5125 | =item package NAMESPACE |
5126 | ||
6fa4d285 DG |
5127 | =item package NAMESPACE VERSION |
5128 | X<package> X<module> X<namespace> X<version> | |
5129 | ||
8f1da26d | 5130 | =item package NAMESPACE BLOCK |
cb1a09d0 | 5131 | |
4e4da3ac Z |
5132 | =item package NAMESPACE VERSION BLOCK |
5133 | X<package> X<module> X<namespace> X<version> | |
5134 | ||
c17cdb72 NC |
5135 | =for Pod::Functions declare a separate global namespace |
5136 | ||
8f1da26d TC |
5137 | Declares the BLOCK or the rest of the compilation unit as being in the |
5138 | given namespace. The scope of the package declaration is either the | |
4e4da3ac | 5139 | supplied code BLOCK or, in the absence of a BLOCK, from the declaration |
8f1da26d TC |
5140 | itself through the end of current scope (the enclosing block, file, or |
5141 | C<eval>). That is, the forms without a BLOCK are operative through the end | |
5142 | of the current scope, just like the C<my>, C<state>, and C<our> operators. | |
5143 | All unqualified dynamic identifiers in this scope will be in the given | |
5144 | namespace, except where overridden by another C<package> declaration or | |
5145 | when they're one of the special identifiers that qualify into C<main::>, | |
5146 | like C<STDOUT>, C<ARGV>, C<ENV>, and the punctuation variables. | |
4e4da3ac | 5147 | |
3b10bc60 | 5148 | A package statement affects dynamic variables only, including those |
4dd95518 | 5149 | you've used C<local> on, but I<not> lexically-scoped variables, which are created |
8f1da26d | 5150 | with C<my>, C<state>, or C<our>. Typically it would be the first |
3b10bc60 | 5151 | declaration in a file included by C<require> or C<use>. You can switch into a |
5152 | package in more than one place, since this only determines which default | |
5153 | symbol table the compiler uses for the rest of that block. You can refer to | |
5154 | identifiers in other packages than the current one by prefixing the identifier | |
5155 | with the package name and a double colon, as in C<$SomePack::var> | |
5156 | or C<ThatPack::INPUT_HANDLE>. If package name is omitted, the C<main> | |
5157 | package as assumed. That is, C<$::sail> is equivalent to | |
5158 | C<$main::sail> (as well as to C<$main'sail>, still seen in ancient | |
5159 | code, mostly from Perl 4). | |
5160 | ||
bd12309b | 5161 | If VERSION is provided, C<package> sets the C<$VERSION> variable in the given |
a2bff36e DG |
5162 | namespace to a L<version> object with the VERSION provided. VERSION must be a |
5163 | "strict" style version number as defined by the L<version> module: a positive | |
5164 | decimal number (integer or decimal-fraction) without exponentiation or else a | |
5165 | dotted-decimal v-string with a leading 'v' character and at least three | |
5166 | components. You should set C<$VERSION> only once per package. | |
6fa4d285 | 5167 | |
cb1a09d0 AD |
5168 | See L<perlmod/"Packages"> for more information about packages, modules, |
5169 | and classes. See L<perlsub> for other scoping issues. | |
5170 | ||
f5fa2679 NC |
5171 | =item __PACKAGE__ |
5172 | X<__PACKAGE__> | |
5173 | ||
d9b04284 | 5174 | =for Pod::Functions +5.004 the current package |
c17cdb72 | 5175 | |
f5fa2679 NC |
5176 | A special token that returns the name of the package in which it occurs. |
5177 | ||
a0d0e21e | 5178 | =item pipe READHANDLE,WRITEHANDLE |
d74e8afc | 5179 | X<pipe> |
a0d0e21e | 5180 | |
c17cdb72 NC |
5181 | =for Pod::Functions open a pair of connected filehandles |
5182 | ||
a0d0e21e LW |
5183 | Opens a pair of connected pipes like the corresponding system call. |
5184 | Note that if you set up a loop of piped processes, deadlock can occur | |
5185 | unless you are very careful. In addition, note that Perl's pipes use | |
9124316e | 5186 | IO buffering, so you may need to set C<$|> to flush your WRITEHANDLE |
a0d0e21e LW |
5187 | after each command, depending on the application. |
5188 | ||
f7a9f755 TC |
5189 | Returns true on success. |
5190 | ||
96090e4f LB |
5191 | See L<IPC::Open2>, L<IPC::Open3>, and |
5192 | L<perlipc/"Bidirectional Communication with Another Process"> | |
4633a7c4 LW |
5193 | for examples of such things. |
5194 | ||
3b10bc60 | 5195 | On systems that support a close-on-exec flag on files, that flag is set |
5196 | on all newly opened file descriptors whose C<fileno>s are I<higher> than | |
5197 | the current value of $^F (by default 2 for C<STDERR>). See L<perlvar/$^F>. | |
4771b018 | 5198 | |
532eee96 | 5199 | =item pop ARRAY |
d74e8afc | 5200 | X<pop> X<stack> |
a0d0e21e | 5201 | |
f5a93a43 TC |
5202 | =item pop EXPR |
5203 | ||
54310121 | 5204 | =item pop |
28757baa | 5205 | |
c17cdb72 NC |
5206 | =for Pod::Functions remove the last element from an array and return it |
5207 | ||
a0d0e21e | 5208 | Pops and returns the last value of the array, shortening the array by |
cd7f9af7 | 5209 | one element. |
a0d0e21e | 5210 | |
3b10bc60 | 5211 | Returns the undefined value if the array is empty, although this may also |
5212 | happen at other times. If ARRAY is omitted, pops the C<@ARGV> array in the | |
5213 | main program, but the C<@_> array in subroutines, just like C<shift>. | |
a0d0e21e | 5214 | |
f5a93a43 TC |
5215 | Starting with Perl 5.14, C<pop> can take a scalar EXPR, which must hold a |
5216 | reference to an unblessed array. The argument will be dereferenced | |
5217 | automatically. This aspect of C<pop> is considered highly experimental. | |
5218 | The exact behaviour may change in a future version of Perl. | |
cba5a3b0 | 5219 | |
bade7fbc TC |
5220 | To avoid confusing would-be users of your code who are running earlier |
5221 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
5222 | the top of your file to signal that your code will work I<only> on Perls of | |
5223 | a recent vintage: | |
5224 | ||
5225 | use 5.014; # so push/pop/etc work on scalars (experimental) | |
5226 | ||
a0d0e21e | 5227 | =item pos SCALAR |
d74e8afc | 5228 | X<pos> X<match, position> |
a0d0e21e | 5229 | |
54310121 | 5230 | =item pos |
bbce6d69 | 5231 | |
c17cdb72 NC |
5232 | =for Pod::Functions find or set the offset for the last/next m//g search |
5233 | ||
7664c618 | 5234 | Returns the offset of where the last C<m//g> search left off for the |
5235 | variable in question (C<$_> is used when the variable is not | |
391b733c | 5236 | specified). Note that 0 is a valid match offset. C<undef> indicates |
7664c618 | 5237 | that the search position is reset (usually due to match failure, but |
5238 | can also be because no match has yet been run on the scalar). | |
5239 | ||
5240 | C<pos> directly accesses the location used by the regexp engine to | |
5241 | store the offset, so assigning to C<pos> will change that offset, and | |
5242 | so will also influence the C<\G> zero-width assertion in regular | |
391b733c | 5243 | expressions. Both of these effects take place for the next match, so |
7664c618 | 5244 | you can't affect the position with C<pos> during the current match, |
5245 | such as in C<(?{pos() = 5})> or C<s//pos() = 5/e>. | |
5246 | ||
f9179917 FC |
5247 | Setting C<pos> also resets the I<matched with zero-length> flag, described |
5248 | under L<perlre/"Repeated Patterns Matching a Zero-length Substring">. | |
5249 | ||
7664c618 | 5250 | Because a failed C<m//gc> match doesn't reset the offset, the return |
5251 | from C<pos> won't change either in this case. See L<perlre> and | |
44a8e56a | 5252 | L<perlop>. |
a0d0e21e LW |
5253 | |
5254 | =item print FILEHANDLE LIST | |
d74e8afc | 5255 | X<print> |
a0d0e21e | 5256 | |
dee33c94 TC |
5257 | =item print FILEHANDLE |
5258 | ||
a0d0e21e LW |
5259 | =item print LIST |
5260 | ||
5261 | =item print | |
5262 | ||
c17cdb72 NC |
5263 | =for Pod::Functions output a list to a filehandle |
5264 | ||
19799a22 | 5265 | Prints a string or a list of strings. Returns true if successful. |
dee33c94 TC |
5266 | FILEHANDLE may be a scalar variable containing the name of or a reference |
5267 | to the filehandle, thus introducing one level of indirection. (NOTE: If | |
5268 | FILEHANDLE is a variable and the next token is a term, it may be | |
5269 | misinterpreted as an operator unless you interpose a C<+> or put | |
391b733c | 5270 | parentheses around the arguments.) If FILEHANDLE is omitted, prints to the |
8f1da26d TC |
5271 | last selected (see L</select>) output handle. If LIST is omitted, prints |
5272 | C<$_> to the currently selected output handle. To use FILEHANDLE alone to | |
5273 | print the content of C<$_> to it, you must use a real filehandle like | |
5274 | C<FH>, not an indirect one like C<$fh>. To set the default output handle | |
5275 | to something other than STDOUT, use the select operation. | |
5276 | ||
5277 | The current value of C<$,> (if any) is printed between each LIST item. The | |
5278 | current value of C<$\> (if any) is printed after the entire LIST has been | |
5279 | printed. Because print takes a LIST, anything in the LIST is evaluated in | |
5280 | list context, including any subroutines whose return lists you pass to | |
5281 | C<print>. Be careful not to follow the print keyword with a left | |
5282 | parenthesis unless you want the corresponding right parenthesis to | |
5283 | terminate the arguments to the print; put parentheses around all arguments | |
5284 | (or interpose a C<+>, but that doesn't look as good). | |
5285 | ||
5286 | If you're storing handles in an array or hash, or in general whenever | |
5287 | you're using any expression more complex than a bareword handle or a plain, | |
5288 | unsubscripted scalar variable to retrieve it, you will have to use a block | |
5289 | returning the filehandle value instead, in which case the LIST may not be | |
5290 | omitted: | |
4633a7c4 LW |
5291 | |
5292 | print { $files[$i] } "stuff\n"; | |
5293 | print { $OK ? STDOUT : STDERR } "stuff\n"; | |
5294 | ||
785fd561 DG |
5295 | Printing to a closed pipe or socket will generate a SIGPIPE signal. See |
5296 | L<perlipc> for more on signal handling. | |
5297 | ||
5f05dabc | 5298 | =item printf FILEHANDLE FORMAT, LIST |
d74e8afc | 5299 | X<printf> |
a0d0e21e | 5300 | |
dee33c94 TC |
5301 | =item printf FILEHANDLE |
5302 | ||
5f05dabc | 5303 | =item printf FORMAT, LIST |
a0d0e21e | 5304 | |
dee33c94 TC |
5305 | =item printf |
5306 | ||
c17cdb72 NC |
5307 | =for Pod::Functions output a formatted list to a filehandle |
5308 | ||
7660c0ab | 5309 | Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\> |
2ad09a1f FC |
5310 | (the output record separator) is not appended. The FORMAT and the |
5311 | LIST are actually parsed as a single list. The first argument | |
5312 | of the list will be interpreted as the C<printf> format. This | |
5313 | means that C<printf(@_)> will use C<$_[0]> as the format. See | |
01aa884e | 5314 | L<sprintf|/sprintf FORMAT, LIST> for an |
d6ded950 KW |
5315 | explanation of the format argument. If C<use locale> for C<LC_NUMERIC> |
5316 | Look for this throught pod | |
5317 | is in effect and | |
dee33c94 | 5318 | POSIX::setlocale() has been called, the character used for the decimal |
d6ded950 | 5319 | separator in formatted floating-point numbers is affected by the C<LC_NUMERIC> |
dee33c94 | 5320 | locale setting. See L<perllocale> and L<POSIX>. |
a0d0e21e | 5321 | |
2ad09a1f FC |
5322 | For historical reasons, if you omit the list, C<$_> is used as the format; |
5323 | to use FILEHANDLE without a list, you must use a real filehandle like | |
5324 | C<FH>, not an indirect one like C<$fh>. However, this will rarely do what | |
5325 | you want; if $_ contains formatting codes, they will be replaced with the | |
5326 | empty string and a warning will be emitted if warnings are enabled. Just | |
5327 | use C<print> if you want to print the contents of $_. | |
5328 | ||
19799a22 GS |
5329 | Don't fall into the trap of using a C<printf> when a simple |
5330 | C<print> would do. The C<print> is more efficient and less | |
28757baa | 5331 | error prone. |
5332 | ||
da0045b7 | 5333 | =item prototype FUNCTION |
d74e8afc | 5334 | X<prototype> |
da0045b7 | 5335 | |
d9b04284 | 5336 | =for Pod::Functions +5.002 get the prototype (if any) of a subroutine |
c17cdb72 | 5337 | |
da0045b7 | 5338 | Returns the prototype of a function as a string (or C<undef> if the |
5f05dabc | 5339 | function has no prototype). FUNCTION is a reference to, or the name of, |
5340 | the function whose prototype you want to retrieve. | |
da0045b7 | 5341 | |
2b5ab1e7 | 5342 | If FUNCTION is a string starting with C<CORE::>, the rest is taken as a |
85d83254 FC |
5343 | name for a Perl builtin. If the builtin's arguments |
5344 | cannot be adequately expressed by a prototype | |
0a2ca743 RGS |
5345 | (such as C<system>), prototype() returns C<undef>, because the builtin |
5346 | does not really behave like a Perl function. Otherwise, the string | |
5347 | describing the equivalent prototype is returned. | |
b6c543e3 | 5348 | |
532eee96 | 5349 | =item push ARRAY,LIST |
1dc8ecb8 | 5350 | X<push> X<stack> |
a0d0e21e | 5351 | |
f5a93a43 TC |
5352 | =item push EXPR,LIST |
5353 | ||
c17cdb72 NC |
5354 | =for Pod::Functions append one or more elements to an array |
5355 | ||
8f1da26d TC |
5356 | Treats ARRAY as a stack by appending the values of LIST to the end of |
5357 | ARRAY. The length of ARRAY increases by the length of LIST. Has the same | |
5358 | effect as | |
a0d0e21e LW |
5359 | |
5360 | for $value (LIST) { | |
a9a5a0dc | 5361 | $ARRAY[++$#ARRAY] = $value; |
a0d0e21e LW |
5362 | } |
5363 | ||
cde9c211 SP |
5364 | but is more efficient. Returns the number of elements in the array following |
5365 | the completed C<push>. | |
a0d0e21e | 5366 | |
f5a93a43 TC |
5367 | Starting with Perl 5.14, C<push> can take a scalar EXPR, which must hold a |
5368 | reference to an unblessed array. The argument will be dereferenced | |
5369 | automatically. This aspect of C<push> is considered highly experimental. | |
5370 | The exact behaviour may change in a future version of Perl. | |
cba5a3b0 | 5371 | |
bade7fbc TC |
5372 | To avoid confusing would-be users of your code who are running earlier |
5373 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
5374 | the top of your file to signal that your code will work I<only> on Perls of | |
5375 | a recent vintage: | |
5376 | ||
5377 | use 5.014; # so push/pop/etc work on scalars (experimental) | |
5378 | ||
a0d0e21e LW |
5379 | =item q/STRING/ |
5380 | ||
c17cdb72 NC |
5381 | =for Pod::Functions singly quote a string |
5382 | ||
a0d0e21e LW |
5383 | =item qq/STRING/ |
5384 | ||
c17cdb72 NC |
5385 | =for Pod::Functions doubly quote a string |
5386 | ||
a0d0e21e LW |
5387 | =item qw/STRING/ |
5388 | ||
c17cdb72 NC |
5389 | =for Pod::Functions quote a list of words |
5390 | ||
f5fa2679 NC |
5391 | =item qx/STRING/ |
5392 | ||
c17cdb72 NC |
5393 | =for Pod::Functions backquote quote a string |
5394 | ||
1d888ee3 MK |
5395 | Generalized quotes. See L<perlop/"Quote-Like Operators">. |
5396 | ||
5397 | =item qr/STRING/ | |
5398 | ||
d9b04284 | 5399 | =for Pod::Functions +5.005 compile pattern |
c17cdb72 | 5400 | |
1d888ee3 | 5401 | Regexp-like quote. See L<perlop/"Regexp Quote-Like Operators">. |
a0d0e21e LW |
5402 | |
5403 | =item quotemeta EXPR | |
d74e8afc | 5404 | X<quotemeta> X<metacharacter> |
a0d0e21e | 5405 | |
54310121 | 5406 | =item quotemeta |
bbce6d69 | 5407 | |
c17cdb72 NC |
5408 | =for Pod::Functions quote regular expression magic characters |
5409 | ||
4cd68991 KW |
5410 | Returns the value of EXPR with all the ASCII non-"word" |
5411 | characters backslashed. (That is, all ASCII characters not matching | |
a034a98d DD |
5412 | C</[A-Za-z_0-9]/> will be preceded by a backslash in the |
5413 | returned string, regardless of any locale settings.) | |
5414 | This is the internal function implementing | |
7660c0ab | 5415 | the C<\Q> escape in double-quoted strings. |
4cd68991 | 5416 | (See below for the behavior on non-ASCII code points.) |
a0d0e21e | 5417 | |
7660c0ab | 5418 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 5419 | |
9702b155 RGS |
5420 | quotemeta (and C<\Q> ... C<\E>) are useful when interpolating strings into |
5421 | regular expressions, because by default an interpolated variable will be | |
391b733c | 5422 | considered a mini-regular expression. For example: |
9702b155 RGS |
5423 | |
5424 | my $sentence = 'The quick brown fox jumped over the lazy dog'; | |
5425 | my $substring = 'quick.*?fox'; | |
5426 | $sentence =~ s{$substring}{big bad wolf}; | |
5427 | ||
5428 | Will cause C<$sentence> to become C<'The big bad wolf jumped over...'>. | |
5429 | ||
5430 | On the other hand: | |
5431 | ||
5432 | my $sentence = 'The quick brown fox jumped over the lazy dog'; | |
5433 | my $substring = 'quick.*?fox'; | |
5434 | $sentence =~ s{\Q$substring\E}{big bad wolf}; | |
5435 | ||
5436 | Or: | |
5437 | ||
5438 | my $sentence = 'The quick brown fox jumped over the lazy dog'; | |
5439 | my $substring = 'quick.*?fox'; | |
5440 | my $quoted_substring = quotemeta($substring); | |
5441 | $sentence =~ s{$quoted_substring}{big bad wolf}; | |
5442 | ||
391b733c FC |
5443 | Will both leave the sentence as is. |
5444 | Normally, when accepting literal string | |
8f1da26d | 5445 | input from the user, quotemeta() or C<\Q> must be used. |
9702b155 | 5446 | |
4cd68991 KW |
5447 | In Perl v5.14, all non-ASCII characters are quoted in non-UTF-8-encoded |
5448 | strings, but not quoted in UTF-8 strings. | |
2e2b2571 KW |
5449 | |
5450 | Starting in Perl v5.16, Perl adopted a Unicode-defined strategy for | |
5451 | quoting non-ASCII characters; the quoting of ASCII characters is | |
5452 | unchanged. | |
5453 | ||
5454 | Also unchanged is the quoting of non-UTF-8 strings when outside the | |
5455 | scope of a C<use feature 'unicode_strings'>, which is to quote all | |
5456 | characters in the upper Latin1 range. This provides complete backwards | |
5457 | compatibility for old programs which do not use Unicode. (Note that | |
5458 | C<unicode_strings> is automatically enabled within the scope of a | |
5459 | S<C<use v5.12>> or greater.) | |
5460 | ||
20adcf7c KW |
5461 | Within the scope of C<use locale>, all non-ASCII Latin1 code points |
5462 | are quoted whether the string is encoded as UTF-8 or not. As mentioned | |
5463 | above, locale does not affect the quoting of ASCII-range characters. | |
5464 | This protects against those locales where characters such as C<"|"> are | |
5465 | considered to be word characters. | |
5466 | ||
2e2b2571 | 5467 | Otherwise, Perl quotes non-ASCII characters using an adaptation from |
f321be7e | 5468 | Unicode (see L<http://www.unicode.org/reports/tr31/>). |
2e2b2571 KW |
5469 | The only code points that are quoted are those that have any of the |
5470 | Unicode properties: Pattern_Syntax, Pattern_White_Space, White_Space, | |
5471 | Default_Ignorable_Code_Point, or General_Category=Control. | |
5472 | ||
5473 | Of these properties, the two important ones are Pattern_Syntax and | |
5474 | Pattern_White_Space. They have been set up by Unicode for exactly this | |
5475 | purpose of deciding which characters in a regular expression pattern | |
5476 | should be quoted. No character that can be in an identifier has these | |
5477 | properties. | |
5478 | ||
5479 | Perl promises, that if we ever add regular expression pattern | |
5480 | metacharacters to the dozen already defined | |
5481 | (C<\ E<verbar> ( ) [ { ^ $ * + ? .>), that we will only use ones that have the | |
5482 | Pattern_Syntax property. Perl also promises, that if we ever add | |
5483 | characters that are considered to be white space in regular expressions | |
5484 | (currently mostly affected by C</x>), they will all have the | |
5485 | Pattern_White_Space property. | |
5486 | ||
5487 | Unicode promises that the set of code points that have these two | |
5488 | properties will never change, so something that is not quoted in v5.16 | |
5489 | will never need to be quoted in any future Perl release. (Not all the | |
5490 | code points that match Pattern_Syntax have actually had characters | |
5491 | assigned to them; so there is room to grow, but they are quoted | |
5492 | whether assigned or not. Perl, of course, would never use an | |
5493 | unassigned code point as an actual metacharacter.) | |
5494 | ||
5495 | Quoting characters that have the other 3 properties is done to enhance | |
5496 | the readability of the regular expression and not because they actually | |
5497 | need to be quoted for regular expression purposes (characters with the | |
5498 | White_Space property are likely to be indistinguishable on the page or | |
5499 | screen from those with the Pattern_White_Space property; and the other | |
5500 | two properties contain non-printing characters). | |
b29c72cb | 5501 | |
a0d0e21e | 5502 | =item rand EXPR |
d74e8afc | 5503 | X<rand> X<random> |
a0d0e21e LW |
5504 | |
5505 | =item rand | |
5506 | ||
c17cdb72 NC |
5507 | =for Pod::Functions retrieve the next pseudorandom number |
5508 | ||
7660c0ab | 5509 | Returns a random fractional number greater than or equal to C<0> and less |
3e3baf6d | 5510 | than the value of EXPR. (EXPR should be positive.) If EXPR is |
351f3254 | 5511 | omitted, the value C<1> is used. Currently EXPR with the value C<0> is |
3b10bc60 | 5512 | also special-cased as C<1> (this was undocumented before Perl 5.8.0 |
5513 | and is subject to change in future versions of Perl). Automatically calls | |
351f3254 | 5514 | C<srand> unless C<srand> has already been called. See also C<srand>. |
a0d0e21e | 5515 | |
6063ba18 WM |
5516 | Apply C<int()> to the value returned by C<rand()> if you want random |
5517 | integers instead of random fractional numbers. For example, | |
5518 | ||
5519 | int(rand(10)) | |
5520 | ||
5521 | returns a random integer between C<0> and C<9>, inclusive. | |
5522 | ||
2f9daede | 5523 | (Note: If your rand function consistently returns numbers that are too |
a0d0e21e | 5524 | large or too small, then your version of Perl was probably compiled |
2f9daede | 5525 | with the wrong number of RANDBITS.) |
a0d0e21e | 5526 | |
9700c45b JV |
5527 | B<C<rand()> is not cryptographically secure. You should not rely |
5528 | on it in security-sensitive situations.> As of this writing, a | |
5529 | number of third-party CPAN modules offer random number generators | |
5530 | intended by their authors to be cryptographically secure, | |
416e3a83 AMS |
5531 | including: L<Data::Entropy>, L<Crypt::Random>, L<Math::Random::Secure>, |
5532 | and L<Math::TrulyRandom>. | |
9700c45b | 5533 | |
a0d0e21e | 5534 | =item read FILEHANDLE,SCALAR,LENGTH,OFFSET |
f723aae1 | 5535 | X<read> X<file, read> |
a0d0e21e LW |
5536 | |
5537 | =item read FILEHANDLE,SCALAR,LENGTH | |
5538 | ||
c17cdb72 NC |
5539 | =for Pod::Functions fixed-length buffered input from a filehandle |
5540 | ||
9124316e JH |
5541 | Attempts to read LENGTH I<characters> of data into variable SCALAR |
5542 | from the specified FILEHANDLE. Returns the number of characters | |
b5fe5ca2 | 5543 | actually read, C<0> at end of file, or undef if there was an error (in |
b49f3be6 SG |
5544 | the latter case C<$!> is also set). SCALAR will be grown or shrunk |
5545 | so that the last character actually read is the last character of the | |
5546 | scalar after the read. | |
5547 | ||
5548 | An OFFSET may be specified to place the read data at some place in the | |
5549 | string other than the beginning. A negative OFFSET specifies | |
5550 | placement at that many characters counting backwards from the end of | |
5551 | the string. A positive OFFSET greater than the length of SCALAR | |
5552 | results in the string being padded to the required size with C<"\0"> | |
5553 | bytes before the result of the read is appended. | |
5554 | ||
80d38338 | 5555 | The call is implemented in terms of either Perl's or your system's native |
01aa884e KW |
5556 | fread(3) library function. To get a true read(2) system call, see |
5557 | L<sysread|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>. | |
9124316e JH |
5558 | |
5559 | Note the I<characters>: depending on the status of the filehandle, | |
8f1da26d | 5560 | either (8-bit) bytes or characters are read. By default, all |
9124316e | 5561 | filehandles operate on bytes, but for example if the filehandle has |
fae2c0fb | 5562 | been opened with the C<:utf8> I/O layer (see L</open>, and the C<open> |
8f1da26d | 5563 | pragma, L<open>), the I/O will operate on UTF8-encoded Unicode |
1d714267 JH |
5564 | characters, not bytes. Similarly for the C<:encoding> pragma: |
5565 | in that case pretty much any characters can be read. | |
a0d0e21e LW |
5566 | |
5567 | =item readdir DIRHANDLE | |
d74e8afc | 5568 | X<readdir> |
a0d0e21e | 5569 | |
c17cdb72 NC |
5570 | =for Pod::Functions get a directory from a directory handle |
5571 | ||
19799a22 | 5572 | Returns the next directory entry for a directory opened by C<opendir>. |
5a964f20 | 5573 | If used in list context, returns all the rest of the entries in the |
3b10bc60 | 5574 | directory. If there are no more entries, returns the undefined value in |
5575 | scalar context and the empty list in list context. | |
a0d0e21e | 5576 | |
19799a22 | 5577 | If you're planning to filetest the return values out of a C<readdir>, you'd |
5f05dabc | 5578 | better prepend the directory in question. Otherwise, because we didn't |
19799a22 | 5579 | C<chdir> there, it would have been testing the wrong file. |
cb1a09d0 | 5580 | |
b0169937 GS |
5581 | opendir(my $dh, $some_dir) || die "can't opendir $some_dir: $!"; |
5582 | @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh); | |
5583 | closedir $dh; | |
cb1a09d0 | 5584 | |
e9fa405d | 5585 | As of Perl 5.12 you can use a bare C<readdir> in a C<while> loop, |
114c60ec BG |
5586 | which will set C<$_> on every iteration. |
5587 | ||
5588 | opendir(my $dh, $some_dir) || die; | |
5589 | while(readdir $dh) { | |
5590 | print "$some_dir/$_\n"; | |
5591 | } | |
5592 | closedir $dh; | |
5593 | ||
bade7fbc TC |
5594 | To avoid confusing would-be users of your code who are running earlier |
5595 | versions of Perl with mysterious failures, put this sort of thing at the | |
5596 | top of your file to signal that your code will work I<only> on Perls of a | |
5597 | recent vintage: | |
5598 | ||
5599 | use 5.012; # so readdir assigns to $_ in a lone while test | |
5600 | ||
84902520 | 5601 | =item readline EXPR |
e4b7ebf3 RGS |
5602 | |
5603 | =item readline | |
d74e8afc | 5604 | X<readline> X<gets> X<fgets> |
84902520 | 5605 | |
c17cdb72 NC |
5606 | =for Pod::Functions fetch a record from a file |
5607 | ||
e4b7ebf3 | 5608 | Reads from the filehandle whose typeglob is contained in EXPR (or from |
8f1da26d | 5609 | C<*ARGV> if EXPR is not provided). In scalar context, each call reads and |
80d38338 | 5610 | returns the next line until end-of-file is reached, whereupon the |
0f03d336 | 5611 | subsequent call returns C<undef>. In list context, reads until end-of-file |
e4b7ebf3 | 5612 | is reached and returns a list of lines. Note that the notion of "line" |
80d38338 | 5613 | used here is whatever you may have defined with C<$/> or |
e4b7ebf3 | 5614 | C<$INPUT_RECORD_SEPARATOR>). See L<perlvar/"$/">. |
fbad3eb5 | 5615 | |
0f03d336 | 5616 | When C<$/> is set to C<undef>, when C<readline> is in scalar |
80d38338 | 5617 | context (i.e., file slurp mode), and when an empty file is read, it |
449bc448 | 5618 | returns C<''> the first time, followed by C<undef> subsequently. |
fbad3eb5 | 5619 | |
61eff3bc JH |
5620 | This is the internal function implementing the C<< <EXPR> >> |
5621 | operator, but you can use it directly. The C<< <EXPR> >> | |
84902520 TB |
5622 | operator is discussed in more detail in L<perlop/"I/O Operators">. |
5623 | ||
5a964f20 | 5624 | $line = <STDIN>; |
5ed4f2ec | 5625 | $line = readline(*STDIN); # same thing |
5a964f20 | 5626 | |
0f03d336 | 5627 | If C<readline> encounters an operating system error, C<$!> will be set |
5628 | with the corresponding error message. It can be helpful to check | |
5629 | C<$!> when you are reading from filehandles you don't trust, such as a | |
5630 | tty or a socket. The following example uses the operator form of | |
5631 | C<readline> and dies if the result is not defined. | |
5632 | ||
5ed4f2ec | 5633 | while ( ! eof($fh) ) { |
5634 | defined( $_ = <$fh> ) or die "readline failed: $!"; | |
5635 | ... | |
5636 | } | |
0f03d336 | 5637 | |
5638 | Note that you have can't handle C<readline> errors that way with the | |
391b733c | 5639 | C<ARGV> filehandle. In that case, you have to open each element of |
0f03d336 | 5640 | C<@ARGV> yourself since C<eof> handles C<ARGV> differently. |
5641 | ||
5642 | foreach my $arg (@ARGV) { | |
5643 | open(my $fh, $arg) or warn "Can't open $arg: $!"; | |
5644 | ||
5645 | while ( ! eof($fh) ) { | |
5646 | defined( $_ = <$fh> ) | |
5647 | or die "readline failed for $arg: $!"; | |
5648 | ... | |
00cb5da1 | 5649 | } |
00cb5da1 | 5650 | } |
e00e4ce9 | 5651 | |
a0d0e21e | 5652 | =item readlink EXPR |
d74e8afc | 5653 | X<readlink> |
a0d0e21e | 5654 | |
54310121 | 5655 | =item readlink |
bbce6d69 | 5656 | |
c17cdb72 NC |
5657 | =for Pod::Functions determine where a symbolic link is pointing |
5658 | ||
a0d0e21e | 5659 | Returns the value of a symbolic link, if symbolic links are |
3b10bc60 | 5660 | implemented. If not, raises an exception. If there is a system |
184e9718 | 5661 | error, returns the undefined value and sets C<$!> (errno). If EXPR is |
7660c0ab | 5662 | omitted, uses C<$_>. |
a0d0e21e | 5663 | |
ea9eb35a BJ |
5664 | Portability issues: L<perlport/readlink>. |
5665 | ||
84902520 | 5666 | =item readpipe EXPR |
8d7403e6 RGS |
5667 | |
5668 | =item readpipe | |
d74e8afc | 5669 | X<readpipe> |
84902520 | 5670 | |
c17cdb72 NC |
5671 | =for Pod::Functions execute a system command and collect standard output |
5672 | ||
5a964f20 | 5673 | EXPR is executed as a system command. |
84902520 TB |
5674 | The collected standard output of the command is returned. |
5675 | In scalar context, it comes back as a single (potentially | |
5676 | multi-line) string. In list context, returns a list of lines | |
7660c0ab | 5677 | (however you've defined lines with C<$/> or C<$INPUT_RECORD_SEPARATOR>). |
84902520 TB |
5678 | This is the internal function implementing the C<qx/EXPR/> |
5679 | operator, but you can use it directly. The C<qx/EXPR/> | |
5680 | operator is discussed in more detail in L<perlop/"I/O Operators">. | |
8d7403e6 | 5681 | If EXPR is omitted, uses C<$_>. |
84902520 | 5682 | |
399388f4 | 5683 | =item recv SOCKET,SCALAR,LENGTH,FLAGS |
d74e8afc | 5684 | X<recv> |
a0d0e21e | 5685 | |
c17cdb72 NC |
5686 | =for Pod::Functions receive a message over a Socket |
5687 | ||
9124316e JH |
5688 | Receives a message on a socket. Attempts to receive LENGTH characters |
5689 | of data into variable SCALAR from the specified SOCKET filehandle. | |
5690 | SCALAR will be grown or shrunk to the length actually read. Takes the | |
5691 | same flags as the system call of the same name. Returns the address | |
5692 | of the sender if SOCKET's protocol supports this; returns an empty | |
5693 | string otherwise. If there's an error, returns the undefined value. | |
5694 | This call is actually implemented in terms of recvfrom(2) system call. | |
5695 | See L<perlipc/"UDP: Message Passing"> for examples. | |
5696 | ||
5697 | Note the I<characters>: depending on the status of the socket, either | |
5698 | (8-bit) bytes or characters are received. By default all sockets | |
5699 | operate on bytes, but for example if the socket has been changed using | |
740d4bb2 | 5700 | binmode() to operate with the C<:encoding(utf8)> I/O layer (see the |
8f1da26d | 5701 | C<open> pragma, L<open>), the I/O will operate on UTF8-encoded Unicode |
740d4bb2 JW |
5702 | characters, not bytes. Similarly for the C<:encoding> pragma: in that |
5703 | case pretty much any characters can be read. | |
a0d0e21e LW |
5704 | |
5705 | =item redo LABEL | |
d74e8afc | 5706 | X<redo> |
a0d0e21e | 5707 | |
8a7e748e FC |
5708 | =item redo EXPR |
5709 | ||
a0d0e21e LW |
5710 | =item redo |
5711 | ||
c17cdb72 NC |
5712 | =for Pod::Functions start this loop iteration over again |
5713 | ||
a0d0e21e | 5714 | The C<redo> command restarts the loop block without evaluating the |
98293880 | 5715 | conditional again. The C<continue> block, if any, is not executed. If |
a0d0e21e | 5716 | the LABEL is omitted, the command refers to the innermost enclosing |
8a7e748e FC |
5717 | loop. The C<redo EXPR> form, available starting in Perl 5.18.0, allows a |
5718 | label name to be computed at run time, and is otherwise identical to C<redo | |
5719 | LABEL>. Programs that want to lie to themselves about what was just input | |
cf264981 | 5720 | normally use this command: |
a0d0e21e LW |
5721 | |
5722 | # a simpleminded Pascal comment stripper | |
5723 | # (warning: assumes no { or } in strings) | |
4633a7c4 | 5724 | LINE: while (<STDIN>) { |
a9a5a0dc VP |
5725 | while (s|({.*}.*){.*}|$1 |) {} |
5726 | s|{.*}| |; | |
5727 | if (s|{.*| |) { | |
5728 | $front = $_; | |
5729 | while (<STDIN>) { | |
5730 | if (/}/) { # end of comment? | |
5731 | s|^|$front\{|; | |
5732 | redo LINE; | |
5733 | } | |
5734 | } | |
5ed4f2ec | 5735 | } |
a9a5a0dc | 5736 | print; |
a0d0e21e LW |
5737 | } |
5738 | ||
80d38338 | 5739 | C<redo> cannot be used to retry a block that returns a value such as |
8f1da26d | 5740 | C<eval {}>, C<sub {}>, or C<do {}>, and should not be used to exit |
2b5ab1e7 | 5741 | a grep() or map() operation. |
4968c1e4 | 5742 | |
6c1372ed GS |
5743 | Note that a block by itself is semantically identical to a loop |
5744 | that executes once. Thus C<redo> inside such a block will effectively | |
5745 | turn it into a looping construct. | |
5746 | ||
98293880 | 5747 | See also L</continue> for an illustration of how C<last>, C<next>, and |
1d2dff63 GS |
5748 | C<redo> work. |
5749 | ||
2ba1f20a FC |
5750 | Unlike most named operators, this has the same precedence as assignment. |
5751 | It is also exempt from the looks-like-a-function rule, so | |
5752 | C<redo ("foo")."bar"> will cause "bar" to be part of the argument to | |
5753 | C<redo>. | |
5754 | ||
a0d0e21e | 5755 | =item ref EXPR |
d74e8afc | 5756 | X<ref> X<reference> |
a0d0e21e | 5757 | |
54310121 | 5758 | =item ref |
bbce6d69 | 5759 | |
c17cdb72 NC |
5760 | =for Pod::Functions find out the type of thing being referenced |
5761 | ||
8a2e0804 | 5762 | Returns a non-empty string if EXPR is a reference, the empty |
0373590a BB |
5763 | string otherwise. If EXPR is not specified, C<$_> will be used. The |
5764 | value returned depends on the type of thing the reference is a reference to. | |
5765 | ||
a0d0e21e LW |
5766 | Builtin types include: |
5767 | ||
a0d0e21e LW |
5768 | SCALAR |
5769 | ARRAY | |
5770 | HASH | |
5771 | CODE | |
19799a22 | 5772 | REF |
a0d0e21e | 5773 | GLOB |
19799a22 | 5774 | LVALUE |
cc10766d RGS |
5775 | FORMAT |
5776 | IO | |
5777 | VSTRING | |
5778 | Regexp | |
a0d0e21e | 5779 | |
0373590a | 5780 | You can think of C<ref> as a C<typeof> operator. |
a0d0e21e LW |
5781 | |
5782 | if (ref($r) eq "HASH") { | |
a9a5a0dc | 5783 | print "r is a reference to a hash.\n"; |
54310121 | 5784 | } |
2b5ab1e7 | 5785 | unless (ref($r)) { |
a9a5a0dc | 5786 | print "r is not a reference at all.\n"; |
54310121 | 5787 | } |
a0d0e21e | 5788 | |
85dd5c8b | 5789 | The return value C<LVALUE> indicates a reference to an lvalue that is not |
391b733c FC |
5790 | a variable. You get this from taking the reference of function calls like |
5791 | C<pos()> or C<substr()>. C<VSTRING> is returned if the reference points | |
603c58be | 5792 | to a L<version string|perldata/"Version Strings">. |
85dd5c8b WL |
5793 | |
5794 | The result C<Regexp> indicates that the argument is a regular expression | |
5795 | resulting from C<qr//>. | |
5796 | ||
0373590a BB |
5797 | If the referenced object has been blessed into a package, then that package |
5798 | name is returned instead. But don't use that, as it's now considered | |
5799 | "bad practice". For one reason, an object could be using a class called | |
5800 | C<Regexp> or C<IO>, or even C<HASH>. Also, C<ref> doesn't take into account | |
5801 | subclasses, like C<isa> does. | |
5802 | ||
24968583 TC |
5803 | Instead, use C<blessed> (in the L<Scalar::Util> module) for boolean |
5804 | checks, C<isa> for specific class checks and C<reftype> (also from | |
5805 | L<Scalar::Util>) for type checks. (See L<perlobj> for details and a | |
0373590a BB |
5806 | C<blessed/isa> example.) |
5807 | ||
a0d0e21e LW |
5808 | See also L<perlref>. |
5809 | ||
5810 | =item rename OLDNAME,NEWNAME | |
d74e8afc | 5811 | X<rename> X<move> X<mv> X<ren> |
a0d0e21e | 5812 | |
c17cdb72 NC |
5813 | =for Pod::Functions change a filename |
5814 | ||
19799a22 GS |
5815 | Changes the name of a file; an existing file NEWNAME will be |
5816 | clobbered. Returns true for success, false otherwise. | |
5817 | ||
2b5ab1e7 TC |
5818 | Behavior of this function varies wildly depending on your system |
5819 | implementation. For example, it will usually not work across file system | |
5820 | boundaries, even though the system I<mv> command sometimes compensates | |
5821 | for this. Other restrictions include whether it works on directories, | |
5822 | open files, or pre-existing files. Check L<perlport> and either the | |
5823 | rename(2) manpage or equivalent system documentation for details. | |
a0d0e21e | 5824 | |
dd184578 RGS |
5825 | For a platform independent C<move> function look at the L<File::Copy> |
5826 | module. | |
5827 | ||
ea9eb35a BJ |
5828 | Portability issues: L<perlport/rename>. |
5829 | ||
16070b82 | 5830 | =item require VERSION |
d74e8afc | 5831 | X<require> |
16070b82 | 5832 | |
a0d0e21e LW |
5833 | =item require EXPR |
5834 | ||
5835 | =item require | |
5836 | ||
c17cdb72 NC |
5837 | =for Pod::Functions load in external functions from a library at runtime |
5838 | ||
3b825e41 RK |
5839 | Demands a version of Perl specified by VERSION, or demands some semantics |
5840 | specified by EXPR or by C<$_> if EXPR is not supplied. | |
44dcb63b | 5841 | |
3b825e41 RK |
5842 | VERSION may be either a numeric argument such as 5.006, which will be |
5843 | compared to C<$]>, or a literal of the form v5.6.1, which will be compared | |
3b10bc60 | 5844 | to C<$^V> (aka $PERL_VERSION). An exception is raised if |
3b825e41 RK |
5845 | VERSION is greater than the version of the current Perl interpreter. |
5846 | Compare with L</use>, which can do a similar check at compile time. | |
5847 | ||
5848 | Specifying VERSION as a literal of the form v5.6.1 should generally be | |
5849 | avoided, because it leads to misleading error messages under earlier | |
cf264981 | 5850 | versions of Perl that do not support this syntax. The equivalent numeric |
3b825e41 | 5851 | version should be used instead. |
44dcb63b | 5852 | |
5ed4f2ec | 5853 | require v5.6.1; # run time version check |
5854 | require 5.6.1; # ditto | |
f7051f2c FC |
5855 | require 5.006_001; # ditto; preferred for backwards |
5856 | compatibility | |
a0d0e21e | 5857 | |
362eead3 RGS |
5858 | Otherwise, C<require> demands that a library file be included if it |
5859 | hasn't already been included. The file is included via the do-FILE | |
73c71df6 CW |
5860 | mechanism, which is essentially just a variety of C<eval> with the |
5861 | caveat that lexical variables in the invoking script will be invisible | |
bf8b9e96 DG |
5862 | to the included code. If it were implemented in pure Perl, it |
5863 | would have semantics similar to the following: | |
5864 | ||
5865 | use Carp 'croak'; | |
5866 | use version; | |
a0d0e21e LW |
5867 | |
5868 | sub require { | |
3b927101 DM |
5869 | my ($filename) = @_; |
5870 | if ( my $version = eval { version->parse($filename) } ) { | |
5871 | if ( $version > $^V ) { | |
e29828a5 FC |
5872 | my $vn = $version->normal; |
5873 | croak "Perl $vn required--this is only $^V, stopped"; | |
3b927101 DM |
5874 | } |
5875 | return 1; | |
5876 | } | |
5877 | ||
5878 | if (exists $INC{$filename}) { | |
5879 | return 1 if $INC{$filename}; | |
5880 | croak "Compilation failed in require"; | |
5881 | } | |
5882 | ||
5883 | foreach $prefix (@INC) { | |
5884 | if (ref($prefix)) { | |
5885 | #... do other stuff - see text below .... | |
5886 | } | |
5887 | # (see text below about possible appending of .pmc | |
5888 | # suffix to $filename) | |
5889 | my $realfilename = "$prefix/$filename"; | |
5890 | next if ! -e $realfilename || -d _ || -b _; | |
5891 | $INC{$filename} = $realfilename; | |
e29828a5 FC |
5892 | my $result = do($realfilename); |
5893 | # but run in caller's namespace | |
3b927101 DM |
5894 | |
5895 | if (!defined $result) { | |
5896 | $INC{$filename} = undef; | |
5897 | croak $@ ? "$@Compilation failed in require" | |
5898 | : "Can't locate $filename: $!\n"; | |
5899 | } | |
5900 | if (!$result) { | |
5901 | delete $INC{$filename}; | |
5902 | croak "$filename did not return true value"; | |
5903 | } | |
5904 | $! = 0; | |
5905 | return $result; | |
5906 | } | |
5907 | croak "Can't locate $filename in \@INC ..."; | |
a0d0e21e LW |
5908 | } |
5909 | ||
5910 | Note that the file will not be included twice under the same specified | |
a12755f0 SB |
5911 | name. |
5912 | ||
5913 | The file must return true as the last statement to indicate | |
a0d0e21e | 5914 | successful execution of any initialization code, so it's customary to |
19799a22 GS |
5915 | end such a file with C<1;> unless you're sure it'll return true |
5916 | otherwise. But it's better just to put the C<1;>, in case you add more | |
a0d0e21e LW |
5917 | statements. |
5918 | ||
54310121 | 5919 | If EXPR is a bareword, the require assumes a "F<.pm>" extension and |
da0045b7 | 5920 | replaces "F<::>" with "F</>" in the filename for you, |
54310121 | 5921 | to make it easy to load standard modules. This form of loading of |
a0d0e21e LW |
5922 | modules does not risk altering your namespace. |
5923 | ||
ee580363 GS |
5924 | In other words, if you try this: |
5925 | ||
5ed4f2ec | 5926 | require Foo::Bar; # a splendid bareword |
ee580363 | 5927 | |
b76cc8ba | 5928 | The require function will actually look for the "F<Foo/Bar.pm>" file in the |
7660c0ab | 5929 | directories specified in the C<@INC> array. |
ee580363 | 5930 | |
5a964f20 | 5931 | But if you try this: |
ee580363 GS |
5932 | |
5933 | $class = 'Foo::Bar'; | |
5ed4f2ec | 5934 | require $class; # $class is not a bareword |
5a964f20 | 5935 | #or |
5ed4f2ec | 5936 | require "Foo::Bar"; # not a bareword because of the "" |
ee580363 | 5937 | |
b76cc8ba | 5938 | The require function will look for the "F<Foo::Bar>" file in the @INC array and |
19799a22 | 5939 | will complain about not finding "F<Foo::Bar>" there. In this case you can do: |
ee580363 GS |
5940 | |
5941 | eval "require $class"; | |
5942 | ||
3b10bc60 | 5943 | Now that you understand how C<require> looks for files with a |
a91233bf RGS |
5944 | bareword argument, there is a little extra functionality going on behind |
5945 | the scenes. Before C<require> looks for a "F<.pm>" extension, it will | |
391b733c | 5946 | first look for a similar filename with a "F<.pmc>" extension. If this file |
a91233bf RGS |
5947 | is found, it will be loaded in place of any file ending in a "F<.pm>" |
5948 | extension. | |
662cc546 | 5949 | |
8f1da26d | 5950 | You can also insert hooks into the import facility by putting Perl code |
1c3d5054 | 5951 | directly into the @INC array. There are three forms of hooks: subroutine |
8f1da26d | 5952 | references, array references, and blessed objects. |
d54b56d5 RGS |
5953 | |
5954 | Subroutine references are the simplest case. When the inclusion system | |
5955 | walks through @INC and encounters a subroutine, this subroutine gets | |
3b10bc60 | 5956 | called with two parameters, the first a reference to itself, and the |
5957 | second the name of the file to be included (e.g., "F<Foo/Bar.pm>"). The | |
5e5128ba | 5958 | subroutine should return either nothing or else a list of up to four |
3b10bc60 | 5959 | values in the following order: |
1f0bdf18 NC |
5960 | |
5961 | =over | |
5962 | ||
5963 | =item 1 | |
5964 | ||
5e5128ba FC |
5965 | A reference to a scalar, containing any initial source code to prepend to |
5966 | the file or generator output. | |
1f0bdf18 | 5967 | |
cec0e1a7 | 5968 | =item 2 |
1f0bdf18 | 5969 | |
5e5128ba FC |
5970 | A filehandle, from which the file will be read. |
5971 | ||
5972 | =item 3 | |
5973 | ||
391b733c | 5974 | A reference to a subroutine. If there is no filehandle (previous item), |
60d352b3 | 5975 | then this subroutine is expected to generate one line of source code per |
8f1da26d TC |
5976 | call, writing the line into C<$_> and returning 1, then finally at end of |
5977 | file returning 0. If there is a filehandle, then the subroutine will be | |
b8921b3e | 5978 | called to act as a simple source filter, with the line as read in C<$_>. |
60d352b3 RGS |
5979 | Again, return 1 for each valid line, and 0 after all lines have been |
5980 | returned. | |
1f0bdf18 | 5981 | |
5e5128ba | 5982 | =item 4 |
1f0bdf18 | 5983 | |
391b733c | 5984 | Optional state for the subroutine. The state is passed in as C<$_[1]>. A |
1f0bdf18 NC |
5985 | reference to the subroutine itself is passed in as C<$_[0]>. |
5986 | ||
5987 | =back | |
5988 | ||
5989 | If an empty list, C<undef>, or nothing that matches the first 3 values above | |
3b10bc60 | 5990 | is returned, then C<require> looks at the remaining elements of @INC. |
5991 | Note that this filehandle must be a real filehandle (strictly a typeglob | |
8f1da26d TC |
5992 | or reference to a typeglob, whether blessed or unblessed); tied filehandles |
5993 | will be ignored and processing will stop there. | |
d54b56d5 RGS |
5994 | |
5995 | If the hook is an array reference, its first element must be a subroutine | |
5996 | reference. This subroutine is called as above, but the first parameter is | |
3b10bc60 | 5997 | the array reference. This lets you indirectly pass arguments to |
d54b56d5 RGS |
5998 | the subroutine. |
5999 | ||
6000 | In other words, you can write: | |
6001 | ||
6002 | push @INC, \&my_sub; | |
6003 | sub my_sub { | |
a9a5a0dc VP |
6004 | my ($coderef, $filename) = @_; # $coderef is \&my_sub |
6005 | ... | |
d54b56d5 RGS |
6006 | } |
6007 | ||
6008 | or: | |
6009 | ||
6010 | push @INC, [ \&my_sub, $x, $y, ... ]; | |
6011 | sub my_sub { | |
a9a5a0dc VP |
6012 | my ($arrayref, $filename) = @_; |
6013 | # Retrieve $x, $y, ... | |
6014 | my @parameters = @$arrayref[1..$#$arrayref]; | |
6015 | ... | |
d54b56d5 RGS |
6016 | } |
6017 | ||
cf264981 | 6018 | If the hook is an object, it must provide an INC method that will be |
d54b56d5 | 6019 | called as above, the first parameter being the object itself. (Note that |
92c6daad NC |
6020 | you must fully qualify the sub's name, as unqualified C<INC> is always forced |
6021 | into package C<main>.) Here is a typical code layout: | |
d54b56d5 RGS |
6022 | |
6023 | # In Foo.pm | |
6024 | package Foo; | |
6025 | sub new { ... } | |
6026 | sub Foo::INC { | |
a9a5a0dc VP |
6027 | my ($self, $filename) = @_; |
6028 | ... | |
d54b56d5 RGS |
6029 | } |
6030 | ||
6031 | # In the main program | |
797f796a | 6032 | push @INC, Foo->new(...); |
d54b56d5 | 6033 | |
3b10bc60 | 6034 | These hooks are also permitted to set the %INC entry |
391b733c | 6035 | corresponding to the files they have loaded. See L<perlvar/%INC>. |
9ae8cd5b | 6036 | |
ee580363 | 6037 | For a yet-more-powerful import facility, see L</use> and L<perlmod>. |
a0d0e21e LW |
6038 | |
6039 | =item reset EXPR | |
d74e8afc | 6040 | X<reset> |
a0d0e21e LW |
6041 | |
6042 | =item reset | |
6043 | ||
c17cdb72 NC |
6044 | =for Pod::Functions clear all variables of a given name |
6045 | ||
a0d0e21e | 6046 | Generally used in a C<continue> block at the end of a loop to clear |
7660c0ab | 6047 | variables and reset C<??> searches so that they work again. The |
a0d0e21e LW |
6048 | expression is interpreted as a list of single characters (hyphens |
6049 | allowed for ranges). All variables and arrays beginning with one of | |
6050 | those letters are reset to their pristine state. If the expression is | |
3b10bc60 | 6051 | omitted, one-match searches (C<?pattern?>) are reset to match again. |
6052 | Only resets variables or searches in the current package. Always returns | |
6053 | 1. Examples: | |
a0d0e21e | 6054 | |
5ed4f2ec | 6055 | reset 'X'; # reset all X variables |
6056 | reset 'a-z'; # reset lower case variables | |
6057 | reset; # just reset ?one-time? searches | |
a0d0e21e | 6058 | |
7660c0ab | 6059 | Resetting C<"A-Z"> is not recommended because you'll wipe out your |
2b5ab1e7 | 6060 | C<@ARGV> and C<@INC> arrays and your C<%ENV> hash. Resets only package |
3b10bc60 | 6061 | variables; lexical variables are unaffected, but they clean themselves |
2b5ab1e7 TC |
6062 | up on scope exit anyway, so you'll probably want to use them instead. |
6063 | See L</my>. | |
a0d0e21e | 6064 | |
54310121 | 6065 | =item return EXPR |
d74e8afc | 6066 | X<return> |
54310121 | 6067 | |
6068 | =item return | |
6069 | ||
c17cdb72 NC |
6070 | =for Pod::Functions get out of a function early |
6071 | ||
b76cc8ba | 6072 | Returns from a subroutine, C<eval>, or C<do FILE> with the value |
5a964f20 | 6073 | given in EXPR. Evaluation of EXPR may be in list, scalar, or void |
54310121 | 6074 | context, depending on how the return value will be used, and the context |
01aa884e | 6075 | may vary from one execution to the next (see L</wantarray>). If no EXPR |
2b5ab1e7 | 6076 | is given, returns an empty list in list context, the undefined value in |
3b10bc60 | 6077 | scalar context, and (of course) nothing at all in void context. |
a0d0e21e | 6078 | |
3b10bc60 | 6079 | (In the absence of an explicit C<return>, a subroutine, eval, |
6080 | or do FILE automatically returns the value of the last expression | |
2b5ab1e7 | 6081 | evaluated.) |
a0d0e21e | 6082 | |
85897674 EB |
6083 | Unlike most named operators, this is also exempt from the |
6084 | looks-like-a-function rule, so C<return ("foo")."bar"> will | |
6085 | cause "bar" to be part of the argument to C<return>. | |
6086 | ||
a0d0e21e | 6087 | =item reverse LIST |
d74e8afc | 6088 | X<reverse> X<rev> X<invert> |
a0d0e21e | 6089 | |
c17cdb72 NC |
6090 | =for Pod::Functions flip a string or a list |
6091 | ||
5a964f20 TC |
6092 | In list context, returns a list value consisting of the elements |
6093 | of LIST in the opposite order. In scalar context, concatenates the | |
2b5ab1e7 | 6094 | elements of LIST and returns a string value with all characters |
a0ed51b3 | 6095 | in the opposite order. |
4633a7c4 | 6096 | |
9649ed94 | 6097 | print join(", ", reverse "world", "Hello"); # Hello, world |
4633a7c4 | 6098 | |
9649ed94 | 6099 | print scalar reverse "dlrow ,", "olleH"; # Hello, world |
2f9daede | 6100 | |
2d713cbd RGS |
6101 | Used without arguments in scalar context, reverse() reverses C<$_>. |
6102 | ||
9649ed94 | 6103 | $_ = "dlrow ,olleH"; |
f7051f2c FC |
6104 | print reverse; # No output, list context |
6105 | print scalar reverse; # Hello, world | |
9649ed94 | 6106 | |
437d4214 | 6107 | Note that reversing an array to itself (as in C<@a = reverse @a>) will |
e1f15c13 FC |
6108 | preserve non-existent elements whenever possible; i.e., for non-magical |
6109 | arrays or for tied arrays with C<EXISTS> and C<DELETE> methods. | |
437d4214 | 6110 | |
2f9daede TP |
6111 | This operator is also handy for inverting a hash, although there are some |
6112 | caveats. If a value is duplicated in the original hash, only one of those | |
6113 | can be represented as a key in the inverted hash. Also, this has to | |
6114 | unwind one hash and build a whole new one, which may take some time | |
2b5ab1e7 | 6115 | on a large hash, such as from a DBM file. |
2f9daede | 6116 | |
5ed4f2ec | 6117 | %by_name = reverse %by_address; # Invert the hash |
a0d0e21e LW |
6118 | |
6119 | =item rewinddir DIRHANDLE | |
d74e8afc | 6120 | X<rewinddir> |
a0d0e21e | 6121 | |
c17cdb72 NC |
6122 | =for Pod::Functions reset directory handle |
6123 | ||
a0d0e21e | 6124 | Sets the current position to the beginning of the directory for the |
19799a22 | 6125 | C<readdir> routine on DIRHANDLE. |
a0d0e21e | 6126 | |
ea9eb35a BJ |
6127 | Portability issues: L<perlport/rewinddir>. |
6128 | ||
a0d0e21e | 6129 | =item rindex STR,SUBSTR,POSITION |
d74e8afc | 6130 | X<rindex> |
a0d0e21e LW |
6131 | |
6132 | =item rindex STR,SUBSTR | |
6133 | ||
c17cdb72 NC |
6134 | =for Pod::Functions right-to-left substring search |
6135 | ||
ff551661 | 6136 | Works just like index() except that it returns the position of the I<last> |
a0d0e21e | 6137 | occurrence of SUBSTR in STR. If POSITION is specified, returns the |
ff551661 | 6138 | last occurrence beginning at or before that position. |
a0d0e21e LW |
6139 | |
6140 | =item rmdir FILENAME | |
d74e8afc | 6141 | X<rmdir> X<rd> X<directory, remove> |
a0d0e21e | 6142 | |
54310121 | 6143 | =item rmdir |
bbce6d69 | 6144 | |
c17cdb72 NC |
6145 | =for Pod::Functions remove a directory |
6146 | ||
974da8e5 | 6147 | Deletes the directory specified by FILENAME if that directory is |
8f1da26d | 6148 | empty. If it succeeds it returns true; otherwise it returns false and |
974da8e5 | 6149 | sets C<$!> (errno). If FILENAME is omitted, uses C<$_>. |
a0d0e21e | 6150 | |
e1020413 | 6151 | To remove a directory tree recursively (C<rm -rf> on Unix) look at |
dd184578 RGS |
6152 | the C<rmtree> function of the L<File::Path> module. |
6153 | ||
a0d0e21e LW |
6154 | =item s/// |
6155 | ||
c17cdb72 NC |
6156 | =for Pod::Functions replace a pattern with a string |
6157 | ||
9f4b9cd0 | 6158 | The substitution operator. See L<perlop/"Regexp Quote-Like Operators">. |
a0d0e21e | 6159 | |
0d863452 RH |
6160 | =item say FILEHANDLE LIST |
6161 | X<say> | |
6162 | ||
dee33c94 TC |
6163 | =item say FILEHANDLE |
6164 | ||
0d863452 RH |
6165 | =item say LIST |
6166 | ||
6167 | =item say | |
6168 | ||
d9b04284 | 6169 | =for Pod::Functions +say output a list to a filehandle, appending a newline |
c17cdb72 | 6170 | |
dee33c94 TC |
6171 | Just like C<print>, but implicitly appends a newline. C<say LIST> is |
6172 | simply an abbreviation for C<{ local $\ = "\n"; print LIST }>. To use | |
6173 | FILEHANDLE without a LIST to print the contents of C<$_> to it, you must | |
6174 | use a real filehandle like C<FH>, not an indirect one like C<$fh>. | |
f406c1e8 | 6175 | |
4a904372 FC |
6176 | This keyword is available only when the C<"say"> feature |
6177 | is enabled, or when prefixed with C<CORE::>; see | |
8f1da26d TC |
6178 | L<feature>. Alternately, include a C<use v5.10> or later to the current |
6179 | scope. | |
0d863452 | 6180 | |
a0d0e21e | 6181 | =item scalar EXPR |
d74e8afc | 6182 | X<scalar> X<context> |
a0d0e21e | 6183 | |
c17cdb72 NC |
6184 | =for Pod::Functions force a scalar context |
6185 | ||
5a964f20 | 6186 | Forces EXPR to be interpreted in scalar context and returns the value |
54310121 | 6187 | of EXPR. |
cb1a09d0 AD |
6188 | |
6189 | @counts = ( scalar @a, scalar @b, scalar @c ); | |
6190 | ||
54310121 | 6191 | There is no equivalent operator to force an expression to |
2b5ab1e7 | 6192 | be interpolated in list context because in practice, this is never |
cb1a09d0 AD |
6193 | needed. If you really wanted to do so, however, you could use |
6194 | the construction C<@{[ (some expression) ]}>, but usually a simple | |
6195 | C<(some expression)> suffices. | |
a0d0e21e | 6196 | |
8f1da26d TC |
6197 | Because C<scalar> is a unary operator, if you accidentally use a |
6198 | parenthesized list for the EXPR, this behaves as a scalar comma expression, | |
6199 | evaluating all but the last element in void context and returning the final | |
6200 | element evaluated in scalar context. This is seldom what you want. | |
62c18ce2 GS |
6201 | |
6202 | The following single statement: | |
6203 | ||
5ed4f2ec | 6204 | print uc(scalar(&foo,$bar)),$baz; |
62c18ce2 GS |
6205 | |
6206 | is the moral equivalent of these two: | |
6207 | ||
5ed4f2ec | 6208 | &foo; |
6209 | print(uc($bar),$baz); | |
62c18ce2 GS |
6210 | |
6211 | See L<perlop> for more details on unary operators and the comma operator. | |
6212 | ||
a0d0e21e | 6213 | =item seek FILEHANDLE,POSITION,WHENCE |
d74e8afc | 6214 | X<seek> X<fseek> X<filehandle, position> |
a0d0e21e | 6215 | |
c17cdb72 NC |
6216 | =for Pod::Functions reposition file pointer for random-access I/O |
6217 | ||
19799a22 | 6218 | Sets FILEHANDLE's position, just like the C<fseek> call of C<stdio>. |
8903cb82 | 6219 | FILEHANDLE may be an expression whose value gives the name of the |
9124316e | 6220 | filehandle. The values for WHENCE are C<0> to set the new position |
8f1da26d TC |
6221 | I<in bytes> to POSITION; C<1> to set it to the current position plus |
6222 | POSITION; and C<2> to set it to EOF plus POSITION, typically | |
6223 | negative. For WHENCE you may use the constants C<SEEK_SET>, | |
9124316e | 6224 | C<SEEK_CUR>, and C<SEEK_END> (start of the file, current position, end |
8f1da26d | 6225 | of the file) from the L<Fcntl> module. Returns C<1> on success, false |
9124316e JH |
6226 | otherwise. |
6227 | ||
6228 | Note the I<in bytes>: even if the filehandle has been set to | |
740d4bb2 | 6229 | operate on characters (for example by using the C<:encoding(utf8)> open |
fae2c0fb | 6230 | layer), tell() will return byte offsets, not character offsets |
9124316e | 6231 | (because implementing that would render seek() and tell() rather slow). |
8903cb82 | 6232 | |
3b10bc60 | 6233 | If you want to position the file for C<sysread> or C<syswrite>, don't use |
6234 | C<seek>, because buffering makes its effect on the file's read-write position | |
19799a22 | 6235 | unpredictable and non-portable. Use C<sysseek> instead. |
a0d0e21e | 6236 | |
2b5ab1e7 TC |
6237 | Due to the rules and rigors of ANSI C, on some systems you have to do a |
6238 | seek whenever you switch between reading and writing. Amongst other | |
6239 | things, this may have the effect of calling stdio's clearerr(3). | |
6240 | A WHENCE of C<1> (C<SEEK_CUR>) is useful for not moving the file position: | |
cb1a09d0 AD |
6241 | |
6242 | seek(TEST,0,1); | |
6243 | ||
6244 | This is also useful for applications emulating C<tail -f>. Once you hit | |
3b10bc60 | 6245 | EOF on your read and then sleep for a while, you (probably) have to stick in a |
6246 | dummy seek() to reset things. The C<seek> doesn't change the position, | |
8903cb82 | 6247 | but it I<does> clear the end-of-file condition on the handle, so that the |
3b10bc60 | 6248 | next C<< <FILE> >> makes Perl try again to read something. (We hope.) |
cb1a09d0 | 6249 | |
3b10bc60 | 6250 | If that doesn't work (some I/O implementations are particularly |
6251 | cantankerous), you might need something like this: | |
cb1a09d0 AD |
6252 | |
6253 | for (;;) { | |
a9a5a0dc | 6254 | for ($curpos = tell(FILE); $_ = <FILE>; |
f86cebdf | 6255 | $curpos = tell(FILE)) { |
a9a5a0dc VP |
6256 | # search for some stuff and put it into files |
6257 | } | |
6258 | sleep($for_a_while); | |
6259 | seek(FILE, $curpos, 0); | |
cb1a09d0 AD |
6260 | } |
6261 | ||
a0d0e21e | 6262 | =item seekdir DIRHANDLE,POS |
d74e8afc | 6263 | X<seekdir> |
a0d0e21e | 6264 | |
c17cdb72 NC |
6265 | =for Pod::Functions reposition directory pointer |
6266 | ||
19799a22 | 6267 | Sets the current position for the C<readdir> routine on DIRHANDLE. POS |
cf264981 SP |
6268 | must be a value returned by C<telldir>. C<seekdir> also has the same caveats |
6269 | about possible directory compaction as the corresponding system library | |
a0d0e21e LW |
6270 | routine. |
6271 | ||
6272 | =item select FILEHANDLE | |
d74e8afc | 6273 | X<select> X<filehandle, default> |
a0d0e21e LW |
6274 | |
6275 | =item select | |
6276 | ||
c17cdb72 NC |
6277 | =for Pod::Functions reset default output or do I/O multiplexing |
6278 | ||
b5dffda6 RGS |
6279 | Returns the currently selected filehandle. If FILEHANDLE is supplied, |
6280 | sets the new current default filehandle for output. This has two | |
8f1da26d | 6281 | effects: first, a C<write> or a C<print> without a filehandle |
a0d0e21e | 6282 | default to this FILEHANDLE. Second, references to variables related to |
8f1da26d TC |
6283 | output will refer to this output channel. |
6284 | ||
6285 | For example, to set the top-of-form format for more than one | |
6286 | output channel, you might do the following: | |
a0d0e21e LW |
6287 | |
6288 | select(REPORT1); | |
6289 | $^ = 'report1_top'; | |
6290 | select(REPORT2); | |
6291 | $^ = 'report2_top'; | |
6292 | ||
6293 | FILEHANDLE may be an expression whose value gives the name of the | |
6294 | actual filehandle. Thus: | |
6295 | ||
6296 | $oldfh = select(STDERR); $| = 1; select($oldfh); | |
6297 | ||
4633a7c4 LW |
6298 | Some programmers may prefer to think of filehandles as objects with |
6299 | methods, preferring to write the last example as: | |
a0d0e21e | 6300 | |
28757baa | 6301 | use IO::Handle; |
a0d0e21e LW |
6302 | STDERR->autoflush(1); |
6303 | ||
ea9eb35a BJ |
6304 | Portability issues: L<perlport/select>. |
6305 | ||
a0d0e21e | 6306 | =item select RBITS,WBITS,EBITS,TIMEOUT |
d74e8afc | 6307 | X<select> |
a0d0e21e | 6308 | |
3b10bc60 | 6309 | This calls the select(2) syscall with the bit masks specified, which |
19799a22 | 6310 | can be constructed using C<fileno> and C<vec>, along these lines: |
a0d0e21e LW |
6311 | |
6312 | $rin = $win = $ein = ''; | |
f0815dd4 TC |
6313 | vec($rin, fileno(STDIN), 1) = 1; |
6314 | vec($win, fileno(STDOUT), 1) = 1; | |
a0d0e21e LW |
6315 | $ein = $rin | $win; |
6316 | ||
3b10bc60 | 6317 | If you want to select on many filehandles, you may wish to write a |
6318 | subroutine like this: | |
a0d0e21e LW |
6319 | |
6320 | sub fhbits { | |
f0815dd4 TC |
6321 | my @fhlist = @_; |
6322 | my $bits = ""; | |
6323 | for my $fh (@fhlist) { | |
6324 | vec($bits, fileno($fh), 1) = 1; | |
a9a5a0dc | 6325 | } |
f0815dd4 | 6326 | return $bits; |
a0d0e21e | 6327 | } |
f0815dd4 | 6328 | $rin = fhbits(*STDIN, *TTY, *MYSOCK); |
a0d0e21e LW |
6329 | |
6330 | The usual idiom is: | |
6331 | ||
6332 | ($nfound,$timeleft) = | |
6333 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); | |
6334 | ||
54310121 | 6335 | or to block until something becomes ready just do this |
a0d0e21e LW |
6336 | |
6337 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); | |
6338 | ||
19799a22 GS |
6339 | Most systems do not bother to return anything useful in $timeleft, so |
6340 | calling select() in scalar context just returns $nfound. | |
c07a80fd | 6341 | |
5f05dabc | 6342 | Any of the bit masks can also be undef. The timeout, if specified, is |
a0d0e21e | 6343 | in seconds, which may be fractional. Note: not all implementations are |
be119125 | 6344 | capable of returning the $timeleft. If not, they always return |
19799a22 | 6345 | $timeleft equal to the supplied $timeout. |
a0d0e21e | 6346 | |
ff68c719 | 6347 | You can effect a sleep of 250 milliseconds this way: |
a0d0e21e LW |
6348 | |
6349 | select(undef, undef, undef, 0.25); | |
6350 | ||
b09fc1d8 | 6351 | Note that whether C<select> gets restarted after signals (say, SIGALRM) |
8b0ac1d7 MHM |
6352 | is implementation-dependent. See also L<perlport> for notes on the |
6353 | portability of C<select>. | |
40454f26 | 6354 | |
f0815dd4 | 6355 | On error, C<select> behaves just like select(2): it returns |
4189264e | 6356 | -1 and sets C<$!>. |
353e5636 | 6357 | |
8f1da26d TC |
6358 | On some Unixes, select(2) may report a socket file descriptor as "ready for |
6359 | reading" even when no data is available, and thus any subsequent C<read> | |
391b733c FC |
6360 | would block. This can be avoided if you always use O_NONBLOCK on the |
6361 | socket. See select(2) and fcntl(2) for further details. | |
ec8ce15a | 6362 | |
f0815dd4 TC |
6363 | The standard C<IO::Select> module provides a user-friendlier interface |
6364 | to C<select>, mostly because it does all the bit-mask work for you. | |
6365 | ||
19799a22 | 6366 | B<WARNING>: One should not attempt to mix buffered I/O (like C<read> |
61eff3bc | 6367 | or <FH>) with C<select>, except as permitted by POSIX, and even |
19799a22 | 6368 | then only on POSIX systems. You have to use C<sysread> instead. |
a0d0e21e | 6369 | |
ea9eb35a BJ |
6370 | Portability issues: L<perlport/select>. |
6371 | ||
a0d0e21e | 6372 | =item semctl ID,SEMNUM,CMD,ARG |
d74e8afc | 6373 | X<semctl> |
a0d0e21e | 6374 | |
c17cdb72 NC |
6375 | =for Pod::Functions SysV semaphore control operations |
6376 | ||
3b10bc60 | 6377 | Calls the System V IPC function semctl(2). You'll probably have to say |
0ade1984 JH |
6378 | |
6379 | use IPC::SysV; | |
6380 | ||
6381 | first to get the correct constant definitions. If CMD is IPC_STAT or | |
cf264981 | 6382 | GETALL, then ARG must be a variable that will hold the returned |
e4038a1f MS |
6383 | semid_ds structure or semaphore value array. Returns like C<ioctl>: |
6384 | the undefined value for error, "C<0 but true>" for zero, or the actual | |
6385 | return value otherwise. The ARG must consist of a vector of native | |
106325ad | 6386 | short integers, which may be created with C<pack("s!",(0)x$nsem)>. |
4755096e GS |
6387 | See also L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::Semaphore> |
6388 | documentation. | |
a0d0e21e | 6389 | |
ea9eb35a BJ |
6390 | Portability issues: L<perlport/semctl>. |
6391 | ||
a0d0e21e | 6392 | =item semget KEY,NSEMS,FLAGS |
d74e8afc | 6393 | X<semget> |
a0d0e21e | 6394 | |
c17cdb72 NC |
6395 | =for Pod::Functions get set of SysV semaphores |
6396 | ||
3b10bc60 | 6397 | Calls the System V IPC function semget(2). Returns the semaphore id, or |
8f1da26d | 6398 | the undefined value on error. See also |
4755096e GS |
6399 | L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::SysV::Semaphore> |
6400 | documentation. | |
a0d0e21e | 6401 | |
ea9eb35a BJ |
6402 | Portability issues: L<perlport/semget>. |
6403 | ||
a0d0e21e | 6404 | =item semop KEY,OPSTRING |
d74e8afc | 6405 | X<semop> |
a0d0e21e | 6406 | |
c17cdb72 NC |
6407 | =for Pod::Functions SysV semaphore operations |
6408 | ||
80d38338 | 6409 | Calls the System V IPC function semop(2) for semaphore operations |
5354997a | 6410 | such as signalling and waiting. OPSTRING must be a packed array of |
a0d0e21e | 6411 | semop structures. Each semop structure can be generated with |
cf264981 SP |
6412 | C<pack("s!3", $semnum, $semop, $semflag)>. The length of OPSTRING |
6413 | implies the number of semaphore operations. Returns true if | |
8f1da26d | 6414 | successful, false on error. As an example, the |
19799a22 | 6415 | following code waits on semaphore $semnum of semaphore id $semid: |
a0d0e21e | 6416 | |
f878ba33 | 6417 | $semop = pack("s!3", $semnum, -1, 0); |
a0d0e21e LW |
6418 | die "Semaphore trouble: $!\n" unless semop($semid, $semop); |
6419 | ||
4755096e GS |
6420 | To signal the semaphore, replace C<-1> with C<1>. See also |
6421 | L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::SysV::Semaphore> | |
6422 | documentation. | |
a0d0e21e | 6423 | |
ea9eb35a BJ |
6424 | Portability issues: L<perlport/semop>. |
6425 | ||
a0d0e21e | 6426 | =item send SOCKET,MSG,FLAGS,TO |
d74e8afc | 6427 | X<send> |
a0d0e21e LW |
6428 | |
6429 | =item send SOCKET,MSG,FLAGS | |
6430 | ||
c17cdb72 NC |
6431 | =for Pod::Functions send a message over a socket |
6432 | ||
3b10bc60 | 6433 | Sends a message on a socket. Attempts to send the scalar MSG to the SOCKET |
6434 | filehandle. Takes the same flags as the system call of the same name. On | |
6435 | unconnected sockets, you must specify a destination to I<send to>, in which | |
6436 | case it does a sendto(2) syscall. Returns the number of characters sent, | |
6437 | or the undefined value on error. The sendmsg(2) syscall is currently | |
6438 | unimplemented. See L<perlipc/"UDP: Message Passing"> for examples. | |
9124316e JH |
6439 | |
6440 | Note the I<characters>: depending on the status of the socket, either | |
6441 | (8-bit) bytes or characters are sent. By default all sockets operate | |
6442 | on bytes, but for example if the socket has been changed using | |
740d4bb2 JW |
6443 | binmode() to operate with the C<:encoding(utf8)> I/O layer (see |
6444 | L</open>, or the C<open> pragma, L<open>), the I/O will operate on UTF-8 | |
6445 | encoded Unicode characters, not bytes. Similarly for the C<:encoding> | |
6446 | pragma: in that case pretty much any characters can be sent. | |
a0d0e21e LW |
6447 | |
6448 | =item setpgrp PID,PGRP | |
d74e8afc | 6449 | X<setpgrp> X<group> |
a0d0e21e | 6450 | |
c17cdb72 NC |
6451 | =for Pod::Functions set the process group of a process |
6452 | ||
7660c0ab | 6453 | Sets the current process group for the specified PID, C<0> for the current |
3b10bc60 | 6454 | process. Raises an exception when used on a machine that doesn't |
81777298 GS |
6455 | implement POSIX setpgid(2) or BSD setpgrp(2). If the arguments are omitted, |
6456 | it defaults to C<0,0>. Note that the BSD 4.2 version of C<setpgrp> does not | |
6457 | accept any arguments, so only C<setpgrp(0,0)> is portable. See also | |
6458 | C<POSIX::setsid()>. | |
a0d0e21e | 6459 | |
ea9eb35a BJ |
6460 | Portability issues: L<perlport/setpgrp>. |
6461 | ||
a0d0e21e | 6462 | =item setpriority WHICH,WHO,PRIORITY |
d74e8afc | 6463 | X<setpriority> X<priority> X<nice> X<renice> |
a0d0e21e | 6464 | |
c17cdb72 NC |
6465 | =for Pod::Functions set a process's nice value |
6466 | ||
a0d0e21e | 6467 | Sets the current priority for a process, a process group, or a user. |
3b10bc60 | 6468 | (See setpriority(2).) Raises an exception when used on a machine |
f86cebdf | 6469 | that doesn't implement setpriority(2). |
a0d0e21e | 6470 | |
ea9eb35a BJ |
6471 | Portability issues: L<perlport/setpriority>. |
6472 | ||
a0d0e21e | 6473 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL |
d74e8afc | 6474 | X<setsockopt> |
a0d0e21e | 6475 | |
c17cdb72 NC |
6476 | =for Pod::Functions set some socket options |
6477 | ||
8f1da26d TC |
6478 | Sets the socket option requested. Returns C<undef> on error. |
6479 | Use integer constants provided by the C<Socket> module for | |
23d0437f GA |
6480 | LEVEL and OPNAME. Values for LEVEL can also be obtained from |
6481 | getprotobyname. OPTVAL might either be a packed string or an integer. | |
6482 | An integer OPTVAL is shorthand for pack("i", OPTVAL). | |
6483 | ||
3b10bc60 | 6484 | An example disabling Nagle's algorithm on a socket: |
23d0437f GA |
6485 | |
6486 | use Socket qw(IPPROTO_TCP TCP_NODELAY); | |
6487 | setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1); | |
a0d0e21e | 6488 | |
ea9eb35a BJ |
6489 | Portability issues: L<perlport/setsockopt>. |
6490 | ||
532eee96 | 6491 | =item shift ARRAY |
d74e8afc | 6492 | X<shift> |
a0d0e21e | 6493 | |
f5a93a43 TC |
6494 | =item shift EXPR |
6495 | ||
a0d0e21e LW |
6496 | =item shift |
6497 | ||
c17cdb72 NC |
6498 | =for Pod::Functions remove the first element of an array, and return it |
6499 | ||
a0d0e21e LW |
6500 | Shifts the first value of the array off and returns it, shortening the |
6501 | array by 1 and moving everything down. If there are no elements in the | |
6502 | array, returns the undefined value. If ARRAY is omitted, shifts the | |
7660c0ab | 6503 | C<@_> array within the lexical scope of subroutines and formats, and the |
80d38338 | 6504 | C<@ARGV> array outside a subroutine and also within the lexical scopes |
3c10abe3 | 6505 | established by the C<eval STRING>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>, |
8f1da26d | 6506 | C<UNITCHECK {}>, and C<END {}> constructs. |
4f25aa18 | 6507 | |
f5a93a43 TC |
6508 | Starting with Perl 5.14, C<shift> can take a scalar EXPR, which must hold a |
6509 | reference to an unblessed array. The argument will be dereferenced | |
6510 | automatically. This aspect of C<shift> is considered highly experimental. | |
6511 | The exact behaviour may change in a future version of Perl. | |
cba5a3b0 | 6512 | |
bade7fbc TC |
6513 | To avoid confusing would-be users of your code who are running earlier |
6514 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
6515 | the top of your file to signal that your code will work I<only> on Perls of | |
6516 | a recent vintage: | |
6517 | ||
6518 | use 5.014; # so push/pop/etc work on scalars (experimental) | |
6519 | ||
a1b2c429 | 6520 | See also C<unshift>, C<push>, and C<pop>. C<shift> and C<unshift> do the |
19799a22 | 6521 | same thing to the left end of an array that C<pop> and C<push> do to the |
977336f5 | 6522 | right end. |
a0d0e21e LW |
6523 | |
6524 | =item shmctl ID,CMD,ARG | |
d74e8afc | 6525 | X<shmctl> |
a0d0e21e | 6526 | |
c17cdb72 NC |
6527 | =for Pod::Functions SysV shared memory operations |
6528 | ||
0ade1984 JH |
6529 | Calls the System V IPC function shmctl. You'll probably have to say |
6530 | ||
6531 | use IPC::SysV; | |
6532 | ||
7660c0ab | 6533 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
cf264981 | 6534 | then ARG must be a variable that will hold the returned C<shmid_ds> |
8f1da26d TC |
6535 | structure. Returns like ioctl: C<undef> for error; "C<0> but |
6536 | true" for zero; and the actual return value otherwise. | |
4755096e | 6537 | See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation. |
a0d0e21e | 6538 | |
ea9eb35a BJ |
6539 | Portability issues: L<perlport/shmctl>. |
6540 | ||
a0d0e21e | 6541 | =item shmget KEY,SIZE,FLAGS |
d74e8afc | 6542 | X<shmget> |
a0d0e21e | 6543 | |
c17cdb72 NC |
6544 | =for Pod::Functions get SysV shared memory segment identifier |
6545 | ||
a0d0e21e | 6546 | Calls the System V IPC function shmget. Returns the shared memory |
8f1da26d | 6547 | segment id, or C<undef> on error. |
4755096e | 6548 | See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation. |
a0d0e21e | 6549 | |
ea9eb35a BJ |
6550 | Portability issues: L<perlport/shmget>. |
6551 | ||
a0d0e21e | 6552 | =item shmread ID,VAR,POS,SIZE |
d74e8afc ITB |
6553 | X<shmread> |
6554 | X<shmwrite> | |
a0d0e21e | 6555 | |
c17cdb72 NC |
6556 | =for Pod::Functions read SysV shared memory |
6557 | ||
a0d0e21e LW |
6558 | =item shmwrite ID,STRING,POS,SIZE |
6559 | ||
c17cdb72 NC |
6560 | =for Pod::Functions write SysV shared memory |
6561 | ||
a0d0e21e LW |
6562 | Reads or writes the System V shared memory segment ID starting at |
6563 | position POS for size SIZE by attaching to it, copying in/out, and | |
5a964f20 | 6564 | detaching from it. When reading, VAR must be a variable that will |
a0d0e21e LW |
6565 | hold the data read. When writing, if STRING is too long, only SIZE |
6566 | bytes are used; if STRING is too short, nulls are written to fill out | |
8f1da26d | 6567 | SIZE bytes. Return true if successful, false on error. |
391b733c | 6568 | shmread() taints the variable. See also L<perlipc/"SysV IPC">, |
8f1da26d | 6569 | C<IPC::SysV>, and the C<IPC::Shareable> module from CPAN. |
a0d0e21e | 6570 | |
ea9eb35a BJ |
6571 | Portability issues: L<perlport/shmread> and L<perlport/shmwrite>. |
6572 | ||
a0d0e21e | 6573 | =item shutdown SOCKET,HOW |
d74e8afc | 6574 | X<shutdown> |
a0d0e21e | 6575 | |
c17cdb72 NC |
6576 | =for Pod::Functions close down just half of a socket connection |
6577 | ||
a0d0e21e | 6578 | Shuts down a socket connection in the manner indicated by HOW, which |
3b10bc60 | 6579 | has the same interpretation as in the syscall of the same name. |
a0d0e21e | 6580 | |
f86cebdf GS |
6581 | shutdown(SOCKET, 0); # I/we have stopped reading data |
6582 | shutdown(SOCKET, 1); # I/we have stopped writing data | |
6583 | shutdown(SOCKET, 2); # I/we have stopped using this socket | |
5a964f20 TC |
6584 | |
6585 | This is useful with sockets when you want to tell the other | |
6586 | side you're done writing but not done reading, or vice versa. | |
b76cc8ba | 6587 | It's also a more insistent form of close because it also |
19799a22 | 6588 | disables the file descriptor in any forked copies in other |
5a964f20 TC |
6589 | processes. |
6590 | ||
3b10bc60 | 6591 | Returns C<1> for success; on error, returns C<undef> if |
f126b98b PF |
6592 | the first argument is not a valid filehandle, or returns C<0> and sets |
6593 | C<$!> for any other failure. | |
6594 | ||
a0d0e21e | 6595 | =item sin EXPR |
d74e8afc | 6596 | X<sin> X<sine> X<asin> X<arcsine> |
a0d0e21e | 6597 | |
54310121 | 6598 | =item sin |
bbce6d69 | 6599 | |
c17cdb72 NC |
6600 | =for Pod::Functions return the sine of a number |
6601 | ||
a0d0e21e | 6602 | Returns the sine of EXPR (expressed in radians). If EXPR is omitted, |
7660c0ab | 6603 | returns sine of C<$_>. |
a0d0e21e | 6604 | |
ca6e1c26 | 6605 | For the inverse sine operation, you may use the C<Math::Trig::asin> |
28757baa | 6606 | function, or use this relation: |
6607 | ||
6608 | sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) } | |
6609 | ||
a0d0e21e | 6610 | =item sleep EXPR |
d74e8afc | 6611 | X<sleep> X<pause> |
a0d0e21e LW |
6612 | |
6613 | =item sleep | |
6614 | ||
c17cdb72 NC |
6615 | =for Pod::Functions block for some number of seconds |
6616 | ||
80d38338 TC |
6617 | Causes the script to sleep for (integer) EXPR seconds, or forever if no |
6618 | argument is given. Returns the integer number of seconds actually slept. | |
b48653af | 6619 | |
7660c0ab | 6620 | May be interrupted if the process receives a signal such as C<SIGALRM>. |
b48653af MS |
6621 | |
6622 | eval { | |
6623 | local $SIG{ALARM} = sub { die "Alarm!\n" }; | |
6624 | sleep; | |
6625 | }; | |
6626 | die $@ unless $@ eq "Alarm!\n"; | |
6627 | ||
6628 | You probably cannot mix C<alarm> and C<sleep> calls, because C<sleep> | |
6629 | is often implemented using C<alarm>. | |
a0d0e21e LW |
6630 | |
6631 | On some older systems, it may sleep up to a full second less than what | |
6632 | you requested, depending on how it counts seconds. Most modern systems | |
5a964f20 TC |
6633 | always sleep the full amount. They may appear to sleep longer than that, |
6634 | however, because your process might not be scheduled right away in a | |
6635 | busy multitasking system. | |
a0d0e21e | 6636 | |
2bc69794 BS |
6637 | For delays of finer granularity than one second, the Time::HiRes module |
6638 | (from CPAN, and starting from Perl 5.8 part of the standard | |
6639 | distribution) provides usleep(). You may also use Perl's four-argument | |
6640 | version of select() leaving the first three arguments undefined, or you | |
6641 | might be able to use the C<syscall> interface to access setitimer(2) if | |
391b733c | 6642 | your system supports it. See L<perlfaq8> for details. |
cb1a09d0 | 6643 | |
b6e2112e | 6644 | See also the POSIX module's C<pause> function. |
5f05dabc | 6645 | |
a0d0e21e | 6646 | =item socket SOCKET,DOMAIN,TYPE,PROTOCOL |
d74e8afc | 6647 | X<socket> |
a0d0e21e | 6648 | |
c17cdb72 NC |
6649 | =for Pod::Functions create a socket |
6650 | ||
a0d0e21e | 6651 | Opens a socket of the specified kind and attaches it to filehandle |
19799a22 | 6652 | SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for |
3b10bc60 | 6653 | the syscall of the same name. You should C<use Socket> first |
19799a22 GS |
6654 | to get the proper definitions imported. See the examples in |
6655 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 6656 | |
8d2a6795 GS |
6657 | On systems that support a close-on-exec flag on files, the flag will |
6658 | be set for the newly opened file descriptor, as determined by the | |
6659 | value of $^F. See L<perlvar/$^F>. | |
6660 | ||
a0d0e21e | 6661 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL |
d74e8afc | 6662 | X<socketpair> |
a0d0e21e | 6663 | |
c17cdb72 NC |
6664 | =for Pod::Functions create a pair of sockets |
6665 | ||
a0d0e21e | 6666 | Creates an unnamed pair of sockets in the specified domain, of the |
5f05dabc | 6667 | specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as |
3b10bc60 | 6668 | for the syscall of the same name. If unimplemented, raises an exception. |
6669 | Returns true if successful. | |
a0d0e21e | 6670 | |
8d2a6795 GS |
6671 | On systems that support a close-on-exec flag on files, the flag will |
6672 | be set for the newly opened file descriptors, as determined by the value | |
6673 | of $^F. See L<perlvar/$^F>. | |
6674 | ||
19799a22 | 6675 | Some systems defined C<pipe> in terms of C<socketpair>, in which a call |
5a964f20 TC |
6676 | to C<pipe(Rdr, Wtr)> is essentially: |
6677 | ||
6678 | use Socket; | |
6679 | socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC); | |
6680 | shutdown(Rdr, 1); # no more writing for reader | |
6681 | shutdown(Wtr, 0); # no more reading for writer | |
6682 | ||
02fc2eee NC |
6683 | See L<perlipc> for an example of socketpair use. Perl 5.8 and later will |
6684 | emulate socketpair using IP sockets to localhost if your system implements | |
6685 | sockets but not socketpair. | |
5a964f20 | 6686 | |
ea9eb35a BJ |
6687 | Portability issues: L<perlport/socketpair>. |
6688 | ||
a0d0e21e | 6689 | =item sort SUBNAME LIST |
d74e8afc | 6690 | X<sort> X<qsort> X<quicksort> X<mergesort> |
a0d0e21e LW |
6691 | |
6692 | =item sort BLOCK LIST | |
6693 | ||
6694 | =item sort LIST | |
6695 | ||
c17cdb72 NC |
6696 | =for Pod::Functions sort a list of values |
6697 | ||
41d39f30 | 6698 | In list context, this sorts the LIST and returns the sorted list value. |
9fdc1d08 | 6699 | In scalar context, the behaviour of C<sort()> is undefined. |
41d39f30 A |
6700 | |
6701 | If SUBNAME or BLOCK is omitted, C<sort>s in standard string comparison | |
6702 | order. If SUBNAME is specified, it gives the name of a subroutine | |
6703 | that returns an integer less than, equal to, or greater than C<0>, | |
3b10bc60 | 6704 | depending on how the elements of the list are to be ordered. (The |
6705 | C<< <=> >> and C<cmp> operators are extremely useful in such routines.) | |
41d39f30 A |
6706 | SUBNAME may be a scalar variable name (unsubscripted), in which case |
6707 | the value provides the name of (or a reference to) the actual | |
6708 | subroutine to use. In place of a SUBNAME, you can provide a BLOCK as | |
6709 | an anonymous, in-line sort subroutine. | |
a0d0e21e | 6710 | |
8f1da26d TC |
6711 | If the subroutine's prototype is C<($$)>, the elements to be compared are |
6712 | passed by reference in C<@_>, as for a normal subroutine. This is slower | |
6713 | than unprototyped subroutines, where the elements to be compared are passed | |
6714 | into the subroutine as the package global variables $a and $b (see example | |
6715 | below). Note that in the latter case, it is usually highly counter-productive | |
6716 | to declare $a and $b as lexicals. | |
43481408 | 6717 | |
51707595 FC |
6718 | If the subroutine is an XSUB, the elements to be compared are pushed on to |
6719 | the stack, the way arguments are usually passed to XSUBs. $a and $b are | |
6720 | not set. | |
6721 | ||
c106e8bb RH |
6722 | The values to be compared are always passed by reference and should not |
6723 | be modified. | |
a0d0e21e | 6724 | |
0a753a76 | 6725 | You also cannot exit out of the sort block or subroutine using any of the |
19799a22 | 6726 | loop control operators described in L<perlsyn> or with C<goto>. |
0a753a76 | 6727 | |
66cbab2c KW |
6728 | When C<use locale> (but not C<use locale 'not_characters'>) is in |
6729 | effect, C<sort LIST> sorts LIST according to the | |
a034a98d DD |
6730 | current collation locale. See L<perllocale>. |
6731 | ||
db5021a3 MS |
6732 | sort() returns aliases into the original list, much as a for loop's index |
6733 | variable aliases the list elements. That is, modifying an element of a | |
6734 | list returned by sort() (for example, in a C<foreach>, C<map> or C<grep>) | |
6735 | actually modifies the element in the original list. This is usually | |
6736 | something to be avoided when writing clear code. | |
6737 | ||
58c7fc7c | 6738 | Perl 5.6 and earlier used a quicksort algorithm to implement sort. |
8f1da26d | 6739 | That algorithm was not stable, so I<could> go quadratic. (A I<stable> sort |
58c7fc7c JH |
6740 | preserves the input order of elements that compare equal. Although |
6741 | quicksort's run time is O(NlogN) when averaged over all arrays of | |
6742 | length N, the time can be O(N**2), I<quadratic> behavior, for some | |
6743 | inputs.) In 5.7, the quicksort implementation was replaced with | |
cf264981 | 6744 | a stable mergesort algorithm whose worst-case behavior is O(NlogN). |
58c7fc7c JH |
6745 | But benchmarks indicated that for some inputs, on some platforms, |
6746 | the original quicksort was faster. 5.8 has a sort pragma for | |
6747 | limited control of the sort. Its rather blunt control of the | |
cf264981 | 6748 | underlying algorithm may not persist into future Perls, but the |
58c7fc7c | 6749 | ability to characterize the input or output in implementation |
c25fe68d | 6750 | independent ways quite probably will. See L<the sort pragma|sort>. |
c16425f1 | 6751 | |
a0d0e21e LW |
6752 | Examples: |
6753 | ||
6754 | # sort lexically | |
6755 | @articles = sort @files; | |
f703fc96 | 6756 | |
a0d0e21e LW |
6757 | # same thing, but with explicit sort routine |
6758 | @articles = sort {$a cmp $b} @files; | |
f703fc96 | 6759 | |
cb1a09d0 | 6760 | # now case-insensitively |
628253b8 | 6761 | @articles = sort {fc($a) cmp fc($b)} @files; |
f703fc96 | 6762 | |
a0d0e21e LW |
6763 | # same thing in reversed order |
6764 | @articles = sort {$b cmp $a} @files; | |
f703fc96 | 6765 | |
a0d0e21e LW |
6766 | # sort numerically ascending |
6767 | @articles = sort {$a <=> $b} @files; | |
f703fc96 | 6768 | |
a0d0e21e LW |
6769 | # sort numerically descending |
6770 | @articles = sort {$b <=> $a} @files; | |
f703fc96 | 6771 | |
19799a22 GS |
6772 | # this sorts the %age hash by value instead of key |
6773 | # using an in-line function | |
6774 | @eldest = sort { $age{$b} <=> $age{$a} } keys %age; | |
f703fc96 | 6775 | |
a0d0e21e LW |
6776 | # sort using explicit subroutine name |
6777 | sub byage { | |
4d0444a3 | 6778 | $age{$a} <=> $age{$b}; # presuming numeric |
a0d0e21e LW |
6779 | } |
6780 | @sortedclass = sort byage @class; | |
f703fc96 | 6781 | |
19799a22 GS |
6782 | sub backwards { $b cmp $a } |
6783 | @harry = qw(dog cat x Cain Abel); | |
6784 | @george = qw(gone chased yz Punished Axed); | |
a0d0e21e | 6785 | print sort @harry; |
e1d16ab7 | 6786 | # prints AbelCaincatdogx |
a0d0e21e | 6787 | print sort backwards @harry; |
e1d16ab7 | 6788 | # prints xdogcatCainAbel |
a0d0e21e | 6789 | print sort @george, 'to', @harry; |
e1d16ab7 | 6790 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz |
a0d0e21e | 6791 | |
54310121 | 6792 | # inefficiently sort by descending numeric compare using |
6793 | # the first integer after the first = sign, or the | |
cb1a09d0 AD |
6794 | # whole record case-insensitively otherwise |
6795 | ||
e1d16ab7 | 6796 | my @new = sort { |
6797 | ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0] | |
4d0444a3 | 6798 | || |
628253b8 | 6799 | fc($a) cmp fc($b) |
cb1a09d0 AD |
6800 | } @old; |
6801 | ||
6802 | # same thing, but much more efficiently; | |
6803 | # we'll build auxiliary indices instead | |
6804 | # for speed | |
e1d16ab7 | 6805 | my @nums = @caps = (); |
54310121 | 6806 | for (@old) { |
e1d16ab7 | 6807 | push @nums, ( /=(\d+)/ ? $1 : undef ); |
628253b8 | 6808 | push @caps, fc($_); |
54310121 | 6809 | } |
cb1a09d0 | 6810 | |
e1d16ab7 | 6811 | my @new = @old[ sort { |
4d0444a3 FC |
6812 | $nums[$b] <=> $nums[$a] |
6813 | || | |
6814 | $caps[$a] cmp $caps[$b] | |
6815 | } 0..$#old | |
6816 | ]; | |
cb1a09d0 | 6817 | |
19799a22 | 6818 | # same thing, but without any temps |
cb1a09d0 | 6819 | @new = map { $_->[0] } |
19799a22 | 6820 | sort { $b->[1] <=> $a->[1] |
4d0444a3 FC |
6821 | || |
6822 | $a->[2] cmp $b->[2] | |
628253b8 | 6823 | } map { [$_, /=(\d+)/, fc($_)] } @old; |
61eff3bc | 6824 | |
43481408 GS |
6825 | # using a prototype allows you to use any comparison subroutine |
6826 | # as a sort subroutine (including other package's subroutines) | |
6827 | package other; | |
f7051f2c FC |
6828 | sub backwards ($$) { $_[1] cmp $_[0]; } # $a and $b are |
6829 | # not set here | |
43481408 GS |
6830 | package main; |
6831 | @new = sort other::backwards @old; | |
f703fc96 | 6832 | |
58c7fc7c JH |
6833 | # guarantee stability, regardless of algorithm |
6834 | use sort 'stable'; | |
6835 | @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old; | |
f703fc96 | 6836 | |
268e9d79 JL |
6837 | # force use of mergesort (not portable outside Perl 5.8) |
6838 | use sort '_mergesort'; # note discouraging _ | |
58c7fc7c | 6839 | @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old; |
58c7fc7c | 6840 | |
1cb246e8 | 6841 | Warning: syntactical care is required when sorting the list returned from |
391b733c | 6842 | a function. If you want to sort the list returned by the function call |
1cb246e8 | 6843 | C<find_records(@key)>, you can use: |
a9320c62 | 6844 | |
a9320c62 B |
6845 | @contact = sort { $a cmp $b } find_records @key; |
6846 | @contact = sort +find_records(@key); | |
6847 | @contact = sort &find_records(@key); | |
6848 | @contact = sort(find_records(@key)); | |
6849 | ||
6850 | If instead you want to sort the array @key with the comparison routine | |
1cb246e8 RGS |
6851 | C<find_records()> then you can use: |
6852 | ||
a9320c62 B |
6853 | @contact = sort { find_records() } @key; |
6854 | @contact = sort find_records(@key); | |
6855 | @contact = sort(find_records @key); | |
6856 | @contact = sort(find_records (@key)); | |
6857 | ||
19799a22 GS |
6858 | If you're using strict, you I<must not> declare $a |
6859 | and $b as lexicals. They are package globals. That means | |
1cb246e8 | 6860 | that if you're in the C<main> package and type |
13a2d996 | 6861 | |
47223a36 | 6862 | @articles = sort {$b <=> $a} @files; |
13a2d996 | 6863 | |
47223a36 JH |
6864 | then C<$a> and C<$b> are C<$main::a> and C<$main::b> (or C<$::a> and C<$::b>), |
6865 | but if you're in the C<FooPack> package, it's the same as typing | |
cb1a09d0 AD |
6866 | |
6867 | @articles = sort {$FooPack::b <=> $FooPack::a} @files; | |
6868 | ||
55497cff | 6869 | The comparison function is required to behave. If it returns |
7660c0ab A |
6870 | inconsistent results (sometimes saying C<$x[1]> is less than C<$x[2]> and |
6871 | sometimes saying the opposite, for example) the results are not | |
6872 | well-defined. | |
55497cff | 6873 | |
03190201 | 6874 | Because C<< <=> >> returns C<undef> when either operand is C<NaN> |
1bd4e8e3 | 6875 | (not-a-number), be careful when sorting with a |
8f1da26d TC |
6876 | comparison function like C<< $a <=> $b >> any lists that might contain a |
6877 | C<NaN>. The following example takes advantage that C<NaN != NaN> to | |
3b10bc60 | 6878 | eliminate any C<NaN>s from the input list. |
03190201 JL |
6879 | |
6880 | @result = sort { $a <=> $b } grep { $_ == $_ } @input; | |
6881 | ||
f5a93a43 | 6882 | =item splice ARRAY or EXPR,OFFSET,LENGTH,LIST |
d74e8afc | 6883 | X<splice> |
a0d0e21e | 6884 | |
f5a93a43 | 6885 | =item splice ARRAY or EXPR,OFFSET,LENGTH |
a0d0e21e | 6886 | |
f5a93a43 | 6887 | =item splice ARRAY or EXPR,OFFSET |
a0d0e21e | 6888 | |
f5a93a43 | 6889 | =item splice ARRAY or EXPR |
453f9044 | 6890 | |
c17cdb72 NC |
6891 | =for Pod::Functions add or remove elements anywhere in an array |
6892 | ||
a0d0e21e | 6893 | Removes the elements designated by OFFSET and LENGTH from an array, and |
5a964f20 TC |
6894 | replaces them with the elements of LIST, if any. In list context, |
6895 | returns the elements removed from the array. In scalar context, | |
43051805 | 6896 | returns the last element removed, or C<undef> if no elements are |
48cdf507 | 6897 | removed. The array grows or shrinks as necessary. |
19799a22 | 6898 | If OFFSET is negative then it starts that far from the end of the array. |
48cdf507 | 6899 | If LENGTH is omitted, removes everything from OFFSET onward. |
d0920e03 MJD |
6900 | If LENGTH is negative, removes the elements from OFFSET onward |
6901 | except for -LENGTH elements at the end of the array. | |
391b733c | 6902 | If both OFFSET and LENGTH are omitted, removes everything. If OFFSET is |
8e602cc9 EB |
6903 | past the end of the array and a LENGTH was provided, Perl issues a warning, |
6904 | and splices at the end of the array. | |
453f9044 | 6905 | |
e1dccc0d | 6906 | The following equivalences hold (assuming C<< $#a >= $i >> ) |
a0d0e21e | 6907 | |
5ed4f2ec | 6908 | push(@a,$x,$y) splice(@a,@a,0,$x,$y) |
6909 | pop(@a) splice(@a,-1) | |
6910 | shift(@a) splice(@a,0,1) | |
6911 | unshift(@a,$x,$y) splice(@a,0,0,$x,$y) | |
6912 | $a[$i] = $y splice(@a,$i,1,$y) | |
a0d0e21e | 6913 | |
498b759b RS |
6914 | C<splice> can be used, for example, to implement n-ary queue processing: |
6915 | ||
6916 | sub nary_print { | |
6917 | my $n = shift; | |
6918 | while (my @next_n = splice @_, 0, $n) { | |
6919 | say join q{ -- }, @next_n; | |
6920 | } | |
a0d0e21e | 6921 | } |
498b759b RS |
6922 | |
6923 | nary_print(3, qw(a b c d e f g h)); | |
6924 | # prints: | |
6925 | # a -- b -- c | |
6926 | # d -- e -- f | |
6927 | # g -- h | |
a0d0e21e | 6928 | |
f5a93a43 TC |
6929 | Starting with Perl 5.14, C<splice> can take scalar EXPR, which must hold a |
6930 | reference to an unblessed array. The argument will be dereferenced | |
6931 | automatically. This aspect of C<splice> is considered highly experimental. | |
6932 | The exact behaviour may change in a future version of Perl. | |
532eee96 | 6933 | |
bade7fbc TC |
6934 | To avoid confusing would-be users of your code who are running earlier |
6935 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
6936 | the top of your file to signal that your code will work I<only> on Perls of | |
6937 | a recent vintage: | |
6938 | ||
6939 | use 5.014; # so push/pop/etc work on scalars (experimental) | |
6940 | ||
a0d0e21e | 6941 | =item split /PATTERN/,EXPR,LIMIT |
d74e8afc | 6942 | X<split> |
a0d0e21e LW |
6943 | |
6944 | =item split /PATTERN/,EXPR | |
6945 | ||
6946 | =item split /PATTERN/ | |
6947 | ||
6948 | =item split | |
6949 | ||
c17cdb72 NC |
6950 | =for Pod::Functions split up a string using a regexp delimiter |
6951 | ||
bd467585 MW |
6952 | Splits the string EXPR into a list of strings and returns the |
6953 | list in list context, or the size of the list in scalar context. | |
a0d0e21e | 6954 | |
bd467585 | 6955 | If only PATTERN is given, EXPR defaults to C<$_>. |
a0d0e21e | 6956 | |
bd467585 MW |
6957 | Anything in EXPR that matches PATTERN is taken to be a separator |
6958 | that separates the EXPR into substrings (called "I<fields>") that | |
6959 | do B<not> include the separator. Note that a separator may be | |
6960 | longer than one character or even have no characters at all (the | |
6961 | empty string, which is a zero-width match). | |
6962 | ||
6963 | The PATTERN need not be constant; an expression may be used | |
6964 | to specify a pattern that varies at runtime. | |
6965 | ||
6966 | If PATTERN matches the empty string, the EXPR is split at the match | |
6967 | position (between characters). As an example, the following: | |
6968 | ||
6969 | print join(':', split('b', 'abc')), "\n"; | |
6970 | ||
6971 | uses the 'b' in 'abc' as a separator to produce the output 'a:c'. | |
6972 | However, this: | |
6973 | ||
6974 | print join(':', split('', 'abc')), "\n"; | |
6975 | ||
6976 | uses empty string matches as separators to produce the output | |
6977 | 'a:b:c'; thus, the empty string may be used to split EXPR into a | |
6978 | list of its component characters. | |
6979 | ||
6980 | As a special case for C<split>, the empty pattern given in | |
6981 | L<match operator|perlop/"m/PATTERN/msixpodualgc"> syntax (C<//>) specifically matches the empty string, which is contrary to its usual | |
6982 | interpretation as the last successful match. | |
6983 | ||
6984 | If PATTERN is C</^/>, then it is treated as if it used the | |
6985 | L<multiline modifier|perlreref/OPERATORS> (C</^/m>), since it | |
6986 | isn't much use otherwise. | |
6987 | ||
6988 | As another special case, C<split> emulates the default behavior of the | |
6989 | command line tool B<awk> when the PATTERN is either omitted or a I<literal | |
6990 | string> composed of a single space character (such as S<C<' '>> or | |
6991 | S<C<"\x20">>, but not e.g. S<C</ />>). In this case, any leading | |
6992 | whitespace in EXPR is removed before splitting occurs, and the PATTERN is | |
6993 | instead treated as if it were C</\s+/>; in particular, this means that | |
6994 | I<any> contiguous whitespace (not just a single space character) is used as | |
6995 | a separator. However, this special treatment can be avoided by specifying | |
6996 | the pattern S<C</ />> instead of the string S<C<" ">>, thereby allowing | |
7161e5c2 | 6997 | only a single space character to be a separator. In earlier Perls this |
fdde5e9b YO |
6998 | special case was restricted to the use of a plain S<C<" ">> as the |
6999 | pattern argument to split, in Perl 5.18.0 and later this special case is | |
7000 | triggered by any expression which evaluates as the simple string S<C<" ">>. | |
bd467585 MW |
7001 | |
7002 | If omitted, PATTERN defaults to a single space, S<C<" ">>, triggering | |
7003 | the previously described I<awk> emulation. | |
fb73857a | 7004 | |
836e0ee7 | 7005 | If LIMIT is specified and positive, it represents the maximum number |
bd467585 MW |
7006 | of fields into which the EXPR may be split; in other words, LIMIT is |
7007 | one greater than the maximum number of times EXPR may be split. Thus, | |
7008 | the LIMIT value C<1> means that EXPR may be split a maximum of zero | |
7009 | times, producing a maximum of one field (namely, the entire value of | |
7010 | EXPR). For instance: | |
a0d0e21e | 7011 | |
bd467585 | 7012 | print join(':', split(//, 'abc', 1)), "\n"; |
a0d0e21e | 7013 | |
bd467585 | 7014 | produces the output 'abc', and this: |
a0d0e21e | 7015 | |
bd467585 | 7016 | print join(':', split(//, 'abc', 2)), "\n"; |
a0d0e21e | 7017 | |
bd467585 | 7018 | produces the output 'a:bc', and each of these: |
6de67870 | 7019 | |
bd467585 MW |
7020 | print join(':', split(//, 'abc', 3)), "\n"; |
7021 | print join(':', split(//, 'abc', 4)), "\n"; | |
52ea55c9 | 7022 | |
bd467585 | 7023 | produces the output 'a:b:c'. |
52ea55c9 | 7024 | |
bd467585 MW |
7025 | If LIMIT is negative, it is treated as if it were instead arbitrarily |
7026 | large; as many fields as possible are produced. | |
0156e0fd | 7027 | |
bd467585 MW |
7028 | If LIMIT is omitted (or, equivalently, zero), then it is usually |
7029 | treated as if it were instead negative but with the exception that | |
7030 | trailing empty fields are stripped (empty leading fields are always | |
7031 | preserved); if all fields are empty, then all fields are considered to | |
7032 | be trailing (and are thus stripped in this case). Thus, the following: | |
0156e0fd | 7033 | |
bd467585 | 7034 | print join(':', split(',', 'a,b,c,,,')), "\n"; |
12977212 | 7035 | |
bd467585 | 7036 | produces the output 'a:b:c', but the following: |
12977212 | 7037 | |
bd467585 | 7038 | print join(':', split(',', 'a,b,c,,,', -1)), "\n"; |
0156e0fd | 7039 | |
bd467585 | 7040 | produces the output 'a:b:c:::'. |
a0d0e21e | 7041 | |
bd467585 MW |
7042 | In time-critical applications, it is worthwhile to avoid splitting |
7043 | into more fields than necessary. Thus, when assigning to a list, | |
7044 | if LIMIT is omitted (or zero), then LIMIT is treated as though it | |
7045 | were one larger than the number of variables in the list; for the | |
e05ccd69 | 7046 | following, LIMIT is implicitly 3: |
a0d0e21e | 7047 | |
e05ccd69 | 7048 | ($login, $passwd) = split(/:/); |
a0d0e21e | 7049 | |
bd467585 MW |
7050 | Note that splitting an EXPR that evaluates to the empty string always |
7051 | produces zero fields, regardless of the LIMIT specified. | |
a0d0e21e | 7052 | |
bd467585 | 7053 | An empty leading field is produced when there is a positive-width |
0d3e3823 | 7054 | match at the beginning of EXPR. For instance: |
a0d0e21e | 7055 | |
bd467585 | 7056 | print join(':', split(/ /, ' abc')), "\n"; |
a0d0e21e | 7057 | |
bd467585 MW |
7058 | produces the output ':abc'. However, a zero-width match at the |
7059 | beginning of EXPR never produces an empty field, so that: | |
a0d0e21e | 7060 | |
bd467585 | 7061 | print join(':', split(//, ' abc')); |
4633a7c4 | 7062 | |
bd467585 | 7063 | produces the output S<' :a:b:c'> (rather than S<': :a:b:c'>). |
4633a7c4 | 7064 | |
bd467585 MW |
7065 | An empty trailing field, on the other hand, is produced when there is a |
7066 | match at the end of EXPR, regardless of the length of the match | |
7067 | (of course, unless a non-zero LIMIT is given explicitly, such fields are | |
0d3e3823 | 7068 | removed, as in the last example). Thus: |
748a9306 | 7069 | |
bd467585 | 7070 | print join(':', split(//, ' abc', -1)), "\n"; |
a0d0e21e | 7071 | |
bd467585 | 7072 | produces the output S<' :a:b:c:'>. |
1ec94568 | 7073 | |
bd467585 MW |
7074 | If the PATTERN contains |
7075 | L<capturing groups|perlretut/Grouping things and hierarchical matching>, | |
7076 | then for each separator, an additional field is produced for each substring | |
7077 | captured by a group (in the order in which the groups are specified, | |
7078 | as per L<backreferences|perlretut/Backreferences>); if any group does not | |
7079 | match, then it captures the C<undef> value instead of a substring. Also, | |
7080 | note that any such additional field is produced whenever there is a | |
7081 | separator (that is, whenever a split occurs), and such an additional field | |
7082 | does B<not> count towards the LIMIT. Consider the following expressions | |
7083 | evaluated in list context (each returned list is provided in the associated | |
7084 | comment): | |
a0d0e21e | 7085 | |
bd467585 MW |
7086 | split(/-|,/, "1-10,20", 3) |
7087 | # ('1', '10', '20') | |
7088 | ||
7089 | split(/(-|,)/, "1-10,20", 3) | |
7090 | # ('1', '-', '10', ',', '20') | |
7091 | ||
7092 | split(/-|(,)/, "1-10,20", 3) | |
7093 | # ('1', undef, '10', ',', '20') | |
a0d0e21e | 7094 | |
bd467585 MW |
7095 | split(/(-)|,/, "1-10,20", 3) |
7096 | # ('1', '-', '10', undef, '20') | |
6de67870 | 7097 | |
bd467585 MW |
7098 | split(/(-)|(,)/, "1-10,20", 3) |
7099 | # ('1', '-', undef, '10', undef, ',', '20') | |
a0d0e21e | 7100 | |
5f05dabc | 7101 | =item sprintf FORMAT, LIST |
d74e8afc | 7102 | X<sprintf> |
a0d0e21e | 7103 | |
c17cdb72 NC |
7104 | =for Pod::Functions formatted print into a string |
7105 | ||
6662521e GS |
7106 | Returns a string formatted by the usual C<printf> conventions of the C |
7107 | library function C<sprintf>. See below for more details | |
01aa884e | 7108 | and see L<sprintf(3)> or L<printf(3)> on your system for an explanation of |
6662521e GS |
7109 | the general principles. |
7110 | ||
7111 | For example: | |
7112 | ||
7113 | # Format number with up to 8 leading zeroes | |
7114 | $result = sprintf("%08d", $number); | |
7115 | ||
7116 | # Round number to 3 digits after decimal point | |
7117 | $rounded = sprintf("%.3f", $number); | |
74a77017 | 7118 | |
3b10bc60 | 7119 | Perl does its own C<sprintf> formatting: it emulates the C |
7120 | function sprintf(3), but doesn't use it except for floating-point | |
7121 | numbers, and even then only standard modifiers are allowed. | |
7122 | Non-standard extensions in your local sprintf(3) are | |
7123 | therefore unavailable from Perl. | |
74a77017 | 7124 | |
194e7b38 | 7125 | Unlike C<printf>, C<sprintf> does not do what you probably mean when you |
391b733c FC |
7126 | pass it an array as your first argument. |
7127 | The array is given scalar context, | |
194e7b38 DC |
7128 | and instead of using the 0th element of the array as the format, Perl will |
7129 | use the count of elements in the array as the format, which is almost never | |
7130 | useful. | |
7131 | ||
19799a22 | 7132 | Perl's C<sprintf> permits the following universally-known conversions: |
74a77017 | 7133 | |
5ed4f2ec | 7134 | %% a percent sign |
7135 | %c a character with the given number | |
7136 | %s a string | |
7137 | %d a signed integer, in decimal | |
7138 | %u an unsigned integer, in decimal | |
7139 | %o an unsigned integer, in octal | |
7140 | %x an unsigned integer, in hexadecimal | |
7141 | %e a floating-point number, in scientific notation | |
7142 | %f a floating-point number, in fixed decimal notation | |
7143 | %g a floating-point number, in %e or %f notation | |
74a77017 | 7144 | |
1b3f7d21 | 7145 | In addition, Perl permits the following widely-supported conversions: |
74a77017 | 7146 | |
5ed4f2ec | 7147 | %X like %x, but using upper-case letters |
7148 | %E like %e, but using an upper-case "E" | |
7149 | %G like %g, but with an upper-case "E" (if applicable) | |
7150 | %b an unsigned integer, in binary | |
7151 | %B like %b, but using an upper-case "B" with the # flag | |
7152 | %p a pointer (outputs the Perl value's address in hexadecimal) | |
7153 | %n special: *stores* the number of characters output so far | |
e3852384 | 7154 | into the next argument in the parameter list |
40bca5ae JH |
7155 | %a hexadecimal floating point |
7156 | %A like %a, but using upper-case letters | |
74a77017 | 7157 | |
1b3f7d21 CS |
7158 | Finally, for backward (and we do mean "backward") compatibility, Perl |
7159 | permits these unnecessary but widely-supported conversions: | |
74a77017 | 7160 | |
5ed4f2ec | 7161 | %i a synonym for %d |
7162 | %D a synonym for %ld | |
7163 | %U a synonym for %lu | |
7164 | %O a synonym for %lo | |
7165 | %F a synonym for %f | |
74a77017 | 7166 | |
7b8dd722 HS |
7167 | Note that the number of exponent digits in the scientific notation produced |
7168 | by C<%e>, C<%E>, C<%g> and C<%G> for numbers with the modulus of the | |
b73fd64e JH |
7169 | exponent less than 100 is system-dependent: it may be three or less |
7170 | (zero-padded as necessary). In other words, 1.23 times ten to the | |
40bca5ae JH |
7171 | 99th may be either "1.23e99" or "1.23e099". Similarly for C<%a> and C<%A>: |
7172 | the exponent or the hexadecimal digits may float: especially the | |
7173 | "long doubles" Perl configuration option may cause surprises. | |
d764f01a | 7174 | |
80d38338 | 7175 | Between the C<%> and the format letter, you may specify several |
7b8dd722 HS |
7176 | additional attributes controlling the interpretation of the format. |
7177 | In order, these are: | |
74a77017 | 7178 | |
7b8dd722 HS |
7179 | =over 4 |
7180 | ||
7181 | =item format parameter index | |
7182 | ||
391b733c | 7183 | An explicit format parameter index, such as C<2$>. By default sprintf |
7b8dd722 | 7184 | will format the next unused argument in the list, but this allows you |
3b10bc60 | 7185 | to take the arguments out of order: |
7b8dd722 HS |
7186 | |
7187 | printf '%2$d %1$d', 12, 34; # prints "34 12" | |
7188 | printf '%3$d %d %1$d', 1, 2, 3; # prints "3 1 1" | |
7189 | ||
7190 | =item flags | |
7191 | ||
7192 | one or more of: | |
e6bb52fd | 7193 | |
7a81c58e A |
7194 | space prefix non-negative number with a space |
7195 | + prefix non-negative number with a plus sign | |
74a77017 CS |
7196 | - left-justify within the field |
7197 | 0 use zeros, not spaces, to right-justify | |
e6bb52fd TS |
7198 | # ensure the leading "0" for any octal, |
7199 | prefix non-zero hexadecimal with "0x" or "0X", | |
7200 | prefix non-zero binary with "0b" or "0B" | |
7b8dd722 HS |
7201 | |
7202 | For example: | |
7203 | ||
e6bb52fd TS |
7204 | printf '<% d>', 12; # prints "< 12>" |
7205 | printf '<%+d>', 12; # prints "<+12>" | |
7206 | printf '<%6s>', 12; # prints "< 12>" | |
7207 | printf '<%-6s>', 12; # prints "<12 >" | |
7208 | printf '<%06s>', 12; # prints "<000012>" | |
7209 | printf '<%#o>', 12; # prints "<014>" | |
7210 | printf '<%#x>', 12; # prints "<0xc>" | |
7211 | printf '<%#X>', 12; # prints "<0XC>" | |
7212 | printf '<%#b>', 12; # prints "<0b1100>" | |
7213 | printf '<%#B>', 12; # prints "<0B1100>" | |
7b8dd722 | 7214 | |
9911cee9 TS |
7215 | When a space and a plus sign are given as the flags at once, |
7216 | a plus sign is used to prefix a positive number. | |
7217 | ||
7218 | printf '<%+ d>', 12; # prints "<+12>" | |
7219 | printf '<% +d>', 12; # prints "<+12>" | |
7220 | ||
e6bb52fd TS |
7221 | When the # flag and a precision are given in the %o conversion, |
7222 | the precision is incremented if it's necessary for the leading "0". | |
7223 | ||
7224 | printf '<%#.5o>', 012; # prints "<00012>" | |
7225 | printf '<%#.5o>', 012345; # prints "<012345>" | |
7226 | printf '<%#.0o>', 0; # prints "<0>" | |
7227 | ||
7b8dd722 HS |
7228 | =item vector flag |
7229 | ||
3b10bc60 | 7230 | This flag tells Perl to interpret the supplied string as a vector of |
391b733c | 7231 | integers, one for each character in the string. Perl applies the format to |
920f3fa9 | 7232 | each integer in turn, then joins the resulting strings with a separator (a |
391b733c | 7233 | dot C<.> by default). This can be useful for displaying ordinal values of |
920f3fa9 | 7234 | characters in arbitrary strings: |
7b8dd722 | 7235 | |
920f3fa9 | 7236 | printf "%vd", "AB\x{100}"; # prints "65.66.256" |
7b8dd722 HS |
7237 | printf "version is v%vd\n", $^V; # Perl's version |
7238 | ||
7239 | Put an asterisk C<*> before the C<v> to override the string to | |
7240 | use to separate the numbers: | |
7241 | ||
7242 | printf "address is %*vX\n", ":", $addr; # IPv6 address | |
7243 | printf "bits are %0*v8b\n", " ", $bits; # random bitstring | |
7244 | ||
7245 | You can also explicitly specify the argument number to use for | |
3b10bc60 | 7246 | the join string using something like C<*2$v>; for example: |
7b8dd722 | 7247 | |
f7051f2c FC |
7248 | printf '%*4$vX %*4$vX %*4$vX', # 3 IPv6 addresses |
7249 | @addr[1..3], ":"; | |
7b8dd722 HS |
7250 | |
7251 | =item (minimum) width | |
7252 | ||
7253 | Arguments are usually formatted to be only as wide as required to | |
391b733c | 7254 | display the given value. You can override the width by putting |
7b8dd722 | 7255 | a number here, or get the width from the next argument (with C<*>) |
3b10bc60 | 7256 | or from a specified argument (e.g., with C<*2$>): |
7b8dd722 | 7257 | |
f7051f2c FC |
7258 | printf "<%s>", "a"; # prints "<a>" |
7259 | printf "<%6s>", "a"; # prints "< a>" | |
7260 | printf "<%*s>", 6, "a"; # prints "< a>" | |
073d6857 | 7261 | printf '<%*2$s>', "a", 6; # prints "< a>" |
f7051f2c | 7262 | printf "<%2s>", "long"; # prints "<long>" (does not truncate) |
7b8dd722 | 7263 | |
19799a22 GS |
7264 | If a field width obtained through C<*> is negative, it has the same |
7265 | effect as the C<-> flag: left-justification. | |
74a77017 | 7266 | |
7b8dd722 | 7267 | =item precision, or maximum width |
d74e8afc | 7268 | X<precision> |
7b8dd722 | 7269 | |
6c8c9a8e | 7270 | You can specify a precision (for numeric conversions) or a maximum |
7b8dd722 | 7271 | width (for string conversions) by specifying a C<.> followed by a number. |
8f1da26d | 7272 | For floating-point formats except C<g> and C<G>, this specifies |
3b10bc60 | 7273 | how many places right of the decimal point to show (the default being 6). |
7274 | For example: | |
7b8dd722 HS |
7275 | |
7276 | # these examples are subject to system-specific variation | |
7277 | printf '<%f>', 1; # prints "<1.000000>" | |
7278 | printf '<%.1f>', 1; # prints "<1.0>" | |
7279 | printf '<%.0f>', 1; # prints "<1>" | |
7280 | printf '<%e>', 10; # prints "<1.000000e+01>" | |
7281 | printf '<%.1e>', 10; # prints "<1.0e+01>" | |
7282 | ||
3b10bc60 | 7283 | For "g" and "G", this specifies the maximum number of digits to show, |
7698aede | 7284 | including those prior to the decimal point and those after it; for |
3b10bc60 | 7285 | example: |
1ff2d182 | 7286 | |
3b10bc60 | 7287 | # These examples are subject to system-specific variation. |
1ff2d182 AS |
7288 | printf '<%g>', 1; # prints "<1>" |
7289 | printf '<%.10g>', 1; # prints "<1>" | |
7290 | printf '<%g>', 100; # prints "<100>" | |
7291 | printf '<%.1g>', 100; # prints "<1e+02>" | |
7292 | printf '<%.2g>', 100.01; # prints "<1e+02>" | |
7293 | printf '<%.5g>', 100.01; # prints "<100.01>" | |
7294 | printf '<%.4g>', 100.01; # prints "<100>" | |
7295 | ||
7b8dd722 | 7296 | For integer conversions, specifying a precision implies that the |
9911cee9 TS |
7297 | output of the number itself should be zero-padded to this width, |
7298 | where the 0 flag is ignored: | |
7299 | ||
7300 | printf '<%.6d>', 1; # prints "<000001>" | |
7301 | printf '<%+.6d>', 1; # prints "<+000001>" | |
7302 | printf '<%-10.6d>', 1; # prints "<000001 >" | |
7303 | printf '<%10.6d>', 1; # prints "< 000001>" | |
7304 | printf '<%010.6d>', 1; # prints "< 000001>" | |
7305 | printf '<%+10.6d>', 1; # prints "< +000001>" | |
7b8dd722 HS |
7306 | |
7307 | printf '<%.6x>', 1; # prints "<000001>" | |
7308 | printf '<%#.6x>', 1; # prints "<0x000001>" | |
7309 | printf '<%-10.6x>', 1; # prints "<000001 >" | |
9911cee9 TS |
7310 | printf '<%10.6x>', 1; # prints "< 000001>" |
7311 | printf '<%010.6x>', 1; # prints "< 000001>" | |
7312 | printf '<%#10.6x>', 1; # prints "< 0x000001>" | |
7b8dd722 HS |
7313 | |
7314 | For string conversions, specifying a precision truncates the string | |
3b10bc60 | 7315 | to fit the specified width: |
7b8dd722 HS |
7316 | |
7317 | printf '<%.5s>', "truncated"; # prints "<trunc>" | |
7318 | printf '<%10.5s>', "truncated"; # prints "< trunc>" | |
7319 | ||
7320 | You can also get the precision from the next argument using C<.*>: | |
b22c7a20 | 7321 | |
7b8dd722 HS |
7322 | printf '<%.6x>', 1; # prints "<000001>" |
7323 | printf '<%.*x>', 6, 1; # prints "<000001>" | |
7324 | ||
3b10bc60 | 7325 | If a precision obtained through C<*> is negative, it counts |
7326 | as having no precision at all. | |
9911cee9 TS |
7327 | |
7328 | printf '<%.*s>', 7, "string"; # prints "<string>" | |
7329 | printf '<%.*s>', 3, "string"; # prints "<str>" | |
7330 | printf '<%.*s>', 0, "string"; # prints "<>" | |
7331 | printf '<%.*s>', -1, "string"; # prints "<string>" | |
7332 | ||
7333 | printf '<%.*d>', 1, 0; # prints "<0>" | |
7334 | printf '<%.*d>', 0, 0; # prints "<>" | |
7335 | printf '<%.*d>', -1, 0; # prints "<0>" | |
7336 | ||
7b8dd722 | 7337 | You cannot currently get the precision from a specified number, |
3b10bc60 | 7338 | but it is intended that this will be possible in the future, for |
7339 | example using C<.*2$>: | |
7b8dd722 | 7340 | |
073d6857 | 7341 | printf '<%.*2$x>', 1, 6; # INVALID, but in future will print |
f7051f2c | 7342 | # "<000001>" |
7b8dd722 HS |
7343 | |
7344 | =item size | |
7345 | ||
7346 | For numeric conversions, you can specify the size to interpret the | |
391b733c | 7347 | number as using C<l>, C<h>, C<V>, C<q>, C<L>, or C<ll>. For integer |
1ff2d182 AS |
7348 | conversions (C<d u o x X b i D U O>), numbers are usually assumed to be |
7349 | whatever the default integer size is on your platform (usually 32 or 64 | |
7350 | bits), but you can override this to use instead one of the standard C types, | |
7351 | as supported by the compiler used to build Perl: | |
7b8dd722 | 7352 | |
f7051f2c | 7353 | hh interpret integer as C type "char" or "unsigned |
09700023 | 7354 | char" on Perl 5.14 or later |
f7051f2c FC |
7355 | h interpret integer as C type "short" or |
7356 | "unsigned short" | |
09700023 | 7357 | j interpret integer as C type "intmax_t" on Perl |
f7051f2c FC |
7358 | 5.14 or later, and only with a C99 compiler |
7359 | (unportable) | |
7360 | l interpret integer as C type "long" or | |
7361 | "unsigned long" | |
7362 | q, L, or ll interpret integer as C type "long long", | |
7363 | "unsigned long long", or "quad" (typically | |
7364 | 64-bit integers) | |
09700023 | 7365 | t interpret integer as C type "ptrdiff_t" on Perl |
f7051f2c | 7366 | 5.14 or later |
09700023 | 7367 | z interpret integer as C type "size_t" on Perl 5.14 |
f7051f2c | 7368 | or later |
3d21943e JV |
7369 | |
7370 | As of 5.14, none of these raises an exception if they are not supported on | |
7371 | your platform. However, if warnings are enabled, a warning of the | |
7372 | C<printf> warning class is issued on an unsupported conversion flag. | |
7373 | Should you instead prefer an exception, do this: | |
7374 | ||
7375 | use warnings FATAL => "printf"; | |
7376 | ||
7377 | If you would like to know about a version dependency before you | |
7378 | start running the program, put something like this at its top: | |
7379 | ||
7380 | use 5.014; # for hh/j/t/z/ printf modifiers | |
7b8dd722 | 7381 | |
3d21943e | 7382 | You can find out whether your Perl supports quads via L<Config>: |
7b8dd722 | 7383 | |
5ed4f2ec | 7384 | use Config; |
f7051f2c FC |
7385 | if ($Config{use64bitint} eq "define" |
7386 | || $Config{longsize} >= 8) { | |
3b10bc60 | 7387 | print "Nice quads!\n"; |
7388 | } | |
1ff2d182 | 7389 | |
3b10bc60 | 7390 | For floating-point conversions (C<e f g E F G>), numbers are usually assumed |
7391 | to be the default floating-point size on your platform (double or long double), | |
7392 | but you can force "long double" with C<q>, C<L>, or C<ll> if your | |
391b733c | 7393 | platform supports them. You can find out whether your Perl supports long |
1ff2d182 AS |
7394 | doubles via L<Config>: |
7395 | ||
5ed4f2ec | 7396 | use Config; |
3b10bc60 | 7397 | print "long doubles\n" if $Config{d_longdbl} eq "define"; |
1ff2d182 | 7398 | |
3b10bc60 | 7399 | You can find out whether Perl considers "long double" to be the default |
7400 | floating-point size to use on your platform via L<Config>: | |
1ff2d182 | 7401 | |
3b10bc60 | 7402 | use Config; |
7403 | if ($Config{uselongdouble} eq "define") { | |
09700023 | 7404 | print "long doubles by default\n"; |
3b10bc60 | 7405 | } |
1ff2d182 | 7406 | |
3b10bc60 | 7407 | It can also be that long doubles and doubles are the same thing: |
1ff2d182 AS |
7408 | |
7409 | use Config; | |
7410 | ($Config{doublesize} == $Config{longdblsize}) && | |
7411 | print "doubles are long doubles\n"; | |
7412 | ||
3b10bc60 | 7413 | The size specifier C<V> has no effect for Perl code, but is supported for |
7414 | compatibility with XS code. It means "use the standard size for a Perl | |
7415 | integer or floating-point number", which is the default. | |
7b8dd722 | 7416 | |
a472f209 HS |
7417 | =item order of arguments |
7418 | ||
3b10bc60 | 7419 | Normally, sprintf() takes the next unused argument as the value to |
391b733c | 7420 | format for each format specification. If the format specification |
a472f209 | 7421 | uses C<*> to require additional arguments, these are consumed from |
3b10bc60 | 7422 | the argument list in the order they appear in the format |
7423 | specification I<before> the value to format. Where an argument is | |
7424 | specified by an explicit index, this does not affect the normal | |
7425 | order for the arguments, even when the explicitly specified index | |
7426 | would have been the next argument. | |
a472f209 HS |
7427 | |
7428 | So: | |
7429 | ||
3b10bc60 | 7430 | printf "<%*.*s>", $a, $b, $c; |
a472f209 | 7431 | |
3b10bc60 | 7432 | uses C<$a> for the width, C<$b> for the precision, and C<$c> |
7433 | as the value to format; while: | |
a472f209 | 7434 | |
073d6857 | 7435 | printf '<%*1$.*s>', $a, $b; |
a472f209 | 7436 | |
3b10bc60 | 7437 | would use C<$a> for the width and precision, and C<$b> as the |
a472f209 HS |
7438 | value to format. |
7439 | ||
3b10bc60 | 7440 | Here are some more examples; be aware that when using an explicit |
7441 | index, the C<$> may need escaping: | |
a472f209 | 7442 | |
f7051f2c FC |
7443 | printf "%2\$d %d\n", 12, 34; # will print "34 12\n" |
7444 | printf "%2\$d %d %d\n", 12, 34; # will print "34 12 34\n" | |
7445 | printf "%3\$d %d %d\n", 12, 34, 56; # will print "56 12 34\n" | |
7446 | printf "%2\$*3\$d %d\n", 12, 34, 3; # will print " 34 12\n" | |
a472f209 | 7447 | |
7b8dd722 | 7448 | =back |
b22c7a20 | 7449 | |
66cbab2c KW |
7450 | If C<use locale> (including C<use locale 'not_characters'>) is in effect |
7451 | and POSIX::setlocale() has been called, | |
3b10bc60 | 7452 | the character used for the decimal separator in formatted floating-point |
d6ded950 | 7453 | numbers is affected by the C<LC_NUMERIC> locale. See L<perllocale> |
7e4353e9 | 7454 | and L<POSIX>. |
a0d0e21e LW |
7455 | |
7456 | =item sqrt EXPR | |
d74e8afc | 7457 | X<sqrt> X<root> X<square root> |
a0d0e21e | 7458 | |
54310121 | 7459 | =item sqrt |
bbce6d69 | 7460 | |
c17cdb72 NC |
7461 | =for Pod::Functions square root function |
7462 | ||
3b10bc60 | 7463 | Return the positive square root of EXPR. If EXPR is omitted, uses |
7464 | C<$_>. Works only for non-negative operands unless you've | |
7465 | loaded the C<Math::Complex> module. | |
2b5ab1e7 TC |
7466 | |
7467 | use Math::Complex; | |
3b10bc60 | 7468 | print sqrt(-4); # prints 2i |
a0d0e21e LW |
7469 | |
7470 | =item srand EXPR | |
d74e8afc | 7471 | X<srand> X<seed> X<randseed> |
a0d0e21e | 7472 | |
93dc8474 CS |
7473 | =item srand |
7474 | ||
c17cdb72 NC |
7475 | =for Pod::Functions seed the random number generator |
7476 | ||
83832992 | 7477 | Sets and returns the random number seed for the C<rand> operator. |
0686c0b8 | 7478 | |
bade7fbc TC |
7479 | The point of the function is to "seed" the C<rand> function so that C<rand> |
7480 | can produce a different sequence each time you run your program. When | |
7481 | called with a parameter, C<srand> uses that for the seed; otherwise it | |
7482 | (semi-)randomly chooses a seed. In either case, starting with Perl 5.14, | |
7483 | it returns the seed. To signal that your code will work I<only> on Perls | |
7484 | of a recent vintage: | |
7485 | ||
7486 | use 5.014; # so srand returns the seed | |
83832992 KW |
7487 | |
7488 | If C<srand()> is not called explicitly, it is called implicitly without a | |
e9fa405d BF |
7489 | parameter at the first use of the C<rand> operator. |
7490 | However, there are a few situations where programs are likely to | |
3c831796 | 7491 | want to call C<srand>. One is for generating predictable results, generally for |
83832992 | 7492 | testing or debugging. There, you use C<srand($seed)>, with the same C<$seed> |
416e3a83 | 7493 | each time. Another case is that you may want to call C<srand()> |
83832992 KW |
7494 | after a C<fork()> to avoid child processes sharing the same seed value as the |
7495 | parent (and consequently each other). | |
7496 | ||
7497 | Do B<not> call C<srand()> (i.e., without an argument) more than once per | |
d460397b | 7498 | process. The internal state of the random number generator should |
0686c0b8 | 7499 | contain more entropy than can be provided by any seed, so calling |
83832992 | 7500 | C<srand()> again actually I<loses> randomness. |
0686c0b8 | 7501 | |
e0b236fe JH |
7502 | Most implementations of C<srand> take an integer and will silently |
7503 | truncate decimal numbers. This means C<srand(42)> will usually | |
7504 | produce the same results as C<srand(42.1)>. To be safe, always pass | |
7505 | C<srand> an integer. | |
0686c0b8 | 7506 | |
83832992 KW |
7507 | A typical use of the returned seed is for a test program which has too many |
7508 | combinations to test comprehensively in the time available to it each run. It | |
7509 | can test a random subset each time, and should there be a failure, log the seed | |
8f1da26d | 7510 | used for that run so that it can later be used to reproduce the same results. |
83832992 | 7511 | |
416e3a83 AMS |
7512 | B<C<rand()> is not cryptographically secure. You should not rely |
7513 | on it in security-sensitive situations.> As of this writing, a | |
7514 | number of third-party CPAN modules offer random number generators | |
7515 | intended by their authors to be cryptographically secure, | |
7516 | including: L<Data::Entropy>, L<Crypt::Random>, L<Math::Random::Secure>, | |
7517 | and L<Math::TrulyRandom>. | |
7518 | ||
a0d0e21e | 7519 | =item stat FILEHANDLE |
435fbc73 | 7520 | X<stat> X<file, status> X<ctime> |
a0d0e21e LW |
7521 | |
7522 | =item stat EXPR | |
7523 | ||
5228a96c SP |
7524 | =item stat DIRHANDLE |
7525 | ||
54310121 | 7526 | =item stat |
bbce6d69 | 7527 | |
c17cdb72 NC |
7528 | =for Pod::Functions get a file's status information |
7529 | ||
1d2dff63 | 7530 | Returns a 13-element list giving the status info for a file, either |
5228a96c | 7531 | the file opened via FILEHANDLE or DIRHANDLE, or named by EXPR. If EXPR is |
8f1da26d | 7532 | omitted, it stats C<$_> (not C<_>!). Returns the empty list if C<stat> fails. Typically |
5228a96c | 7533 | used as follows: |
a0d0e21e LW |
7534 | |
7535 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, | |
7536 | $atime,$mtime,$ctime,$blksize,$blocks) | |
7537 | = stat($filename); | |
7538 | ||
54310121 | 7539 | Not all fields are supported on all filesystem types. Here are the |
61967be2 | 7540 | meanings of the fields: |
c07a80fd | 7541 | |
54310121 | 7542 | 0 dev device number of filesystem |
7543 | 1 ino inode number | |
7544 | 2 mode file mode (type and permissions) | |
7545 | 3 nlink number of (hard) links to the file | |
7546 | 4 uid numeric user ID of file's owner | |
7547 | 5 gid numeric group ID of file's owner | |
7548 | 6 rdev the device identifier (special files only) | |
7549 | 7 size total size of file, in bytes | |
1c74f1bd GS |
7550 | 8 atime last access time in seconds since the epoch |
7551 | 9 mtime last modify time in seconds since the epoch | |
df2a7e48 | 7552 | 10 ctime inode change time in seconds since the epoch (*) |
dd766832 CB |
7553 | 11 blksize preferred I/O size in bytes for interacting with the |
7554 | file (may vary from file to file) | |
7555 | 12 blocks actual number of system-specific blocks allocated | |
7556 | on disk (often, but not always, 512 bytes each) | |
c07a80fd | 7557 | |
7558 | (The epoch was at 00:00 January 1, 1970 GMT.) | |
7559 | ||
391b733c | 7560 | (*) Not all fields are supported on all filesystem types. Notably, the |
3e2557b2 | 7561 | ctime field is non-portable. In particular, you cannot expect it to be a |
8f1da26d | 7562 | "creation time"; see L<perlport/"Files and Filesystems"> for details. |
df2a7e48 | 7563 | |
61967be2 | 7564 | If C<stat> is passed the special filehandle consisting of an underline, no |
a0d0e21e | 7565 | stat is done, but the current contents of the stat structure from the |
61967be2 | 7566 | last C<stat>, C<lstat>, or filetest are returned. Example: |
a0d0e21e LW |
7567 | |
7568 | if (-x $file && (($d) = stat(_)) && $d < 0) { | |
a9a5a0dc | 7569 | print "$file is executable NFS file\n"; |
a0d0e21e LW |
7570 | } |
7571 | ||
ca6e1c26 JH |
7572 | (This works on machines only for which the device number is negative |
7573 | under NFS.) | |
a0d0e21e | 7574 | |
2b5ab1e7 | 7575 | Because the mode contains both the file type and its permissions, you |
b76cc8ba | 7576 | should mask off the file type portion and (s)printf using a C<"%o"> |
2b5ab1e7 TC |
7577 | if you want to see the real permissions. |
7578 | ||
7579 | $mode = (stat($filename))[2]; | |
7580 | printf "Permissions are %04o\n", $mode & 07777; | |
7581 | ||
19799a22 | 7582 | In scalar context, C<stat> returns a boolean value indicating success |
1d2dff63 GS |
7583 | or failure, and, if successful, sets the information associated with |
7584 | the special filehandle C<_>. | |
7585 | ||
dd184578 | 7586 | The L<File::stat> module provides a convenient, by-name access mechanism: |
2b5ab1e7 TC |
7587 | |
7588 | use File::stat; | |
7589 | $sb = stat($filename); | |
b76cc8ba | 7590 | printf "File is %s, size is %s, perm %04o, mtime %s\n", |
a9a5a0dc VP |
7591 | $filename, $sb->size, $sb->mode & 07777, |
7592 | scalar localtime $sb->mtime; | |
2b5ab1e7 | 7593 | |
ca6e1c26 JH |
7594 | You can import symbolic mode constants (C<S_IF*>) and functions |
7595 | (C<S_IS*>) from the Fcntl module: | |
7596 | ||
7597 | use Fcntl ':mode'; | |
7598 | ||
7599 | $mode = (stat($filename))[2]; | |
7600 | ||
7601 | $user_rwx = ($mode & S_IRWXU) >> 6; | |
7602 | $group_read = ($mode & S_IRGRP) >> 3; | |
7603 | $other_execute = $mode & S_IXOTH; | |
7604 | ||
3155e0b0 | 7605 | printf "Permissions are %04o\n", S_IMODE($mode), "\n"; |
ca6e1c26 JH |
7606 | |
7607 | $is_setuid = $mode & S_ISUID; | |
ad605d16 | 7608 | $is_directory = S_ISDIR($mode); |
ca6e1c26 JH |
7609 | |
7610 | You could write the last two using the C<-u> and C<-d> operators. | |
3b10bc60 | 7611 | Commonly available C<S_IF*> constants are: |
ca6e1c26 JH |
7612 | |
7613 | # Permissions: read, write, execute, for user, group, others. | |
7614 | ||
7615 | S_IRWXU S_IRUSR S_IWUSR S_IXUSR | |
7616 | S_IRWXG S_IRGRP S_IWGRP S_IXGRP | |
7617 | S_IRWXO S_IROTH S_IWOTH S_IXOTH | |
61eff3bc | 7618 | |
3cee8101 | 7619 | # Setuid/Setgid/Stickiness/SaveText. |
7df0fd0b | 7620 | # Note that the exact meaning of these is system-dependent. |
ca6e1c26 JH |
7621 | |
7622 | S_ISUID S_ISGID S_ISVTX S_ISTXT | |
7623 | ||
7df0fd0b FC |
7624 | # File types. Not all are necessarily available on |
7625 | # your system. | |
ca6e1c26 | 7626 | |
7df0fd0b FC |
7627 | S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR |
7628 | S_IFIFO S_IFSOCK S_IFWHT S_ENFMT | |
ca6e1c26 | 7629 | |
7df0fd0b FC |
7630 | # The following are compatibility aliases for S_IRUSR, |
7631 | # S_IWUSR, and S_IXUSR. | |
ca6e1c26 JH |
7632 | |
7633 | S_IREAD S_IWRITE S_IEXEC | |
7634 | ||
61967be2 | 7635 | and the C<S_IF*> functions are |
ca6e1c26 | 7636 | |
7df0fd0b FC |
7637 | S_IMODE($mode) the part of $mode containing the permission |
7638 | bits and the setuid/setgid/sticky bits | |
ca6e1c26 | 7639 | |
7df0fd0b FC |
7640 | S_IFMT($mode) the part of $mode containing the file type |
7641 | which can be bit-anded with (for example) | |
7642 | S_IFREG or with the following functions | |
ca6e1c26 | 7643 | |
61967be2 | 7644 | # The operators -f, -d, -l, -b, -c, -p, and -S. |
ca6e1c26 JH |
7645 | |
7646 | S_ISREG($mode) S_ISDIR($mode) S_ISLNK($mode) | |
7647 | S_ISBLK($mode) S_ISCHR($mode) S_ISFIFO($mode) S_ISSOCK($mode) | |
7648 | ||
7649 | # No direct -X operator counterpart, but for the first one | |
7650 | # the -g operator is often equivalent. The ENFMT stands for | |
7651 | # record flocking enforcement, a platform-dependent feature. | |
7652 | ||
7653 | S_ISENFMT($mode) S_ISWHT($mode) | |
7654 | ||
7655 | See your native chmod(2) and stat(2) documentation for more details | |
61967be2 | 7656 | about the C<S_*> constants. To get status info for a symbolic link |
c837d5b4 | 7657 | instead of the target file behind the link, use the C<lstat> function. |
ca6e1c26 | 7658 | |
ea9eb35a BJ |
7659 | Portability issues: L<perlport/stat>. |
7660 | ||
672208d2 | 7661 | =item state VARLIST |
36fb85f3 RGS |
7662 | X<state> |
7663 | ||
672208d2 | 7664 | =item state TYPE VARLIST |
36fb85f3 | 7665 | |
672208d2 | 7666 | =item state VARLIST : ATTRS |
36fb85f3 | 7667 | |
672208d2 | 7668 | =item state TYPE VARLIST : ATTRS |
36fb85f3 | 7669 | |
d9b04284 | 7670 | =for Pod::Functions +state declare and assign a persistent lexical variable |
c17cdb72 | 7671 | |
4a904372 | 7672 | C<state> declares a lexically scoped variable, just like C<my>. |
b708784e | 7673 | However, those variables will never be reinitialized, contrary to |
36fb85f3 RGS |
7674 | lexical variables that are reinitialized each time their enclosing block |
7675 | is entered. | |
e476d66f | 7676 | See L<perlsub/"Persistent Private Variables"> for details. |
36fb85f3 | 7677 | |
672208d2 | 7678 | If more than one variable is listed, the list must be placed in |
7161e5c2 FC |
7679 | parentheses. With a parenthesised list, C<undef> can be used as a |
7680 | dummy placeholder. However, since initialization of state variables in | |
672208d2 JV |
7681 | list context is currently not possible this would serve no purpose. |
7682 | ||
3b10bc60 | 7683 | C<state> variables are enabled only when the C<use feature "state"> pragma |
4a904372 | 7684 | is in effect, unless the keyword is written as C<CORE::state>. |
e476d66f | 7685 | See also L<feature>. |
36fb85f3 | 7686 | |
a0d0e21e | 7687 | =item study SCALAR |
d74e8afc | 7688 | X<study> |
a0d0e21e LW |
7689 | |
7690 | =item study | |
7691 | ||
c17cdb72 NC |
7692 | =for Pod::Functions optimize input data for repeated searches |
7693 | ||
184e9718 | 7694 | Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of |
a0d0e21e LW |
7695 | doing many pattern matches on the string before it is next modified. |
7696 | This may or may not save time, depending on the nature and number of | |
8f1da26d | 7697 | patterns you are searching and the distribution of character |
3b10bc60 | 7698 | frequencies in the string to be searched; you probably want to compare |
8f1da26d | 7699 | run times with and without it to see which is faster. Those loops |
cf264981 | 7700 | that scan for many short constant strings (including the constant |
4185c919 NC |
7701 | parts of more complex patterns) will benefit most. |
7702 | (The way C<study> works is this: a linked list of every | |
a0d0e21e | 7703 | character in the string to be searched is made, so we know, for |
7660c0ab | 7704 | example, where all the C<'k'> characters are. From each search string, |
a0d0e21e LW |
7705 | the rarest character is selected, based on some static frequency tables |
7706 | constructed from some C programs and English text. Only those places | |
7707 | that contain this "rarest" character are examined.) | |
7708 | ||
5a964f20 | 7709 | For example, here is a loop that inserts index producing entries |
a0d0e21e LW |
7710 | before any line containing a certain pattern: |
7711 | ||
7712 | while (<>) { | |
a9a5a0dc VP |
7713 | study; |
7714 | print ".IX foo\n" if /\bfoo\b/; | |
7715 | print ".IX bar\n" if /\bbar\b/; | |
7716 | print ".IX blurfl\n" if /\bblurfl\b/; | |
7717 | # ... | |
7718 | print; | |
a0d0e21e LW |
7719 | } |
7720 | ||
3b10bc60 | 7721 | In searching for C</\bfoo\b/>, only locations in C<$_> that contain C<f> |
951ba7fe | 7722 | will be looked at, because C<f> is rarer than C<o>. In general, this is |
a0d0e21e LW |
7723 | a big win except in pathological cases. The only question is whether |
7724 | it saves you more time than it took to build the linked list in the | |
7725 | first place. | |
7726 | ||
7727 | Note that if you have to look for strings that you don't know till | |
19799a22 | 7728 | runtime, you can build an entire loop as a string and C<eval> that to |
a0d0e21e | 7729 | avoid recompiling all your patterns all the time. Together with |
80d38338 | 7730 | undefining C<$/> to input entire files as one record, this can be quite |
f86cebdf | 7731 | fast, often faster than specialized programs like fgrep(1). The following |
184e9718 | 7732 | scans a list of files (C<@files>) for a list of words (C<@words>), and prints |
a0d0e21e LW |
7733 | out the names of those files that contain a match: |
7734 | ||
7735 | $search = 'while (<>) { study;'; | |
7736 | foreach $word (@words) { | |
a9a5a0dc | 7737 | $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n"; |
a0d0e21e LW |
7738 | } |
7739 | $search .= "}"; | |
7740 | @ARGV = @files; | |
7741 | undef $/; | |
5ed4f2ec | 7742 | eval $search; # this screams |
7743 | $/ = "\n"; # put back to normal input delimiter | |
a0d0e21e | 7744 | foreach $file (sort keys(%seen)) { |
a9a5a0dc | 7745 | print $file, "\n"; |
a0d0e21e LW |
7746 | } |
7747 | ||
1d2de774 | 7748 | =item sub NAME BLOCK |
d74e8afc | 7749 | X<sub> |
cb1a09d0 | 7750 | |
1d2de774 | 7751 | =item sub NAME (PROTO) BLOCK |
cb1a09d0 | 7752 | |
1d2de774 JH |
7753 | =item sub NAME : ATTRS BLOCK |
7754 | ||
7755 | =item sub NAME (PROTO) : ATTRS BLOCK | |
7756 | ||
c17cdb72 NC |
7757 | =for Pod::Functions declare a subroutine, possibly anonymously |
7758 | ||
8f1da26d TC |
7759 | This is subroutine definition, not a real function I<per se>. Without a |
7760 | BLOCK it's just a forward declaration. Without a NAME, it's an anonymous | |
7761 | function declaration, so does return a value: the CODE ref of the closure | |
7762 | just created. | |
cb1a09d0 | 7763 | |
1d2de774 | 7764 | See L<perlsub> and L<perlref> for details about subroutines and |
8f1da26d | 7765 | references; see L<attributes> and L<Attribute::Handlers> for more |
1d2de774 | 7766 | information about attributes. |
cb1a09d0 | 7767 | |
84ed0108 FC |
7768 | =item __SUB__ |
7769 | X<__SUB__> | |
7770 | ||
d9b04284 | 7771 | =for Pod::Functions +current_sub the current subroutine, or C<undef> if not in a subroutine |
c17cdb72 | 7772 | |
a453e28a | 7773 | A special token that returns a reference to the current subroutine, or |
84ed0108 FC |
7774 | C<undef> outside of a subroutine. |
7775 | ||
a453e28a DM |
7776 | The behaviour of C<__SUB__> within a regex code block (such as C</(?{...})/>) |
7777 | is subject to change. | |
7778 | ||
84ed0108 FC |
7779 | This token is only available under C<use v5.16> or the "current_sub" |
7780 | feature. See L<feature>. | |
7781 | ||
4fa8e151 FC |
7782 | =item substr EXPR,OFFSET,LENGTH,REPLACEMENT |
7783 | X<substr> X<substring> X<mid> X<left> X<right> | |
7784 | ||
87275199 | 7785 | =item substr EXPR,OFFSET,LENGTH |
a0d0e21e LW |
7786 | |
7787 | =item substr EXPR,OFFSET | |
7788 | ||
c17cdb72 NC |
7789 | =for Pod::Functions get or alter a portion of a string |
7790 | ||
a0d0e21e | 7791 | Extracts a substring out of EXPR and returns it. First character is at |
e1dccc0d | 7792 | offset zero. If OFFSET is negative, starts |
8f1da26d TC |
7793 | that far back from the end of the string. If LENGTH is omitted, returns |
7794 | everything through the end of the string. If LENGTH is negative, leaves that | |
748a9306 LW |
7795 | many characters off the end of the string. |
7796 | ||
e1de3ec0 | 7797 | my $s = "The black cat climbed the green tree"; |
5ed4f2ec | 7798 | my $color = substr $s, 4, 5; # black |
7799 | my $middle = substr $s, 4, -11; # black cat climbed the | |
7800 | my $end = substr $s, 14; # climbed the green tree | |
7801 | my $tail = substr $s, -4; # tree | |
7802 | my $z = substr $s, -4, 2; # tr | |
e1de3ec0 | 7803 | |
2b5ab1e7 | 7804 | You can use the substr() function as an lvalue, in which case EXPR |
87275199 GS |
7805 | must itself be an lvalue. If you assign something shorter than LENGTH, |
7806 | the string will shrink, and if you assign something longer than LENGTH, | |
2b5ab1e7 | 7807 | the string will grow to accommodate it. To keep the string the same |
3b10bc60 | 7808 | length, you may need to pad or chop your value using C<sprintf>. |
a0d0e21e | 7809 | |
87275199 GS |
7810 | If OFFSET and LENGTH specify a substring that is partly outside the |
7811 | string, only the part within the string is returned. If the substring | |
7812 | is beyond either end of the string, substr() returns the undefined | |
7813 | value and produces a warning. When used as an lvalue, specifying a | |
3b10bc60 | 7814 | substring that is entirely outside the string raises an exception. |
87275199 GS |
7815 | Here's an example showing the behavior for boundary cases: |
7816 | ||
7817 | my $name = 'fred'; | |
5ed4f2ec | 7818 | substr($name, 4) = 'dy'; # $name is now 'freddy' |
3b10bc60 | 7819 | my $null = substr $name, 6, 2; # returns "" (no warning) |
5ed4f2ec | 7820 | my $oops = substr $name, 7; # returns undef, with warning |
3b10bc60 | 7821 | substr($name, 7) = 'gap'; # raises an exception |
87275199 | 7822 | |
2b5ab1e7 | 7823 | An alternative to using substr() as an lvalue is to specify the |
7b8d334a | 7824 | replacement string as the 4th argument. This allows you to replace |
2b5ab1e7 TC |
7825 | parts of the EXPR and return what was there before in one operation, |
7826 | just as you can with splice(). | |
7b8d334a | 7827 | |
e1de3ec0 | 7828 | my $s = "The black cat climbed the green tree"; |
5ed4f2ec | 7829 | my $z = substr $s, 14, 7, "jumped from"; # climbed |
e1de3ec0 GS |
7830 | # $s is now "The black cat jumped from the green tree" |
7831 | ||
8f1da26d | 7832 | Note that the lvalue returned by the three-argument version of substr() acts as |
91f73676 DM |
7833 | a 'magic bullet'; each time it is assigned to, it remembers which part |
7834 | of the original string is being modified; for example: | |
7835 | ||
7836 | $x = '1234'; | |
7837 | for (substr($x,1,2)) { | |
5ed4f2ec | 7838 | $_ = 'a'; print $x,"\n"; # prints 1a4 |
7839 | $_ = 'xyz'; print $x,"\n"; # prints 1xyz4 | |
91f73676 | 7840 | $x = '56789'; |
5ed4f2ec | 7841 | $_ = 'pq'; print $x,"\n"; # prints 5pq9 |
91f73676 DM |
7842 | } |
7843 | ||
1d95ad8b FC |
7844 | With negative offsets, it remembers its position from the end of the string |
7845 | when the target string is modified: | |
7846 | ||
7847 | $x = '1234'; | |
7848 | for (substr($x, -3, 2)) { | |
7849 | $_ = 'a'; print $x,"\n"; # prints 1a4, as above | |
7850 | $x = 'abcdefg'; | |
7851 | print $_,"\n"; # prints f | |
7852 | } | |
7853 | ||
b8c25b3c | 7854 | Prior to Perl version 5.10, the result of using an lvalue multiple times was |
1d95ad8b | 7855 | unspecified. Prior to 5.16, the result with negative offsets was |
91f73676 | 7856 | unspecified. |
c67bbae0 | 7857 | |
a0d0e21e | 7858 | =item symlink OLDFILE,NEWFILE |
d74e8afc | 7859 | X<symlink> X<link> X<symbolic link> X<link, symbolic> |
a0d0e21e | 7860 | |
c17cdb72 NC |
7861 | =for Pod::Functions create a symbolic link to a file |
7862 | ||
a0d0e21e | 7863 | Creates a new filename symbolically linked to the old filename. |
7660c0ab | 7864 | Returns C<1> for success, C<0> otherwise. On systems that don't support |
3b10bc60 | 7865 | symbolic links, raises an exception. To check for that, |
a0d0e21e LW |
7866 | use eval: |
7867 | ||
2b5ab1e7 | 7868 | $symlink_exists = eval { symlink("",""); 1 }; |
a0d0e21e | 7869 | |
ea9eb35a BJ |
7870 | Portability issues: L<perlport/symlink>. |
7871 | ||
5702da47 | 7872 | =item syscall NUMBER, LIST |
d74e8afc | 7873 | X<syscall> X<system call> |
a0d0e21e | 7874 | |
c17cdb72 NC |
7875 | =for Pod::Functions execute an arbitrary system call |
7876 | ||
a0d0e21e LW |
7877 | Calls the system call specified as the first element of the list, |
7878 | passing the remaining elements as arguments to the system call. If | |
3b10bc60 | 7879 | unimplemented, raises an exception. The arguments are interpreted |
a0d0e21e LW |
7880 | as follows: if a given argument is numeric, the argument is passed as |
7881 | an int. If not, the pointer to the string value is passed. You are | |
7882 | responsible to make sure a string is pre-extended long enough to | |
a3cb178b | 7883 | receive any result that might be written into a string. You can't use a |
19799a22 | 7884 | string literal (or other read-only string) as an argument to C<syscall> |
a3cb178b GS |
7885 | because Perl has to assume that any string pointer might be written |
7886 | through. If your | |
a0d0e21e | 7887 | integer arguments are not literals and have never been interpreted in a |
7660c0ab | 7888 | numeric context, you may need to add C<0> to them to force them to look |
19799a22 | 7889 | like numbers. This emulates the C<syswrite> function (or vice versa): |
a0d0e21e | 7890 | |
5ed4f2ec | 7891 | require 'syscall.ph'; # may need to run h2ph |
a3cb178b GS |
7892 | $s = "hi there\n"; |
7893 | syscall(&SYS_write, fileno(STDOUT), $s, length $s); | |
a0d0e21e | 7894 | |
3b10bc60 | 7895 | Note that Perl supports passing of up to only 14 arguments to your syscall, |
7896 | which in practice should (usually) suffice. | |
a0d0e21e | 7897 | |
fb73857a | 7898 | Syscall returns whatever value returned by the system call it calls. |
19799a22 | 7899 | If the system call fails, C<syscall> returns C<-1> and sets C<$!> (errno). |
8f1da26d TC |
7900 | Note that some system calls I<can> legitimately return C<-1>. The proper |
7901 | way to handle such calls is to assign C<$!=0> before the call, then | |
7902 | check the value of C<$!> if C<syscall> returns C<-1>. | |
fb73857a | 7903 | |
7904 | There's a problem with C<syscall(&SYS_pipe)>: it returns the file | |
8f1da26d | 7905 | number of the read end of the pipe it creates, but there is no way |
b76cc8ba | 7906 | to retrieve the file number of the other end. You can avoid this |
19799a22 | 7907 | problem by using C<pipe> instead. |
fb73857a | 7908 | |
ea9eb35a BJ |
7909 | Portability issues: L<perlport/syscall>. |
7910 | ||
c07a80fd | 7911 | =item sysopen FILEHANDLE,FILENAME,MODE |
d74e8afc | 7912 | X<sysopen> |
c07a80fd | 7913 | |
7914 | =item sysopen FILEHANDLE,FILENAME,MODE,PERMS | |
7915 | ||
d9b04284 | 7916 | =for Pod::Functions +5.002 open a file, pipe, or descriptor |
c17cdb72 | 7917 | |
8f1da26d TC |
7918 | Opens the file whose filename is given by FILENAME, and associates it with |
7919 | FILEHANDLE. If FILEHANDLE is an expression, its value is used as the real | |
391b733c | 7920 | filehandle wanted; an undefined scalar will be suitably autovivified. This |
8f1da26d TC |
7921 | function calls the underlying operating system's I<open>(2) function with the |
7922 | parameters FILENAME, MODE, and PERMS. | |
c07a80fd | 7923 | |
7924 | The possible values and flag bits of the MODE parameter are | |
8f1da26d TC |
7925 | system-dependent; they are available via the standard module C<Fcntl>. See |
7926 | the documentation of your operating system's I<open>(2) syscall to see | |
7927 | which values and flag bits are available. You may combine several flags | |
ea2b5ef6 JH |
7928 | using the C<|>-operator. |
7929 | ||
7930 | Some of the most common values are C<O_RDONLY> for opening the file in | |
7931 | read-only mode, C<O_WRONLY> for opening the file in write-only mode, | |
c188b257 | 7932 | and C<O_RDWR> for opening the file in read-write mode. |
d74e8afc | 7933 | X<O_RDONLY> X<O_RDWR> X<O_WRONLY> |
ea2b5ef6 | 7934 | |
adf5897a | 7935 | For historical reasons, some values work on almost every system |
3b10bc60 | 7936 | supported by Perl: 0 means read-only, 1 means write-only, and 2 |
adf5897a | 7937 | means read/write. We know that these values do I<not> work under |
043fec90 | 7938 | OS/390 and on the Macintosh; you probably don't want to |
4af147f6 | 7939 | use them in new code. |
c07a80fd | 7940 | |
19799a22 | 7941 | If the file named by FILENAME does not exist and the C<open> call creates |
7660c0ab | 7942 | it (typically because MODE includes the C<O_CREAT> flag), then the value of |
5a964f20 | 7943 | PERMS specifies the permissions of the newly created file. If you omit |
19799a22 | 7944 | the PERMS argument to C<sysopen>, Perl uses the octal value C<0666>. |
5a964f20 | 7945 | These permission values need to be in octal, and are modified by your |
0591cd52 | 7946 | process's current C<umask>. |
d74e8afc | 7947 | X<O_CREAT> |
0591cd52 | 7948 | |
ea2b5ef6 JH |
7949 | In many systems the C<O_EXCL> flag is available for opening files in |
7950 | exclusive mode. This is B<not> locking: exclusiveness means here that | |
c188b257 PF |
7951 | if the file already exists, sysopen() fails. C<O_EXCL> may not work |
7952 | on network filesystems, and has no effect unless the C<O_CREAT> flag | |
7953 | is set as well. Setting C<O_CREAT|O_EXCL> prevents the file from | |
7954 | being opened if it is a symbolic link. It does not protect against | |
7955 | symbolic links in the file's path. | |
d74e8afc | 7956 | X<O_EXCL> |
c188b257 PF |
7957 | |
7958 | Sometimes you may want to truncate an already-existing file. This | |
7959 | can be done using the C<O_TRUNC> flag. The behavior of | |
7960 | C<O_TRUNC> with C<O_RDONLY> is undefined. | |
d74e8afc | 7961 | X<O_TRUNC> |
ea2b5ef6 | 7962 | |
19799a22 | 7963 | You should seldom if ever use C<0644> as argument to C<sysopen>, because |
2b5ab1e7 TC |
7964 | that takes away the user's option to have a more permissive umask. |
7965 | Better to omit it. See the perlfunc(1) entry on C<umask> for more | |
7966 | on this. | |
c07a80fd | 7967 | |
4af147f6 | 7968 | Note that C<sysopen> depends on the fdopen() C library function. |
e1020413 | 7969 | On many Unix systems, fdopen() is known to fail when file descriptors |
391b733c | 7970 | exceed a certain value, typically 255. If you need more file |
97cb92d6 | 7971 | descriptors than that, consider using the POSIX::open() function. |
4af147f6 | 7972 | |
2b5ab1e7 | 7973 | See L<perlopentut> for a kinder, gentler explanation of opening files. |
28757baa | 7974 | |
ea9eb35a BJ |
7975 | Portability issues: L<perlport/sysopen>. |
7976 | ||
a0d0e21e | 7977 | =item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET |
d74e8afc | 7978 | X<sysread> |
a0d0e21e LW |
7979 | |
7980 | =item sysread FILEHANDLE,SCALAR,LENGTH | |
7981 | ||
c17cdb72 NC |
7982 | =for Pod::Functions fixed-length unbuffered input from a filehandle |
7983 | ||
3874323d | 7984 | Attempts to read LENGTH bytes of data into variable SCALAR from the |
3b10bc60 | 7985 | specified FILEHANDLE, using the read(2). It bypasses |
3874323d JH |
7986 | buffered IO, so mixing this with other kinds of reads, C<print>, |
7987 | C<write>, C<seek>, C<tell>, or C<eof> can cause confusion because the | |
7988 | perlio or stdio layers usually buffers data. Returns the number of | |
7989 | bytes actually read, C<0> at end of file, or undef if there was an | |
7990 | error (in the latter case C<$!> is also set). SCALAR will be grown or | |
7991 | shrunk so that the last byte actually read is the last byte of the | |
7992 | scalar after the read. | |
ff68c719 | 7993 | |
7994 | An OFFSET may be specified to place the read data at some place in the | |
7995 | string other than the beginning. A negative OFFSET specifies | |
9124316e JH |
7996 | placement at that many characters counting backwards from the end of |
7997 | the string. A positive OFFSET greater than the length of SCALAR | |
7998 | results in the string being padded to the required size with C<"\0"> | |
7999 | bytes before the result of the read is appended. | |
a0d0e21e | 8000 | |
2b5ab1e7 | 8001 | There is no syseof() function, which is ok, since eof() doesn't work |
80d38338 | 8002 | well on device files (like ttys) anyway. Use sysread() and check |
19799a22 | 8003 | for a return value for 0 to decide whether you're done. |
2b5ab1e7 | 8004 | |
3874323d JH |
8005 | Note that if the filehandle has been marked as C<:utf8> Unicode |
8006 | characters are read instead of bytes (the LENGTH, OFFSET, and the | |
5eadf7c5 | 8007 | return value of sysread() are in Unicode characters). |
3874323d JH |
8008 | The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer. |
8009 | See L</binmode>, L</open>, and the C<open> pragma, L<open>. | |
8010 | ||
137443ea | 8011 | =item sysseek FILEHANDLE,POSITION,WHENCE |
d74e8afc | 8012 | X<sysseek> X<lseek> |
137443ea | 8013 | |
d9b04284 | 8014 | =for Pod::Functions +5.004 position I/O pointer on handle used with sysread and syswrite |
c17cdb72 | 8015 | |
8f1da26d TC |
8016 | Sets FILEHANDLE's system position in bytes using lseek(2). FILEHANDLE may |
8017 | be an expression whose value gives the name of the filehandle. The values | |
8018 | for WHENCE are C<0> to set the new position to POSITION; C<1> to set the it | |
8019 | to the current position plus POSITION; and C<2> to set it to EOF plus | |
8020 | POSITION, typically negative. | |
9124316e JH |
8021 | |
8022 | Note the I<in bytes>: even if the filehandle has been set to operate | |
740d4bb2 JW |
8023 | on characters (for example by using the C<:encoding(utf8)> I/O layer), |
8024 | tell() will return byte offsets, not character offsets (because | |
80d38338 | 8025 | implementing that would render sysseek() unacceptably slow). |
9124316e | 8026 | |
8f1da26d TC |
8027 | sysseek() bypasses normal buffered IO, so mixing it with reads other |
8028 | than C<sysread> (for example C<< <> >> or read()) C<print>, C<write>, | |
9124316e | 8029 | C<seek>, C<tell>, or C<eof> may cause confusion. |
86989e5d JH |
8030 | |
8031 | For WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>, | |
8032 | and C<SEEK_END> (start of the file, current position, end of the file) | |
8033 | from the Fcntl module. Use of the constants is also more portable | |
8034 | than relying on 0, 1, and 2. For example to define a "systell" function: | |
8035 | ||
5ed4f2ec | 8036 | use Fcntl 'SEEK_CUR'; |
8037 | sub systell { sysseek($_[0], 0, SEEK_CUR) } | |
8903cb82 | 8038 | |
8039 | Returns the new position, or the undefined value on failure. A position | |
19799a22 GS |
8040 | of zero is returned as the string C<"0 but true">; thus C<sysseek> returns |
8041 | true on success and false on failure, yet you can still easily determine | |
8903cb82 | 8042 | the new position. |
137443ea | 8043 | |
a0d0e21e | 8044 | =item system LIST |
d74e8afc | 8045 | X<system> X<shell> |
a0d0e21e | 8046 | |
8bf3b016 GS |
8047 | =item system PROGRAM LIST |
8048 | ||
c17cdb72 NC |
8049 | =for Pod::Functions run a separate program |
8050 | ||
19799a22 | 8051 | Does exactly the same thing as C<exec LIST>, except that a fork is |
8f1da26d | 8052 | done first and the parent process waits for the child process to |
80d38338 | 8053 | exit. Note that argument processing varies depending on the |
19799a22 GS |
8054 | number of arguments. If there is more than one argument in LIST, |
8055 | or if LIST is an array with more than one value, starts the program | |
8056 | given by the first element of the list with arguments given by the | |
8057 | rest of the list. If there is only one scalar argument, the argument | |
8058 | is checked for shell metacharacters, and if there are any, the | |
8059 | entire argument is passed to the system's command shell for parsing | |
8060 | (this is C</bin/sh -c> on Unix platforms, but varies on other | |
8061 | platforms). If there are no shell metacharacters in the argument, | |
8062 | it is split into words and passed directly to C<execvp>, which is | |
94d4006a TS |
8063 | more efficient. On Windows, only the C<system PROGRAM LIST> syntax will |
8064 | reliably avoid using the shell; C<system LIST>, even with more than one | |
8065 | element, will fall back to the shell if the first spawn fails. | |
19799a22 | 8066 | |
e9fa405d | 8067 | Perl will attempt to flush all files opened for |
0f897271 GS |
8068 | output before any operation that may do a fork, but this may not be |
8069 | supported on some platforms (see L<perlport>). To be safe, you may need | |
8070 | to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method | |
8071 | of C<IO::Handle> on any open handles. | |
a2008d6d | 8072 | |
9d6eb86e | 8073 | The return value is the exit status of the program as returned by the |
25379e53 | 8074 | C<wait> call. To get the actual exit value, shift right by eight (see |
391b733c | 8075 | below). See also L</exec>. This is I<not> what you want to use to capture |
8f1da26d | 8076 | the output from a command; for that you should use merely backticks or |
d5a9bfb0 | 8077 | C<qx//>, as described in L<perlop/"`STRING`">. Return value of -1 |
25379e53 RGS |
8078 | indicates a failure to start the program or an error of the wait(2) system |
8079 | call (inspect $! for the reason). | |
a0d0e21e | 8080 | |
1af1c0d6 JV |
8081 | If you'd like to make C<system> (and many other bits of Perl) die on error, |
8082 | have a look at the L<autodie> pragma. | |
8083 | ||
19799a22 GS |
8084 | Like C<exec>, C<system> allows you to lie to a program about its name if |
8085 | you use the C<system PROGRAM LIST> syntax. Again, see L</exec>. | |
8bf3b016 | 8086 | |
4c2e8b59 BD |
8087 | Since C<SIGINT> and C<SIGQUIT> are ignored during the execution of |
8088 | C<system>, if you expect your program to terminate on receipt of these | |
8089 | signals you will need to arrange to do so yourself based on the return | |
8090 | value. | |
28757baa | 8091 | |
8092 | @args = ("command", "arg1", "arg2"); | |
54310121 | 8093 | system(@args) == 0 |
a9a5a0dc | 8094 | or die "system @args failed: $?" |
28757baa | 8095 | |
95da743b | 8096 | If you'd like to manually inspect C<system>'s failure, you can check all |
1af1c0d6 | 8097 | possible failure modes by inspecting C<$?> like this: |
28757baa | 8098 | |
4ef107a6 | 8099 | if ($? == -1) { |
a9a5a0dc | 8100 | print "failed to execute: $!\n"; |
4ef107a6 DM |
8101 | } |
8102 | elsif ($? & 127) { | |
a9a5a0dc VP |
8103 | printf "child died with signal %d, %s coredump\n", |
8104 | ($? & 127), ($? & 128) ? 'with' : 'without'; | |
4ef107a6 DM |
8105 | } |
8106 | else { | |
a9a5a0dc | 8107 | printf "child exited with value %d\n", $? >> 8; |
4ef107a6 DM |
8108 | } |
8109 | ||
3b10bc60 | 8110 | Alternatively, you may inspect the value of C<${^CHILD_ERROR_NATIVE}> |
8111 | with the C<W*()> calls from the POSIX module. | |
9d6eb86e | 8112 | |
3b10bc60 | 8113 | When C<system>'s arguments are executed indirectly by the shell, |
8114 | results and return codes are subject to its quirks. | |
c8db1d39 | 8115 | See L<perlop/"`STRING`"> and L</exec> for details. |
bb32b41a | 8116 | |
0a18a49b | 8117 | Since C<system> does a C<fork> and C<wait> it may affect a C<SIGCHLD> |
391b733c | 8118 | handler. See L<perlipc> for details. |
0a18a49b | 8119 | |
ea9eb35a BJ |
8120 | Portability issues: L<perlport/system>. |
8121 | ||
a0d0e21e | 8122 | =item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET |
d74e8afc | 8123 | X<syswrite> |
a0d0e21e LW |
8124 | |
8125 | =item syswrite FILEHANDLE,SCALAR,LENGTH | |
8126 | ||
145d37e2 GA |
8127 | =item syswrite FILEHANDLE,SCALAR |
8128 | ||
c17cdb72 NC |
8129 | =for Pod::Functions fixed-length unbuffered output to a filehandle |
8130 | ||
3874323d | 8131 | Attempts to write LENGTH bytes of data from variable SCALAR to the |
3b10bc60 | 8132 | specified FILEHANDLE, using write(2). If LENGTH is |
3874323d | 8133 | not specified, writes whole SCALAR. It bypasses buffered IO, so |
9124316e | 8134 | mixing this with reads (other than C<sysread())>, C<print>, C<write>, |
3874323d | 8135 | C<seek>, C<tell>, or C<eof> may cause confusion because the perlio and |
8f1da26d | 8136 | stdio layers usually buffer data. Returns the number of bytes |
3874323d JH |
8137 | actually written, or C<undef> if there was an error (in this case the |
8138 | errno variable C<$!> is also set). If the LENGTH is greater than the | |
3b10bc60 | 8139 | data available in the SCALAR after the OFFSET, only as much data as is |
3874323d | 8140 | available will be written. |
ff68c719 | 8141 | |
8142 | An OFFSET may be specified to write the data from some part of the | |
8143 | string other than the beginning. A negative OFFSET specifies writing | |
9124316e | 8144 | that many characters counting backwards from the end of the string. |
3b10bc60 | 8145 | If SCALAR is of length zero, you can only use an OFFSET of 0. |
9124316e | 8146 | |
8f1da26d | 8147 | B<WARNING>: If the filehandle is marked C<:utf8>, Unicode characters |
3b10bc60 | 8148 | encoded in UTF-8 are written instead of bytes, and the LENGTH, OFFSET, and |
8f1da26d | 8149 | return value of syswrite() are in (UTF8-encoded Unicode) characters. |
3874323d | 8150 | The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer. |
8f1da26d TC |
8151 | Alternately, if the handle is not marked with an encoding but you |
8152 | attempt to write characters with code points over 255, raises an exception. | |
3874323d | 8153 | See L</binmode>, L</open>, and the C<open> pragma, L<open>. |
a0d0e21e LW |
8154 | |
8155 | =item tell FILEHANDLE | |
d74e8afc | 8156 | X<tell> |
a0d0e21e LW |
8157 | |
8158 | =item tell | |
8159 | ||
c17cdb72 NC |
8160 | =for Pod::Functions get current seekpointer on a filehandle |
8161 | ||
9124316e JH |
8162 | Returns the current position I<in bytes> for FILEHANDLE, or -1 on |
8163 | error. FILEHANDLE may be an expression whose value gives the name of | |
8164 | the actual filehandle. If FILEHANDLE is omitted, assumes the file | |
8165 | last read. | |
8166 | ||
8167 | Note the I<in bytes>: even if the filehandle has been set to | |
740d4bb2 JW |
8168 | operate on characters (for example by using the C<:encoding(utf8)> open |
8169 | layer), tell() will return byte offsets, not character offsets (because | |
8170 | that would render seek() and tell() rather slow). | |
2b5ab1e7 | 8171 | |
cfd73201 JH |
8172 | The return value of tell() for the standard streams like the STDIN |
8173 | depends on the operating system: it may return -1 or something else. | |
8174 | tell() on pipes, fifos, and sockets usually returns -1. | |
8175 | ||
19799a22 | 8176 | There is no C<systell> function. Use C<sysseek(FH, 0, 1)> for that. |
a0d0e21e | 8177 | |
3b10bc60 | 8178 | Do not use tell() (or other buffered I/O operations) on a filehandle |
8f1da26d | 8179 | that has been manipulated by sysread(), syswrite(), or sysseek(). |
59c9df15 | 8180 | Those functions ignore the buffering, while tell() does not. |
9124316e | 8181 | |
a0d0e21e | 8182 | =item telldir DIRHANDLE |
d74e8afc | 8183 | X<telldir> |
a0d0e21e | 8184 | |
c17cdb72 NC |
8185 | =for Pod::Functions get current seekpointer on a directory handle |
8186 | ||
19799a22 GS |
8187 | Returns the current position of the C<readdir> routines on DIRHANDLE. |
8188 | Value may be given to C<seekdir> to access a particular location in a | |
cf264981 SP |
8189 | directory. C<telldir> has the same caveats about possible directory |
8190 | compaction as the corresponding system library routine. | |
a0d0e21e | 8191 | |
4633a7c4 | 8192 | =item tie VARIABLE,CLASSNAME,LIST |
d74e8afc | 8193 | X<tie> |
a0d0e21e | 8194 | |
d9b04284 | 8195 | =for Pod::Functions +5.002 bind a variable to an object class |
c17cdb72 | 8196 | |
4633a7c4 LW |
8197 | This function binds a variable to a package class that will provide the |
8198 | implementation for the variable. VARIABLE is the name of the variable | |
8199 | to be enchanted. CLASSNAME is the name of a class implementing objects | |
64c33bad BG |
8200 | of correct type. Any additional arguments are passed to the |
8201 | appropriate constructor | |
8a059744 GS |
8202 | method of the class (meaning C<TIESCALAR>, C<TIEHANDLE>, C<TIEARRAY>, |
8203 | or C<TIEHASH>). Typically these are arguments such as might be passed | |
64c33bad BG |
8204 | to the C<dbm_open()> function of C. The object returned by the |
8205 | constructor is also returned by the C<tie> function, which would be useful | |
8a059744 | 8206 | if you want to access other methods in CLASSNAME. |
a0d0e21e | 8207 | |
19799a22 | 8208 | Note that functions such as C<keys> and C<values> may return huge lists |
1d2dff63 | 8209 | when used on large objects, like DBM files. You may prefer to use the |
19799a22 | 8210 | C<each> function to iterate over such. Example: |
a0d0e21e LW |
8211 | |
8212 | # print out history file offsets | |
4633a7c4 | 8213 | use NDBM_File; |
da0045b7 | 8214 | tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0); |
a0d0e21e | 8215 | while (($key,$val) = each %HIST) { |
a9a5a0dc | 8216 | print $key, ' = ', unpack('L',$val), "\n"; |
a0d0e21e LW |
8217 | } |
8218 | untie(%HIST); | |
8219 | ||
aa689395 | 8220 | A class implementing a hash should have the following methods: |
a0d0e21e | 8221 | |
4633a7c4 | 8222 | TIEHASH classname, LIST |
a0d0e21e LW |
8223 | FETCH this, key |
8224 | STORE this, key, value | |
8225 | DELETE this, key | |
8a059744 | 8226 | CLEAR this |
a0d0e21e LW |
8227 | EXISTS this, key |
8228 | FIRSTKEY this | |
8229 | NEXTKEY this, lastkey | |
a3bcc51e | 8230 | SCALAR this |
8a059744 | 8231 | DESTROY this |
d7da42b7 | 8232 | UNTIE this |
a0d0e21e | 8233 | |
4633a7c4 | 8234 | A class implementing an ordinary array should have the following methods: |
a0d0e21e | 8235 | |
4633a7c4 | 8236 | TIEARRAY classname, LIST |
a0d0e21e LW |
8237 | FETCH this, key |
8238 | STORE this, key, value | |
8a059744 GS |
8239 | FETCHSIZE this |
8240 | STORESIZE this, count | |
8241 | CLEAR this | |
8242 | PUSH this, LIST | |
8243 | POP this | |
8244 | SHIFT this | |
8245 | UNSHIFT this, LIST | |
8246 | SPLICE this, offset, length, LIST | |
8247 | EXTEND this, count | |
7c25cd54 DM |
8248 | DELETE this, key |
8249 | EXISTS this, key | |
8a059744 | 8250 | DESTROY this |
d7da42b7 | 8251 | UNTIE this |
8a059744 | 8252 | |
3b10bc60 | 8253 | A class implementing a filehandle should have the following methods: |
8a059744 GS |
8254 | |
8255 | TIEHANDLE classname, LIST | |
8256 | READ this, scalar, length, offset | |
8257 | READLINE this | |
8258 | GETC this | |
8259 | WRITE this, scalar, length, offset | |
8260 | PRINT this, LIST | |
8261 | PRINTF this, format, LIST | |
e08f2115 GA |
8262 | BINMODE this |
8263 | EOF this | |
8264 | FILENO this | |
8265 | SEEK this, position, whence | |
8266 | TELL this | |
8267 | OPEN this, mode, LIST | |
8a059744 GS |
8268 | CLOSE this |
8269 | DESTROY this | |
d7da42b7 | 8270 | UNTIE this |
a0d0e21e | 8271 | |
4633a7c4 | 8272 | A class implementing a scalar should have the following methods: |
a0d0e21e | 8273 | |
4633a7c4 | 8274 | TIESCALAR classname, LIST |
54310121 | 8275 | FETCH this, |
a0d0e21e | 8276 | STORE this, value |
8a059744 | 8277 | DESTROY this |
d7da42b7 | 8278 | UNTIE this |
8a059744 GS |
8279 | |
8280 | Not all methods indicated above need be implemented. See L<perltie>, | |
2b5ab1e7 | 8281 | L<Tie::Hash>, L<Tie::Array>, L<Tie::Scalar>, and L<Tie::Handle>. |
a0d0e21e | 8282 | |
3b10bc60 | 8283 | Unlike C<dbmopen>, the C<tie> function will not C<use> or C<require> a module |
8284 | for you; you need to do that explicitly yourself. See L<DB_File> | |
19799a22 | 8285 | or the F<Config> module for interesting C<tie> implementations. |
4633a7c4 | 8286 | |
b687b08b | 8287 | For further details see L<perltie>, L<"tied VARIABLE">. |
cc6b7395 | 8288 | |
f3cbc334 | 8289 | =item tied VARIABLE |
d74e8afc | 8290 | X<tied> |
f3cbc334 | 8291 | |
c17cdb72 NC |
8292 | =for Pod::Functions get a reference to the object underlying a tied variable |
8293 | ||
f3cbc334 | 8294 | Returns a reference to the object underlying VARIABLE (the same value |
19799a22 | 8295 | that was originally returned by the C<tie> call that bound the variable |
f3cbc334 RS |
8296 | to a package.) Returns the undefined value if VARIABLE isn't tied to a |
8297 | package. | |
8298 | ||
a0d0e21e | 8299 | =item time |
d74e8afc | 8300 | X<time> X<epoch> |
a0d0e21e | 8301 | |
c17cdb72 NC |
8302 | =for Pod::Functions return number of seconds since 1970 |
8303 | ||
da0045b7 | 8304 | Returns the number of non-leap seconds since whatever time the system |
ef4d88db | 8305 | considers to be the epoch, suitable for feeding to C<gmtime> and |
391b733c | 8306 | C<localtime>. On most systems the epoch is 00:00:00 UTC, January 1, 1970; |
ef4d88db NC |
8307 | a prominent exception being Mac OS Classic which uses 00:00:00, January 1, |
8308 | 1904 in the current local time zone for its epoch. | |
a0d0e21e | 8309 | |
8f1da26d TC |
8310 | For measuring time in better granularity than one second, use the |
8311 | L<Time::HiRes> module from Perl 5.8 onwards (or from CPAN before then), or, | |
8312 | if you have gettimeofday(2), you may be able to use the C<syscall> | |
8313 | interface of Perl. See L<perlfaq8> for details. | |
68f8bed4 | 8314 | |
435fbc73 GS |
8315 | For date and time processing look at the many related modules on CPAN. |
8316 | For a comprehensive date and time representation look at the | |
8317 | L<DateTime> module. | |
8318 | ||
a0d0e21e | 8319 | =item times |
d74e8afc | 8320 | X<times> |
a0d0e21e | 8321 | |
c17cdb72 NC |
8322 | =for Pod::Functions return elapsed time for self and child processes |
8323 | ||
8f1da26d TC |
8324 | Returns a four-element list giving the user and system times in |
8325 | seconds for this process and any exited children of this process. | |
a0d0e21e LW |
8326 | |
8327 | ($user,$system,$cuser,$csystem) = times; | |
8328 | ||
dc19f4fb MJD |
8329 | In scalar context, C<times> returns C<$user>. |
8330 | ||
3b10bc60 | 8331 | Children's times are only included for terminated children. |
2a958fe2 | 8332 | |
ea9eb35a BJ |
8333 | Portability issues: L<perlport/times>. |
8334 | ||
a0d0e21e LW |
8335 | =item tr/// |
8336 | ||
c17cdb72 NC |
8337 | =for Pod::Functions transliterate a string |
8338 | ||
9f4b9cd0 | 8339 | The transliteration operator. Same as C<y///>. See |
cdf6c183 | 8340 | L<perlop/"Quote-Like Operators">. |
a0d0e21e LW |
8341 | |
8342 | =item truncate FILEHANDLE,LENGTH | |
d74e8afc | 8343 | X<truncate> |
a0d0e21e LW |
8344 | |
8345 | =item truncate EXPR,LENGTH | |
8346 | ||
c17cdb72 NC |
8347 | =for Pod::Functions shorten a file |
8348 | ||
a0d0e21e | 8349 | Truncates the file opened on FILEHANDLE, or named by EXPR, to the |
3b10bc60 | 8350 | specified length. Raises an exception if truncate isn't implemented |
8f1da26d | 8351 | on your system. Returns true if successful, C<undef> on error. |
a0d0e21e | 8352 | |
90ddc76f MS |
8353 | The behavior is undefined if LENGTH is greater than the length of the |
8354 | file. | |
8355 | ||
8577f58c | 8356 | The position in the file of FILEHANDLE is left unchanged. You may want to |
96090e4f | 8357 | call L<seek|/"seek FILEHANDLE,POSITION,WHENCE"> before writing to the file. |
8577f58c | 8358 | |
ea9eb35a BJ |
8359 | Portability issues: L<perlport/truncate>. |
8360 | ||
a0d0e21e | 8361 | =item uc EXPR |
d74e8afc | 8362 | X<uc> X<uppercase> X<toupper> |
a0d0e21e | 8363 | |
54310121 | 8364 | =item uc |
bbce6d69 | 8365 | |
c17cdb72 NC |
8366 | =for Pod::Functions return upper-case version of a string |
8367 | ||
a0d0e21e | 8368 | Returns an uppercased version of EXPR. This is the internal function |
3980dc9c | 8369 | implementing the C<\U> escape in double-quoted strings. |
983ffd37 | 8370 | It does not attempt to do titlecase mapping on initial letters. See |
3980dc9c | 8371 | L</ucfirst> for that. |
a0d0e21e | 8372 | |
7660c0ab | 8373 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 8374 | |
3980dc9c KW |
8375 | This function behaves the same way under various pragma, such as in a locale, |
8376 | as L</lc> does. | |
8377 | ||
a0d0e21e | 8378 | =item ucfirst EXPR |
d74e8afc | 8379 | X<ucfirst> X<uppercase> |
a0d0e21e | 8380 | |
54310121 | 8381 | =item ucfirst |
bbce6d69 | 8382 | |
c17cdb72 NC |
8383 | =for Pod::Functions return a string with just the next letter in upper case |
8384 | ||
ad0029c4 JH |
8385 | Returns the value of EXPR with the first character in uppercase |
8386 | (titlecase in Unicode). This is the internal function implementing | |
3980dc9c | 8387 | the C<\u> escape in double-quoted strings. |
a0d0e21e | 8388 | |
7660c0ab | 8389 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 8390 | |
3980dc9c KW |
8391 | This function behaves the same way under various pragma, such as in a locale, |
8392 | as L</lc> does. | |
8393 | ||
a0d0e21e | 8394 | =item umask EXPR |
d74e8afc | 8395 | X<umask> |
a0d0e21e LW |
8396 | |
8397 | =item umask | |
8398 | ||
c17cdb72 NC |
8399 | =for Pod::Functions set file creation mode mask |
8400 | ||
2f9daede | 8401 | Sets the umask for the process to EXPR and returns the previous value. |
eec2d3df GS |
8402 | If EXPR is omitted, merely returns the current umask. |
8403 | ||
0591cd52 NT |
8404 | The Unix permission C<rwxr-x---> is represented as three sets of three |
8405 | bits, or three octal digits: C<0750> (the leading 0 indicates octal | |
b5a41e52 | 8406 | and isn't one of the digits). The C<umask> value is such a number |
0591cd52 NT |
8407 | representing disabled permissions bits. The permission (or "mode") |
8408 | values you pass C<mkdir> or C<sysopen> are modified by your umask, so | |
8409 | even if you tell C<sysopen> to create a file with permissions C<0777>, | |
8f1da26d | 8410 | if your umask is C<0022>, then the file will actually be created with |
0591cd52 NT |
8411 | permissions C<0755>. If your C<umask> were C<0027> (group can't |
8412 | write; others can't read, write, or execute), then passing | |
8f1da26d TC |
8413 | C<sysopen> C<0666> would create a file with mode C<0640> (because |
8414 | C<0666 &~ 027> is C<0640>). | |
0591cd52 NT |
8415 | |
8416 | Here's some advice: supply a creation mode of C<0666> for regular | |
19799a22 GS |
8417 | files (in C<sysopen>) and one of C<0777> for directories (in |
8418 | C<mkdir>) and executable files. This gives users the freedom of | |
0591cd52 NT |
8419 | choice: if they want protected files, they might choose process umasks |
8420 | of C<022>, C<027>, or even the particularly antisocial mask of C<077>. | |
8421 | Programs should rarely if ever make policy decisions better left to | |
8422 | the user. The exception to this is when writing files that should be | |
8423 | kept private: mail files, web browser cookies, I<.rhosts> files, and | |
8424 | so on. | |
8425 | ||
f86cebdf | 8426 | If umask(2) is not implemented on your system and you are trying to |
3b10bc60 | 8427 | restrict access for I<yourself> (i.e., C<< (EXPR & 0700) > 0 >>), |
8428 | raises an exception. If umask(2) is not implemented and you are | |
eec2d3df GS |
8429 | not trying to restrict access for yourself, returns C<undef>. |
8430 | ||
8431 | Remember that a umask is a number, usually given in octal; it is I<not> a | |
8432 | string of octal digits. See also L</oct>, if all you have is a string. | |
a0d0e21e | 8433 | |
ea9eb35a BJ |
8434 | Portability issues: L<perlport/umask>. |
8435 | ||
a0d0e21e | 8436 | =item undef EXPR |
d74e8afc | 8437 | X<undef> X<undefine> |
a0d0e21e LW |
8438 | |
8439 | =item undef | |
8440 | ||
c17cdb72 NC |
8441 | =for Pod::Functions remove a variable or function definition |
8442 | ||
54310121 | 8443 | Undefines the value of EXPR, which must be an lvalue. Use only on a |
19799a22 | 8444 | scalar value, an array (using C<@>), a hash (using C<%>), a subroutine |
3b10bc60 | 8445 | (using C<&>), or a typeglob (using C<*>). Saying C<undef $hash{$key}> |
20408e3c | 8446 | will probably not do what you expect on most predefined variables or |
4509d391 | 8447 | DBM list values, so don't do that; see L</delete>. Always returns the |
20408e3c GS |
8448 | undefined value. You can omit the EXPR, in which case nothing is |
8449 | undefined, but you still get an undefined value that you could, for | |
3b10bc60 | 8450 | instance, return from a subroutine, assign to a variable, or pass as a |
20408e3c | 8451 | parameter. Examples: |
a0d0e21e LW |
8452 | |
8453 | undef $foo; | |
f86cebdf | 8454 | undef $bar{'blurfl'}; # Compare to: delete $bar{'blurfl'}; |
a0d0e21e | 8455 | undef @ary; |
aa689395 | 8456 | undef %hash; |
a0d0e21e | 8457 | undef &mysub; |
20408e3c | 8458 | undef *xyz; # destroys $xyz, @xyz, %xyz, &xyz, etc. |
54310121 | 8459 | return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it; |
2f9daede TP |
8460 | select undef, undef, undef, 0.25; |
8461 | ($a, $b, undef, $c) = &foo; # Ignore third value returned | |
a0d0e21e | 8462 | |
5a964f20 TC |
8463 | Note that this is a unary operator, not a list operator. |
8464 | ||
a0d0e21e | 8465 | =item unlink LIST |
dd184578 | 8466 | X<unlink> X<delete> X<remove> X<rm> X<del> |
a0d0e21e | 8467 | |
54310121 | 8468 | =item unlink |
bbce6d69 | 8469 | |
c17cdb72 NC |
8470 | =for Pod::Functions remove one link to a file |
8471 | ||
391b733c FC |
8472 | Deletes a list of files. On success, it returns the number of files |
8473 | it successfully deleted. On failure, it returns false and sets C<$!> | |
40ea6f68 | 8474 | (errno): |
a0d0e21e | 8475 | |
40ea6f68 | 8476 | my $unlinked = unlink 'a', 'b', 'c'; |
a0d0e21e | 8477 | unlink @goners; |
40ea6f68 | 8478 | unlink glob "*.bak"; |
a0d0e21e | 8479 | |
40ea6f68 | 8480 | On error, C<unlink> will not tell you which files it could not remove. |
734c9e01 | 8481 | If you want to know which files you could not remove, try them one |
40ea6f68 | 8482 | at a time: |
a0d0e21e | 8483 | |
40ea6f68 | 8484 | foreach my $file ( @goners ) { |
8485 | unlink $file or warn "Could not unlink $file: $!"; | |
3b10bc60 | 8486 | } |
40ea6f68 | 8487 | |
8488 | Note: C<unlink> will not attempt to delete directories unless you are | |
391b733c | 8489 | superuser and the B<-U> flag is supplied to Perl. Even if these |
40ea6f68 | 8490 | conditions are met, be warned that unlinking a directory can inflict |
8491 | damage on your filesystem. Finally, using C<unlink> on directories is | |
8492 | not supported on many operating systems. Use C<rmdir> instead. | |
8493 | ||
8494 | If LIST is omitted, C<unlink> uses C<$_>. | |
bbce6d69 | 8495 | |
a0d0e21e | 8496 | =item unpack TEMPLATE,EXPR |
d74e8afc | 8497 | X<unpack> |
a0d0e21e | 8498 | |
13dcffc6 CS |
8499 | =item unpack TEMPLATE |
8500 | ||
c17cdb72 NC |
8501 | =for Pod::Functions convert binary structure into normal perl variables |
8502 | ||
19799a22 | 8503 | C<unpack> does the reverse of C<pack>: it takes a string |
2b6c5635 | 8504 | and expands it out into a list of values. |
19799a22 | 8505 | (In scalar context, it returns merely the first value produced.) |
2b6c5635 | 8506 | |
eae68503 | 8507 | If EXPR is omitted, unpacks the C<$_> string. |
3980dc9c | 8508 | See L<perlpacktut> for an introduction to this function. |
13dcffc6 | 8509 | |
2b6c5635 GS |
8510 | The string is broken into chunks described by the TEMPLATE. Each chunk |
8511 | is converted separately to a value. Typically, either the string is a result | |
f337b084 | 8512 | of C<pack>, or the characters of the string represent a C structure of some |
2b6c5635 GS |
8513 | kind. |
8514 | ||
19799a22 | 8515 | The TEMPLATE has the same format as in the C<pack> function. |
a0d0e21e LW |
8516 | Here's a subroutine that does substring: |
8517 | ||
8518 | sub substr { | |
5ed4f2ec | 8519 | my($what,$where,$howmuch) = @_; |
8520 | unpack("x$where a$howmuch", $what); | |
a0d0e21e LW |
8521 | } |
8522 | ||
8523 | and then there's | |
8524 | ||
f337b084 | 8525 | sub ordinal { unpack("W",$_[0]); } # same as ord() |
a0d0e21e | 8526 | |
2b6c5635 | 8527 | In addition to fields allowed in pack(), you may prefix a field with |
61eff3bc JH |
8528 | a %<number> to indicate that |
8529 | you want a <number>-bit checksum of the items instead of the items | |
2b6c5635 GS |
8530 | themselves. Default is a 16-bit checksum. Checksum is calculated by |
8531 | summing numeric values of expanded values (for string fields the sum of | |
8f1da26d | 8532 | C<ord($char)> is taken; for bit fields the sum of zeroes and ones). |
2b6c5635 GS |
8533 | |
8534 | For example, the following | |
a0d0e21e LW |
8535 | computes the same number as the System V sum program: |
8536 | ||
19799a22 | 8537 | $checksum = do { |
5ed4f2ec | 8538 | local $/; # slurp! |
8539 | unpack("%32W*",<>) % 65535; | |
19799a22 | 8540 | }; |
a0d0e21e LW |
8541 | |
8542 | The following efficiently counts the number of set bits in a bit vector: | |
8543 | ||
8544 | $setbits = unpack("%32b*", $selectmask); | |
8545 | ||
951ba7fe | 8546 | The C<p> and C<P> formats should be used with care. Since Perl |
3160c391 GS |
8547 | has no way of checking whether the value passed to C<unpack()> |
8548 | corresponds to a valid memory location, passing a pointer value that's | |
8549 | not known to be valid is likely to have disastrous consequences. | |
8550 | ||
49704364 WL |
8551 | If there are more pack codes or if the repeat count of a field or a group |
8552 | is larger than what the remainder of the input string allows, the result | |
3b10bc60 | 8553 | is not well defined: the repeat count may be decreased, or |
8554 | C<unpack()> may produce empty strings or zeros, or it may raise an exception. | |
8555 | If the input string is longer than one described by the TEMPLATE, | |
8556 | the remainder of that input string is ignored. | |
2b6c5635 | 8557 | |
851646ae | 8558 | See L</pack> for more examples and notes. |
5a929a98 | 8559 | |
532eee96 | 8560 | =item unshift ARRAY,LIST |
d74e8afc | 8561 | X<unshift> |
a0d0e21e | 8562 | |
f5a93a43 TC |
8563 | =item unshift EXPR,LIST |
8564 | ||
c17cdb72 NC |
8565 | =for Pod::Functions prepend more elements to the beginning of a list |
8566 | ||
19799a22 | 8567 | Does the opposite of a C<shift>. Or the opposite of a C<push>, |
a0d0e21e | 8568 | depending on how you look at it. Prepends list to the front of the |
8f1da26d | 8569 | array and returns the new number of elements in the array. |
a0d0e21e | 8570 | |
76e4c2bb | 8571 | unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/; |
a0d0e21e LW |
8572 | |
8573 | Note the LIST is prepended whole, not one element at a time, so the | |
19799a22 | 8574 | prepended elements stay in the same order. Use C<reverse> to do the |
a0d0e21e LW |
8575 | reverse. |
8576 | ||
f5a93a43 TC |
8577 | Starting with Perl 5.14, C<unshift> can take a scalar EXPR, which must hold |
8578 | a reference to an unblessed array. The argument will be dereferenced | |
8579 | automatically. This aspect of C<unshift> is considered highly | |
8580 | experimental. The exact behaviour may change in a future version of Perl. | |
cba5a3b0 | 8581 | |
bade7fbc TC |
8582 | To avoid confusing would-be users of your code who are running earlier |
8583 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
8584 | the top of your file to signal that your code will work I<only> on Perls of | |
8585 | a recent vintage: | |
8586 | ||
8587 | use 5.014; # so push/pop/etc work on scalars (experimental) | |
8588 | ||
8589 | =item untie VARIABLE | |
8590 | X<untie> | |
8591 | ||
c17cdb72 NC |
8592 | =for Pod::Functions break a tie binding to a variable |
8593 | ||
bade7fbc TC |
8594 | Breaks the binding between a variable and a package. |
8595 | (See L<tie|/tie VARIABLE,CLASSNAME,LIST>.) | |
8596 | Has no effect if the variable is not tied. | |
8597 | ||
f6c8478c | 8598 | =item use Module VERSION LIST |
d74e8afc | 8599 | X<use> X<module> X<import> |
f6c8478c GS |
8600 | |
8601 | =item use Module VERSION | |
8602 | ||
a0d0e21e LW |
8603 | =item use Module LIST |
8604 | ||
8605 | =item use Module | |
8606 | ||
da0045b7 | 8607 | =item use VERSION |
8608 | ||
c17cdb72 NC |
8609 | =for Pod::Functions load in a module at compile time and import its namespace |
8610 | ||
a0d0e21e LW |
8611 | Imports some semantics into the current package from the named module, |
8612 | generally by aliasing certain subroutine or variable names into your | |
8613 | package. It is exactly equivalent to | |
8614 | ||
6d9d0573 | 8615 | BEGIN { require Module; Module->import( LIST ); } |
a0d0e21e | 8616 | |
54310121 | 8617 | except that Module I<must> be a bareword. |
08ed3542 | 8618 | The importation can be made conditional by using the L<if> module. |
da0045b7 | 8619 | |
bd12309b DG |
8620 | In the peculiar C<use VERSION> form, VERSION may be either a positive |
8621 | decimal fraction such as 5.006, which will be compared to C<$]>, or a v-string | |
8622 | of the form v5.6.1, which will be compared to C<$^V> (aka $PERL_VERSION). An | |
3b10bc60 | 8623 | exception is raised if VERSION is greater than the version of the |
c986422f RGS |
8624 | current Perl interpreter; Perl will not attempt to parse the rest of the |
8625 | file. Compare with L</require>, which can do a similar check at run time. | |
8626 | Symmetrically, C<no VERSION> allows you to specify that you want a version | |
3b10bc60 | 8627 | of Perl older than the specified one. |
3b825e41 RK |
8628 | |
8629 | Specifying VERSION as a literal of the form v5.6.1 should generally be | |
8630 | avoided, because it leads to misleading error messages under earlier | |
2e8342de RGS |
8631 | versions of Perl (that is, prior to 5.6.0) that do not support this |
8632 | syntax. The equivalent numeric version should be used instead. | |
fbc891ce | 8633 | |
5ed4f2ec | 8634 | use v5.6.1; # compile time version check |
8635 | use 5.6.1; # ditto | |
8636 | use 5.006_001; # ditto; preferred for backwards compatibility | |
16070b82 GS |
8637 | |
8638 | This is often useful if you need to check the current Perl version before | |
2e8342de RGS |
8639 | C<use>ing library modules that won't work with older versions of Perl. |
8640 | (We try not to do this more than we have to.) | |
da0045b7 | 8641 | |
b39691c2 | 8642 | C<use VERSION> also lexically enables all features available in the requested |
4653ec93 | 8643 | version as defined by the C<feature> pragma, disabling any features |
1b8bf4b9 | 8644 | not in the requested version's feature bundle. See L<feature>. |
3b10bc60 | 8645 | Similarly, if the specified Perl version is greater than or equal to |
e9fa405d | 8646 | 5.12.0, strictures are enabled lexically as |
4653ec93 | 8647 | with C<use strict>. Any explicit use of |
70397346 | 8648 | C<use strict> or C<no strict> overrides C<use VERSION>, even if it comes |
2a2626d8 FC |
8649 | before it. Later use of C<use VERSION> |
8650 | will override all behavior of a previous | |
b39691c2 | 8651 | C<use VERSION>, possibly removing the C<strict> and C<feature> added by |
2a2626d8 FC |
8652 | C<use VERSION>. C<use VERSION> does not |
8653 | load the F<feature.pm> or F<strict.pm> | |
b39691c2 | 8654 | files. |
7dfde25d | 8655 | |
19799a22 | 8656 | The C<BEGIN> forces the C<require> and C<import> to happen at compile time. The |
7660c0ab | 8657 | C<require> makes sure the module is loaded into memory if it hasn't been |
3b10bc60 | 8658 | yet. The C<import> is not a builtin; it's just an ordinary static method |
19799a22 | 8659 | call into the C<Module> package to tell the module to import the list of |
a0d0e21e | 8660 | features back into the current package. The module can implement its |
19799a22 GS |
8661 | C<import> method any way it likes, though most modules just choose to |
8662 | derive their C<import> method via inheritance from the C<Exporter> class that | |
8663 | is defined in the C<Exporter> module. See L<Exporter>. If no C<import> | |
593b9c14 YST |
8664 | method can be found then the call is skipped, even if there is an AUTOLOAD |
8665 | method. | |
cb1a09d0 | 8666 | |
31686daf JP |
8667 | If you do not want to call the package's C<import> method (for instance, |
8668 | to stop your namespace from being altered), explicitly supply the empty list: | |
cb1a09d0 AD |
8669 | |
8670 | use Module (); | |
8671 | ||
8672 | That is exactly equivalent to | |
8673 | ||
5a964f20 | 8674 | BEGIN { require Module } |
a0d0e21e | 8675 | |
da0045b7 | 8676 | If the VERSION argument is present between Module and LIST, then the |
71be2cbc | 8677 | C<use> will call the VERSION method in class Module with the given |
8678 | version as an argument. The default VERSION method, inherited from | |
44dcb63b | 8679 | the UNIVERSAL class, croaks if the given version is larger than the |
b76cc8ba | 8680 | value of the variable C<$Module::VERSION>. |
f6c8478c GS |
8681 | |
8682 | Again, there is a distinction between omitting LIST (C<import> called | |
8683 | with no arguments) and an explicit empty LIST C<()> (C<import> not | |
8684 | called). Note that there is no comma after VERSION! | |
da0045b7 | 8685 | |
a0d0e21e LW |
8686 | Because this is a wide-open interface, pragmas (compiler directives) |
8687 | are also implemented this way. Currently implemented pragmas are: | |
8688 | ||
f3798619 | 8689 | use constant; |
4633a7c4 | 8690 | use diagnostics; |
f3798619 | 8691 | use integer; |
4438c4b7 JH |
8692 | use sigtrap qw(SEGV BUS); |
8693 | use strict qw(subs vars refs); | |
8694 | use subs qw(afunc blurfl); | |
8695 | use warnings qw(all); | |
58c7fc7c | 8696 | use sort qw(stable _quicksort _mergesort); |
a0d0e21e | 8697 | |
19799a22 | 8698 | Some of these pseudo-modules import semantics into the current |
5a964f20 TC |
8699 | block scope (like C<strict> or C<integer>, unlike ordinary modules, |
8700 | which import symbols into the current package (which are effective | |
8701 | through the end of the file). | |
a0d0e21e | 8702 | |
c362798e Z |
8703 | Because C<use> takes effect at compile time, it doesn't respect the |
8704 | ordinary flow control of the code being compiled. In particular, putting | |
8705 | a C<use> inside the false branch of a conditional doesn't prevent it | |
3b10bc60 | 8706 | from being processed. If a module or pragma only needs to be loaded |
c362798e Z |
8707 | conditionally, this can be done using the L<if> pragma: |
8708 | ||
8709 | use if $] < 5.008, "utf8"; | |
8710 | use if WANT_WARNINGS, warnings => qw(all); | |
8711 | ||
8f1da26d | 8712 | There's a corresponding C<no> declaration that unimports meanings imported |
19799a22 | 8713 | by C<use>, i.e., it calls C<unimport Module LIST> instead of C<import>. |
80d38338 TC |
8714 | It behaves just as C<import> does with VERSION, an omitted or empty LIST, |
8715 | or no unimport method being found. | |
a0d0e21e LW |
8716 | |
8717 | no integer; | |
8718 | no strict 'refs'; | |
4438c4b7 | 8719 | no warnings; |
a0d0e21e | 8720 | |
e0de7c21 | 8721 | Care should be taken when using the C<no VERSION> form of C<no>. It is |
8f1da26d | 8722 | I<only> meant to be used to assert that the running Perl is of a earlier |
e0de7c21 RS |
8723 | version than its argument and I<not> to undo the feature-enabling side effects |
8724 | of C<use VERSION>. | |
8725 | ||
ac634a9a | 8726 | See L<perlmodlib> for a list of standard modules and pragmas. See L<perlrun> |
3b10bc60 | 8727 | for the C<-M> and C<-m> command-line options to Perl that give C<use> |
31686daf | 8728 | functionality from the command-line. |
a0d0e21e LW |
8729 | |
8730 | =item utime LIST | |
d74e8afc | 8731 | X<utime> |
a0d0e21e | 8732 | |
c17cdb72 NC |
8733 | =for Pod::Functions set a file's last access and modify times |
8734 | ||
a0d0e21e | 8735 | Changes the access and modification times on each file of a list of |
8f1da26d | 8736 | files. The first two elements of the list must be the NUMERIC access |
a0d0e21e | 8737 | and modification times, in that order. Returns the number of files |
46cdf678 | 8738 | successfully changed. The inode change time of each file is set |
4bc2a53d | 8739 | to the current time. For example, this code has the same effect as the |
a4142048 WL |
8740 | Unix touch(1) command when the files I<already exist> and belong to |
8741 | the user running the program: | |
a0d0e21e LW |
8742 | |
8743 | #!/usr/bin/perl | |
2c21a326 GA |
8744 | $atime = $mtime = time; |
8745 | utime $atime, $mtime, @ARGV; | |
4bc2a53d | 8746 | |
e9fa405d | 8747 | Since Perl 5.8.0, if the first two elements of the list are C<undef>, |
3b10bc60 | 8748 | the utime(2) syscall from your C library is called with a null second |
391b733c | 8749 | argument. On most systems, this will set the file's access and |
80d38338 | 8750 | modification times to the current time (i.e., equivalent to the example |
3b10bc60 | 8751 | above) and will work even on files you don't own provided you have write |
a4142048 | 8752 | permission: |
c6f7b413 | 8753 | |
3b10bc60 | 8754 | for $file (@ARGV) { |
8755 | utime(undef, undef, $file) | |
8756 | || warn "couldn't touch $file: $!"; | |
8757 | } | |
c6f7b413 | 8758 | |
2c21a326 GA |
8759 | Under NFS this will use the time of the NFS server, not the time of |
8760 | the local machine. If there is a time synchronization problem, the | |
8761 | NFS server and local machine will have different times. The Unix | |
8762 | touch(1) command will in fact normally use this form instead of the | |
8763 | one shown in the first example. | |
8764 | ||
3b10bc60 | 8765 | Passing only one of the first two elements as C<undef> is |
8766 | equivalent to passing a 0 and will not have the effect | |
8767 | described when both are C<undef>. This also triggers an | |
2c21a326 GA |
8768 | uninitialized warning. |
8769 | ||
3b10bc60 | 8770 | On systems that support futimes(2), you may pass filehandles among the |
8771 | files. On systems that don't support futimes(2), passing filehandles raises | |
8772 | an exception. Filehandles must be passed as globs or glob references to be | |
8773 | recognized; barewords are considered filenames. | |
e96b369d | 8774 | |
ea9eb35a BJ |
8775 | Portability issues: L<perlport/utime>. |
8776 | ||
532eee96 | 8777 | =item values HASH |
d74e8afc | 8778 | X<values> |
a0d0e21e | 8779 | |
532eee96 | 8780 | =item values ARRAY |
aeedbbed | 8781 | |
f5a93a43 TC |
8782 | =item values EXPR |
8783 | ||
c17cdb72 NC |
8784 | =for Pod::Functions return a list of the values in a hash |
8785 | ||
bade7fbc TC |
8786 | In list context, returns a list consisting of all the values of the named |
8787 | hash. In Perl 5.12 or later only, will also return a list of the values of | |
8788 | an array; prior to that release, attempting to use an array argument will | |
8789 | produce a syntax error. In scalar context, returns the number of values. | |
504f80c1 | 8790 | |
7bf59113 YO |
8791 | Hash entries are returned in an apparently random order. The actual random |
8792 | order is specific to a given hash; the exact same series of operations | |
7161e5c2 | 8793 | on two hashes may result in a different order for each hash. Any insertion |
7bf59113 YO |
8794 | into the hash may change the order, as will any deletion, with the exception |
8795 | that the most recent key returned by C<each> or C<keys> may be deleted | |
7161e5c2 | 8796 | without changing the order. So long as a given hash is unmodified you may |
7bf59113 | 8797 | rely on C<keys>, C<values> and C<each> to repeatedly return the same order |
7161e5c2 FC |
8798 | as each other. See L<perlsec/"Algorithmic Complexity Attacks"> for |
8799 | details on why hash order is randomized. Aside from the guarantees | |
7bf59113 | 8800 | provided here the exact details of Perl's hash algorithm and the hash |
883f220b TC |
8801 | traversal order are subject to change in any release of Perl. Tied hashes |
8802 | may behave differently to Perl's hashes with respect to changes in order on | |
8803 | insertion and deletion of items. | |
504f80c1 | 8804 | |
aeedbbed | 8805 | As a side effect, calling values() resets the HASH or ARRAY's internal |
391b733c FC |
8806 | iterator, see L</each>. (In particular, calling values() in void context |
8807 | resets the iterator with no other overhead. Apart from resetting the | |
bade7fbc TC |
8808 | iterator, C<values @array> in list context is the same as plain C<@array>. |
8809 | (We recommend that you use void context C<keys @array> for this, but | |
8810 | reasoned that taking C<values @array> out would require more | |
8811 | documentation than leaving it in.) | |
aeedbbed | 8812 | |
8ea1e5d4 GS |
8813 | Note that the values are not copied, which means modifying them will |
8814 | modify the contents of the hash: | |
2b5ab1e7 | 8815 | |
f7051f2c FC |
8816 | for (values %hash) { s/foo/bar/g } # modifies %hash values |
8817 | for (@hash{keys %hash}) { s/foo/bar/g } # same | |
2b5ab1e7 | 8818 | |
f5a93a43 TC |
8819 | Starting with Perl 5.14, C<values> can take a scalar EXPR, which must hold |
8820 | a reference to an unblessed hash or array. The argument will be | |
8821 | dereferenced automatically. This aspect of C<values> is considered highly | |
8822 | experimental. The exact behaviour may change in a future version of Perl. | |
cba5a3b0 DG |
8823 | |
8824 | for (values $hashref) { ... } | |
8825 | for (values $obj->get_arrayref) { ... } | |
8826 | ||
bade7fbc TC |
8827 | To avoid confusing would-be users of your code who are running earlier |
8828 | versions of Perl with mysterious syntax errors, put this sort of thing at | |
8829 | the top of your file to signal that your code will work I<only> on Perls of | |
8830 | a recent vintage: | |
8831 | ||
8832 | use 5.012; # so keys/values/each work on arrays | |
8833 | use 5.014; # so keys/values/each work on scalars (experimental) | |
8834 | ||
19799a22 | 8835 | See also C<keys>, C<each>, and C<sort>. |
a0d0e21e LW |
8836 | |
8837 | =item vec EXPR,OFFSET,BITS | |
d74e8afc | 8838 | X<vec> X<bit> X<bit vector> |
a0d0e21e | 8839 | |
c17cdb72 NC |
8840 | =for Pod::Functions test or set particular bits in a string |
8841 | ||
e69129f1 | 8842 | Treats the string in EXPR as a bit vector made up of elements of |
8f1da26d | 8843 | width BITS and returns the value of the element specified by OFFSET |
e69129f1 GS |
8844 | as an unsigned integer. BITS therefore specifies the number of bits |
8845 | that are reserved for each element in the bit vector. This must | |
8846 | be a power of two from 1 to 32 (or 64, if your platform supports | |
8847 | that). | |
c5a0f51a | 8848 | |
b76cc8ba | 8849 | If BITS is 8, "elements" coincide with bytes of the input string. |
c73032f5 IZ |
8850 | |
8851 | If BITS is 16 or more, bytes of the input string are grouped into chunks | |
8852 | of size BITS/8, and each group is converted to a number as with | |
b1866b2d | 8853 | pack()/unpack() with big-endian formats C<n>/C<N> (and analogously |
c73032f5 IZ |
8854 | for BITS==64). See L<"pack"> for details. |
8855 | ||
8856 | If bits is 4 or less, the string is broken into bytes, then the bits | |
8857 | of each byte are broken into 8/BITS groups. Bits of a byte are | |
8858 | numbered in a little-endian-ish way, as in C<0x01>, C<0x02>, | |
8859 | C<0x04>, C<0x08>, C<0x10>, C<0x20>, C<0x40>, C<0x80>. For example, | |
8860 | breaking the single input byte C<chr(0x36)> into two groups gives a list | |
8861 | C<(0x6, 0x3)>; breaking it into 4 groups gives C<(0x2, 0x1, 0x3, 0x0)>. | |
8862 | ||
81e118e0 JH |
8863 | C<vec> may also be assigned to, in which case parentheses are needed |
8864 | to give the expression the correct precedence as in | |
22dc801b | 8865 | |
8866 | vec($image, $max_x * $x + $y, 8) = 3; | |
a0d0e21e | 8867 | |
fe58ced6 MG |
8868 | If the selected element is outside the string, the value 0 is returned. |
8869 | If an element off the end of the string is written to, Perl will first | |
8870 | extend the string with sufficiently many zero bytes. It is an error | |
80d38338 | 8871 | to try to write off the beginning of the string (i.e., negative OFFSET). |
fac70343 | 8872 | |
2575c402 JW |
8873 | If the string happens to be encoded as UTF-8 internally (and thus has |
8874 | the UTF8 flag set), this is ignored by C<vec>, and it operates on the | |
8875 | internal byte string, not the conceptual character string, even if you | |
8876 | only have characters with values less than 256. | |
246fae53 | 8877 | |
fac70343 GS |
8878 | Strings created with C<vec> can also be manipulated with the logical |
8879 | operators C<|>, C<&>, C<^>, and C<~>. These operators will assume a bit | |
8880 | vector operation is desired when both operands are strings. | |
c5a0f51a | 8881 | See L<perlop/"Bitwise String Operators">. |
a0d0e21e | 8882 | |
7660c0ab | 8883 | The following code will build up an ASCII string saying C<'PerlPerlPerl'>. |
19799a22 | 8884 | The comments show the string after each step. Note that this code works |
cca87523 GS |
8885 | in the same way on big-endian or little-endian machines. |
8886 | ||
8887 | my $foo = ''; | |
5ed4f2ec | 8888 | vec($foo, 0, 32) = 0x5065726C; # 'Perl' |
e69129f1 GS |
8889 | |
8890 | # $foo eq "Perl" eq "\x50\x65\x72\x6C", 32 bits | |
5ed4f2ec | 8891 | print vec($foo, 0, 8); # prints 80 == 0x50 == ord('P') |
8892 | ||
8893 | vec($foo, 2, 16) = 0x5065; # 'PerlPe' | |
8894 | vec($foo, 3, 16) = 0x726C; # 'PerlPerl' | |
8895 | vec($foo, 8, 8) = 0x50; # 'PerlPerlP' | |
8896 | vec($foo, 9, 8) = 0x65; # 'PerlPerlPe' | |
8897 | vec($foo, 20, 4) = 2; # 'PerlPerlPe' . "\x02" | |
8898 | vec($foo, 21, 4) = 7; # 'PerlPerlPer' | |
8899 | # 'r' is "\x72" | |
8900 | vec($foo, 45, 2) = 3; # 'PerlPerlPer' . "\x0c" | |
8901 | vec($foo, 93, 1) = 1; # 'PerlPerlPer' . "\x2c" | |
8902 | vec($foo, 94, 1) = 1; # 'PerlPerlPerl' | |
8903 | # 'l' is "\x6c" | |
cca87523 | 8904 | |
19799a22 | 8905 | To transform a bit vector into a string or list of 0's and 1's, use these: |
a0d0e21e LW |
8906 | |
8907 | $bits = unpack("b*", $vector); | |
8908 | @bits = split(//, unpack("b*", $vector)); | |
8909 | ||
7660c0ab | 8910 | If you know the exact length in bits, it can be used in place of the C<*>. |
a0d0e21e | 8911 | |
e69129f1 GS |
8912 | Here is an example to illustrate how the bits actually fall in place: |
8913 | ||
f7051f2c FC |
8914 | #!/usr/bin/perl -wl |
8915 | ||
8916 | print <<'EOT'; | |
8917 | 0 1 2 3 | |
8918 | unpack("V",$_) 01234567890123456789012345678901 | |
8919 | ------------------------------------------------------------------ | |
8920 | EOT | |
8921 | ||
8922 | for $w (0..3) { | |
8923 | $width = 2**$w; | |
8924 | for ($shift=0; $shift < $width; ++$shift) { | |
8925 | for ($off=0; $off < 32/$width; ++$off) { | |
8926 | $str = pack("B*", "0"x32); | |
8927 | $bits = (1<<$shift); | |
8928 | vec($str, $off, $width) = $bits; | |
8929 | $res = unpack("b*",$str); | |
8930 | $val = unpack("V", $str); | |
8931 | write; | |
8932 | } | |
8933 | } | |
8934 | } | |
8935 | ||
8936 | format STDOUT = | |
8937 | vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> | |
8938 | $off, $width, $bits, $val, $res | |
8939 | . | |
8940 | __END__ | |
e69129f1 | 8941 | |
80d38338 TC |
8942 | Regardless of the machine architecture on which it runs, the |
8943 | example above should print the following table: | |
e69129f1 | 8944 | |
f7051f2c FC |
8945 | 0 1 2 3 |
8946 | unpack("V",$_) 01234567890123456789012345678901 | |
8947 | ------------------------------------------------------------------ | |
8948 | vec($_, 0, 1) = 1 == 1 10000000000000000000000000000000 | |
8949 | vec($_, 1, 1) = 1 == 2 01000000000000000000000000000000 | |
8950 | vec($_, 2, 1) = 1 == 4 00100000000000000000000000000000 | |
8951 | vec($_, 3, 1) = 1 == 8 00010000000000000000000000000000 | |
8952 | vec($_, 4, 1) = 1 == 16 00001000000000000000000000000000 | |
8953 | vec($_, 5, 1) = 1 == 32 00000100000000000000000000000000 | |
8954 | vec($_, 6, 1) = 1 == 64 00000010000000000000000000000000 | |
8955 | vec($_, 7, 1) = 1 == 128 00000001000000000000000000000000 | |
8956 | vec($_, 8, 1) = 1 == 256 00000000100000000000000000000000 | |
8957 | vec($_, 9, 1) = 1 == 512 00000000010000000000000000000000 | |
8958 | vec($_,10, 1) = 1 == 1024 00000000001000000000000000000000 | |
8959 | vec($_,11, 1) = 1 == 2048 00000000000100000000000000000000 | |
8960 | vec($_,12, 1) = 1 == 4096 00000000000010000000000000000000 | |
8961 | vec($_,13, 1) = 1 == 8192 00000000000001000000000000000000 | |
8962 | vec($_,14, 1) = 1 == 16384 00000000000000100000000000000000 | |
8963 | vec($_,15, 1) = 1 == 32768 00000000000000010000000000000000 | |
8964 | vec($_,16, 1) = 1 == 65536 00000000000000001000000000000000 | |
8965 | vec($_,17, 1) = 1 == 131072 00000000000000000100000000000000 | |
8966 | vec($_,18, 1) = 1 == 262144 00000000000000000010000000000000 | |
8967 | vec($_,19, 1) = 1 == 524288 00000000000000000001000000000000 | |
8968 | vec($_,20, 1) = 1 == 1048576 00000000000000000000100000000000 | |
8969 | vec($_,21, 1) = 1 == 2097152 00000000000000000000010000000000 | |
8970 | vec($_,22, 1) = 1 == 4194304 00000000000000000000001000000000 | |
8971 | vec($_,23, 1) = 1 == 8388608 00000000000000000000000100000000 | |
8972 | vec($_,24, 1) = 1 == 16777216 00000000000000000000000010000000 | |
8973 | vec($_,25, 1) = 1 == 33554432 00000000000000000000000001000000 | |
8974 | vec($_,26, 1) = 1 == 67108864 00000000000000000000000000100000 | |
8975 | vec($_,27, 1) = 1 == 134217728 00000000000000000000000000010000 | |
8976 | vec($_,28, 1) = 1 == 268435456 00000000000000000000000000001000 | |
8977 | vec($_,29, 1) = 1 == 536870912 00000000000000000000000000000100 | |
8978 | vec($_,30, 1) = 1 == 1073741824 00000000000000000000000000000010 | |
8979 | vec($_,31, 1) = 1 == 2147483648 00000000000000000000000000000001 | |
8980 | vec($_, 0, 2) = 1 == 1 10000000000000000000000000000000 | |
8981 | vec($_, 1, 2) = 1 == 4 00100000000000000000000000000000 | |
8982 | vec($_, 2, 2) = 1 == 16 00001000000000000000000000000000 | |
8983 | vec($_, 3, 2) = 1 == 64 00000010000000000000000000000000 | |
8984 | vec($_, 4, 2) = 1 == 256 00000000100000000000000000000000 | |
8985 | vec($_, 5, 2) = 1 == 1024 00000000001000000000000000000000 | |
8986 | vec($_, 6, 2) = 1 == 4096 00000000000010000000000000000000 | |
8987 | vec($_, 7, 2) = 1 == 16384 00000000000000100000000000000000 | |
8988 | vec($_, 8, 2) = 1 == 65536 00000000000000001000000000000000 | |
8989 | vec($_, 9, 2) = 1 == 262144 00000000000000000010000000000000 | |
8990 | vec($_,10, 2) = 1 == 1048576 00000000000000000000100000000000 | |
8991 | vec($_,11, 2) = 1 == 4194304 00000000000000000000001000000000 | |
8992 | vec($_,12, 2) = 1 == 16777216 00000000000000000000000010000000 | |
8993 | vec($_,13, 2) = 1 == 67108864 00000000000000000000000000100000 | |
8994 | vec($_,14, 2) = 1 == 268435456 00000000000000000000000000001000 | |
8995 | vec($_,15, 2) = 1 == 1073741824 00000000000000000000000000000010 | |
8996 | vec($_, 0, 2) = 2 == 2 01000000000000000000000000000000 | |
8997 | vec($_, 1, 2) = 2 == 8 00010000000000000000000000000000 | |
8998 | vec($_, 2, 2) = 2 == 32 00000100000000000000000000000000 | |
8999 | vec($_, 3, 2) = 2 == 128 00000001000000000000000000000000 | |
9000 | vec($_, 4, 2) = 2 == 512 00000000010000000000000000000000 | |
9001 | vec($_, 5, 2) = 2 == 2048 00000000000100000000000000000000 | |
9002 | vec($_, 6, 2) = 2 == 8192 00000000000001000000000000000000 | |
9003 | vec($_, 7, 2) = 2 == 32768 00000000000000010000000000000000 | |
9004 | vec($_, 8, 2) = 2 == 131072 00000000000000000100000000000000 | |
9005 | vec($_, 9, 2) = 2 == 524288 00000000000000000001000000000000 | |
9006 | vec($_,10, 2) = 2 == 2097152 00000000000000000000010000000000 | |
9007 | vec($_,11, 2) = 2 == 8388608 00000000000000000000000100000000 | |
9008 | vec($_,12, 2) = 2 == 33554432 00000000000000000000000001000000 | |
9009 | vec($_,13, 2) = 2 == 134217728 00000000000000000000000000010000 | |
9010 | vec($_,14, 2) = 2 == 536870912 00000000000000000000000000000100 | |
9011 | vec($_,15, 2) = 2 == 2147483648 00000000000000000000000000000001 | |
9012 | vec($_, 0, 4) = 1 == 1 10000000000000000000000000000000 | |
9013 | vec($_, 1, 4) = 1 == 16 00001000000000000000000000000000 | |
9014 | vec($_, 2, 4) = 1 == 256 00000000100000000000000000000000 | |
9015 | vec($_, 3, 4) = 1 == 4096 00000000000010000000000000000000 | |
9016 | vec($_, 4, 4) = 1 == 65536 00000000000000001000000000000000 | |
9017 | vec($_, 5, 4) = 1 == 1048576 00000000000000000000100000000000 | |
9018 | vec($_, 6, 4) = 1 == 16777216 00000000000000000000000010000000 | |
9019 | vec($_, 7, 4) = 1 == 268435456 00000000000000000000000000001000 | |
9020 | vec($_, 0, 4) = 2 == 2 01000000000000000000000000000000 | |
9021 | vec($_, 1, 4) = 2 == 32 00000100000000000000000000000000 | |
9022 | vec($_, 2, 4) = 2 == 512 00000000010000000000000000000000 | |
9023 | vec($_, 3, 4) = 2 == 8192 00000000000001000000000000000000 | |
9024 | vec($_, 4, 4) = 2 == 131072 00000000000000000100000000000000 | |
9025 | vec($_, 5, 4) = 2 == 2097152 00000000000000000000010000000000 | |
9026 | vec($_, 6, 4) = 2 == 33554432 00000000000000000000000001000000 | |
9027 | vec($_, 7, 4) = 2 == 536870912 00000000000000000000000000000100 | |
9028 | vec($_, 0, 4) = 4 == 4 00100000000000000000000000000000 | |
9029 | vec($_, 1, 4) = 4 == 64 00000010000000000000000000000000 | |
9030 | vec($_, 2, 4) = 4 == 1024 00000000001000000000000000000000 | |
9031 | vec($_, 3, 4) = 4 == 16384 00000000000000100000000000000000 | |
9032 | vec($_, 4, 4) = 4 == 262144 00000000000000000010000000000000 | |
9033 | vec($_, 5, 4) = 4 == 4194304 00000000000000000000001000000000 | |
9034 | vec($_, 6, 4) = 4 == 67108864 00000000000000000000000000100000 | |
9035 | vec($_, 7, 4) = 4 == 1073741824 00000000000000000000000000000010 | |
9036 | vec($_, 0, 4) = 8 == 8 00010000000000000000000000000000 | |
9037 | vec($_, 1, 4) = 8 == 128 00000001000000000000000000000000 | |
9038 | vec($_, 2, 4) = 8 == 2048 00000000000100000000000000000000 | |
9039 | vec($_, 3, 4) = 8 == 32768 00000000000000010000000000000000 | |
9040 | vec($_, 4, 4) = 8 == 524288 00000000000000000001000000000000 | |
9041 | vec($_, 5, 4) = 8 == 8388608 00000000000000000000000100000000 | |
9042 | vec($_, 6, 4) = 8 == 134217728 00000000000000000000000000010000 | |
9043 | vec($_, 7, 4) = 8 == 2147483648 00000000000000000000000000000001 | |
9044 | vec($_, 0, 8) = 1 == 1 10000000000000000000000000000000 | |
9045 | vec($_, 1, 8) = 1 == 256 00000000100000000000000000000000 | |
9046 | vec($_, 2, 8) = 1 == 65536 00000000000000001000000000000000 | |
9047 | vec($_, 3, 8) = 1 == 16777216 00000000000000000000000010000000 | |
9048 | vec($_, 0, 8) = 2 == 2 01000000000000000000000000000000 | |
9049 | vec($_, 1, 8) = 2 == 512 00000000010000000000000000000000 | |
9050 | vec($_, 2, 8) = 2 == 131072 00000000000000000100000000000000 | |
9051 | vec($_, 3, 8) = 2 == 33554432 00000000000000000000000001000000 | |
9052 | vec($_, 0, 8) = 4 == 4 00100000000000000000000000000000 | |
9053 | vec($_, 1, 8) = 4 == 1024 00000000001000000000000000000000 | |
9054 | vec($_, 2, 8) = 4 == 262144 00000000000000000010000000000000 | |
9055 | vec($_, 3, 8) = 4 == 67108864 00000000000000000000000000100000 | |
9056 | vec($_, 0, 8) = 8 == 8 00010000000000000000000000000000 | |
9057 | vec($_, 1, 8) = 8 == 2048 00000000000100000000000000000000 | |
9058 | vec($_, 2, 8) = 8 == 524288 00000000000000000001000000000000 | |
9059 | vec($_, 3, 8) = 8 == 134217728 00000000000000000000000000010000 | |
9060 | vec($_, 0, 8) = 16 == 16 00001000000000000000000000000000 | |
9061 | vec($_, 1, 8) = 16 == 4096 00000000000010000000000000000000 | |
9062 | vec($_, 2, 8) = 16 == 1048576 00000000000000000000100000000000 | |
9063 | vec($_, 3, 8) = 16 == 268435456 00000000000000000000000000001000 | |
9064 | vec($_, 0, 8) = 32 == 32 00000100000000000000000000000000 | |
9065 | vec($_, 1, 8) = 32 == 8192 00000000000001000000000000000000 | |
9066 | vec($_, 2, 8) = 32 == 2097152 00000000000000000000010000000000 | |
9067 | vec($_, 3, 8) = 32 == 536870912 00000000000000000000000000000100 | |
9068 | vec($_, 0, 8) = 64 == 64 00000010000000000000000000000000 | |
9069 | vec($_, 1, 8) = 64 == 16384 00000000000000100000000000000000 | |
9070 | vec($_, 2, 8) = 64 == 4194304 00000000000000000000001000000000 | |
9071 | vec($_, 3, 8) = 64 == 1073741824 00000000000000000000000000000010 | |
9072 | vec($_, 0, 8) = 128 == 128 00000001000000000000000000000000 | |
9073 | vec($_, 1, 8) = 128 == 32768 00000000000000010000000000000000 | |
9074 | vec($_, 2, 8) = 128 == 8388608 00000000000000000000000100000000 | |
9075 | vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001 | |
e69129f1 | 9076 | |
a0d0e21e | 9077 | =item wait |
d74e8afc | 9078 | X<wait> |
a0d0e21e | 9079 | |
c17cdb72 NC |
9080 | =for Pod::Functions wait for any child process to die |
9081 | ||
3b10bc60 | 9082 | Behaves like wait(2) on your system: it waits for a child |
2b5ab1e7 | 9083 | process to terminate and returns the pid of the deceased process, or |
e5218da5 | 9084 | C<-1> if there are no child processes. The status is returned in C<$?> |
ca8d723e | 9085 | and C<${^CHILD_ERROR_NATIVE}>. |
2b5ab1e7 TC |
9086 | Note that a return value of C<-1> could mean that child processes are |
9087 | being automatically reaped, as described in L<perlipc>. | |
a0d0e21e | 9088 | |
c69ca1d4 | 9089 | If you use wait in your handler for $SIG{CHLD} it may accidentally for the |
391b733c | 9090 | child created by qx() or system(). See L<perlipc> for details. |
0a18a49b | 9091 | |
ea9eb35a BJ |
9092 | Portability issues: L<perlport/wait>. |
9093 | ||
a0d0e21e | 9094 | =item waitpid PID,FLAGS |
d74e8afc | 9095 | X<waitpid> |
a0d0e21e | 9096 | |
2a364e7e | 9097 | =for Pod::Functions wait for a particular child process to die |
c17cdb72 | 9098 | |
2b5ab1e7 TC |
9099 | Waits for a particular child process to terminate and returns the pid of |
9100 | the deceased process, or C<-1> if there is no such child process. On some | |
9101 | systems, a value of 0 indicates that there are processes still running. | |
ca8d723e | 9102 | The status is returned in C<$?> and C<${^CHILD_ERROR_NATIVE}>. If you say |
a0d0e21e | 9103 | |
5f05dabc | 9104 | use POSIX ":sys_wait_h"; |
5a964f20 | 9105 | #... |
b76cc8ba | 9106 | do { |
a9a5a0dc | 9107 | $kid = waitpid(-1, WNOHANG); |
84b74420 | 9108 | } while $kid > 0; |
a0d0e21e | 9109 | |
2b5ab1e7 TC |
9110 | then you can do a non-blocking wait for all pending zombie processes. |
9111 | Non-blocking wait is available on machines supporting either the | |
3b10bc60 | 9112 | waitpid(2) or wait4(2) syscalls. However, waiting for a particular |
2b5ab1e7 TC |
9113 | pid with FLAGS of C<0> is implemented everywhere. (Perl emulates the |
9114 | system call by remembering the status values of processes that have | |
9115 | exited but have not been harvested by the Perl script yet.) | |
a0d0e21e | 9116 | |
2b5ab1e7 TC |
9117 | Note that on some systems, a return value of C<-1> could mean that child |
9118 | processes are being automatically reaped. See L<perlipc> for details, | |
9119 | and for other examples. | |
5a964f20 | 9120 | |
ea9eb35a BJ |
9121 | Portability issues: L<perlport/waitpid>. |
9122 | ||
a0d0e21e | 9123 | =item wantarray |
d74e8afc | 9124 | X<wantarray> X<context> |
a0d0e21e | 9125 | |
c17cdb72 NC |
9126 | =for Pod::Functions get void vs scalar vs list context of current subroutine call |
9127 | ||
cc37eb0b | 9128 | Returns true if the context of the currently executing subroutine or |
20f13e4a | 9129 | C<eval> is looking for a list value. Returns false if the context is |
cc37eb0b RGS |
9130 | looking for a scalar. Returns the undefined value if the context is |
9131 | looking for no value (void context). | |
a0d0e21e | 9132 | |
5ed4f2ec | 9133 | return unless defined wantarray; # don't bother doing more |
54310121 | 9134 | my @a = complex_calculation(); |
9135 | return wantarray ? @a : "@a"; | |
a0d0e21e | 9136 | |
20f13e4a | 9137 | C<wantarray()>'s result is unspecified in the top level of a file, |
3c10abe3 AG |
9138 | in a C<BEGIN>, C<UNITCHECK>, C<CHECK>, C<INIT> or C<END> block, or |
9139 | in a C<DESTROY> method. | |
20f13e4a | 9140 | |
19799a22 GS |
9141 | This function should have been named wantlist() instead. |
9142 | ||
a0d0e21e | 9143 | =item warn LIST |
d74e8afc | 9144 | X<warn> X<warning> X<STDERR> |
a0d0e21e | 9145 | |
c17cdb72 NC |
9146 | =for Pod::Functions print debugging info |
9147 | ||
2d6d0015 | 9148 | Prints the value of LIST to STDERR. If the last element of LIST does |
afd8c9c8 DM |
9149 | not end in a newline, it appends the same file/line number text as C<die> |
9150 | does. | |
774d564b | 9151 | |
a96d0188 | 9152 | If the output is empty and C<$@> already contains a value (typically from a |
7660c0ab | 9153 | previous eval) that value is used after appending C<"\t...caught"> |
19799a22 GS |
9154 | to C<$@>. This is useful for staying almost, but not entirely similar to |
9155 | C<die>. | |
43051805 | 9156 | |
7660c0ab | 9157 | If C<$@> is empty then the string C<"Warning: Something's wrong"> is used. |
43051805 | 9158 | |
774d564b | 9159 | No message is printed if there is a C<$SIG{__WARN__}> handler |
9160 | installed. It is the handler's responsibility to deal with the message | |
19799a22 | 9161 | as it sees fit (like, for instance, converting it into a C<die>). Most |
80d38338 | 9162 | handlers must therefore arrange to actually display the |
19799a22 | 9163 | warnings that they are not prepared to deal with, by calling C<warn> |
774d564b | 9164 | again in the handler. Note that this is quite safe and will not |
9165 | produce an endless loop, since C<__WARN__> hooks are not called from | |
9166 | inside one. | |
9167 | ||
9168 | You will find this behavior is slightly different from that of | |
9169 | C<$SIG{__DIE__}> handlers (which don't suppress the error text, but can | |
19799a22 | 9170 | instead call C<die> again to change it). |
774d564b | 9171 | |
9172 | Using a C<__WARN__> handler provides a powerful way to silence all | |
9173 | warnings (even the so-called mandatory ones). An example: | |
9174 | ||
9175 | # wipe out *all* compile-time warnings | |
9176 | BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } } | |
9177 | my $foo = 10; | |
9178 | my $foo = 20; # no warning about duplicate my $foo, | |
9179 | # but hey, you asked for it! | |
9180 | # no compile-time or run-time warnings before here | |
9181 | $DOWARN = 1; | |
9182 | ||
9183 | # run-time warnings enabled after here | |
9184 | warn "\$foo is alive and $foo!"; # does show up | |
9185 | ||
8f1da26d | 9186 | See L<perlvar> for details on setting C<%SIG> entries and for more |
2b5ab1e7 TC |
9187 | examples. See the Carp module for other kinds of warnings using its |
9188 | carp() and cluck() functions. | |
a0d0e21e LW |
9189 | |
9190 | =item write FILEHANDLE | |
d74e8afc | 9191 | X<write> |
a0d0e21e LW |
9192 | |
9193 | =item write EXPR | |
9194 | ||
9195 | =item write | |
9196 | ||
c17cdb72 NC |
9197 | =for Pod::Functions print a picture record |
9198 | ||
5a964f20 | 9199 | Writes a formatted record (possibly multi-line) to the specified FILEHANDLE, |
a0d0e21e | 9200 | using the format associated with that file. By default the format for |
54310121 | 9201 | a file is the one having the same name as the filehandle, but the |
19799a22 | 9202 | format for the current output channel (see the C<select> function) may be set |
184e9718 | 9203 | explicitly by assigning the name of the format to the C<$~> variable. |
a0d0e21e | 9204 | |
8f1da26d TC |
9205 | Top of form processing is handled automatically: if there is insufficient |
9206 | room on the current page for the formatted record, the page is advanced by | |
dbaf95ac FC |
9207 | writing a form feed and a special top-of-page |
9208 | format is used to format the new | |
8f1da26d | 9209 | page header before the record is written. By default, the top-of-page |
dbaf95ac FC |
9210 | format is the name of the filehandle with "_TOP" appended, or "top" |
9211 | in the current package if the former does not exist. This would be a | |
8f1da26d TC |
9212 | problem with autovivified filehandles, but it may be dynamically set to the |
9213 | format of your choice by assigning the name to the C<$^> variable while | |
9214 | that filehandle is selected. The number of lines remaining on the current | |
9215 | page is in variable C<$->, which can be set to C<0> to force a new page. | |
a0d0e21e LW |
9216 | |
9217 | If FILEHANDLE is unspecified, output goes to the current default output | |
9218 | channel, which starts out as STDOUT but may be changed by the | |
19799a22 | 9219 | C<select> operator. If the FILEHANDLE is an EXPR, then the expression |
a0d0e21e LW |
9220 | is evaluated and the resulting string is used to look up the name of |
9221 | the FILEHANDLE at run time. For more on formats, see L<perlform>. | |
9222 | ||
19799a22 | 9223 | Note that write is I<not> the opposite of C<read>. Unfortunately. |
a0d0e21e LW |
9224 | |
9225 | =item y/// | |
9226 | ||
c17cdb72 NC |
9227 | =for Pod::Functions transliterate a string |
9228 | ||
9f4b9cd0 | 9229 | The transliteration operator. Same as C<tr///>. See |
cdf6c183 | 9230 | L<perlop/"Quote-Like Operators">. |
a0d0e21e LW |
9231 | |
9232 | =back | |
8f1da26d | 9233 | |
8f0d6a61 RS |
9234 | =head2 Non-function Keywords by Cross-reference |
9235 | ||
1336785e RS |
9236 | =head3 perldata |
9237 | ||
9238 | =over | |
9239 | ||
9240 | =item __DATA__ | |
9241 | ||
9242 | =item __END__ | |
9243 | ||
de9ddc26 | 9244 | These keywords are documented in L<perldata/"Special Literals">. |
1336785e RS |
9245 | |
9246 | =back | |
9247 | ||
9248 | =head3 perlmod | |
9249 | ||
9250 | =over | |
9251 | ||
9252 | =item BEGIN | |
9253 | ||
9254 | =item CHECK | |
9255 | ||
1336785e RS |
9256 | =item END |
9257 | ||
9258 | =item INIT | |
9259 | ||
9260 | =item UNITCHECK | |
9261 | ||
de9ddc26 | 9262 | These compile phase keywords are documented in L<perlmod/"BEGIN, UNITCHECK, CHECK, INIT and END">. |
1336785e RS |
9263 | |
9264 | =back | |
9265 | ||
081753c8 NC |
9266 | =head3 perlobj |
9267 | ||
9268 | =over | |
9269 | ||
9270 | =item DESTROY | |
9271 | ||
de9ddc26 | 9272 | This method keyword is documented in L<perlobj/"Destructors">. |
081753c8 NC |
9273 | |
9274 | =back | |
9275 | ||
8f0d6a61 RS |
9276 | =head3 perlop |
9277 | ||
9278 | =over | |
9279 | ||
9280 | =item and | |
9281 | ||
9282 | =item cmp | |
9283 | ||
9284 | =item eq | |
9285 | ||
9286 | =item ge | |
9287 | ||
9288 | =item gt | |
9289 | ||
8f0d6a61 RS |
9290 | =item le |
9291 | ||
9292 | =item lt | |
9293 | ||
9294 | =item ne | |
9295 | ||
9296 | =item not | |
9297 | ||
9298 | =item or | |
9299 | ||
9300 | =item x | |
9301 | ||
9302 | =item xor | |
9303 | ||
9304 | These operators are documented in L<perlop>. | |
9305 | ||
9306 | =back | |
9307 | ||
1336785e RS |
9308 | =head3 perlsub |
9309 | ||
9310 | =over | |
9311 | ||
9312 | =item AUTOLOAD | |
9313 | ||
de9ddc26 | 9314 | This keyword is documented in L<perlsub/"Autoloading">. |
1336785e RS |
9315 | |
9316 | =back | |
9317 | ||
41cf8e73 | 9318 | =head3 perlsyn |
8f0d6a61 RS |
9319 | |
9320 | =over | |
9321 | ||
9322 | =item else | |
9323 | ||
8f0d6a61 RS |
9324 | =item elsif |
9325 | ||
9326 | =item for | |
9327 | ||
9328 | =item foreach | |
9329 | ||
21f8b926 KW |
9330 | =item if |
9331 | ||
8f0d6a61 RS |
9332 | =item unless |
9333 | ||
9334 | =item until | |
9335 | ||
9336 | =item while | |
9337 | ||
de9ddc26 | 9338 | These flow-control keywords are documented in L<perlsyn/"Compound Statements">. |
8f0d6a61 | 9339 | |
d4a03217 AB |
9340 | =item elseif |
9341 | ||
444d4f5c FC |
9342 | The "else if" keyword is spelled C<elsif> in Perl. There's no C<elif> |
9343 | or C<else if> either. It does parse C<elseif>, but only to warn you | |
d4a03217 AB |
9344 | about not using it. |
9345 | ||
9346 | See the documentation for flow-control keywords in L<perlsyn/"Compound | |
9347 | Statements">. | |
9348 | ||
8f0d6a61 RS |
9349 | =back |
9350 | ||
dba7b065 NC |
9351 | =over |
9352 | ||
9353 | =item default | |
9354 | ||
9355 | =item given | |
9356 | ||
9357 | =item when | |
9358 | ||
9359 | These flow-control keywords related to the experimental switch feature are | |
2248d90c | 9360 | documented in L<perlsyn/"Switch Statements">. |
dba7b065 NC |
9361 | |
9362 | =back | |
9363 | ||
8f1da26d | 9364 | =cut |