Commit | Line | Data |
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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 | |
15 | operator. A unary operator generally provides a scalar context to its | |
2b5ab1e7 | 16 | argument, while a list operator may provide either scalar or list |
a0d0e21e | 17 | contexts for its arguments. If it does both, the scalar arguments will |
5f05dabc | 18 | be first, and the list argument will follow. (Note that there can ever |
0f31cffe | 19 | be only 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 | |
24 | list (and provide list context for the elements of the list) are shown | |
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. | |
cf264981 | 29 | Commas should separate 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 | |
5f05dabc | 33 | parentheses.) If you use the parentheses, the simple (but occasionally |
19799a22 | 34 | surprising) rule is this: It I<looks> like a function, therefore it I<is> a |
a0d0e21e LW |
35 | function, and precedence doesn't matter. Otherwise it's a list |
36 | operator or unary operator, and precedence does matter. And whitespace | |
37 | between the function and left parenthesis doesn't count--so you need to | |
38 | be careful sometimes: | |
39 | ||
68dc0745 | 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, |
54310121 | 58 | nonabortive failure is generally indicated in a scalar context by |
a0d0e21e LW |
59 | returning the undefined value, and in a list context by returning the |
60 | null list. | |
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. | |
a0d0e21e | 65 | Each operator and function decides which sort of value it 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 | ||
81 | In general, functions in Perl that serve as wrappers for system calls | |
f86cebdf | 82 | of the same name (like chown(2), fork(2), closedir(2), etc.) all 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, | |
19799a22 GS |
85 | which return C<-1> on failure. Exceptions to this rule are C<wait>, |
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 | ||
cb1a09d0 | 89 | =head2 Perl Functions by Category |
d74e8afc | 90 | X<function> |
cb1a09d0 AD |
91 | |
92 | Here are Perl's functions (including things that look like | |
5a964f20 | 93 | functions, like some keywords and named operators) |
cb1a09d0 AD |
94 | arranged by category. Some functions appear in more |
95 | than one place. | |
96 | ||
13a2d996 | 97 | =over 4 |
cb1a09d0 AD |
98 | |
99 | =item Functions for SCALARs or strings | |
d74e8afc | 100 | X<scalar> X<string> X<character> |
cb1a09d0 | 101 | |
22fae026 | 102 | C<chomp>, C<chop>, C<chr>, C<crypt>, C<hex>, C<index>, C<lc>, C<lcfirst>, |
1dc8ecb8 | 103 | C<length>, C<oct>, C<ord>, C<pack>, C<q//>, C<qq//>, C<reverse>, |
945c54fd | 104 | C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///> |
cb1a09d0 AD |
105 | |
106 | =item Regular expressions and pattern matching | |
d74e8afc | 107 | X<regular expression> X<regex> X<regexp> |
cb1a09d0 | 108 | |
ab4f32c2 | 109 | C<m//>, C<pos>, C<quotemeta>, C<s///>, C<split>, C<study>, C<qr//> |
cb1a09d0 AD |
110 | |
111 | =item Numeric functions | |
d74e8afc | 112 | X<numeric> X<number> X<trigonometric> X<trigonometry> |
cb1a09d0 | 113 | |
22fae026 TM |
114 | C<abs>, C<atan2>, C<cos>, C<exp>, C<hex>, C<int>, C<log>, C<oct>, C<rand>, |
115 | C<sin>, C<sqrt>, C<srand> | |
cb1a09d0 AD |
116 | |
117 | =item Functions for real @ARRAYs | |
d74e8afc | 118 | X<array> |
cb1a09d0 | 119 | |
22fae026 | 120 | C<pop>, C<push>, C<shift>, C<splice>, C<unshift> |
cb1a09d0 AD |
121 | |
122 | =item Functions for list data | |
d74e8afc | 123 | X<list> |
cb1a09d0 | 124 | |
1dc8ecb8 | 125 | C<grep>, C<join>, C<map>, C<qw//>, C<reverse>, C<sort>, C<unpack> |
cb1a09d0 AD |
126 | |
127 | =item Functions for real %HASHes | |
d74e8afc | 128 | X<hash> |
cb1a09d0 | 129 | |
22fae026 | 130 | C<delete>, C<each>, C<exists>, C<keys>, C<values> |
cb1a09d0 AD |
131 | |
132 | =item Input and output functions | |
d74e8afc | 133 | X<I/O> X<input> X<output> X<dbm> |
cb1a09d0 | 134 | |
22fae026 TM |
135 | C<binmode>, C<close>, C<closedir>, C<dbmclose>, C<dbmopen>, C<die>, C<eof>, |
136 | C<fileno>, C<flock>, C<format>, C<getc>, C<print>, C<printf>, C<read>, | |
0d863452 | 137 | C<readdir>, C<rewinddir>, C<say>, C<seek>, C<seekdir>, C<select>, C<syscall>, |
22fae026 TM |
138 | C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>, C<truncate>, |
139 | C<warn>, C<write> | |
cb1a09d0 AD |
140 | |
141 | =item Functions for fixed length data or records | |
142 | ||
22fae026 | 143 | C<pack>, C<read>, C<syscall>, C<sysread>, C<syswrite>, C<unpack>, C<vec> |
cb1a09d0 AD |
144 | |
145 | =item Functions for filehandles, files, or directories | |
d74e8afc | 146 | X<file> X<filehandle> X<directory> X<pipe> X<link> X<symlink> |
cb1a09d0 | 147 | |
22fae026 | 148 | C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>, |
5ff3f7a4 | 149 | C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>, |
1e278fd9 JH |
150 | C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<sysopen>, |
151 | C<umask>, C<unlink>, C<utime> | |
cb1a09d0 | 152 | |
cf264981 | 153 | =item Keywords related to the control flow of your Perl program |
d74e8afc | 154 | X<control flow> |
cb1a09d0 | 155 | |
98293880 JH |
156 | C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<eval>, C<exit>, |
157 | C<goto>, C<last>, C<next>, C<redo>, C<return>, C<sub>, C<wantarray> | |
cb1a09d0 | 158 | |
0d863452 RH |
159 | =item Keywords related to switch |
160 | ||
36fb85f3 | 161 | C<break>, C<continue>, C<given>, C<when>, C<default> |
0d863452 RH |
162 | |
163 | (These are only available if you enable the "switch" feature. | |
164 | See L<feature> and L<perlsyn/"Switch statements">.) | |
165 | ||
54310121 | 166 | =item Keywords related to scoping |
cb1a09d0 | 167 | |
36fb85f3 RGS |
168 | C<caller>, C<import>, C<local>, C<my>, C<our>, C<state>, C<package>, |
169 | C<use> | |
170 | ||
171 | (C<state> is only available if the "state" feature is enabled. See | |
172 | L<feature>.) | |
cb1a09d0 AD |
173 | |
174 | =item Miscellaneous functions | |
175 | ||
36fb85f3 | 176 | C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<our>, |
834df1c5 | 177 | C<reset>, C<scalar>, C<state>, C<undef>, C<wantarray> |
cb1a09d0 AD |
178 | |
179 | =item Functions for processes and process groups | |
d74e8afc | 180 | X<process> X<pid> X<process id> |
cb1a09d0 | 181 | |
22fae026 | 182 | C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>, |
1dc8ecb8 | 183 | C<pipe>, C<qx//>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>, |
22fae026 | 184 | C<times>, C<wait>, C<waitpid> |
cb1a09d0 AD |
185 | |
186 | =item Keywords related to perl modules | |
d74e8afc | 187 | X<module> |
cb1a09d0 | 188 | |
22fae026 | 189 | C<do>, C<import>, C<no>, C<package>, C<require>, C<use> |
cb1a09d0 | 190 | |
353c6505 | 191 | =item Keywords related to classes and object-orientation |
d74e8afc | 192 | X<object> X<class> X<package> |
cb1a09d0 | 193 | |
22fae026 TM |
194 | C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>, |
195 | C<untie>, C<use> | |
cb1a09d0 AD |
196 | |
197 | =item Low-level socket functions | |
d74e8afc | 198 | X<socket> X<sock> |
cb1a09d0 | 199 | |
22fae026 TM |
200 | C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>, |
201 | C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>, | |
737dd4b4 | 202 | C<socket>, C<socketpair> |
cb1a09d0 AD |
203 | |
204 | =item System V interprocess communication functions | |
d74e8afc | 205 | X<IPC> X<System V> X<semaphore> X<shared memory> X<memory> X<message> |
cb1a09d0 | 206 | |
22fae026 TM |
207 | C<msgctl>, C<msgget>, C<msgrcv>, C<msgsnd>, C<semctl>, C<semget>, C<semop>, |
208 | C<shmctl>, C<shmget>, C<shmread>, C<shmwrite> | |
cb1a09d0 AD |
209 | |
210 | =item Fetching user and group info | |
d74e8afc | 211 | X<user> X<group> X<password> X<uid> X<gid> X<passwd> X</etc/passwd> |
cb1a09d0 | 212 | |
22fae026 TM |
213 | C<endgrent>, C<endhostent>, C<endnetent>, C<endpwent>, C<getgrent>, |
214 | C<getgrgid>, C<getgrnam>, C<getlogin>, C<getpwent>, C<getpwnam>, | |
215 | C<getpwuid>, C<setgrent>, C<setpwent> | |
cb1a09d0 AD |
216 | |
217 | =item Fetching network info | |
d74e8afc | 218 | X<network> X<protocol> X<host> X<hostname> X<IP> X<address> X<service> |
cb1a09d0 | 219 | |
22fae026 TM |
220 | C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>, |
221 | C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>, | |
222 | C<getprotobyname>, C<getprotobynumber>, C<getprotoent>, | |
223 | C<getservbyname>, C<getservbyport>, C<getservent>, C<sethostent>, | |
224 | C<setnetent>, C<setprotoent>, C<setservent> | |
cb1a09d0 AD |
225 | |
226 | =item Time-related functions | |
d74e8afc | 227 | X<time> X<date> |
cb1a09d0 | 228 | |
22fae026 | 229 | C<gmtime>, C<localtime>, C<time>, C<times> |
cb1a09d0 | 230 | |
37798a01 | 231 | =item Functions new in perl5 |
d74e8afc | 232 | X<perl5> |
37798a01 | 233 | |
834df1c5 SP |
234 | C<abs>, C<bless>, C<break>, C<chomp>, C<chr>, C<continue>, C<default>, |
235 | C<exists>, C<formline>, C<given>, C<glob>, C<import>, C<lc>, C<lcfirst>, | |
1dc8ecb8 | 236 | C<lock>, C<map>, C<my>, C<no>, C<our>, C<prototype>, C<qr//>, C<qw//>, C<qx//>, |
834df1c5 SP |
237 | C<readline>, C<readpipe>, C<ref>, C<sub>*, C<sysopen>, C<tie>, C<tied>, C<uc>, |
238 | C<ucfirst>, C<untie>, C<use>, C<when> | |
37798a01 | 239 | |
240 | * - C<sub> was a keyword in perl4, but in perl5 it is an | |
5a964f20 | 241 | operator, which can be used in expressions. |
37798a01 | 242 | |
243 | =item Functions obsoleted in perl5 | |
244 | ||
22fae026 | 245 | C<dbmclose>, C<dbmopen> |
37798a01 | 246 | |
cb1a09d0 AD |
247 | =back |
248 | ||
60f9f73c | 249 | =head2 Portability |
d74e8afc | 250 | X<portability> X<Unix> X<portable> |
60f9f73c | 251 | |
2b5ab1e7 TC |
252 | Perl was born in Unix and can therefore access all common Unix |
253 | system calls. In non-Unix environments, the functionality of some | |
254 | Unix system calls may not be available, or details of the available | |
255 | functionality may differ slightly. The Perl functions affected | |
60f9f73c JH |
256 | by this are: |
257 | ||
258 | C<-X>, C<binmode>, C<chmod>, C<chown>, C<chroot>, C<crypt>, | |
259 | C<dbmclose>, C<dbmopen>, C<dump>, C<endgrent>, C<endhostent>, | |
260 | C<endnetent>, C<endprotoent>, C<endpwent>, C<endservent>, C<exec>, | |
ef5a6dd7 JH |
261 | C<fcntl>, C<flock>, C<fork>, C<getgrent>, C<getgrgid>, C<gethostbyname>, |
262 | C<gethostent>, C<getlogin>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>, | |
54d7b083 | 263 | C<getppid>, C<getpgrp>, C<getpriority>, C<getprotobynumber>, |
60f9f73c JH |
264 | C<getprotoent>, C<getpwent>, C<getpwnam>, C<getpwuid>, |
265 | C<getservbyport>, C<getservent>, C<getsockopt>, C<glob>, C<ioctl>, | |
266 | C<kill>, C<link>, C<lstat>, C<msgctl>, C<msgget>, C<msgrcv>, | |
2b5ab1e7 | 267 | C<msgsnd>, C<open>, C<pipe>, C<readlink>, C<rename>, C<select>, C<semctl>, |
60f9f73c JH |
268 | C<semget>, C<semop>, C<setgrent>, C<sethostent>, C<setnetent>, |
269 | C<setpgrp>, C<setpriority>, C<setprotoent>, C<setpwent>, | |
270 | C<setservent>, C<setsockopt>, C<shmctl>, C<shmget>, C<shmread>, | |
737dd4b4 | 271 | C<shmwrite>, C<socket>, C<socketpair>, |
80cbd5ad JH |
272 | C<stat>, C<symlink>, C<syscall>, C<sysopen>, C<system>, |
273 | C<times>, C<truncate>, C<umask>, C<unlink>, | |
2b5ab1e7 | 274 | C<utime>, C<wait>, C<waitpid> |
60f9f73c JH |
275 | |
276 | For more information about the portability of these functions, see | |
277 | L<perlport> and other available platform-specific documentation. | |
278 | ||
cb1a09d0 AD |
279 | =head2 Alphabetical Listing of Perl Functions |
280 | ||
a0d0e21e LW |
281 | =over 8 |
282 | ||
5b3c99c0 | 283 | =item -X FILEHANDLE |
d74e8afc ITB |
284 | 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> |
285 | 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 | 286 | |
5b3c99c0 | 287 | =item -X EXPR |
a0d0e21e | 288 | |
5228a96c SP |
289 | =item -X DIRHANDLE |
290 | ||
5b3c99c0 | 291 | =item -X |
a0d0e21e LW |
292 | |
293 | A file test, where X is one of the letters listed below. This unary | |
5228a96c SP |
294 | operator takes one argument, either a filename, a filehandle, or a dirhandle, |
295 | and tests the associated file to see if something is true about it. If the | |
7660c0ab | 296 | argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN. |
19799a22 | 297 | Unless otherwise documented, it returns C<1> for true and C<''> for false, or |
a0d0e21e | 298 | the undefined value if the file doesn't exist. Despite the funny |
d0821a6a | 299 | names, precedence is the same as any other named unary operator. The |
a0d0e21e LW |
300 | operator may be any of: |
301 | ||
302 | -r File is readable by effective uid/gid. | |
303 | -w File is writable by effective uid/gid. | |
304 | -x File is executable by effective uid/gid. | |
305 | -o File is owned by effective uid. | |
306 | ||
307 | -R File is readable by real uid/gid. | |
308 | -W File is writable by real uid/gid. | |
309 | -X File is executable by real uid/gid. | |
310 | -O File is owned by real uid. | |
311 | ||
312 | -e File exists. | |
8e7e0aa8 MJD |
313 | -z File has zero size (is empty). |
314 | -s File has nonzero size (returns size in bytes). | |
a0d0e21e LW |
315 | |
316 | -f File is a plain file. | |
317 | -d File is a directory. | |
318 | -l File is a symbolic link. | |
9c4d0f16 | 319 | -p File is a named pipe (FIFO), or Filehandle is a pipe. |
a0d0e21e LW |
320 | -S File is a socket. |
321 | -b File is a block special file. | |
322 | -c File is a character special file. | |
323 | -t Filehandle is opened to a tty. | |
324 | ||
325 | -u File has setuid bit set. | |
326 | -g File has setgid bit set. | |
327 | -k File has sticky bit set. | |
328 | ||
121910a4 | 329 | -T File is an ASCII text file (heuristic guess). |
2cdbc966 | 330 | -B File is a "binary" file (opposite of -T). |
a0d0e21e | 331 | |
95a3fe12 | 332 | -M Script start time minus file modification time, in days. |
a0d0e21e | 333 | -A Same for access time. |
95a3fe12 | 334 | -C Same for inode change time (Unix, may differ for other platforms) |
a0d0e21e | 335 | |
a0d0e21e LW |
336 | Example: |
337 | ||
338 | while (<>) { | |
5b3eff12 | 339 | chomp; |
a0d0e21e | 340 | next unless -f $_; # ignore specials |
5a964f20 | 341 | #... |
a0d0e21e LW |
342 | } |
343 | ||
5ff3f7a4 GS |
344 | The interpretation of the file permission operators C<-r>, C<-R>, |
345 | C<-w>, C<-W>, C<-x>, and C<-X> is by default based solely on the mode | |
346 | of the file and the uids and gids of the user. There may be other | |
ecae030f MO |
347 | reasons you can't actually read, write, or execute the file: for |
348 | example network filesystem access controls, ACLs (access control lists), | |
349 | read-only filesystems, and unrecognized executable formats. Note | |
350 | that the use of these six specific operators to verify if some operation | |
351 | is possible is usually a mistake, because it may be open to race | |
352 | conditions. | |
5ff3f7a4 | 353 | |
2b5ab1e7 TC |
354 | Also note that, for the superuser on the local filesystems, the C<-r>, |
355 | C<-R>, C<-w>, and C<-W> tests always return 1, and C<-x> and C<-X> return 1 | |
5ff3f7a4 GS |
356 | if any execute bit is set in the mode. Scripts run by the superuser |
357 | may thus need to do a stat() to determine the actual mode of the file, | |
2b5ab1e7 | 358 | or temporarily set their effective uid to something else. |
5ff3f7a4 GS |
359 | |
360 | If you are using ACLs, there is a pragma called C<filetest> that may | |
361 | produce more accurate results than the bare stat() mode bits. | |
5ff3f7a4 GS |
362 | When under the C<use filetest 'access'> the above-mentioned filetests |
363 | will test whether the permission can (not) be granted using the | |
468541a8 | 364 | access() family of system calls. Also note that the C<-x> and C<-X> may |
5ff3f7a4 GS |
365 | under this pragma return true even if there are no execute permission |
366 | bits set (nor any extra execute permission ACLs). This strangeness is | |
ecae030f MO |
367 | due to the underlying system calls' definitions. Note also that, due to |
368 | the implementation of C<use filetest 'access'>, the C<_> special | |
369 | filehandle won't cache the results of the file tests when this pragma is | |
370 | in effect. Read the documentation for the C<filetest> pragma for more | |
371 | information. | |
5ff3f7a4 | 372 | |
a0d0e21e LW |
373 | Note that C<-s/a/b/> does not do a negated substitution. Saying |
374 | C<-exp($foo)> still works as expected, however--only single letters | |
375 | following a minus are interpreted as file tests. | |
376 | ||
377 | The C<-T> and C<-B> switches work as follows. The first block or so of the | |
378 | file is examined for odd characters such as strange control codes or | |
61eff3bc | 379 | characters with the high bit set. If too many strange characters (>30%) |
cf264981 | 380 | are found, it's a C<-B> file; otherwise it's a C<-T> file. Also, any file |
a0d0e21e | 381 | containing null in the first block is considered a binary file. If C<-T> |
9124316e | 382 | or C<-B> is used on a filehandle, the current IO buffer is examined |
19799a22 | 383 | rather than the first block. Both C<-T> and C<-B> return true on a null |
54310121 | 384 | file, or a file at EOF when testing a filehandle. Because you have to |
4633a7c4 LW |
385 | read a file to do the C<-T> test, on most occasions you want to use a C<-f> |
386 | against the file first, as in C<next unless -f $file && -T $file>. | |
a0d0e21e | 387 | |
19799a22 | 388 | If any of the file tests (or either the C<stat> or C<lstat> operators) are given |
28757baa | 389 | the special filehandle consisting of a solitary underline, then the stat |
a0d0e21e LW |
390 | structure of the previous file test (or stat operator) is used, saving |
391 | a system call. (This doesn't work with C<-t>, and you need to remember | |
392 | that lstat() and C<-l> will leave values in the stat structure for the | |
5c9aa243 | 393 | symbolic link, not the real file.) (Also, if the stat buffer was filled by |
cf264981 | 394 | an C<lstat> call, C<-T> and C<-B> will reset it with the results of C<stat _>). |
5c9aa243 | 395 | Example: |
a0d0e21e LW |
396 | |
397 | print "Can do.\n" if -r $a || -w _ || -x _; | |
398 | ||
399 | stat($filename); | |
400 | print "Readable\n" if -r _; | |
401 | print "Writable\n" if -w _; | |
402 | print "Executable\n" if -x _; | |
403 | print "Setuid\n" if -u _; | |
404 | print "Setgid\n" if -g _; | |
405 | print "Sticky\n" if -k _; | |
406 | print "Text\n" if -T _; | |
407 | print "Binary\n" if -B _; | |
408 | ||
fbb0b3b3 RGS |
409 | As of Perl 5.9.1, as a form of purely syntactic sugar, you can stack file |
410 | test operators, in a way that C<-f -w -x $file> is equivalent to | |
cf264981 | 411 | C<-x $file && -w _ && -f _>. (This is only syntax fancy: if you use |
fbb0b3b3 RGS |
412 | the return value of C<-f $file> as an argument to another filetest |
413 | operator, no special magic will happen.) | |
414 | ||
a0d0e21e | 415 | =item abs VALUE |
d74e8afc | 416 | X<abs> X<absolute> |
a0d0e21e | 417 | |
54310121 | 418 | =item abs |
bbce6d69 | 419 | |
a0d0e21e | 420 | Returns the absolute value of its argument. |
7660c0ab | 421 | If VALUE is omitted, uses C<$_>. |
a0d0e21e LW |
422 | |
423 | =item accept NEWSOCKET,GENERICSOCKET | |
d74e8afc | 424 | X<accept> |
a0d0e21e | 425 | |
f86cebdf | 426 | Accepts an incoming socket connect, just as the accept(2) system call |
19799a22 | 427 | does. Returns the packed address if it succeeded, false otherwise. |
2b5ab1e7 | 428 | See the example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e | 429 | |
8d2a6795 GS |
430 | On systems that support a close-on-exec flag on files, the flag will |
431 | be set for the newly opened file descriptor, as determined by the | |
432 | value of $^F. See L<perlvar/$^F>. | |
433 | ||
a0d0e21e | 434 | =item alarm SECONDS |
d74e8afc ITB |
435 | X<alarm> |
436 | X<SIGALRM> | |
437 | X<timer> | |
a0d0e21e | 438 | |
54310121 | 439 | =item alarm |
bbce6d69 | 440 | |
a0d0e21e | 441 | Arranges to have a SIGALRM delivered to this process after the |
cf264981 | 442 | specified number of wallclock seconds has elapsed. If SECONDS is not |
d400eac8 JH |
443 | specified, the value stored in C<$_> is used. (On some machines, |
444 | unfortunately, the elapsed time may be up to one second less or more | |
445 | than you specified because of how seconds are counted, and process | |
446 | scheduling may delay the delivery of the signal even further.) | |
447 | ||
448 | Only one timer may be counting at once. Each call disables the | |
449 | previous timer, and an argument of C<0> may be supplied to cancel the | |
450 | previous timer without starting a new one. The returned value is the | |
451 | amount of time remaining on the previous timer. | |
a0d0e21e | 452 | |
2bc69794 BS |
453 | For delays of finer granularity than one second, the Time::HiRes module |
454 | (from CPAN, and starting from Perl 5.8 part of the standard | |
455 | distribution) provides ualarm(). You may also use Perl's four-argument | |
456 | version of select() leaving the first three arguments undefined, or you | |
457 | might be able to use the C<syscall> interface to access setitimer(2) if | |
458 | your system supports it. See L<perlfaq8> for details. | |
2b5ab1e7 | 459 | |
68f8bed4 JH |
460 | It is usually a mistake to intermix C<alarm> and C<sleep> calls. |
461 | (C<sleep> may be internally implemented in your system with C<alarm>) | |
a0d0e21e | 462 | |
19799a22 GS |
463 | If you want to use C<alarm> to time out a system call you need to use an |
464 | C<eval>/C<die> pair. You can't rely on the alarm causing the system call to | |
f86cebdf | 465 | fail with C<$!> set to C<EINTR> because Perl sets up signal handlers to |
19799a22 | 466 | restart system calls on some systems. Using C<eval>/C<die> always works, |
5a964f20 | 467 | modulo the caveats given in L<perlipc/"Signals">. |
ff68c719 | 468 | |
469 | eval { | |
f86cebdf | 470 | local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required |
36477c24 | 471 | alarm $timeout; |
ff68c719 | 472 | $nread = sysread SOCKET, $buffer, $size; |
36477c24 | 473 | alarm 0; |
ff68c719 | 474 | }; |
ff68c719 | 475 | if ($@) { |
f86cebdf | 476 | die unless $@ eq "alarm\n"; # propagate unexpected errors |
ff68c719 | 477 | # timed out |
478 | } | |
479 | else { | |
480 | # didn't | |
481 | } | |
482 | ||
91d81acc JH |
483 | For more information see L<perlipc>. |
484 | ||
a0d0e21e | 485 | =item atan2 Y,X |
d74e8afc | 486 | X<atan2> X<arctangent> X<tan> X<tangent> |
a0d0e21e LW |
487 | |
488 | Returns the arctangent of Y/X in the range -PI to PI. | |
489 | ||
ca6e1c26 | 490 | For the tangent operation, you may use the C<Math::Trig::tan> |
28757baa | 491 | function, or use the familiar relation: |
492 | ||
493 | sub tan { sin($_[0]) / cos($_[0]) } | |
494 | ||
a1021d57 RGS |
495 | The return value for C<atan2(0,0)> is implementation-defined; consult |
496 | your atan2(3) manpage for more information. | |
bf5f1b4c | 497 | |
a0d0e21e | 498 | =item bind SOCKET,NAME |
d74e8afc | 499 | X<bind> |
a0d0e21e LW |
500 | |
501 | Binds a network address to a socket, just as the bind system call | |
19799a22 | 502 | does. Returns true if it succeeded, false otherwise. NAME should be a |
4633a7c4 LW |
503 | packed address of the appropriate type for the socket. See the examples in |
504 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 505 | |
fae2c0fb | 506 | =item binmode FILEHANDLE, LAYER |
d74e8afc | 507 | X<binmode> X<binary> X<text> X<DOS> X<Windows> |
1c1fc3ea | 508 | |
a0d0e21e LW |
509 | =item binmode FILEHANDLE |
510 | ||
1cbfc93d NIS |
511 | Arranges for FILEHANDLE to be read or written in "binary" or "text" |
512 | mode on systems where the run-time libraries distinguish between | |
513 | binary and text files. If FILEHANDLE is an expression, the value is | |
514 | taken as the name of the filehandle. Returns true on success, | |
b5fe5ca2 | 515 | otherwise it returns C<undef> and sets C<$!> (errno). |
1cbfc93d | 516 | |
d807c6f4 JH |
517 | On some systems (in general, DOS and Windows-based systems) binmode() |
518 | is necessary when you're not working with a text file. For the sake | |
519 | of portability it is a good idea to always use it when appropriate, | |
520 | and to never use it when it isn't appropriate. Also, people can | |
521 | set their I/O to be by default UTF-8 encoded Unicode, not bytes. | |
522 | ||
523 | In other words: regardless of platform, use binmode() on binary data, | |
524 | like for example images. | |
525 | ||
526 | If LAYER is present it is a single string, but may contain multiple | |
527 | directives. The directives alter the behaviour of the file handle. | |
528 | When LAYER is present using binmode on text file makes sense. | |
529 | ||
fae2c0fb | 530 | If LAYER is omitted or specified as C<:raw> the filehandle is made |
0226bbdb NIS |
531 | suitable for passing binary data. This includes turning off possible CRLF |
532 | translation and marking it as bytes (as opposed to Unicode characters). | |
749683d2 | 533 | Note that, despite what may be implied in I<"Programming Perl"> (the |
165a9987 PJ |
534 | Camel) or elsewhere, C<:raw> is I<not> simply the inverse of C<:crlf> |
535 | -- other layers which would affect the binary nature of the stream are | |
0226bbdb NIS |
536 | I<also> disabled. See L<PerlIO>, L<perlrun> and the discussion about the |
537 | PERLIO environment variable. | |
01e6739c | 538 | |
d807c6f4 JH |
539 | The C<:bytes>, C<:crlf>, and C<:utf8>, and any other directives of the |
540 | form C<:...>, are called I/O I<layers>. The C<open> pragma can be used to | |
541 | establish default I/O layers. See L<open>. | |
542 | ||
fae2c0fb RGS |
543 | I<The LAYER parameter of the binmode() function is described as "DISCIPLINE" |
544 | in "Programming Perl, 3rd Edition". However, since the publishing of this | |
545 | book, by many known as "Camel III", the consensus of the naming of this | |
546 | functionality has moved from "discipline" to "layer". All documentation | |
547 | of this version of Perl therefore refers to "layers" rather than to | |
548 | "disciplines". Now back to the regularly scheduled documentation...> | |
549 | ||
6902c96a T |
550 | To mark FILEHANDLE as UTF-8, use C<:utf8> or C<:encoding(utf8)>. |
551 | C<:utf8> just marks the data as UTF-8 without further checking, | |
552 | while C<:encoding(utf8)> checks the data for actually being valid | |
553 | UTF-8. More details can be found in L<PerlIO::encoding>. | |
1cbfc93d | 554 | |
ed53a2bb | 555 | In general, binmode() should be called after open() but before any I/O |
01e6739c NIS |
556 | is done on the filehandle. Calling binmode() will normally flush any |
557 | pending buffered output data (and perhaps pending input data) on the | |
fae2c0fb | 558 | handle. An exception to this is the C<:encoding> layer that |
01e6739c | 559 | changes the default character encoding of the handle, see L<open>. |
fae2c0fb | 560 | The C<:encoding> layer sometimes needs to be called in |
3874323d JH |
561 | mid-stream, and it doesn't flush the stream. The C<:encoding> |
562 | also implicitly pushes on top of itself the C<:utf8> layer because | |
563 | internally Perl will operate on UTF-8 encoded Unicode characters. | |
16fe6d59 | 564 | |
19799a22 | 565 | The operating system, device drivers, C libraries, and Perl run-time |
30168b04 GS |
566 | system all work together to let the programmer treat a single |
567 | character (C<\n>) as the line terminator, irrespective of the external | |
568 | representation. On many operating systems, the native text file | |
569 | representation matches the internal representation, but on some | |
570 | platforms the external representation of C<\n> is made up of more than | |
571 | one character. | |
572 | ||
68bd7414 NIS |
573 | Mac OS, all variants of Unix, and Stream_LF files on VMS use a single |
574 | character to end each line in the external representation of text (even | |
5e12dbfa | 575 | though that single character is CARRIAGE RETURN on Mac OS and LINE FEED |
01e6739c NIS |
576 | on Unix and most VMS files). In other systems like OS/2, DOS and the |
577 | various flavors of MS-Windows your program sees a C<\n> as a simple C<\cJ>, | |
578 | but what's stored in text files are the two characters C<\cM\cJ>. That | |
579 | means that, if you don't use binmode() on these systems, C<\cM\cJ> | |
580 | sequences on disk will be converted to C<\n> on input, and any C<\n> in | |
581 | your program will be converted back to C<\cM\cJ> on output. This is what | |
582 | you want for text files, but it can be disastrous for binary files. | |
30168b04 GS |
583 | |
584 | Another consequence of using binmode() (on some systems) is that | |
585 | special end-of-file markers will be seen as part of the data stream. | |
586 | For systems from the Microsoft family this means that if your binary | |
4375e838 | 587 | data contains C<\cZ>, the I/O subsystem will regard it as the end of |
30168b04 GS |
588 | the file, unless you use binmode(). |
589 | ||
590 | binmode() is not only important for readline() and print() operations, | |
591 | but also when using read(), seek(), sysread(), syswrite() and tell() | |
592 | (see L<perlport> for more details). See the C<$/> and C<$\> variables | |
593 | in L<perlvar> for how to manually set your input and output | |
594 | line-termination sequences. | |
a0d0e21e | 595 | |
4633a7c4 | 596 | =item bless REF,CLASSNAME |
d74e8afc | 597 | X<bless> |
a0d0e21e LW |
598 | |
599 | =item bless REF | |
600 | ||
2b5ab1e7 TC |
601 | This function tells the thingy referenced by REF that it is now an object |
602 | in the CLASSNAME package. If CLASSNAME is omitted, the current package | |
19799a22 | 603 | is used. Because a C<bless> is often the last thing in a constructor, |
2b5ab1e7 | 604 | it returns the reference for convenience. Always use the two-argument |
cf264981 SP |
605 | version if a derived class might inherit the function doing the blessing. |
606 | See L<perltoot> and L<perlobj> for more about the blessing (and blessings) | |
607 | of objects. | |
a0d0e21e | 608 | |
57668c4d | 609 | Consider always blessing objects in CLASSNAMEs that are mixed case. |
2b5ab1e7 | 610 | Namespaces with all lowercase names are considered reserved for |
cf264981 | 611 | Perl pragmata. Builtin types have all uppercase names. To prevent |
2b5ab1e7 TC |
612 | confusion, you may wish to avoid such package names as well. Make sure |
613 | that CLASSNAME is a true value. | |
60ad88b8 GS |
614 | |
615 | See L<perlmod/"Perl Modules">. | |
616 | ||
0d863452 RH |
617 | =item break |
618 | ||
619 | Break out of a C<given()> block. | |
620 | ||
621 | This keyword is enabled by the "switch" feature: see L<feature> | |
622 | for more information. | |
623 | ||
a0d0e21e | 624 | =item caller EXPR |
d74e8afc | 625 | X<caller> X<call stack> X<stack> X<stack trace> |
a0d0e21e LW |
626 | |
627 | =item caller | |
628 | ||
5a964f20 | 629 | Returns the context of the current subroutine call. In scalar context, |
28757baa | 630 | returns the caller's package name if there is a caller, that is, if |
19799a22 | 631 | we're in a subroutine or C<eval> or C<require>, and the undefined value |
5a964f20 | 632 | otherwise. In list context, returns |
a0d0e21e | 633 | |
ee6b43cc | 634 | # 0 1 2 |
748a9306 | 635 | ($package, $filename, $line) = caller; |
a0d0e21e LW |
636 | |
637 | With EXPR, it returns some extra information that the debugger uses to | |
638 | print a stack trace. The value of EXPR indicates how many call frames | |
639 | to go back before the current one. | |
640 | ||
ee6b43cc | 641 | # 0 1 2 3 4 |
f3aa04c2 | 642 | ($package, $filename, $line, $subroutine, $hasargs, |
ee6b43cc | 643 | |
644 | # 5 6 7 8 9 10 | |
b3ca2e83 | 645 | $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash) |
ee6b43cc | 646 | = caller($i); |
e7ea3e70 | 647 | |
951ba7fe | 648 | Here $subroutine may be C<(eval)> if the frame is not a subroutine |
19799a22 | 649 | call, but an C<eval>. In such a case additional elements $evaltext and |
7660c0ab | 650 | C<$is_require> are set: C<$is_require> is true if the frame is created by a |
19799a22 | 651 | C<require> or C<use> statement, $evaltext contains the text of the |
277ddfaf | 652 | C<eval EXPR> statement. In particular, for an C<eval BLOCK> statement, |
cc1c2e42 | 653 | $subroutine is C<(eval)>, but $evaltext is undefined. (Note also that |
0fc9dec4 RGS |
654 | each C<use> statement creates a C<require> frame inside an C<eval EXPR> |
655 | frame.) $subroutine may also be C<(unknown)> if this particular | |
656 | subroutine happens to have been deleted from the symbol table. | |
657 | C<$hasargs> is true if a new instance of C<@_> was set up for the frame. | |
658 | C<$hints> and C<$bitmask> contain pragmatic hints that the caller was | |
659 | compiled with. The C<$hints> and C<$bitmask> values are subject to change | |
660 | between versions of Perl, and are not meant for external use. | |
748a9306 | 661 | |
b3ca2e83 NC |
662 | C<$hinthash> is a reference to a hash containing the value of C<%^H> when the |
663 | caller was compiled, or C<undef> if C<%^H> was empty. Do not modify the values | |
664 | of this hash, as they are the actual values stored in the optree. | |
665 | ||
748a9306 | 666 | Furthermore, when called from within the DB package, caller returns more |
7660c0ab | 667 | detailed information: it sets the list variable C<@DB::args> to be the |
54310121 | 668 | arguments with which the subroutine was invoked. |
748a9306 | 669 | |
7660c0ab | 670 | Be aware that the optimizer might have optimized call frames away before |
19799a22 | 671 | C<caller> had a chance to get the information. That means that C<caller(N)> |
7660c0ab | 672 | might not return information about the call frame you expect it do, for |
b76cc8ba | 673 | C<< N > 1 >>. In particular, C<@DB::args> might have information from the |
19799a22 | 674 | previous time C<caller> was called. |
7660c0ab | 675 | |
a0d0e21e | 676 | =item chdir EXPR |
d74e8afc ITB |
677 | X<chdir> |
678 | X<cd> | |
f723aae1 | 679 | X<directory, change> |
a0d0e21e | 680 | |
c4aca7d0 GA |
681 | =item chdir FILEHANDLE |
682 | ||
683 | =item chdir DIRHANDLE | |
684 | ||
ce2984c3 PF |
685 | =item chdir |
686 | ||
ffce7b87 | 687 | Changes the working directory to EXPR, if possible. If EXPR is omitted, |
0bfc1ec4 | 688 | changes to the directory specified by C<$ENV{HOME}>, if set; if not, |
ffce7b87 | 689 | changes to the directory specified by C<$ENV{LOGDIR}>. (Under VMS, the |
b4ad75f0 AMS |
690 | variable C<$ENV{SYS$LOGIN}> is also checked, and used if it is set.) If |
691 | neither is set, C<chdir> does nothing. It returns true upon success, | |
692 | false otherwise. See the example under C<die>. | |
a0d0e21e | 693 | |
c4aca7d0 GA |
694 | On systems that support fchdir, you might pass a file handle or |
695 | directory handle as argument. On systems that don't support fchdir, | |
696 | passing handles produces a fatal error at run time. | |
697 | ||
a0d0e21e | 698 | =item chmod LIST |
d74e8afc | 699 | X<chmod> X<permission> X<mode> |
a0d0e21e LW |
700 | |
701 | Changes the permissions of a list of files. The first element of the | |
4633a7c4 | 702 | list must be the numerical mode, which should probably be an octal |
4ad40acf | 703 | number, and which definitely should I<not> be a string of octal digits: |
2f9daede | 704 | C<0644> is okay, C<'0644'> is not. Returns the number of files |
dc848c6f | 705 | successfully changed. See also L</oct>, if all you have is a string. |
a0d0e21e LW |
706 | |
707 | $cnt = chmod 0755, 'foo', 'bar'; | |
708 | chmod 0755, @executables; | |
f86cebdf GS |
709 | $mode = '0644'; chmod $mode, 'foo'; # !!! sets mode to |
710 | # --w----r-T | |
2f9daede TP |
711 | $mode = '0644'; chmod oct($mode), 'foo'; # this is better |
712 | $mode = 0644; chmod $mode, 'foo'; # this is best | |
a0d0e21e | 713 | |
c4aca7d0 GA |
714 | On systems that support fchmod, you might pass file handles among the |
715 | files. On systems that don't support fchmod, passing file handles | |
345da378 GA |
716 | produces a fatal error at run time. The file handles must be passed |
717 | as globs or references to be recognized. Barewords are considered | |
718 | file names. | |
c4aca7d0 GA |
719 | |
720 | open(my $fh, "<", "foo"); | |
721 | my $perm = (stat $fh)[2] & 07777; | |
722 | chmod($perm | 0600, $fh); | |
723 | ||
ca6e1c26 JH |
724 | You can also import the symbolic C<S_I*> constants from the Fcntl |
725 | module: | |
726 | ||
727 | use Fcntl ':mode'; | |
728 | ||
729 | chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables; | |
730 | # This is identical to the chmod 0755 of the above example. | |
731 | ||
a0d0e21e | 732 | =item chomp VARIABLE |
d74e8afc | 733 | X<chomp> X<INPUT_RECORD_SEPARATOR> X<$/> X<newline> X<eol> |
a0d0e21e | 734 | |
313c9f5c | 735 | =item chomp( LIST ) |
a0d0e21e LW |
736 | |
737 | =item chomp | |
738 | ||
2b5ab1e7 TC |
739 | This safer version of L</chop> removes any trailing string |
740 | that corresponds to the current value of C<$/> (also known as | |
28757baa | 741 | $INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total |
742 | number of characters removed from all its arguments. It's often used to | |
743 | remove the newline from the end of an input record when you're worried | |
2b5ab1e7 TC |
744 | that the final record may be missing its newline. When in paragraph |
745 | mode (C<$/ = "">), it removes all trailing newlines from the string. | |
4c5a6083 GS |
746 | When in slurp mode (C<$/ = undef>) or fixed-length record mode (C<$/> is |
747 | a reference to an integer or the like, see L<perlvar>) chomp() won't | |
b76cc8ba | 748 | remove anything. |
19799a22 | 749 | If VARIABLE is omitted, it chomps C<$_>. Example: |
a0d0e21e LW |
750 | |
751 | while (<>) { | |
752 | chomp; # avoid \n on last field | |
753 | @array = split(/:/); | |
5a964f20 | 754 | # ... |
a0d0e21e LW |
755 | } |
756 | ||
4bf21a6d RD |
757 | If VARIABLE is a hash, it chomps the hash's values, but not its keys. |
758 | ||
a0d0e21e LW |
759 | You can actually chomp anything that's an lvalue, including an assignment: |
760 | ||
761 | chomp($cwd = `pwd`); | |
762 | chomp($answer = <STDIN>); | |
763 | ||
764 | If you chomp a list, each element is chomped, and the total number of | |
765 | characters removed is returned. | |
766 | ||
15e44fd8 RGS |
767 | Note that parentheses are necessary when you're chomping anything |
768 | that is not a simple variable. This is because C<chomp $cwd = `pwd`;> | |
769 | is interpreted as C<(chomp $cwd) = `pwd`;>, rather than as | |
770 | C<chomp( $cwd = `pwd` )> which you might expect. Similarly, | |
771 | C<chomp $a, $b> is interpreted as C<chomp($a), $b> rather than | |
772 | as C<chomp($a, $b)>. | |
773 | ||
a0d0e21e | 774 | =item chop VARIABLE |
d74e8afc | 775 | X<chop> |
a0d0e21e | 776 | |
313c9f5c | 777 | =item chop( LIST ) |
a0d0e21e LW |
778 | |
779 | =item chop | |
780 | ||
781 | Chops off the last character of a string and returns the character | |
5b3eff12 | 782 | chopped. It is much more efficient than C<s/.$//s> because it neither |
7660c0ab | 783 | scans nor copies the string. If VARIABLE is omitted, chops C<$_>. |
4bf21a6d RD |
784 | If VARIABLE is a hash, it chops the hash's values, but not its keys. |
785 | ||
5b3eff12 | 786 | You can actually chop anything that's an lvalue, including an assignment. |
a0d0e21e LW |
787 | |
788 | If you chop a list, each element is chopped. Only the value of the | |
19799a22 | 789 | last C<chop> is returned. |
a0d0e21e | 790 | |
19799a22 | 791 | Note that C<chop> returns the last character. To return all but the last |
748a9306 LW |
792 | character, use C<substr($string, 0, -1)>. |
793 | ||
15e44fd8 RGS |
794 | See also L</chomp>. |
795 | ||
a0d0e21e | 796 | =item chown LIST |
d74e8afc | 797 | X<chown> X<owner> X<user> X<group> |
a0d0e21e LW |
798 | |
799 | Changes the owner (and group) of a list of files. The first two | |
19799a22 GS |
800 | elements of the list must be the I<numeric> uid and gid, in that |
801 | order. A value of -1 in either position is interpreted by most | |
802 | systems to leave that value unchanged. Returns the number of files | |
803 | successfully changed. | |
a0d0e21e LW |
804 | |
805 | $cnt = chown $uid, $gid, 'foo', 'bar'; | |
806 | chown $uid, $gid, @filenames; | |
807 | ||
c4aca7d0 GA |
808 | On systems that support fchown, you might pass file handles among the |
809 | files. On systems that don't support fchown, passing file handles | |
345da378 GA |
810 | produces a fatal error at run time. The file handles must be passed |
811 | as globs or references to be recognized. Barewords are considered | |
812 | file names. | |
c4aca7d0 | 813 | |
54310121 | 814 | Here's an example that looks up nonnumeric uids in the passwd file: |
a0d0e21e LW |
815 | |
816 | print "User: "; | |
19799a22 | 817 | chomp($user = <STDIN>); |
5a964f20 | 818 | print "Files: "; |
19799a22 | 819 | chomp($pattern = <STDIN>); |
a0d0e21e LW |
820 | |
821 | ($login,$pass,$uid,$gid) = getpwnam($user) | |
822 | or die "$user not in passwd file"; | |
823 | ||
5a964f20 | 824 | @ary = glob($pattern); # expand filenames |
a0d0e21e LW |
825 | chown $uid, $gid, @ary; |
826 | ||
54310121 | 827 | On most systems, you are not allowed to change the ownership of the |
4633a7c4 LW |
828 | file unless you're the superuser, although you should be able to change |
829 | the group to any of your secondary groups. On insecure systems, these | |
830 | restrictions may be relaxed, but this is not a portable assumption. | |
19799a22 GS |
831 | On POSIX systems, you can detect this condition this way: |
832 | ||
833 | use POSIX qw(sysconf _PC_CHOWN_RESTRICTED); | |
834 | $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED); | |
4633a7c4 | 835 | |
a0d0e21e | 836 | =item chr NUMBER |
d74e8afc | 837 | X<chr> X<character> X<ASCII> X<Unicode> |
a0d0e21e | 838 | |
54310121 | 839 | =item chr |
bbce6d69 | 840 | |
a0d0e21e | 841 | Returns the character represented by that NUMBER in the character set. |
a0ed51b3 | 842 | For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and |
2575c402 | 843 | chr(0x263a) is a Unicode smiley face. |
aaa68c4a | 844 | |
8a064bd6 | 845 | Negative values give the Unicode replacement character (chr(0xfffd)), |
5f0135eb | 846 | except under the L<bytes> pragma, where low eight bits of the value |
8a064bd6 JH |
847 | (truncated to an integer) are used. |
848 | ||
974da8e5 JH |
849 | If NUMBER is omitted, uses C<$_>. |
850 | ||
b76cc8ba | 851 | For the reverse, use L</ord>. |
a0d0e21e | 852 | |
2575c402 JW |
853 | Note that characters from 128 to 255 (inclusive) are by default |
854 | internally not encoded as UTF-8 for backward compatibility reasons. | |
974da8e5 | 855 | |
2575c402 | 856 | See L<perlunicode> for more about Unicode. |
bbce6d69 | 857 | |
a0d0e21e | 858 | =item chroot FILENAME |
d74e8afc | 859 | X<chroot> X<root> |
a0d0e21e | 860 | |
54310121 | 861 | =item chroot |
bbce6d69 | 862 | |
5a964f20 | 863 | This function works like the system call by the same name: it makes the |
4633a7c4 | 864 | named directory the new root directory for all further pathnames that |
951ba7fe | 865 | begin with a C</> by your process and all its children. (It doesn't |
28757baa | 866 | change your current working directory, which is unaffected.) For security |
4633a7c4 | 867 | reasons, this call is restricted to the superuser. If FILENAME is |
19799a22 | 868 | omitted, does a C<chroot> to C<$_>. |
a0d0e21e LW |
869 | |
870 | =item close FILEHANDLE | |
d74e8afc | 871 | X<close> |
a0d0e21e | 872 | |
6a518fbc TP |
873 | =item close |
874 | ||
e0f13c26 RGS |
875 | Closes the file or pipe associated with the file handle, flushes the IO |
876 | buffers, and closes the system file descriptor. Returns true if those | |
877 | operations have succeeded and if no error was reported by any PerlIO | |
878 | layer. Closes the currently selected filehandle if the argument is | |
879 | omitted. | |
fb73857a | 880 | |
881 | You don't have to close FILEHANDLE if you are immediately going to do | |
19799a22 GS |
882 | another C<open> on it, because C<open> will close it for you. (See |
883 | C<open>.) However, an explicit C<close> on an input file resets the line | |
884 | counter (C<$.>), while the implicit close done by C<open> does not. | |
fb73857a | 885 | |
dede8123 RGS |
886 | If the file handle came from a piped open, C<close> will additionally |
887 | return false if one of the other system calls involved fails, or if the | |
fb73857a | 888 | program exits with non-zero status. (If the only problem was that the |
dede8123 | 889 | program exited non-zero, C<$!> will be set to C<0>.) Closing a pipe |
2b5ab1e7 | 890 | also waits for the process executing on the pipe to complete, in case you |
b76cc8ba | 891 | want to look at the output of the pipe afterwards, and |
e5218da5 GA |
892 | implicitly puts the exit status value of that command into C<$?> and |
893 | C<${^CHILD_ERROR_NATIVE}>. | |
5a964f20 | 894 | |
73689b13 GS |
895 | Prematurely closing the read end of a pipe (i.e. before the process |
896 | writing to it at the other end has closed it) will result in a | |
897 | SIGPIPE being delivered to the writer. If the other end can't | |
898 | handle that, be sure to read all the data before closing the pipe. | |
899 | ||
fb73857a | 900 | Example: |
a0d0e21e | 901 | |
fb73857a | 902 | open(OUTPUT, '|sort >foo') # pipe to sort |
903 | or die "Can't start sort: $!"; | |
5a964f20 | 904 | #... # print stuff to output |
fb73857a | 905 | close OUTPUT # wait for sort to finish |
906 | or warn $! ? "Error closing sort pipe: $!" | |
907 | : "Exit status $? from sort"; | |
908 | open(INPUT, 'foo') # get sort's results | |
909 | or die "Can't open 'foo' for input: $!"; | |
a0d0e21e | 910 | |
5a964f20 TC |
911 | FILEHANDLE may be an expression whose value can be used as an indirect |
912 | filehandle, usually the real filehandle name. | |
a0d0e21e LW |
913 | |
914 | =item closedir DIRHANDLE | |
d74e8afc | 915 | X<closedir> |
a0d0e21e | 916 | |
19799a22 | 917 | Closes a directory opened by C<opendir> and returns the success of that |
5a964f20 TC |
918 | system call. |
919 | ||
a0d0e21e | 920 | =item connect SOCKET,NAME |
d74e8afc | 921 | X<connect> |
a0d0e21e LW |
922 | |
923 | Attempts to connect to a remote socket, just as the connect system call | |
19799a22 | 924 | does. Returns true if it succeeded, false otherwise. NAME should be a |
4633a7c4 LW |
925 | packed address of the appropriate type for the socket. See the examples in |
926 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 927 | |
cb1a09d0 | 928 | =item continue BLOCK |
d74e8afc | 929 | X<continue> |
cb1a09d0 | 930 | |
0d863452 RH |
931 | =item continue |
932 | ||
cf264981 SP |
933 | C<continue> is actually a flow control statement rather than a function. If |
934 | there is a C<continue> BLOCK attached to a BLOCK (typically in a C<while> or | |
98293880 JH |
935 | C<foreach>), it is always executed just before the conditional is about to |
936 | be evaluated again, just like the third part of a C<for> loop in C. Thus | |
cb1a09d0 AD |
937 | it can be used to increment a loop variable, even when the loop has been |
938 | continued via the C<next> statement (which is similar to the C C<continue> | |
939 | statement). | |
940 | ||
98293880 | 941 | C<last>, C<next>, or C<redo> may appear within a C<continue> |
19799a22 GS |
942 | block. C<last> and C<redo> will behave as if they had been executed within |
943 | the main block. So will C<next>, but since it will execute a C<continue> | |
1d2dff63 GS |
944 | block, it may be more entertaining. |
945 | ||
946 | while (EXPR) { | |
947 | ### redo always comes here | |
948 | do_something; | |
949 | } continue { | |
950 | ### next always comes here | |
951 | do_something_else; | |
952 | # then back the top to re-check EXPR | |
953 | } | |
954 | ### last always comes here | |
955 | ||
956 | Omitting the C<continue> section is semantically equivalent to using an | |
19799a22 | 957 | empty one, logically enough. In that case, C<next> goes directly back |
1d2dff63 GS |
958 | to check the condition at the top of the loop. |
959 | ||
0d863452 RH |
960 | If the "switch" feature is enabled, C<continue> is also a |
961 | function that will break out of the current C<when> or C<default> | |
962 | block, and fall through to the next case. See L<feature> and | |
963 | L<perlsyn/"Switch statements"> for more information. | |
964 | ||
965 | ||
a0d0e21e | 966 | =item cos EXPR |
d74e8afc | 967 | X<cos> X<cosine> X<acos> X<arccosine> |
a0d0e21e | 968 | |
d6217f1e GS |
969 | =item cos |
970 | ||
5a964f20 | 971 | Returns the cosine of EXPR (expressed in radians). If EXPR is omitted, |
7660c0ab | 972 | takes cosine of C<$_>. |
a0d0e21e | 973 | |
ca6e1c26 | 974 | For the inverse cosine operation, you may use the C<Math::Trig::acos()> |
28757baa | 975 | function, or use this relation: |
976 | ||
977 | sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) } | |
978 | ||
a0d0e21e | 979 | =item crypt PLAINTEXT,SALT |
d74e8afc | 980 | X<crypt> X<digest> X<hash> X<salt> X<plaintext> X<password> |
f723aae1 | 981 | X<decrypt> X<cryptography> X<passwd> X<encrypt> |
a0d0e21e | 982 | |
ef2e6798 MS |
983 | Creates a digest string exactly like the crypt(3) function in the C |
984 | library (assuming that you actually have a version there that has not | |
cf264981 | 985 | been extirpated as a potential munitions). |
ef2e6798 MS |
986 | |
987 | crypt() is a one-way hash function. The PLAINTEXT and SALT is turned | |
988 | into a short string, called a digest, which is returned. The same | |
989 | PLAINTEXT and SALT will always return the same string, but there is no | |
990 | (known) way to get the original PLAINTEXT from the hash. Small | |
991 | changes in the PLAINTEXT or SALT will result in large changes in the | |
992 | digest. | |
993 | ||
994 | There is no decrypt function. This function isn't all that useful for | |
995 | cryptography (for that, look for F<Crypt> modules on your nearby CPAN | |
996 | mirror) and the name "crypt" is a bit of a misnomer. Instead it is | |
997 | primarily used to check if two pieces of text are the same without | |
998 | having to transmit or store the text itself. An example is checking | |
999 | if a correct password is given. The digest of the password is stored, | |
cf264981 | 1000 | not the password itself. The user types in a password that is |
ef2e6798 MS |
1001 | crypt()'d with the same salt as the stored digest. If the two digests |
1002 | match the password is correct. | |
1003 | ||
1004 | When verifying an existing digest string you should use the digest as | |
1005 | the salt (like C<crypt($plain, $digest) eq $digest>). The SALT used | |
cf264981 | 1006 | to create the digest is visible as part of the digest. This ensures |
ef2e6798 MS |
1007 | crypt() will hash the new string with the same salt as the digest. |
1008 | This allows your code to work with the standard L<crypt|/crypt> and | |
1009 | with more exotic implementations. In other words, do not assume | |
1010 | anything about the returned string itself, or how many bytes in the | |
1011 | digest matter. | |
85c16d83 JH |
1012 | |
1013 | Traditionally the result is a string of 13 bytes: two first bytes of | |
1014 | the salt, followed by 11 bytes from the set C<[./0-9A-Za-z]>, and only | |
ef2e6798 MS |
1015 | the first eight bytes of the digest string mattered, but alternative |
1016 | hashing schemes (like MD5), higher level security schemes (like C2), | |
1017 | and implementations on non-UNIX platforms may produce different | |
1018 | strings. | |
85c16d83 JH |
1019 | |
1020 | When choosing a new salt create a random two character string whose | |
1021 | characters come from the set C<[./0-9A-Za-z]> (like C<join '', ('.', | |
d3989d75 CW |
1022 | '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]>). This set of |
1023 | characters is just a recommendation; the characters allowed in | |
1024 | the salt depend solely on your system's crypt library, and Perl can't | |
1025 | restrict what salts C<crypt()> accepts. | |
e71965be | 1026 | |
a0d0e21e | 1027 | Here's an example that makes sure that whoever runs this program knows |
cf264981 | 1028 | their password: |
a0d0e21e LW |
1029 | |
1030 | $pwd = (getpwuid($<))[1]; | |
a0d0e21e LW |
1031 | |
1032 | system "stty -echo"; | |
1033 | print "Password: "; | |
e71965be | 1034 | chomp($word = <STDIN>); |
a0d0e21e LW |
1035 | print "\n"; |
1036 | system "stty echo"; | |
1037 | ||
e71965be | 1038 | if (crypt($word, $pwd) ne $pwd) { |
a0d0e21e LW |
1039 | die "Sorry...\n"; |
1040 | } else { | |
1041 | print "ok\n"; | |
54310121 | 1042 | } |
a0d0e21e | 1043 | |
9f8f0c9d | 1044 | Of course, typing in your own password to whoever asks you |
748a9306 | 1045 | for it is unwise. |
a0d0e21e | 1046 | |
ef2e6798 | 1047 | The L<crypt|/crypt> function is unsuitable for hashing large quantities |
19799a22 | 1048 | of data, not least of all because you can't get the information |
ef2e6798 | 1049 | back. Look at the L<Digest> module for more robust algorithms. |
19799a22 | 1050 | |
f2791508 JH |
1051 | If using crypt() on a Unicode string (which I<potentially> has |
1052 | characters with codepoints above 255), Perl tries to make sense | |
1053 | of the situation by trying to downgrade (a copy of the string) | |
1054 | the string back to an eight-bit byte string before calling crypt() | |
1055 | (on that copy). If that works, good. If not, crypt() dies with | |
1056 | C<Wide character in crypt>. | |
85c16d83 | 1057 | |
aa689395 | 1058 | =item dbmclose HASH |
d74e8afc | 1059 | X<dbmclose> |
a0d0e21e | 1060 | |
19799a22 | 1061 | [This function has been largely superseded by the C<untie> function.] |
a0d0e21e | 1062 | |
aa689395 | 1063 | Breaks the binding between a DBM file and a hash. |
a0d0e21e | 1064 | |
19799a22 | 1065 | =item dbmopen HASH,DBNAME,MASK |
d74e8afc | 1066 | X<dbmopen> X<dbm> X<ndbm> X<sdbm> X<gdbm> |
a0d0e21e | 1067 | |
19799a22 | 1068 | [This function has been largely superseded by the C<tie> function.] |
a0d0e21e | 1069 | |
7b8d334a | 1070 | This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a |
19799a22 GS |
1071 | hash. HASH is the name of the hash. (Unlike normal C<open>, the first |
1072 | argument is I<not> a filehandle, even though it looks like one). DBNAME | |
aa689395 | 1073 | is the name of the database (without the F<.dir> or F<.pag> extension if |
1074 | any). If the database does not exist, it is created with protection | |
19799a22 GS |
1075 | specified by MASK (as modified by the C<umask>). If your system supports |
1076 | only the older DBM functions, you may perform only one C<dbmopen> in your | |
aa689395 | 1077 | program. In older versions of Perl, if your system had neither DBM nor |
19799a22 | 1078 | ndbm, calling C<dbmopen> produced a fatal error; it now falls back to |
aa689395 | 1079 | sdbm(3). |
1080 | ||
1081 | If you don't have write access to the DBM file, you can only read hash | |
1082 | variables, not set them. If you want to test whether you can write, | |
19799a22 | 1083 | either use file tests or try setting a dummy hash entry inside an C<eval>, |
aa689395 | 1084 | which will trap the error. |
a0d0e21e | 1085 | |
19799a22 GS |
1086 | Note that functions such as C<keys> and C<values> may return huge lists |
1087 | when used on large DBM files. You may prefer to use the C<each> | |
a0d0e21e LW |
1088 | function to iterate over large DBM files. Example: |
1089 | ||
1090 | # print out history file offsets | |
1091 | dbmopen(%HIST,'/usr/lib/news/history',0666); | |
1092 | while (($key,$val) = each %HIST) { | |
1093 | print $key, ' = ', unpack('L',$val), "\n"; | |
1094 | } | |
1095 | dbmclose(%HIST); | |
1096 | ||
cb1a09d0 | 1097 | See also L<AnyDBM_File> for a more general description of the pros and |
184e9718 | 1098 | cons of the various dbm approaches, as well as L<DB_File> for a particularly |
cb1a09d0 | 1099 | rich implementation. |
4633a7c4 | 1100 | |
2b5ab1e7 TC |
1101 | You can control which DBM library you use by loading that library |
1102 | before you call dbmopen(): | |
1103 | ||
1104 | use DB_File; | |
1105 | dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db") | |
1106 | or die "Can't open netscape history file: $!"; | |
1107 | ||
a0d0e21e | 1108 | =item defined EXPR |
d74e8afc | 1109 | X<defined> X<undef> X<undefined> |
a0d0e21e | 1110 | |
54310121 | 1111 | =item defined |
bbce6d69 | 1112 | |
2f9daede TP |
1113 | Returns a Boolean value telling whether EXPR has a value other than |
1114 | the undefined value C<undef>. If EXPR is not present, C<$_> will be | |
1115 | checked. | |
1116 | ||
1117 | Many operations return C<undef> to indicate failure, end of file, | |
1118 | system error, uninitialized variable, and other exceptional | |
1119 | conditions. This function allows you to distinguish C<undef> from | |
1120 | other values. (A simple Boolean test will not distinguish among | |
7660c0ab | 1121 | C<undef>, zero, the empty string, and C<"0">, which are all equally |
2f9daede | 1122 | false.) Note that since C<undef> is a valid scalar, its presence |
19799a22 | 1123 | doesn't I<necessarily> indicate an exceptional condition: C<pop> |
2f9daede TP |
1124 | returns C<undef> when its argument is an empty array, I<or> when the |
1125 | element to return happens to be C<undef>. | |
1126 | ||
f10b0346 GS |
1127 | You may also use C<defined(&func)> to check whether subroutine C<&func> |
1128 | has ever been defined. The return value is unaffected by any forward | |
04891299 | 1129 | declarations of C<&func>. Note that a subroutine which is not defined |
847c7ebe DD |
1130 | may still be callable: its package may have an C<AUTOLOAD> method that |
1131 | makes it spring into existence the first time that it is called -- see | |
1132 | L<perlsub>. | |
f10b0346 GS |
1133 | |
1134 | Use of C<defined> on aggregates (hashes and arrays) is deprecated. It | |
1135 | used to report whether memory for that aggregate has ever been | |
1136 | allocated. This behavior may disappear in future versions of Perl. | |
1137 | You should instead use a simple test for size: | |
1138 | ||
1139 | if (@an_array) { print "has array elements\n" } | |
1140 | if (%a_hash) { print "has hash members\n" } | |
2f9daede TP |
1141 | |
1142 | When used on a hash element, it tells you whether the value is defined, | |
dc848c6f | 1143 | not whether the key exists in the hash. Use L</exists> for the latter |
2f9daede | 1144 | purpose. |
a0d0e21e LW |
1145 | |
1146 | Examples: | |
1147 | ||
1148 | print if defined $switch{'D'}; | |
1149 | print "$val\n" while defined($val = pop(@ary)); | |
1150 | die "Can't readlink $sym: $!" | |
1151 | unless defined($value = readlink $sym); | |
a0d0e21e | 1152 | sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } |
2f9daede | 1153 | $debugging = 0 unless defined $debugging; |
a0d0e21e | 1154 | |
19799a22 | 1155 | Note: Many folks tend to overuse C<defined>, and then are surprised to |
7660c0ab | 1156 | discover that the number C<0> and C<""> (the zero-length string) are, in fact, |
2f9daede | 1157 | defined values. For example, if you say |
a5f75d66 AD |
1158 | |
1159 | "ab" =~ /a(.*)b/; | |
1160 | ||
7660c0ab | 1161 | The pattern match succeeds, and C<$1> is defined, despite the fact that it |
cf264981 | 1162 | matched "nothing". It didn't really fail to match anything. Rather, it |
2b5ab1e7 | 1163 | matched something that happened to be zero characters long. This is all |
a5f75d66 | 1164 | very above-board and honest. When a function returns an undefined value, |
2f9daede | 1165 | it's an admission that it couldn't give you an honest answer. So you |
19799a22 | 1166 | should use C<defined> only when you're questioning the integrity of what |
7660c0ab | 1167 | you're trying to do. At other times, a simple comparison to C<0> or C<""> is |
2f9daede TP |
1168 | what you want. |
1169 | ||
dc848c6f | 1170 | See also L</undef>, L</exists>, L</ref>. |
2f9daede | 1171 | |
a0d0e21e | 1172 | =item delete EXPR |
d74e8afc | 1173 | X<delete> |
a0d0e21e | 1174 | |
01020589 GS |
1175 | Given an expression that specifies a hash element, array element, hash slice, |
1176 | or array slice, deletes the specified element(s) from the hash or array. | |
8216c1fd | 1177 | In the case of an array, if the array elements happen to be at the end, |
b76cc8ba | 1178 | the size of the array will shrink to the highest element that tests |
8216c1fd | 1179 | true for exists() (or 0 if no such element exists). |
a0d0e21e | 1180 | |
eba0920a EM |
1181 | Returns a list with the same number of elements as the number of elements |
1182 | for which deletion was attempted. Each element of that list consists of | |
1183 | either the value of the element deleted, or the undefined value. In scalar | |
1184 | context, this means that you get the value of the last element deleted (or | |
1185 | the undefined value if that element did not exist). | |
1186 | ||
1187 | %hash = (foo => 11, bar => 22, baz => 33); | |
1188 | $scalar = delete $hash{foo}; # $scalar is 11 | |
1189 | $scalar = delete @hash{qw(foo bar)}; # $scalar is 22 | |
1190 | @array = delete @hash{qw(foo bar baz)}; # @array is (undef,undef,33) | |
1191 | ||
1192 | Deleting from C<%ENV> modifies the environment. Deleting from | |
01020589 GS |
1193 | a hash tied to a DBM file deletes the entry from the DBM file. Deleting |
1194 | from a C<tie>d hash or array may not necessarily return anything. | |
1195 | ||
8ea97a1e GS |
1196 | Deleting an array element effectively returns that position of the array |
1197 | to its initial, uninitialized state. Subsequently testing for the same | |
cf264981 SP |
1198 | element with exists() will return false. Also, deleting array elements |
1199 | in the middle of an array will not shift the index of the elements | |
1200 | after them down. Use splice() for that. See L</exists>. | |
8ea97a1e | 1201 | |
01020589 | 1202 | The following (inefficiently) deletes all the values of %HASH and @ARRAY: |
a0d0e21e | 1203 | |
5f05dabc | 1204 | foreach $key (keys %HASH) { |
1205 | delete $HASH{$key}; | |
a0d0e21e LW |
1206 | } |
1207 | ||
01020589 GS |
1208 | foreach $index (0 .. $#ARRAY) { |
1209 | delete $ARRAY[$index]; | |
1210 | } | |
1211 | ||
1212 | And so do these: | |
5f05dabc | 1213 | |
01020589 GS |
1214 | delete @HASH{keys %HASH}; |
1215 | ||
9740c838 | 1216 | delete @ARRAY[0 .. $#ARRAY]; |
5f05dabc | 1217 | |
2b5ab1e7 | 1218 | But both of these are slower than just assigning the empty list |
01020589 GS |
1219 | or undefining %HASH or @ARRAY: |
1220 | ||
1221 | %HASH = (); # completely empty %HASH | |
1222 | undef %HASH; # forget %HASH ever existed | |
2b5ab1e7 | 1223 | |
01020589 GS |
1224 | @ARRAY = (); # completely empty @ARRAY |
1225 | undef @ARRAY; # forget @ARRAY ever existed | |
2b5ab1e7 TC |
1226 | |
1227 | Note that the EXPR can be arbitrarily complicated as long as the final | |
01020589 GS |
1228 | operation is a hash element, array element, hash slice, or array slice |
1229 | lookup: | |
a0d0e21e LW |
1230 | |
1231 | delete $ref->[$x][$y]{$key}; | |
5f05dabc | 1232 | delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys}; |
a0d0e21e | 1233 | |
01020589 GS |
1234 | delete $ref->[$x][$y][$index]; |
1235 | delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices]; | |
1236 | ||
a0d0e21e | 1237 | =item die LIST |
d74e8afc | 1238 | X<die> X<throw> X<exception> X<raise> X<$@> X<abort> |
a0d0e21e | 1239 | |
19799a22 GS |
1240 | Outside an C<eval>, prints the value of LIST to C<STDERR> and |
1241 | exits with the current value of C<$!> (errno). If C<$!> is C<0>, | |
61eff3bc JH |
1242 | exits with the value of C<<< ($? >> 8) >>> (backtick `command` |
1243 | status). If C<<< ($? >> 8) >>> is C<0>, exits with C<255>. Inside | |
19799a22 GS |
1244 | an C<eval(),> the error message is stuffed into C<$@> and the |
1245 | C<eval> is terminated with the undefined value. This makes | |
1246 | C<die> the way to raise an exception. | |
a0d0e21e LW |
1247 | |
1248 | Equivalent examples: | |
1249 | ||
1250 | die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; | |
54310121 | 1251 | chdir '/usr/spool/news' or die "Can't cd to spool: $!\n" |
a0d0e21e | 1252 | |
ccac6780 | 1253 | If the last element of LIST does not end in a newline, the current |
df37ec69 WW |
1254 | script line number and input line number (if any) are also printed, |
1255 | and a newline is supplied. Note that the "input line number" (also | |
1256 | known as "chunk") is subject to whatever notion of "line" happens to | |
1257 | be currently in effect, and is also available as the special variable | |
1258 | C<$.>. See L<perlvar/"$/"> and L<perlvar/"$.">. | |
1259 | ||
1260 | Hint: sometimes appending C<", stopped"> to your message will cause it | |
1261 | to make better sense when the string C<"at foo line 123"> is appended. | |
1262 | Suppose you are running script "canasta". | |
a0d0e21e LW |
1263 | |
1264 | die "/etc/games is no good"; | |
1265 | die "/etc/games is no good, stopped"; | |
1266 | ||
1267 | produce, respectively | |
1268 | ||
1269 | /etc/games is no good at canasta line 123. | |
1270 | /etc/games is no good, stopped at canasta line 123. | |
1271 | ||
2b5ab1e7 | 1272 | See also exit(), warn(), and the Carp module. |
a0d0e21e | 1273 | |
7660c0ab A |
1274 | If LIST is empty and C<$@> already contains a value (typically from a |
1275 | previous eval) that value is reused after appending C<"\t...propagated">. | |
fb73857a | 1276 | This is useful for propagating exceptions: |
1277 | ||
1278 | eval { ... }; | |
1279 | die unless $@ =~ /Expected exception/; | |
1280 | ||
ad216e65 JH |
1281 | If LIST is empty and C<$@> contains an object reference that has a |
1282 | C<PROPAGATE> method, that method will be called with additional file | |
1283 | and line number parameters. The return value replaces the value in | |
28a5cf3b | 1284 | C<$@>. i.e. as if C<< $@ = eval { $@->PROPAGATE(__FILE__, __LINE__) }; >> |
ad216e65 JH |
1285 | were called. |
1286 | ||
7660c0ab | 1287 | If C<$@> is empty then the string C<"Died"> is used. |
fb73857a | 1288 | |
52531d10 GS |
1289 | die() can also be called with a reference argument. If this happens to be |
1290 | trapped within an eval(), $@ contains the reference. This behavior permits | |
1291 | a more elaborate exception handling implementation using objects that | |
4375e838 | 1292 | maintain arbitrary state about the nature of the exception. Such a scheme |
52531d10 | 1293 | is sometimes preferable to matching particular string values of $@ using |
746d7dd7 GL |
1294 | regular expressions. Because $@ is a global variable, and eval() may be |
1295 | used within object implementations, care must be taken that analyzing the | |
1296 | error object doesn't replace the reference in the global variable. The | |
1297 | easiest solution is to make a local copy of the reference before doing | |
1298 | other manipulations. Here's an example: | |
52531d10 | 1299 | |
da279afe | 1300 | use Scalar::Util 'blessed'; |
1301 | ||
52531d10 | 1302 | eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) }; |
746d7dd7 GL |
1303 | if (my $ev_err = $@) { |
1304 | if (blessed($ev_err) && $ev_err->isa("Some::Module::Exception")) { | |
52531d10 GS |
1305 | # handle Some::Module::Exception |
1306 | } | |
1307 | else { | |
1308 | # handle all other possible exceptions | |
1309 | } | |
1310 | } | |
1311 | ||
19799a22 | 1312 | Because perl will stringify uncaught exception messages before displaying |
52531d10 GS |
1313 | them, you may want to overload stringification operations on such custom |
1314 | exception objects. See L<overload> for details about that. | |
1315 | ||
19799a22 GS |
1316 | You can arrange for a callback to be run just before the C<die> |
1317 | does its deed, by setting the C<$SIG{__DIE__}> hook. The associated | |
1318 | handler will be called with the error text and can change the error | |
1319 | message, if it sees fit, by calling C<die> again. See | |
1320 | L<perlvar/$SIG{expr}> for details on setting C<%SIG> entries, and | |
cf264981 | 1321 | L<"eval BLOCK"> for some examples. Although this feature was |
19799a22 GS |
1322 | to be run only right before your program was to exit, this is not |
1323 | currently the case--the C<$SIG{__DIE__}> hook is currently called | |
1324 | even inside eval()ed blocks/strings! If one wants the hook to do | |
1325 | nothing in such situations, put | |
fb73857a | 1326 | |
1327 | die @_ if $^S; | |
1328 | ||
19799a22 GS |
1329 | as the first line of the handler (see L<perlvar/$^S>). Because |
1330 | this promotes strange action at a distance, this counterintuitive | |
b76cc8ba | 1331 | behavior may be fixed in a future release. |
774d564b | 1332 | |
a0d0e21e | 1333 | =item do BLOCK |
d74e8afc | 1334 | X<do> X<block> |
a0d0e21e LW |
1335 | |
1336 | Not really a function. Returns the value of the last command in the | |
6b275a1f RGS |
1337 | sequence of commands indicated by BLOCK. When modified by the C<while> or |
1338 | C<until> loop modifier, executes the BLOCK once before testing the loop | |
1339 | condition. (On other statements the loop modifiers test the conditional | |
1340 | first.) | |
a0d0e21e | 1341 | |
4968c1e4 | 1342 | C<do BLOCK> does I<not> count as a loop, so the loop control statements |
2b5ab1e7 TC |
1343 | C<next>, C<last>, or C<redo> cannot be used to leave or restart the block. |
1344 | See L<perlsyn> for alternative strategies. | |
4968c1e4 | 1345 | |
a0d0e21e | 1346 | =item do SUBROUTINE(LIST) |
d74e8afc | 1347 | X<do> |
a0d0e21e | 1348 | |
cf264981 | 1349 | This form of subroutine call is deprecated. See L<perlsub>. |
a0d0e21e LW |
1350 | |
1351 | =item do EXPR | |
d74e8afc | 1352 | X<do> |
a0d0e21e LW |
1353 | |
1354 | Uses the value of EXPR as a filename and executes the contents of the | |
ea63ef19 | 1355 | file as a Perl script. |
a0d0e21e LW |
1356 | |
1357 | do 'stat.pl'; | |
1358 | ||
1359 | is just like | |
1360 | ||
986b19de | 1361 | eval `cat stat.pl`; |
a0d0e21e | 1362 | |
2b5ab1e7 | 1363 | except that it's more efficient and concise, keeps track of the current |
ea63ef19 | 1364 | filename for error messages, searches the @INC directories, and updates |
2b5ab1e7 TC |
1365 | C<%INC> if the file is found. See L<perlvar/Predefined Names> for these |
1366 | variables. It also differs in that code evaluated with C<do FILENAME> | |
1367 | cannot see lexicals in the enclosing scope; C<eval STRING> does. It's the | |
1368 | same, however, in that it does reparse the file every time you call it, | |
1369 | so you probably don't want to do this inside a loop. | |
a0d0e21e | 1370 | |
8e30cc93 | 1371 | If C<do> cannot read the file, it returns undef and sets C<$!> to the |
2b5ab1e7 | 1372 | error. If C<do> can read the file but cannot compile it, it |
8e30cc93 MG |
1373 | returns undef and sets an error message in C<$@>. If the file is |
1374 | successfully compiled, C<do> returns the value of the last expression | |
1375 | evaluated. | |
1376 | ||
a0d0e21e | 1377 | Note that inclusion of library modules is better done with the |
19799a22 | 1378 | C<use> and C<require> operators, which also do automatic error checking |
4633a7c4 | 1379 | and raise an exception if there's a problem. |
a0d0e21e | 1380 | |
5a964f20 TC |
1381 | You might like to use C<do> to read in a program configuration |
1382 | file. Manual error checking can be done this way: | |
1383 | ||
b76cc8ba | 1384 | # read in config files: system first, then user |
f86cebdf | 1385 | for $file ("/share/prog/defaults.rc", |
b76cc8ba | 1386 | "$ENV{HOME}/.someprogrc") |
2b5ab1e7 | 1387 | { |
5a964f20 | 1388 | unless ($return = do $file) { |
f86cebdf GS |
1389 | warn "couldn't parse $file: $@" if $@; |
1390 | warn "couldn't do $file: $!" unless defined $return; | |
1391 | warn "couldn't run $file" unless $return; | |
5a964f20 TC |
1392 | } |
1393 | } | |
1394 | ||
a0d0e21e | 1395 | =item dump LABEL |
d74e8afc | 1396 | X<dump> X<core> X<undump> |
a0d0e21e | 1397 | |
1614b0e3 JD |
1398 | =item dump |
1399 | ||
19799a22 GS |
1400 | This function causes an immediate core dump. See also the B<-u> |
1401 | command-line switch in L<perlrun>, which does the same thing. | |
1402 | Primarily this is so that you can use the B<undump> program (not | |
1403 | supplied) to turn your core dump into an executable binary after | |
1404 | having initialized all your variables at the beginning of the | |
1405 | program. When the new binary is executed it will begin by executing | |
1406 | a C<goto LABEL> (with all the restrictions that C<goto> suffers). | |
1407 | Think of it as a goto with an intervening core dump and reincarnation. | |
1408 | If C<LABEL> is omitted, restarts the program from the top. | |
1409 | ||
1410 | B<WARNING>: Any files opened at the time of the dump will I<not> | |
1411 | be open any more when the program is reincarnated, with possible | |
b76cc8ba | 1412 | resulting confusion on the part of Perl. |
19799a22 | 1413 | |
59f521f4 RGS |
1414 | This function is now largely obsolete, mostly because it's very hard to |
1415 | convert a core file into an executable. That's why you should now invoke | |
1416 | it as C<CORE::dump()>, if you don't want to be warned against a possible | |
ac206dc8 | 1417 | typo. |
19799a22 | 1418 | |
aa689395 | 1419 | =item each HASH |
d74e8afc | 1420 | X<each> X<hash, iterator> |
aa689395 | 1421 | |
aeedbbed NC |
1422 | =item each ARRAY |
1423 | X<array, iterator> | |
1424 | ||
5a964f20 | 1425 | When called in list context, returns a 2-element list consisting of the |
aeedbbed NC |
1426 | key and value for the next element of a hash, or the index and value for |
1427 | the next element of an array, so that you can iterate over it. When called | |
1428 | in scalar context, returns only the key for the next element in the hash | |
1429 | (or the index for an array). | |
2f9daede | 1430 | |
aeedbbed | 1431 | Hash entries are returned in an apparently random order. The actual random |
504f80c1 JH |
1432 | order is subject to change in future versions of perl, but it is |
1433 | guaranteed to be in the same order as either the C<keys> or C<values> | |
4546b9e6 | 1434 | function would produce on the same (unmodified) hash. Since Perl |
22883ac5 | 1435 | 5.8.2 the ordering can be different even between different runs of Perl |
4546b9e6 | 1436 | for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">). |
ab192400 | 1437 | |
aeedbbed NC |
1438 | When the hash or array is entirely read, a null array is returned in list |
1439 | context (which when assigned produces a false (C<0>) value), and C<undef> in | |
19799a22 | 1440 | scalar context. The next call to C<each> after that will start iterating |
aeedbbed NC |
1441 | again. There is a single iterator for each hash or array, shared by all |
1442 | C<each>, C<keys>, and C<values> function calls in the program; it can be | |
1443 | reset by reading all the elements from the hash or array, or by evaluating | |
1444 | C<keys HASH>, C<values HASH>, C<keys ARRAY>, or C<values ARRAY>. If you add | |
1445 | or delete elements of a hash while you're | |
74fc8b5f MJD |
1446 | iterating over it, you may get entries skipped or duplicated, so |
1447 | don't. Exception: It is always safe to delete the item most recently | |
1448 | returned by C<each()>, which means that the following code will work: | |
1449 | ||
1450 | while (($key, $value) = each %hash) { | |
1451 | print $key, "\n"; | |
1452 | delete $hash{$key}; # This is safe | |
1453 | } | |
aa689395 | 1454 | |
f86cebdf | 1455 | The following prints out your environment like the printenv(1) program, |
aa689395 | 1456 | only in a different order: |
a0d0e21e LW |
1457 | |
1458 | while (($key,$value) = each %ENV) { | |
1459 | print "$key=$value\n"; | |
1460 | } | |
1461 | ||
19799a22 | 1462 | See also C<keys>, C<values> and C<sort>. |
a0d0e21e LW |
1463 | |
1464 | =item eof FILEHANDLE | |
d74e8afc ITB |
1465 | X<eof> |
1466 | X<end of file> | |
1467 | X<end-of-file> | |
a0d0e21e | 1468 | |
4633a7c4 LW |
1469 | =item eof () |
1470 | ||
a0d0e21e LW |
1471 | =item eof |
1472 | ||
1473 | Returns 1 if the next read on FILEHANDLE will return end of file, or if | |
1474 | FILEHANDLE is not open. FILEHANDLE may be an expression whose value | |
5a964f20 | 1475 | gives the real filehandle. (Note that this function actually |
19799a22 | 1476 | reads a character and then C<ungetc>s it, so isn't very useful in an |
748a9306 | 1477 | interactive context.) Do not read from a terminal file (or call |
19799a22 | 1478 | C<eof(FILEHANDLE)> on it) after end-of-file is reached. File types such |
748a9306 LW |
1479 | as terminals may lose the end-of-file condition if you do. |
1480 | ||
820475bd GS |
1481 | An C<eof> without an argument uses the last file read. Using C<eof()> |
1482 | with empty parentheses is very different. It refers to the pseudo file | |
1483 | formed from the files listed on the command line and accessed via the | |
61eff3bc JH |
1484 | C<< <> >> operator. Since C<< <> >> isn't explicitly opened, |
1485 | as a normal filehandle is, an C<eof()> before C<< <> >> has been | |
820475bd | 1486 | used will cause C<@ARGV> to be examined to determine if input is |
67408cae | 1487 | available. Similarly, an C<eof()> after C<< <> >> has returned |
efdd0218 RB |
1488 | end-of-file will assume you are processing another C<@ARGV> list, |
1489 | and if you haven't set C<@ARGV>, will read input from C<STDIN>; | |
1490 | see L<perlop/"I/O Operators">. | |
820475bd | 1491 | |
61eff3bc | 1492 | In a C<< while (<>) >> loop, C<eof> or C<eof(ARGV)> can be used to |
820475bd GS |
1493 | detect the end of each file, C<eof()> will only detect the end of the |
1494 | last file. Examples: | |
a0d0e21e | 1495 | |
748a9306 LW |
1496 | # reset line numbering on each input file |
1497 | while (<>) { | |
b76cc8ba | 1498 | next if /^\s*#/; # skip comments |
748a9306 | 1499 | print "$.\t$_"; |
5a964f20 TC |
1500 | } continue { |
1501 | close ARGV if eof; # Not eof()! | |
748a9306 LW |
1502 | } |
1503 | ||
a0d0e21e LW |
1504 | # insert dashes just before last line of last file |
1505 | while (<>) { | |
6ac88b13 | 1506 | if (eof()) { # check for end of last file |
a0d0e21e LW |
1507 | print "--------------\n"; |
1508 | } | |
1509 | print; | |
6ac88b13 | 1510 | last if eof(); # needed if we're reading from a terminal |
a0d0e21e LW |
1511 | } |
1512 | ||
a0d0e21e | 1513 | Practical hint: you almost never need to use C<eof> in Perl, because the |
3ce0d271 GS |
1514 | input operators typically return C<undef> when they run out of data, or if |
1515 | there was an error. | |
a0d0e21e LW |
1516 | |
1517 | =item eval EXPR | |
d74e8afc | 1518 | X<eval> X<try> X<catch> X<evaluate> X<parse> X<execute> |
f723aae1 | 1519 | X<error, handling> X<exception, handling> |
a0d0e21e LW |
1520 | |
1521 | =item eval BLOCK | |
1522 | ||
ce2984c3 PF |
1523 | =item eval |
1524 | ||
c7cc6f1c GS |
1525 | In the first form, the return value of EXPR is parsed and executed as if it |
1526 | were a little Perl program. The value of the expression (which is itself | |
5a964f20 | 1527 | determined within scalar context) is first parsed, and if there weren't any |
be3174d2 GS |
1528 | errors, executed in the lexical context of the current Perl program, so |
1529 | that any variable settings or subroutine and format definitions remain | |
cf264981 | 1530 | afterwards. Note that the value is parsed every time the C<eval> executes. |
be3174d2 GS |
1531 | If EXPR is omitted, evaluates C<$_>. This form is typically used to |
1532 | delay parsing and subsequent execution of the text of EXPR until run time. | |
c7cc6f1c GS |
1533 | |
1534 | In the second form, the code within the BLOCK is parsed only once--at the | |
cf264981 | 1535 | same time the code surrounding the C<eval> itself was parsed--and executed |
c7cc6f1c GS |
1536 | within the context of the current Perl program. This form is typically |
1537 | used to trap exceptions more efficiently than the first (see below), while | |
1538 | also providing the benefit of checking the code within BLOCK at compile | |
1539 | time. | |
1540 | ||
1541 | The final semicolon, if any, may be omitted from the value of EXPR or within | |
1542 | the BLOCK. | |
1543 | ||
1544 | In both forms, the value returned is the value of the last expression | |
5a964f20 | 1545 | evaluated inside the mini-program; a return statement may be also used, just |
c7cc6f1c | 1546 | as with subroutines. The expression providing the return value is evaluated |
cf264981 SP |
1547 | in void, scalar, or list context, depending on the context of the C<eval> |
1548 | itself. See L</wantarray> for more on how the evaluation context can be | |
1549 | determined. | |
a0d0e21e | 1550 | |
19799a22 GS |
1551 | If there is a syntax error or runtime error, or a C<die> statement is |
1552 | executed, an undefined value is returned by C<eval>, and C<$@> is set to the | |
a0d0e21e | 1553 | error message. If there was no error, C<$@> is guaranteed to be a null |
19799a22 | 1554 | string. Beware that using C<eval> neither silences perl from printing |
c7cc6f1c | 1555 | warnings to STDERR, nor does it stuff the text of warning messages into C<$@>. |
d9984052 A |
1556 | To do either of those, you have to use the C<$SIG{__WARN__}> facility, or |
1557 | turn off warnings inside the BLOCK or EXPR using S<C<no warnings 'all'>>. | |
1558 | See L</warn>, L<perlvar>, L<warnings> and L<perllexwarn>. | |
a0d0e21e | 1559 | |
19799a22 GS |
1560 | Note that, because C<eval> traps otherwise-fatal errors, it is useful for |
1561 | determining whether a particular feature (such as C<socket> or C<symlink>) | |
a0d0e21e LW |
1562 | is implemented. It is also Perl's exception trapping mechanism, where |
1563 | the die operator is used to raise exceptions. | |
1564 | ||
5f1da31c NT |
1565 | If you want to trap errors when loading an XS module, some problems with |
1566 | the binary interface (such as Perl version skew) may be fatal even with | |
1567 | C<eval> unless C<$ENV{PERL_DL_NONLAZY}> is set. See L<perlrun>. | |
1568 | ||
a0d0e21e LW |
1569 | If the code to be executed doesn't vary, you may use the eval-BLOCK |
1570 | form to trap run-time errors without incurring the penalty of | |
1571 | recompiling each time. The error, if any, is still returned in C<$@>. | |
1572 | Examples: | |
1573 | ||
54310121 | 1574 | # make divide-by-zero nonfatal |
a0d0e21e LW |
1575 | eval { $answer = $a / $b; }; warn $@ if $@; |
1576 | ||
1577 | # same thing, but less efficient | |
1578 | eval '$answer = $a / $b'; warn $@ if $@; | |
1579 | ||
1580 | # a compile-time error | |
5a964f20 | 1581 | eval { $answer = }; # WRONG |
a0d0e21e LW |
1582 | |
1583 | # a run-time error | |
1584 | eval '$answer ='; # sets $@ | |
1585 | ||
cf264981 SP |
1586 | Using the C<eval{}> form as an exception trap in libraries does have some |
1587 | issues. Due to the current arguably broken state of C<__DIE__> hooks, you | |
1588 | may wish not to trigger any C<__DIE__> hooks that user code may have installed. | |
2b5ab1e7 TC |
1589 | You can use the C<local $SIG{__DIE__}> construct for this purpose, |
1590 | as shown in this example: | |
774d564b | 1591 | |
1592 | # a very private exception trap for divide-by-zero | |
f86cebdf GS |
1593 | eval { local $SIG{'__DIE__'}; $answer = $a / $b; }; |
1594 | warn $@ if $@; | |
774d564b | 1595 | |
1596 | This is especially significant, given that C<__DIE__> hooks can call | |
19799a22 | 1597 | C<die> again, which has the effect of changing their error messages: |
774d564b | 1598 | |
1599 | # __DIE__ hooks may modify error messages | |
1600 | { | |
f86cebdf GS |
1601 | local $SIG{'__DIE__'} = |
1602 | sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x }; | |
c7cc6f1c GS |
1603 | eval { die "foo lives here" }; |
1604 | print $@ if $@; # prints "bar lives here" | |
774d564b | 1605 | } |
1606 | ||
19799a22 | 1607 | Because this promotes action at a distance, this counterintuitive behavior |
2b5ab1e7 TC |
1608 | may be fixed in a future release. |
1609 | ||
19799a22 | 1610 | With an C<eval>, you should be especially careful to remember what's |
a0d0e21e LW |
1611 | being looked at when: |
1612 | ||
1613 | eval $x; # CASE 1 | |
1614 | eval "$x"; # CASE 2 | |
1615 | ||
1616 | eval '$x'; # CASE 3 | |
1617 | eval { $x }; # CASE 4 | |
1618 | ||
5a964f20 | 1619 | eval "\$$x++"; # CASE 5 |
a0d0e21e LW |
1620 | $$x++; # CASE 6 |
1621 | ||
2f9daede | 1622 | Cases 1 and 2 above behave identically: they run the code contained in |
19799a22 | 1623 | the variable $x. (Although case 2 has misleading double quotes making |
2f9daede | 1624 | the reader wonder what else might be happening (nothing is).) Cases 3 |
7660c0ab | 1625 | and 4 likewise behave in the same way: they run the code C<'$x'>, which |
19799a22 | 1626 | does nothing but return the value of $x. (Case 4 is preferred for |
2f9daede TP |
1627 | purely visual reasons, but it also has the advantage of compiling at |
1628 | compile-time instead of at run-time.) Case 5 is a place where | |
19799a22 | 1629 | normally you I<would> like to use double quotes, except that in this |
2f9daede TP |
1630 | particular situation, you can just use symbolic references instead, as |
1631 | in case 6. | |
a0d0e21e | 1632 | |
8a5a710d DN |
1633 | The assignment to C<$@> occurs before restoration of localised variables, |
1634 | which means a temporary is required if you want to mask some but not all | |
1635 | errors: | |
1636 | ||
1637 | # alter $@ on nefarious repugnancy only | |
1638 | { | |
1639 | my $e; | |
1640 | { | |
1641 | local $@; # protect existing $@ | |
1642 | eval { test_repugnancy() }; | |
1643 | # $@ =~ /nefarious/ and die $@; # DOES NOT WORK | |
1644 | $@ =~ /nefarious/ and $e = $@; | |
1645 | } | |
1646 | die $e if defined $e | |
1647 | } | |
1648 | ||
4968c1e4 | 1649 | C<eval BLOCK> does I<not> count as a loop, so the loop control statements |
2b5ab1e7 | 1650 | C<next>, C<last>, or C<redo> cannot be used to leave or restart the block. |
4968c1e4 | 1651 | |
d819b83a DM |
1652 | Note that as a very special case, an C<eval ''> executed within the C<DB> |
1653 | package doesn't see the usual surrounding lexical scope, but rather the | |
1654 | scope of the first non-DB piece of code that called it. You don't normally | |
1655 | need to worry about this unless you are writing a Perl debugger. | |
1656 | ||
a0d0e21e | 1657 | =item exec LIST |
d74e8afc | 1658 | X<exec> X<execute> |
a0d0e21e | 1659 | |
8bf3b016 GS |
1660 | =item exec PROGRAM LIST |
1661 | ||
19799a22 GS |
1662 | The C<exec> function executes a system command I<and never returns>-- |
1663 | use C<system> instead of C<exec> if you want it to return. It fails and | |
1664 | returns false only if the command does not exist I<and> it is executed | |
fb73857a | 1665 | directly instead of via your system's command shell (see below). |
a0d0e21e | 1666 | |
19799a22 GS |
1667 | Since it's a common mistake to use C<exec> instead of C<system>, Perl |
1668 | warns you if there is a following statement which isn't C<die>, C<warn>, | |
1669 | or C<exit> (if C<-w> is set - but you always do that). If you | |
1670 | I<really> want to follow an C<exec> with some other statement, you | |
55d729e4 GS |
1671 | can use one of these styles to avoid the warning: |
1672 | ||
5a964f20 TC |
1673 | exec ('foo') or print STDERR "couldn't exec foo: $!"; |
1674 | { exec ('foo') }; print STDERR "couldn't exec foo: $!"; | |
55d729e4 | 1675 | |
5a964f20 | 1676 | If there is more than one argument in LIST, or if LIST is an array |
f86cebdf | 1677 | with more than one value, calls execvp(3) with the arguments in LIST. |
5a964f20 TC |
1678 | If there is only one scalar argument or an array with one element in it, |
1679 | the argument is checked for shell metacharacters, and if there are any, | |
1680 | the entire argument is passed to the system's command shell for parsing | |
1681 | (this is C</bin/sh -c> on Unix platforms, but varies on other platforms). | |
1682 | If there are no shell metacharacters in the argument, it is split into | |
b76cc8ba | 1683 | words and passed directly to C<execvp>, which is more efficient. |
19799a22 | 1684 | Examples: |
a0d0e21e | 1685 | |
19799a22 GS |
1686 | exec '/bin/echo', 'Your arguments are: ', @ARGV; |
1687 | exec "sort $outfile | uniq"; | |
a0d0e21e LW |
1688 | |
1689 | If you don't really want to execute the first argument, but want to lie | |
1690 | to the program you are executing about its own name, you can specify | |
1691 | the program you actually want to run as an "indirect object" (without a | |
1692 | comma) in front of the LIST. (This always forces interpretation of the | |
54310121 | 1693 | LIST as a multivalued list, even if there is only a single scalar in |
a0d0e21e LW |
1694 | the list.) Example: |
1695 | ||
1696 | $shell = '/bin/csh'; | |
1697 | exec $shell '-sh'; # pretend it's a login shell | |
1698 | ||
1699 | or, more directly, | |
1700 | ||
1701 | exec {'/bin/csh'} '-sh'; # pretend it's a login shell | |
1702 | ||
bb32b41a GS |
1703 | When the arguments get executed via the system shell, results will |
1704 | be subject to its quirks and capabilities. See L<perlop/"`STRING`"> | |
1705 | for details. | |
1706 | ||
19799a22 GS |
1707 | Using an indirect object with C<exec> or C<system> is also more |
1708 | secure. This usage (which also works fine with system()) forces | |
1709 | interpretation of the arguments as a multivalued list, even if the | |
1710 | list had just one argument. That way you're safe from the shell | |
1711 | expanding wildcards or splitting up words with whitespace in them. | |
5a964f20 TC |
1712 | |
1713 | @args = ( "echo surprise" ); | |
1714 | ||
2b5ab1e7 | 1715 | exec @args; # subject to shell escapes |
f86cebdf | 1716 | # if @args == 1 |
2b5ab1e7 | 1717 | exec { $args[0] } @args; # safe even with one-arg list |
5a964f20 TC |
1718 | |
1719 | The first version, the one without the indirect object, ran the I<echo> | |
1720 | program, passing it C<"surprise"> an argument. The second version | |
1721 | didn't--it tried to run a program literally called I<"echo surprise">, | |
1722 | didn't find it, and set C<$?> to a non-zero value indicating failure. | |
1723 | ||
0f897271 GS |
1724 | Beginning with v5.6.0, Perl will attempt to flush all files opened for |
1725 | output before the exec, but this may not be supported on some platforms | |
1726 | (see L<perlport>). To be safe, you may need to set C<$|> ($AUTOFLUSH | |
1727 | in English) or call the C<autoflush()> method of C<IO::Handle> on any | |
1728 | open handles in order to avoid lost output. | |
1729 | ||
19799a22 | 1730 | Note that C<exec> will not call your C<END> blocks, nor will it call |
7660c0ab A |
1731 | any C<DESTROY> methods in your objects. |
1732 | ||
a0d0e21e | 1733 | =item exists EXPR |
d74e8afc | 1734 | X<exists> X<autovivification> |
a0d0e21e | 1735 | |
01020589 | 1736 | Given an expression that specifies a hash element or array element, |
8ea97a1e | 1737 | returns true if the specified element in the hash or array has ever |
95731d22 | 1738 | been initialized, even if the corresponding value is undefined. |
a0d0e21e | 1739 | |
01020589 GS |
1740 | print "Exists\n" if exists $hash{$key}; |
1741 | print "Defined\n" if defined $hash{$key}; | |
1742 | print "True\n" if $hash{$key}; | |
1743 | ||
1744 | print "Exists\n" if exists $array[$index]; | |
1745 | print "Defined\n" if defined $array[$index]; | |
1746 | print "True\n" if $array[$index]; | |
a0d0e21e | 1747 | |
8ea97a1e | 1748 | A hash or array element can be true only if it's defined, and defined if |
a0d0e21e LW |
1749 | it exists, but the reverse doesn't necessarily hold true. |
1750 | ||
afebc493 GS |
1751 | Given an expression that specifies the name of a subroutine, |
1752 | returns true if the specified subroutine has ever been declared, even | |
1753 | if it is undefined. Mentioning a subroutine name for exists or defined | |
847c7ebe DD |
1754 | does not count as declaring it. Note that a subroutine which does not |
1755 | exist may still be callable: its package may have an C<AUTOLOAD> | |
1756 | method that makes it spring into existence the first time that it is | |
1757 | called -- see L<perlsub>. | |
afebc493 GS |
1758 | |
1759 | print "Exists\n" if exists &subroutine; | |
1760 | print "Defined\n" if defined &subroutine; | |
1761 | ||
a0d0e21e | 1762 | Note that the EXPR can be arbitrarily complicated as long as the final |
afebc493 | 1763 | operation is a hash or array key lookup or subroutine name: |
a0d0e21e | 1764 | |
2b5ab1e7 TC |
1765 | if (exists $ref->{A}->{B}->{$key}) { } |
1766 | if (exists $hash{A}{B}{$key}) { } | |
1767 | ||
01020589 GS |
1768 | if (exists $ref->{A}->{B}->[$ix]) { } |
1769 | if (exists $hash{A}{B}[$ix]) { } | |
1770 | ||
afebc493 GS |
1771 | if (exists &{$ref->{A}{B}{$key}}) { } |
1772 | ||
01020589 GS |
1773 | Although the deepest nested array or hash will not spring into existence |
1774 | just because its existence was tested, any intervening ones will. | |
61eff3bc | 1775 | Thus C<< $ref->{"A"} >> and C<< $ref->{"A"}->{"B"} >> will spring |
01020589 GS |
1776 | into existence due to the existence test for the $key element above. |
1777 | This happens anywhere the arrow operator is used, including even: | |
5a964f20 | 1778 | |
2b5ab1e7 TC |
1779 | undef $ref; |
1780 | if (exists $ref->{"Some key"}) { } | |
1781 | print $ref; # prints HASH(0x80d3d5c) | |
1782 | ||
1783 | This surprising autovivification in what does not at first--or even | |
1784 | second--glance appear to be an lvalue context may be fixed in a future | |
5a964f20 | 1785 | release. |
a0d0e21e | 1786 | |
afebc493 GS |
1787 | Use of a subroutine call, rather than a subroutine name, as an argument |
1788 | to exists() is an error. | |
1789 | ||
1790 | exists ⊂ # OK | |
1791 | exists &sub(); # Error | |
1792 | ||
a0d0e21e | 1793 | =item exit EXPR |
d74e8afc | 1794 | X<exit> X<terminate> X<abort> |
a0d0e21e | 1795 | |
ce2984c3 PF |
1796 | =item exit |
1797 | ||
2b5ab1e7 | 1798 | Evaluates EXPR and exits immediately with that value. Example: |
a0d0e21e LW |
1799 | |
1800 | $ans = <STDIN>; | |
1801 | exit 0 if $ans =~ /^[Xx]/; | |
1802 | ||
19799a22 | 1803 | See also C<die>. If EXPR is omitted, exits with C<0> status. The only |
2b5ab1e7 TC |
1804 | universally recognized values for EXPR are C<0> for success and C<1> |
1805 | for error; other values are subject to interpretation depending on the | |
1806 | environment in which the Perl program is running. For example, exiting | |
1807 | 69 (EX_UNAVAILABLE) from a I<sendmail> incoming-mail filter will cause | |
1808 | the mailer to return the item undelivered, but that's not true everywhere. | |
a0d0e21e | 1809 | |
19799a22 GS |
1810 | Don't use C<exit> to abort a subroutine if there's any chance that |
1811 | someone might want to trap whatever error happened. Use C<die> instead, | |
1812 | which can be trapped by an C<eval>. | |
28757baa | 1813 | |
19799a22 | 1814 | The exit() function does not always exit immediately. It calls any |
2b5ab1e7 | 1815 | defined C<END> routines first, but these C<END> routines may not |
19799a22 | 1816 | themselves abort the exit. Likewise any object destructors that need to |
2b5ab1e7 TC |
1817 | be called are called before the real exit. If this is a problem, you |
1818 | can call C<POSIX:_exit($status)> to avoid END and destructor processing. | |
87275199 | 1819 | See L<perlmod> for details. |
5a964f20 | 1820 | |
a0d0e21e | 1821 | =item exp EXPR |
d74e8afc | 1822 | X<exp> X<exponential> X<antilog> X<antilogarithm> X<e> |
a0d0e21e | 1823 | |
54310121 | 1824 | =item exp |
bbce6d69 | 1825 | |
b76cc8ba | 1826 | Returns I<e> (the natural logarithm base) to the power of EXPR. |
a0d0e21e LW |
1827 | If EXPR is omitted, gives C<exp($_)>. |
1828 | ||
1829 | =item fcntl FILEHANDLE,FUNCTION,SCALAR | |
d74e8afc | 1830 | X<fcntl> |
a0d0e21e | 1831 | |
f86cebdf | 1832 | Implements the fcntl(2) function. You'll probably have to say |
a0d0e21e LW |
1833 | |
1834 | use Fcntl; | |
1835 | ||
0ade1984 | 1836 | first to get the correct constant definitions. Argument processing and |
b76cc8ba | 1837 | value return works just like C<ioctl> below. |
a0d0e21e LW |
1838 | For example: |
1839 | ||
1840 | use Fcntl; | |
5a964f20 TC |
1841 | fcntl($filehandle, F_GETFL, $packed_return_buffer) |
1842 | or die "can't fcntl F_GETFL: $!"; | |
1843 | ||
554ad1fc | 1844 | You don't have to check for C<defined> on the return from C<fcntl>. |
951ba7fe GS |
1845 | Like C<ioctl>, it maps a C<0> return from the system call into |
1846 | C<"0 but true"> in Perl. This string is true in boolean context and C<0> | |
2b5ab1e7 TC |
1847 | in numeric context. It is also exempt from the normal B<-w> warnings |
1848 | on improper numeric conversions. | |
5a964f20 | 1849 | |
19799a22 | 1850 | Note that C<fcntl> will produce a fatal error if used on a machine that |
2b5ab1e7 TC |
1851 | doesn't implement fcntl(2). See the Fcntl module or your fcntl(2) |
1852 | manpage to learn what functions are available on your system. | |
a0d0e21e | 1853 | |
be2f7487 TH |
1854 | Here's an example of setting a filehandle named C<REMOTE> to be |
1855 | non-blocking at the system level. You'll have to negotiate C<$|> | |
1856 | on your own, though. | |
1857 | ||
1858 | use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK); | |
1859 | ||
1860 | $flags = fcntl(REMOTE, F_GETFL, 0) | |
1861 | or die "Can't get flags for the socket: $!\n"; | |
1862 | ||
1863 | $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK) | |
1864 | or die "Can't set flags for the socket: $!\n"; | |
1865 | ||
a0d0e21e | 1866 | =item fileno FILEHANDLE |
d74e8afc | 1867 | X<fileno> |
a0d0e21e | 1868 | |
2b5ab1e7 TC |
1869 | Returns the file descriptor for a filehandle, or undefined if the |
1870 | filehandle is not open. This is mainly useful for constructing | |
19799a22 | 1871 | bitmaps for C<select> and low-level POSIX tty-handling operations. |
2b5ab1e7 TC |
1872 | If FILEHANDLE is an expression, the value is taken as an indirect |
1873 | filehandle, generally its name. | |
5a964f20 | 1874 | |
b76cc8ba | 1875 | You can use this to find out whether two handles refer to the |
5a964f20 TC |
1876 | same underlying descriptor: |
1877 | ||
1878 | if (fileno(THIS) == fileno(THAT)) { | |
1879 | print "THIS and THAT are dups\n"; | |
b76cc8ba NIS |
1880 | } |
1881 | ||
1882 | (Filehandles connected to memory objects via new features of C<open> may | |
1883 | return undefined even though they are open.) | |
1884 | ||
a0d0e21e LW |
1885 | |
1886 | =item flock FILEHANDLE,OPERATION | |
d74e8afc | 1887 | X<flock> X<lock> X<locking> |
a0d0e21e | 1888 | |
19799a22 GS |
1889 | Calls flock(2), or an emulation of it, on FILEHANDLE. Returns true |
1890 | for success, false on failure. Produces a fatal error if used on a | |
2b5ab1e7 | 1891 | machine that doesn't implement flock(2), fcntl(2) locking, or lockf(3). |
19799a22 | 1892 | C<flock> is Perl's portable file locking interface, although it locks |
2b5ab1e7 TC |
1893 | only entire files, not records. |
1894 | ||
1895 | Two potentially non-obvious but traditional C<flock> semantics are | |
1896 | that it waits indefinitely until the lock is granted, and that its locks | |
1897 | B<merely advisory>. Such discretionary locks are more flexible, but offer | |
cf264981 SP |
1898 | fewer guarantees. This means that programs that do not also use C<flock> |
1899 | may modify files locked with C<flock>. See L<perlport>, | |
2b5ab1e7 TC |
1900 | your port's specific documentation, or your system-specific local manpages |
1901 | for details. It's best to assume traditional behavior if you're writing | |
1902 | portable programs. (But if you're not, you should as always feel perfectly | |
1903 | free to write for your own system's idiosyncrasies (sometimes called | |
1904 | "features"). Slavish adherence to portability concerns shouldn't get | |
1905 | in the way of your getting your job done.) | |
a3cb178b | 1906 | |
8ebc5c01 | 1907 | OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with |
1908 | LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but | |
ea3105be | 1909 | you can use the symbolic names if you import them from the Fcntl module, |
68dc0745 | 1910 | either individually, or as a group using the ':flock' tag. LOCK_SH |
1911 | requests a shared lock, LOCK_EX requests an exclusive lock, and LOCK_UN | |
ea3105be GS |
1912 | releases a previously requested lock. If LOCK_NB is bitwise-or'ed with |
1913 | LOCK_SH or LOCK_EX then C<flock> will return immediately rather than blocking | |
68dc0745 | 1914 | waiting for the lock (check the return status to see if you got it). |
1915 | ||
2b5ab1e7 TC |
1916 | To avoid the possibility of miscoordination, Perl now flushes FILEHANDLE |
1917 | before locking or unlocking it. | |
8ebc5c01 | 1918 | |
f86cebdf | 1919 | Note that the emulation built with lockf(3) doesn't provide shared |
8ebc5c01 | 1920 | locks, and it requires that FILEHANDLE be open with write intent. These |
2b5ab1e7 | 1921 | are the semantics that lockf(3) implements. Most if not all systems |
f86cebdf | 1922 | implement lockf(3) in terms of fcntl(2) locking, though, so the |
8ebc5c01 | 1923 | differing semantics shouldn't bite too many people. |
1924 | ||
becacb53 TM |
1925 | Note that the fcntl(2) emulation of flock(3) requires that FILEHANDLE |
1926 | be open with read intent to use LOCK_SH and requires that it be open | |
1927 | with write intent to use LOCK_EX. | |
1928 | ||
19799a22 GS |
1929 | Note also that some versions of C<flock> cannot lock things over the |
1930 | network; you would need to use the more system-specific C<fcntl> for | |
f86cebdf GS |
1931 | that. If you like you can force Perl to ignore your system's flock(2) |
1932 | function, and so provide its own fcntl(2)-based emulation, by passing | |
8ebc5c01 | 1933 | the switch C<-Ud_flock> to the F<Configure> program when you configure |
1934 | perl. | |
4633a7c4 LW |
1935 | |
1936 | Here's a mailbox appender for BSD systems. | |
a0d0e21e | 1937 | |
7e1af8bc | 1938 | use Fcntl ':flock'; # import LOCK_* constants |
a0d0e21e LW |
1939 | |
1940 | sub lock { | |
7e1af8bc | 1941 | flock(MBOX,LOCK_EX); |
a0d0e21e LW |
1942 | # and, in case someone appended |
1943 | # while we were waiting... | |
1944 | seek(MBOX, 0, 2); | |
1945 | } | |
1946 | ||
1947 | sub unlock { | |
7e1af8bc | 1948 | flock(MBOX,LOCK_UN); |
a0d0e21e LW |
1949 | } |
1950 | ||
b0169937 | 1951 | open(my $mbox, ">>", "/usr/spool/mail/$ENV{'USER'}") |
a0d0e21e LW |
1952 | or die "Can't open mailbox: $!"; |
1953 | ||
1954 | lock(); | |
b0169937 | 1955 | print $mbox $msg,"\n\n"; |
a0d0e21e LW |
1956 | unlock(); |
1957 | ||
2b5ab1e7 TC |
1958 | On systems that support a real flock(), locks are inherited across fork() |
1959 | calls, whereas those that must resort to the more capricious fcntl() | |
1960 | function lose the locks, making it harder to write servers. | |
1961 | ||
cb1a09d0 | 1962 | See also L<DB_File> for other flock() examples. |
a0d0e21e LW |
1963 | |
1964 | =item fork | |
d74e8afc | 1965 | X<fork> X<child> X<parent> |
a0d0e21e | 1966 | |
2b5ab1e7 TC |
1967 | Does a fork(2) system call to create a new process running the |
1968 | same program at the same point. It returns the child pid to the | |
1969 | parent process, C<0> to the child process, or C<undef> if the fork is | |
1970 | unsuccessful. File descriptors (and sometimes locks on those descriptors) | |
1971 | are shared, while everything else is copied. On most systems supporting | |
1972 | fork(), great care has gone into making it extremely efficient (for | |
1973 | example, using copy-on-write technology on data pages), making it the | |
1974 | dominant paradigm for multitasking over the last few decades. | |
5a964f20 | 1975 | |
0f897271 GS |
1976 | Beginning with v5.6.0, Perl will attempt to flush all files opened for |
1977 | output before forking the child process, but this may not be supported | |
1978 | on some platforms (see L<perlport>). To be safe, you may need to set | |
1979 | C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method of | |
1980 | C<IO::Handle> on any open handles in order to avoid duplicate output. | |
a0d0e21e | 1981 | |
19799a22 | 1982 | If you C<fork> without ever waiting on your children, you will |
2b5ab1e7 TC |
1983 | accumulate zombies. On some systems, you can avoid this by setting |
1984 | C<$SIG{CHLD}> to C<"IGNORE">. See also L<perlipc> for more examples of | |
1985 | forking and reaping moribund children. | |
cb1a09d0 | 1986 | |
28757baa | 1987 | Note that if your forked child inherits system file descriptors like |
1988 | STDIN and STDOUT that are actually connected by a pipe or socket, even | |
2b5ab1e7 | 1989 | if you exit, then the remote server (such as, say, a CGI script or a |
19799a22 | 1990 | backgrounded job launched from a remote shell) won't think you're done. |
2b5ab1e7 | 1991 | You should reopen those to F</dev/null> if it's any issue. |
28757baa | 1992 | |
cb1a09d0 | 1993 | =item format |
d74e8afc | 1994 | X<format> |
cb1a09d0 | 1995 | |
19799a22 | 1996 | Declare a picture format for use by the C<write> function. For |
cb1a09d0 AD |
1997 | example: |
1998 | ||
54310121 | 1999 | format Something = |
cb1a09d0 AD |
2000 | Test: @<<<<<<<< @||||| @>>>>> |
2001 | $str, $%, '$' . int($num) | |
2002 | . | |
2003 | ||
2004 | $str = "widget"; | |
184e9718 | 2005 | $num = $cost/$quantity; |
cb1a09d0 AD |
2006 | $~ = 'Something'; |
2007 | write; | |
2008 | ||
2009 | See L<perlform> for many details and examples. | |
2010 | ||
8903cb82 | 2011 | =item formline PICTURE,LIST |
d74e8afc | 2012 | X<formline> |
a0d0e21e | 2013 | |
5a964f20 | 2014 | This is an internal function used by C<format>s, though you may call it, |
a0d0e21e LW |
2015 | too. It formats (see L<perlform>) a list of values according to the |
2016 | contents of PICTURE, placing the output into the format output | |
7660c0ab | 2017 | accumulator, C<$^A> (or C<$ACCUMULATOR> in English). |
19799a22 | 2018 | Eventually, when a C<write> is done, the contents of |
cf264981 SP |
2019 | C<$^A> are written to some filehandle. You could also read C<$^A> |
2020 | and then set C<$^A> back to C<"">. Note that a format typically | |
19799a22 | 2021 | does one C<formline> per line of form, but the C<formline> function itself |
748a9306 | 2022 | doesn't care how many newlines are embedded in the PICTURE. This means |
4633a7c4 | 2023 | that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line. |
748a9306 LW |
2024 | You may therefore need to use multiple formlines to implement a single |
2025 | record format, just like the format compiler. | |
2026 | ||
19799a22 | 2027 | Be careful if you put double quotes around the picture, because an C<@> |
748a9306 | 2028 | character may be taken to mean the beginning of an array name. |
19799a22 | 2029 | C<formline> always returns true. See L<perlform> for other examples. |
a0d0e21e LW |
2030 | |
2031 | =item getc FILEHANDLE | |
f723aae1 | 2032 | X<getc> X<getchar> X<character> X<file, read> |
a0d0e21e LW |
2033 | |
2034 | =item getc | |
2035 | ||
2036 | Returns the next character from the input file attached to FILEHANDLE, | |
b5fe5ca2 SR |
2037 | or the undefined value at end of file, or if there was an error (in |
2038 | the latter case C<$!> is set). If FILEHANDLE is omitted, reads from | |
2039 | STDIN. This is not particularly efficient. However, it cannot be | |
2040 | used by itself to fetch single characters without waiting for the user | |
2041 | to hit enter. For that, try something more like: | |
4633a7c4 LW |
2042 | |
2043 | if ($BSD_STYLE) { | |
2044 | system "stty cbreak </dev/tty >/dev/tty 2>&1"; | |
2045 | } | |
2046 | else { | |
54310121 | 2047 | system "stty", '-icanon', 'eol', "\001"; |
4633a7c4 LW |
2048 | } |
2049 | ||
2050 | $key = getc(STDIN); | |
2051 | ||
2052 | if ($BSD_STYLE) { | |
2053 | system "stty -cbreak </dev/tty >/dev/tty 2>&1"; | |
2054 | } | |
2055 | else { | |
5f05dabc | 2056 | system "stty", 'icanon', 'eol', '^@'; # ASCII null |
4633a7c4 LW |
2057 | } |
2058 | print "\n"; | |
2059 | ||
54310121 | 2060 | Determination of whether $BSD_STYLE should be set |
2061 | is left as an exercise to the reader. | |
cb1a09d0 | 2062 | |
19799a22 | 2063 | The C<POSIX::getattr> function can do this more portably on |
2b5ab1e7 TC |
2064 | systems purporting POSIX compliance. See also the C<Term::ReadKey> |
2065 | module from your nearest CPAN site; details on CPAN can be found on | |
2066 | L<perlmodlib/CPAN>. | |
a0d0e21e LW |
2067 | |
2068 | =item getlogin | |
d74e8afc | 2069 | X<getlogin> X<login> |
a0d0e21e | 2070 | |
cf264981 | 2071 | This implements the C library function of the same name, which on most |
5a964f20 | 2072 | systems returns the current login from F</etc/utmp>, if any. If null, |
19799a22 | 2073 | use C<getpwuid>. |
a0d0e21e | 2074 | |
f86702cc | 2075 | $login = getlogin || getpwuid($<) || "Kilroy"; |
a0d0e21e | 2076 | |
19799a22 GS |
2077 | Do not consider C<getlogin> for authentication: it is not as |
2078 | secure as C<getpwuid>. | |
4633a7c4 | 2079 | |
a0d0e21e | 2080 | =item getpeername SOCKET |
d74e8afc | 2081 | X<getpeername> X<peer> |
a0d0e21e LW |
2082 | |
2083 | Returns the packed sockaddr address of other end of the SOCKET connection. | |
2084 | ||
4633a7c4 LW |
2085 | use Socket; |
2086 | $hersockaddr = getpeername(SOCK); | |
19799a22 | 2087 | ($port, $iaddr) = sockaddr_in($hersockaddr); |
4633a7c4 LW |
2088 | $herhostname = gethostbyaddr($iaddr, AF_INET); |
2089 | $herstraddr = inet_ntoa($iaddr); | |
a0d0e21e LW |
2090 | |
2091 | =item getpgrp PID | |
d74e8afc | 2092 | X<getpgrp> X<group> |
a0d0e21e | 2093 | |
47e29363 | 2094 | Returns the current process group for the specified PID. Use |
7660c0ab | 2095 | a PID of C<0> to get the current process group for the |
4633a7c4 | 2096 | current process. Will raise an exception if used on a machine that |
f86cebdf | 2097 | doesn't implement getpgrp(2). If PID is omitted, returns process |
19799a22 | 2098 | group of current process. Note that the POSIX version of C<getpgrp> |
7660c0ab | 2099 | does not accept a PID argument, so only C<PID==0> is truly portable. |
a0d0e21e LW |
2100 | |
2101 | =item getppid | |
d74e8afc | 2102 | X<getppid> X<parent> X<pid> |
a0d0e21e LW |
2103 | |
2104 | Returns the process id of the parent process. | |
2105 | ||
4d76a344 RGS |
2106 | Note for Linux users: on Linux, the C functions C<getpid()> and |
2107 | C<getppid()> return different values from different threads. In order to | |
2108 | be portable, this behavior is not reflected by the perl-level function | |
2109 | C<getppid()>, that returns a consistent value across threads. If you want | |
e3256f86 RGS |
2110 | to call the underlying C<getppid()>, you may use the CPAN module |
2111 | C<Linux::Pid>. | |
4d76a344 | 2112 | |
a0d0e21e | 2113 | =item getpriority WHICH,WHO |
d74e8afc | 2114 | X<getpriority> X<priority> X<nice> |
a0d0e21e | 2115 | |
4633a7c4 LW |
2116 | Returns the current priority for a process, a process group, or a user. |
2117 | (See L<getpriority(2)>.) Will raise a fatal exception if used on a | |
f86cebdf | 2118 | machine that doesn't implement getpriority(2). |
a0d0e21e LW |
2119 | |
2120 | =item getpwnam NAME | |
d74e8afc ITB |
2121 | X<getpwnam> X<getgrnam> X<gethostbyname> X<getnetbyname> X<getprotobyname> |
2122 | X<getpwuid> X<getgrgid> X<getservbyname> X<gethostbyaddr> X<getnetbyaddr> | |
2123 | X<getprotobynumber> X<getservbyport> X<getpwent> X<getgrent> X<gethostent> | |
2124 | X<getnetent> X<getprotoent> X<getservent> X<setpwent> X<setgrent> X<sethostent> | |
2125 | X<setnetent> X<setprotoent> X<setservent> X<endpwent> X<endgrent> X<endhostent> | |
2126 | X<endnetent> X<endprotoent> X<endservent> | |
a0d0e21e LW |
2127 | |
2128 | =item getgrnam NAME | |
2129 | ||
2130 | =item gethostbyname NAME | |
2131 | ||
2132 | =item getnetbyname NAME | |
2133 | ||
2134 | =item getprotobyname NAME | |
2135 | ||
2136 | =item getpwuid UID | |
2137 | ||
2138 | =item getgrgid GID | |
2139 | ||
2140 | =item getservbyname NAME,PROTO | |
2141 | ||
2142 | =item gethostbyaddr ADDR,ADDRTYPE | |
2143 | ||
2144 | =item getnetbyaddr ADDR,ADDRTYPE | |
2145 | ||
2146 | =item getprotobynumber NUMBER | |
2147 | ||
2148 | =item getservbyport PORT,PROTO | |
2149 | ||
2150 | =item getpwent | |
2151 | ||
2152 | =item getgrent | |
2153 | ||
2154 | =item gethostent | |
2155 | ||
2156 | =item getnetent | |
2157 | ||
2158 | =item getprotoent | |
2159 | ||
2160 | =item getservent | |
2161 | ||
2162 | =item setpwent | |
2163 | ||
2164 | =item setgrent | |
2165 | ||
2166 | =item sethostent STAYOPEN | |
2167 | ||
2168 | =item setnetent STAYOPEN | |
2169 | ||
2170 | =item setprotoent STAYOPEN | |
2171 | ||
2172 | =item setservent STAYOPEN | |
2173 | ||
2174 | =item endpwent | |
2175 | ||
2176 | =item endgrent | |
2177 | ||
2178 | =item endhostent | |
2179 | ||
2180 | =item endnetent | |
2181 | ||
2182 | =item endprotoent | |
2183 | ||
2184 | =item endservent | |
2185 | ||
2186 | These routines perform the same functions as their counterparts in the | |
5a964f20 | 2187 | system library. In list context, the return values from the |
a0d0e21e LW |
2188 | various get routines are as follows: |
2189 | ||
2190 | ($name,$passwd,$uid,$gid, | |
6ee623d5 | 2191 | $quota,$comment,$gcos,$dir,$shell,$expire) = getpw* |
a0d0e21e LW |
2192 | ($name,$passwd,$gid,$members) = getgr* |
2193 | ($name,$aliases,$addrtype,$length,@addrs) = gethost* | |
2194 | ($name,$aliases,$addrtype,$net) = getnet* | |
2195 | ($name,$aliases,$proto) = getproto* | |
2196 | ($name,$aliases,$port,$proto) = getserv* | |
2197 | ||
2198 | (If the entry doesn't exist you get a null list.) | |
2199 | ||
4602f195 JH |
2200 | The exact meaning of the $gcos field varies but it usually contains |
2201 | the real name of the user (as opposed to the login name) and other | |
2202 | information pertaining to the user. Beware, however, that in many | |
2203 | system users are able to change this information and therefore it | |
106325ad | 2204 | cannot be trusted and therefore the $gcos is tainted (see |
2959b6e3 JH |
2205 | L<perlsec>). The $passwd and $shell, user's encrypted password and |
2206 | login shell, are also tainted, because of the same reason. | |
4602f195 | 2207 | |
5a964f20 | 2208 | In scalar context, you get the name, unless the function was a |
a0d0e21e LW |
2209 | lookup by name, in which case you get the other thing, whatever it is. |
2210 | (If the entry doesn't exist you get the undefined value.) For example: | |
2211 | ||
5a964f20 TC |
2212 | $uid = getpwnam($name); |
2213 | $name = getpwuid($num); | |
2214 | $name = getpwent(); | |
2215 | $gid = getgrnam($name); | |
08a33e13 | 2216 | $name = getgrgid($num); |
5a964f20 TC |
2217 | $name = getgrent(); |
2218 | #etc. | |
a0d0e21e | 2219 | |
4602f195 JH |
2220 | In I<getpw*()> the fields $quota, $comment, and $expire are special |
2221 | cases in the sense that in many systems they are unsupported. If the | |
2222 | $quota is unsupported, it is an empty scalar. If it is supported, it | |
2223 | usually encodes the disk quota. If the $comment field is unsupported, | |
2224 | it is an empty scalar. If it is supported it usually encodes some | |
2225 | administrative comment about the user. In some systems the $quota | |
2226 | field may be $change or $age, fields that have to do with password | |
2227 | aging. In some systems the $comment field may be $class. The $expire | |
2228 | field, if present, encodes the expiration period of the account or the | |
2229 | password. For the availability and the exact meaning of these fields | |
2230 | in your system, please consult your getpwnam(3) documentation and your | |
2231 | F<pwd.h> file. You can also find out from within Perl what your | |
2232 | $quota and $comment fields mean and whether you have the $expire field | |
2233 | by using the C<Config> module and the values C<d_pwquota>, C<d_pwage>, | |
2234 | C<d_pwchange>, C<d_pwcomment>, and C<d_pwexpire>. Shadow password | |
2235 | files are only supported if your vendor has implemented them in the | |
2236 | intuitive fashion that calling the regular C library routines gets the | |
5d3a0a3b | 2237 | shadow versions if you're running under privilege or if there exists |
cf264981 SP |
2238 | the shadow(3) functions as found in System V (this includes Solaris |
2239 | and Linux.) Those systems that implement a proprietary shadow password | |
5d3a0a3b | 2240 | facility are unlikely to be supported. |
6ee623d5 | 2241 | |
19799a22 | 2242 | The $members value returned by I<getgr*()> is a space separated list of |
a0d0e21e LW |
2243 | the login names of the members of the group. |
2244 | ||
2245 | For the I<gethost*()> functions, if the C<h_errno> variable is supported in | |
2246 | C, it will be returned to you via C<$?> if the function call fails. The | |
7660c0ab | 2247 | C<@addrs> value returned by a successful call is a list of the raw |
a0d0e21e LW |
2248 | addresses returned by the corresponding system library call. In the |
2249 | Internet domain, each address is four bytes long and you can unpack it | |
2250 | by saying something like: | |
2251 | ||
f337b084 | 2252 | ($a,$b,$c,$d) = unpack('W4',$addr[0]); |
a0d0e21e | 2253 | |
2b5ab1e7 TC |
2254 | The Socket library makes this slightly easier: |
2255 | ||
2256 | use Socket; | |
2257 | $iaddr = inet_aton("127.1"); # or whatever address | |
2258 | $name = gethostbyaddr($iaddr, AF_INET); | |
2259 | ||
2260 | # or going the other way | |
19799a22 | 2261 | $straddr = inet_ntoa($iaddr); |
2b5ab1e7 | 2262 | |
d760c846 GS |
2263 | In the opposite way, to resolve a hostname to the IP address |
2264 | you can write this: | |
2265 | ||
2266 | use Socket; | |
2267 | $packed_ip = gethostbyname("www.perl.org"); | |
2268 | if (defined $packed_ip) { | |
2269 | $ip_address = inet_ntoa($packed_ip); | |
2270 | } | |
2271 | ||
2272 | Make sure <gethostbyname()> is called in SCALAR context and that | |
2273 | its return value is checked for definedness. | |
2274 | ||
19799a22 GS |
2275 | If you get tired of remembering which element of the return list |
2276 | contains which return value, by-name interfaces are provided | |
2277 | in standard modules: C<File::stat>, C<Net::hostent>, C<Net::netent>, | |
2278 | C<Net::protoent>, C<Net::servent>, C<Time::gmtime>, C<Time::localtime>, | |
2279 | and C<User::grent>. These override the normal built-ins, supplying | |
2280 | versions that return objects with the appropriate names | |
2281 | for each field. For example: | |
5a964f20 TC |
2282 | |
2283 | use File::stat; | |
2284 | use User::pwent; | |
2285 | $is_his = (stat($filename)->uid == pwent($whoever)->uid); | |
2286 | ||
b76cc8ba NIS |
2287 | Even though it looks like they're the same method calls (uid), |
2288 | they aren't, because a C<File::stat> object is different from | |
19799a22 | 2289 | a C<User::pwent> object. |
5a964f20 | 2290 | |
a0d0e21e | 2291 | =item getsockname SOCKET |
d74e8afc | 2292 | X<getsockname> |
a0d0e21e | 2293 | |
19799a22 GS |
2294 | Returns the packed sockaddr address of this end of the SOCKET connection, |
2295 | in case you don't know the address because you have several different | |
2296 | IPs that the connection might have come in on. | |
a0d0e21e | 2297 | |
4633a7c4 LW |
2298 | use Socket; |
2299 | $mysockaddr = getsockname(SOCK); | |
19799a22 | 2300 | ($port, $myaddr) = sockaddr_in($mysockaddr); |
b76cc8ba | 2301 | printf "Connect to %s [%s]\n", |
19799a22 GS |
2302 | scalar gethostbyaddr($myaddr, AF_INET), |
2303 | inet_ntoa($myaddr); | |
a0d0e21e LW |
2304 | |
2305 | =item getsockopt SOCKET,LEVEL,OPTNAME | |
d74e8afc | 2306 | X<getsockopt> |
a0d0e21e | 2307 | |
636e6b1f TH |
2308 | Queries the option named OPTNAME associated with SOCKET at a given LEVEL. |
2309 | Options may exist at multiple protocol levels depending on the socket | |
2310 | type, but at least the uppermost socket level SOL_SOCKET (defined in the | |
2311 | C<Socket> module) will exist. To query options at another level the | |
2312 | protocol number of the appropriate protocol controlling the option | |
2313 | should be supplied. For example, to indicate that an option is to be | |
2314 | interpreted by the TCP protocol, LEVEL should be set to the protocol | |
2315 | number of TCP, which you can get using getprotobyname. | |
2316 | ||
2317 | The call returns a packed string representing the requested socket option, | |
2318 | or C<undef> if there is an error (the error reason will be in $!). What | |
2319 | exactly is in the packed string depends in the LEVEL and OPTNAME, consult | |
2320 | your system documentation for details. A very common case however is that | |
cf264981 | 2321 | the option is an integer, in which case the result will be a packed |
636e6b1f TH |
2322 | integer which you can decode using unpack with the C<i> (or C<I>) format. |
2323 | ||
2324 | An example testing if Nagle's algorithm is turned on on a socket: | |
2325 | ||
4852725b | 2326 | use Socket qw(:all); |
636e6b1f TH |
2327 | |
2328 | defined(my $tcp = getprotobyname("tcp")) | |
2329 | or die "Could not determine the protocol number for tcp"; | |
4852725b DD |
2330 | # my $tcp = IPPROTO_TCP; # Alternative |
2331 | my $packed = getsockopt($socket, $tcp, TCP_NODELAY) | |
2332 | or die "Could not query TCP_NODELAY socket option: $!"; | |
636e6b1f TH |
2333 | my $nodelay = unpack("I", $packed); |
2334 | print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n"; | |
2335 | ||
a0d0e21e LW |
2336 | |
2337 | =item glob EXPR | |
d74e8afc | 2338 | X<glob> X<wildcard> X<filename, expansion> X<expand> |
a0d0e21e | 2339 | |
0a753a76 | 2340 | =item glob |
2341 | ||
d9a9d457 JL |
2342 | In list context, returns a (possibly empty) list of filename expansions on |
2343 | the value of EXPR such as the standard Unix shell F</bin/csh> would do. In | |
2344 | scalar context, glob iterates through such filename expansions, returning | |
2345 | undef when the list is exhausted. This is the internal function | |
2346 | implementing the C<< <*.c> >> operator, but you can use it directly. If | |
2347 | EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is discussed in | |
2348 | more detail in L<perlop/"I/O Operators">. | |
a0d0e21e | 2349 | |
5c0c9249 PF |
2350 | Note that C<glob> will split its arguments on whitespace, treating |
2351 | each segment as separate pattern. As such, C<glob('*.c *.h')> would | |
2352 | match all files with a F<.c> or F<.h> extension. The expression | |
2353 | C<glob('.* *')> would match all files in the current working directory. | |
2354 | ||
3a4b19e4 | 2355 | Beginning with v5.6.0, this operator is implemented using the standard |
5c0c9249 PF |
2356 | C<File::Glob> extension. See L<File::Glob> for details, including |
2357 | C<bsd_glob> which does not treat whitespace as a pattern separator. | |
3a4b19e4 | 2358 | |
a0d0e21e | 2359 | =item gmtime EXPR |
d74e8afc | 2360 | X<gmtime> X<UTC> X<Greenwich> |
a0d0e21e | 2361 | |
ce2984c3 PF |
2362 | =item gmtime |
2363 | ||
435fbc73 GS |
2364 | Works just like L<localtime> but the returned values are |
2365 | localized for the standard Greenwich time zone. | |
a0d0e21e | 2366 | |
435fbc73 GS |
2367 | Note: when called in list context, $isdst, the last value |
2368 | returned by gmtime is always C<0>. There is no | |
2369 | Daylight Saving Time in GMT. | |
0a753a76 | 2370 | |
62aa5637 MS |
2371 | See L<perlport/gmtime> for portability concerns. |
2372 | ||
a0d0e21e | 2373 | =item goto LABEL |
d74e8afc | 2374 | X<goto> X<jump> X<jmp> |
a0d0e21e | 2375 | |
748a9306 LW |
2376 | =item goto EXPR |
2377 | ||
a0d0e21e LW |
2378 | =item goto &NAME |
2379 | ||
7660c0ab | 2380 | The C<goto-LABEL> form finds the statement labeled with LABEL and resumes |
a0d0e21e | 2381 | execution there. It may not be used to go into any construct that |
7660c0ab | 2382 | requires initialization, such as a subroutine or a C<foreach> loop. It |
0a753a76 | 2383 | also can't be used to go into a construct that is optimized away, |
19799a22 | 2384 | or to get out of a block or subroutine given to C<sort>. |
0a753a76 | 2385 | It can be used to go almost anywhere else within the dynamic scope, |
a0d0e21e | 2386 | including out of subroutines, but it's usually better to use some other |
19799a22 | 2387 | construct such as C<last> or C<die>. The author of Perl has never felt the |
7660c0ab | 2388 | need to use this form of C<goto> (in Perl, that is--C is another matter). |
1b6921cb BT |
2389 | (The difference being that C does not offer named loops combined with |
2390 | loop control. Perl does, and this replaces most structured uses of C<goto> | |
2391 | in other languages.) | |
a0d0e21e | 2392 | |
7660c0ab A |
2393 | The C<goto-EXPR> form expects a label name, whose scope will be resolved |
2394 | dynamically. This allows for computed C<goto>s per FORTRAN, but isn't | |
748a9306 LW |
2395 | necessarily recommended if you're optimizing for maintainability: |
2396 | ||
2397 | goto ("FOO", "BAR", "GLARCH")[$i]; | |
2398 | ||
1b6921cb BT |
2399 | The C<goto-&NAME> form is quite different from the other forms of |
2400 | C<goto>. In fact, it isn't a goto in the normal sense at all, and | |
2401 | doesn't have the stigma associated with other gotos. Instead, it | |
2402 | exits the current subroutine (losing any changes set by local()) and | |
2403 | immediately calls in its place the named subroutine using the current | |
2404 | value of @_. This is used by C<AUTOLOAD> subroutines that wish to | |
2405 | load another subroutine and then pretend that the other subroutine had | |
2406 | been called in the first place (except that any modifications to C<@_> | |
6cb9131c GS |
2407 | in the current subroutine are propagated to the other subroutine.) |
2408 | After the C<goto>, not even C<caller> will be able to tell that this | |
2409 | routine was called first. | |
2410 | ||
2411 | NAME needn't be the name of a subroutine; it can be a scalar variable | |
cf264981 | 2412 | containing a code reference, or a block that evaluates to a code |
6cb9131c | 2413 | reference. |
a0d0e21e LW |
2414 | |
2415 | =item grep BLOCK LIST | |
d74e8afc | 2416 | X<grep> |
a0d0e21e LW |
2417 | |
2418 | =item grep EXPR,LIST | |
2419 | ||
2b5ab1e7 TC |
2420 | This is similar in spirit to, but not the same as, grep(1) and its |
2421 | relatives. In particular, it is not limited to using regular expressions. | |
2f9daede | 2422 | |
a0d0e21e | 2423 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
7660c0ab | 2424 | C<$_> to each element) and returns the list value consisting of those |
19799a22 GS |
2425 | elements for which the expression evaluated to true. In scalar |
2426 | context, returns the number of times the expression was true. | |
a0d0e21e LW |
2427 | |
2428 | @foo = grep(!/^#/, @bar); # weed out comments | |
2429 | ||
2430 | or equivalently, | |
2431 | ||
2432 | @foo = grep {!/^#/} @bar; # weed out comments | |
2433 | ||
be3174d2 GS |
2434 | Note that C<$_> is an alias to the list value, so it can be used to |
2435 | modify the elements of the LIST. While this is useful and supported, | |
2436 | it can cause bizarre results if the elements of LIST are not variables. | |
2b5ab1e7 TC |
2437 | Similarly, grep returns aliases into the original list, much as a for |
2438 | loop's index variable aliases the list elements. That is, modifying an | |
19799a22 GS |
2439 | element of a list returned by grep (for example, in a C<foreach>, C<map> |
2440 | or another C<grep>) actually modifies the element in the original list. | |
2b5ab1e7 | 2441 | This is usually something to be avoided when writing clear code. |
a0d0e21e | 2442 | |
a4fb8298 | 2443 | If C<$_> is lexical in the scope where the C<grep> appears (because it has |
cf264981 | 2444 | been declared with C<my $_>) then, in addition to being locally aliased to |
a4fb8298 RGS |
2445 | the list elements, C<$_> keeps being lexical inside the block; i.e. it |
2446 | can't be seen from the outside, avoiding any potential side-effects. | |
2447 | ||
19799a22 | 2448 | See also L</map> for a list composed of the results of the BLOCK or EXPR. |
38325410 | 2449 | |
a0d0e21e | 2450 | =item hex EXPR |
d74e8afc | 2451 | X<hex> X<hexadecimal> |
a0d0e21e | 2452 | |
54310121 | 2453 | =item hex |
bbce6d69 | 2454 | |
2b5ab1e7 | 2455 | Interprets EXPR as a hex string and returns the corresponding value. |
38366c11 | 2456 | (To convert strings that might start with either C<0>, C<0x>, or C<0b>, see |
2b5ab1e7 | 2457 | L</oct>.) If EXPR is omitted, uses C<$_>. |
2f9daede TP |
2458 | |
2459 | print hex '0xAf'; # prints '175' | |
2460 | print hex 'aF'; # same | |
a0d0e21e | 2461 | |
19799a22 | 2462 | Hex strings may only represent integers. Strings that would cause |
53305cf1 | 2463 | integer overflow trigger a warning. Leading whitespace is not stripped, |
38366c11 DN |
2464 | unlike oct(). To present something as hex, look into L</printf>, |
2465 | L</sprintf>, or L</unpack>. | |
19799a22 | 2466 | |
ce2984c3 | 2467 | =item import LIST |
d74e8afc | 2468 | X<import> |
a0d0e21e | 2469 | |
19799a22 | 2470 | There is no builtin C<import> function. It is just an ordinary |
4633a7c4 | 2471 | method (subroutine) defined (or inherited) by modules that wish to export |
19799a22 | 2472 | names to another module. The C<use> function calls the C<import> method |
cea6626f | 2473 | for the package used. See also L</use>, L<perlmod>, and L<Exporter>. |
a0d0e21e LW |
2474 | |
2475 | =item index STR,SUBSTR,POSITION | |
d74e8afc | 2476 | X<index> X<indexOf> X<InStr> |
a0d0e21e LW |
2477 | |
2478 | =item index STR,SUBSTR | |
2479 | ||
2b5ab1e7 TC |
2480 | The index function searches for one string within another, but without |
2481 | the wildcard-like behavior of a full regular-expression pattern match. | |
2482 | It returns the position of the first occurrence of SUBSTR in STR at | |
2483 | or after POSITION. If POSITION is omitted, starts searching from the | |
26f149de YST |
2484 | beginning of the string. POSITION before the beginning of the string |
2485 | or after its end is treated as if it were the beginning or the end, | |
2486 | respectively. POSITION and the return value are based at C<0> (or whatever | |
2b5ab1e7 | 2487 | you've set the C<$[> variable to--but don't do that). If the substring |
cf264981 | 2488 | is not found, C<index> returns one less than the base, ordinarily C<-1>. |
a0d0e21e LW |
2489 | |
2490 | =item int EXPR | |
f723aae1 | 2491 | X<int> X<integer> X<truncate> X<trunc> X<floor> |
a0d0e21e | 2492 | |
54310121 | 2493 | =item int |
bbce6d69 | 2494 | |
7660c0ab | 2495 | Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>. |
2b5ab1e7 TC |
2496 | You should not use this function for rounding: one because it truncates |
2497 | towards C<0>, and two because machine representations of floating point | |
2498 | numbers can sometimes produce counterintuitive results. For example, | |
2499 | C<int(-6.725/0.025)> produces -268 rather than the correct -269; that's | |
2500 | because it's really more like -268.99999999999994315658 instead. Usually, | |
19799a22 | 2501 | the C<sprintf>, C<printf>, or the C<POSIX::floor> and C<POSIX::ceil> |
2b5ab1e7 | 2502 | functions will serve you better than will int(). |
a0d0e21e LW |
2503 | |
2504 | =item ioctl FILEHANDLE,FUNCTION,SCALAR | |
d74e8afc | 2505 | X<ioctl> |
a0d0e21e | 2506 | |
2b5ab1e7 | 2507 | Implements the ioctl(2) function. You'll probably first have to say |
a0d0e21e | 2508 | |
6c567752 | 2509 | require "sys/ioctl.ph"; # probably in $Config{archlib}/sys/ioctl.ph |
a0d0e21e | 2510 | |
a11c483f | 2511 | to get the correct function definitions. If F<sys/ioctl.ph> doesn't |
a0d0e21e | 2512 | exist or doesn't have the correct definitions you'll have to roll your |
61eff3bc | 2513 | own, based on your C header files such as F<< <sys/ioctl.h> >>. |
5a964f20 | 2514 | (There is a Perl script called B<h2ph> that comes with the Perl kit that |
54310121 | 2515 | may help you in this, but it's nontrivial.) SCALAR will be read and/or |
4633a7c4 | 2516 | written depending on the FUNCTION--a pointer to the string value of SCALAR |
19799a22 | 2517 | will be passed as the third argument of the actual C<ioctl> call. (If SCALAR |
4633a7c4 LW |
2518 | has no string value but does have a numeric value, that value will be |
2519 | passed rather than a pointer to the string value. To guarantee this to be | |
19799a22 GS |
2520 | true, add a C<0> to the scalar before using it.) The C<pack> and C<unpack> |
2521 | functions may be needed to manipulate the values of structures used by | |
b76cc8ba | 2522 | C<ioctl>. |
a0d0e21e | 2523 | |
19799a22 | 2524 | The return value of C<ioctl> (and C<fcntl>) is as follows: |
a0d0e21e LW |
2525 | |
2526 | if OS returns: then Perl returns: | |
2527 | -1 undefined value | |
2528 | 0 string "0 but true" | |
2529 | anything else that number | |
2530 | ||
19799a22 | 2531 | Thus Perl returns true on success and false on failure, yet you can |
a0d0e21e LW |
2532 | still easily determine the actual value returned by the operating |
2533 | system: | |
2534 | ||
2b5ab1e7 | 2535 | $retval = ioctl(...) || -1; |
a0d0e21e LW |
2536 | printf "System returned %d\n", $retval; |
2537 | ||
be2f7487 | 2538 | The special string C<"0 but true"> is exempt from B<-w> complaints |
5a964f20 TC |
2539 | about improper numeric conversions. |
2540 | ||
a0d0e21e | 2541 | =item join EXPR,LIST |
d74e8afc | 2542 | X<join> |
a0d0e21e | 2543 | |
2b5ab1e7 TC |
2544 | Joins the separate strings of LIST into a single string with fields |
2545 | separated by the value of EXPR, and returns that new string. Example: | |
a0d0e21e | 2546 | |
2b5ab1e7 | 2547 | $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); |
a0d0e21e | 2548 | |
eb6e2d6f GS |
2549 | Beware that unlike C<split>, C<join> doesn't take a pattern as its |
2550 | first argument. Compare L</split>. | |
a0d0e21e | 2551 | |
aa689395 | 2552 | =item keys HASH |
d74e8afc | 2553 | X<keys> X<key> |
aa689395 | 2554 | |
aeedbbed NC |
2555 | =item keys ARRAY |
2556 | ||
2557 | Returns a list consisting of all the keys of the named hash, or the indices | |
2558 | of an array. (In scalar context, returns the number of keys or indices.) | |
504f80c1 | 2559 | |
aeedbbed | 2560 | The keys of a hash are returned in an apparently random order. The actual |
504f80c1 JH |
2561 | random order is subject to change in future versions of perl, but it |
2562 | is guaranteed to be the same order as either the C<values> or C<each> | |
4546b9e6 JH |
2563 | function produces (given that the hash has not been modified). Since |
2564 | Perl 5.8.1 the ordering is different even between different runs of | |
2565 | Perl for security reasons (see L<perlsec/"Algorithmic Complexity | |
d6df3700 | 2566 | Attacks">). |
504f80c1 | 2567 | |
aeedbbed | 2568 | As a side effect, calling keys() resets the HASH or ARRAY's internal iterator |
cf264981 SP |
2569 | (see L</each>). In particular, calling keys() in void context resets |
2570 | the iterator with no other overhead. | |
a0d0e21e | 2571 | |
aa689395 | 2572 | Here is yet another way to print your environment: |
a0d0e21e LW |
2573 | |
2574 | @keys = keys %ENV; | |
2575 | @values = values %ENV; | |
b76cc8ba | 2576 | while (@keys) { |
a0d0e21e LW |
2577 | print pop(@keys), '=', pop(@values), "\n"; |
2578 | } | |
2579 | ||
2580 | or how about sorted by key: | |
2581 | ||
2582 | foreach $key (sort(keys %ENV)) { | |
2583 | print $key, '=', $ENV{$key}, "\n"; | |
2584 | } | |
2585 | ||
8ea1e5d4 GS |
2586 | The returned values are copies of the original keys in the hash, so |
2587 | modifying them will not affect the original hash. Compare L</values>. | |
2588 | ||
19799a22 | 2589 | To sort a hash by value, you'll need to use a C<sort> function. |
aa689395 | 2590 | Here's a descending numeric sort of a hash by its values: |
4633a7c4 | 2591 | |
5a964f20 | 2592 | foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) { |
4633a7c4 LW |
2593 | printf "%4d %s\n", $hash{$key}, $key; |
2594 | } | |
2595 | ||
19799a22 | 2596 | As an lvalue C<keys> allows you to increase the number of hash buckets |
aa689395 | 2597 | allocated for the given hash. This can gain you a measure of efficiency if |
2598 | you know the hash is going to get big. (This is similar to pre-extending | |
2599 | an array by assigning a larger number to $#array.) If you say | |
55497cff | 2600 | |
2601 | keys %hash = 200; | |
2602 | ||
ab192400 GS |
2603 | then C<%hash> will have at least 200 buckets allocated for it--256 of them, |
2604 | in fact, since it rounds up to the next power of two. These | |
55497cff | 2605 | buckets will be retained even if you do C<%hash = ()>, use C<undef |
2606 | %hash> if you want to free the storage while C<%hash> is still in scope. | |
2607 | You can't shrink the number of buckets allocated for the hash using | |
19799a22 | 2608 | C<keys> in this way (but you needn't worry about doing this by accident, |
aeedbbed NC |
2609 | as trying has no effect). C<keys @array> in an lvalue context is a syntax |
2610 | error. | |
55497cff | 2611 | |
19799a22 | 2612 | See also C<each>, C<values> and C<sort>. |
ab192400 | 2613 | |
b350dd2f | 2614 | =item kill SIGNAL, LIST |
d74e8afc | 2615 | X<kill> X<signal> |
a0d0e21e | 2616 | |
b350dd2f | 2617 | Sends a signal to a list of processes. Returns the number of |
517db077 GS |
2618 | processes successfully signaled (which is not necessarily the |
2619 | same as the number actually killed). | |
a0d0e21e LW |
2620 | |
2621 | $cnt = kill 1, $child1, $child2; | |
2622 | kill 9, @goners; | |
2623 | ||
70fb64f6 | 2624 | If SIGNAL is zero, no signal is sent to the process, but the kill(2) |
6cb9d3e4 | 2625 | system call will check whether it's possible to send a signal to it (that |
70fb64f6 RGS |
2626 | means, to be brief, that the process is owned by the same user, or we are |
2627 | the super-user). This is a useful way to check that a child process is | |
81fd35db DN |
2628 | alive (even if only as a zombie) and hasn't changed its UID. See |
2629 | L<perlport> for notes on the portability of this construct. | |
b350dd2f GS |
2630 | |
2631 | Unlike in the shell, if SIGNAL is negative, it kills | |
4633a7c4 LW |
2632 | process groups instead of processes. (On System V, a negative I<PROCESS> |
2633 | number will also kill process groups, but that's not portable.) That | |
2634 | means you usually want to use positive not negative signals. You may also | |
1e9c1022 JL |
2635 | use a signal name in quotes. |
2636 | ||
2637 | See L<perlipc/"Signals"> for more details. | |
a0d0e21e LW |
2638 | |
2639 | =item last LABEL | |
d74e8afc | 2640 | X<last> X<break> |
a0d0e21e LW |
2641 | |
2642 | =item last | |
2643 | ||
2644 | The C<last> command is like the C<break> statement in C (as used in | |
2645 | loops); it immediately exits the loop in question. If the LABEL is | |
2646 | omitted, the command refers to the innermost enclosing loop. The | |
2647 | C<continue> block, if any, is not executed: | |
2648 | ||
4633a7c4 LW |
2649 | LINE: while (<STDIN>) { |
2650 | last LINE if /^$/; # exit when done with header | |
5a964f20 | 2651 | #... |
a0d0e21e LW |
2652 | } |
2653 | ||
4968c1e4 | 2654 | C<last> cannot be used to exit a block which returns a value such as |
2b5ab1e7 TC |
2655 | C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit |
2656 | a grep() or map() operation. | |
4968c1e4 | 2657 | |
6c1372ed GS |
2658 | Note that a block by itself is semantically identical to a loop |
2659 | that executes once. Thus C<last> can be used to effect an early | |
2660 | exit out of such a block. | |
2661 | ||
98293880 JH |
2662 | See also L</continue> for an illustration of how C<last>, C<next>, and |
2663 | C<redo> work. | |
1d2dff63 | 2664 | |
a0d0e21e | 2665 | =item lc EXPR |
d74e8afc | 2666 | X<lc> X<lowercase> |
a0d0e21e | 2667 | |
54310121 | 2668 | =item lc |
bbce6d69 | 2669 | |
d1be9408 | 2670 | Returns a lowercased version of EXPR. This is the internal function |
ad0029c4 JH |
2671 | implementing the C<\L> escape in double-quoted strings. Respects |
2672 | current LC_CTYPE locale if C<use locale> in force. See L<perllocale> | |
983ffd37 | 2673 | and L<perlunicode> for more details about locale and Unicode support. |
a0d0e21e | 2674 | |
7660c0ab | 2675 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 2676 | |
a0d0e21e | 2677 | =item lcfirst EXPR |
d74e8afc | 2678 | X<lcfirst> X<lowercase> |
a0d0e21e | 2679 | |
54310121 | 2680 | =item lcfirst |
bbce6d69 | 2681 | |
ad0029c4 JH |
2682 | Returns the value of EXPR with the first character lowercased. This |
2683 | is the internal function implementing the C<\l> escape in | |
2684 | double-quoted strings. Respects current LC_CTYPE locale if C<use | |
983ffd37 JH |
2685 | locale> in force. See L<perllocale> and L<perlunicode> for more |
2686 | details about locale and Unicode support. | |
a0d0e21e | 2687 | |
7660c0ab | 2688 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 2689 | |
a0d0e21e | 2690 | =item length EXPR |
d74e8afc | 2691 | X<length> X<size> |
a0d0e21e | 2692 | |
54310121 | 2693 | =item length |
bbce6d69 | 2694 | |
974da8e5 | 2695 | Returns the length in I<characters> of the value of EXPR. If EXPR is |
9f621bb0 NC |
2696 | omitted, returns length of C<$_>. If EXPR is undefined, returns C<undef>. |
2697 | Note that this cannot be used on an entire array or hash to find out how | |
2698 | many elements these have. For that, use C<scalar @array> and C<scalar keys | |
2699 | %hash> respectively. | |
a0d0e21e | 2700 | |
974da8e5 JH |
2701 | Note the I<characters>: if the EXPR is in Unicode, you will get the |
2702 | number of characters, not the number of bytes. To get the length | |
2575c402 JW |
2703 | of the internal string in bytes, use C<bytes::length(EXPR)>, see |
2704 | L<bytes>. Note that the internal encoding is variable, and the number | |
2705 | of bytes usually meaningless. To get the number of bytes that the | |
2706 | string would have when encoded as UTF-8, use | |
2707 | C<length(Encoding::encode_utf8(EXPR))>. | |
974da8e5 | 2708 | |
a0d0e21e | 2709 | =item link OLDFILE,NEWFILE |
d74e8afc | 2710 | X<link> |
a0d0e21e | 2711 | |
19799a22 | 2712 | Creates a new filename linked to the old filename. Returns true for |
b76cc8ba | 2713 | success, false otherwise. |
a0d0e21e LW |
2714 | |
2715 | =item listen SOCKET,QUEUESIZE | |
d74e8afc | 2716 | X<listen> |
a0d0e21e | 2717 | |
19799a22 | 2718 | Does the same thing that the listen system call does. Returns true if |
b76cc8ba | 2719 | it succeeded, false otherwise. See the example in |
cea6626f | 2720 | L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
2721 | |
2722 | =item local EXPR | |
d74e8afc | 2723 | X<local> |
a0d0e21e | 2724 | |
19799a22 | 2725 | You really probably want to be using C<my> instead, because C<local> isn't |
b76cc8ba | 2726 | what most people think of as "local". See |
13a2d996 | 2727 | L<perlsub/"Private Variables via my()"> for details. |
2b5ab1e7 | 2728 | |
5a964f20 TC |
2729 | A local modifies the listed variables to be local to the enclosing |
2730 | block, file, or eval. If more than one value is listed, the list must | |
2731 | be placed in parentheses. See L<perlsub/"Temporary Values via local()"> | |
2732 | for details, including issues with tied arrays and hashes. | |
a0d0e21e | 2733 | |
a0d0e21e | 2734 | =item localtime EXPR |
435fbc73 | 2735 | X<localtime> X<ctime> |
a0d0e21e | 2736 | |
ba053783 AL |
2737 | =item localtime |
2738 | ||
19799a22 | 2739 | Converts a time as returned by the time function to a 9-element list |
5f05dabc | 2740 | with the time analyzed for the local time zone. Typically used as |
a0d0e21e LW |
2741 | follows: |
2742 | ||
54310121 | 2743 | # 0 1 2 3 4 5 6 7 8 |
a0d0e21e | 2744 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
ba053783 | 2745 | localtime(time); |
a0d0e21e | 2746 | |
48a26b3a | 2747 | All list elements are numeric, and come straight out of the C `struct |
ba053783 AL |
2748 | tm'. C<$sec>, C<$min>, and C<$hour> are the seconds, minutes, and hours |
2749 | of the specified time. | |
48a26b3a | 2750 | |
ba053783 AL |
2751 | C<$mday> is the day of the month, and C<$mon> is the month itself, in |
2752 | the range C<0..11> with 0 indicating January and 11 indicating December. | |
2753 | This makes it easy to get a month name from a list: | |
54310121 | 2754 | |
ba053783 AL |
2755 | my @abbr = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec ); |
2756 | print "$abbr[$mon] $mday"; | |
2757 | # $mon=9, $mday=18 gives "Oct 18" | |
abd75f24 | 2758 | |
ba053783 AL |
2759 | C<$year> is the number of years since 1900, not just the last two digits |
2760 | of the year. That is, C<$year> is C<123> in year 2023. The proper way | |
2761 | to get a complete 4-digit year is simply: | |
abd75f24 | 2762 | |
ba053783 | 2763 | $year += 1900; |
abd75f24 | 2764 | |
435fbc73 GS |
2765 | Otherwise you create non-Y2K-compliant programs--and you wouldn't want |
2766 | to do that, would you? | |
2767 | ||
ba053783 AL |
2768 | To get the last two digits of the year (e.g., '01' in 2001) do: |
2769 | ||
2770 | $year = sprintf("%02d", $year % 100); | |
2771 | ||
2772 | C<$wday> is the day of the week, with 0 indicating Sunday and 3 indicating | |
2773 | Wednesday. C<$yday> is the day of the year, in the range C<0..364> | |
2774 | (or C<0..365> in leap years.) | |
2775 | ||
2776 | C<$isdst> is true if the specified time occurs during Daylight Saving | |
2777 | Time, false otherwise. | |
abd75f24 | 2778 | |
e1998452 | 2779 | If EXPR is omitted, C<localtime()> uses the current time (as returned |
e3176d09 | 2780 | by time(3)). |
a0d0e21e | 2781 | |
48a26b3a | 2782 | In scalar context, C<localtime()> returns the ctime(3) value: |
a0d0e21e | 2783 | |
5f05dabc | 2784 | $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994" |
a0d0e21e | 2785 | |
fe86afc2 NC |
2786 | This scalar value is B<not> locale dependent but is a Perl builtin. For GMT |
2787 | instead of local time use the L</gmtime> builtin. See also the | |
2788 | C<Time::Local> module (to convert the second, minutes, hours, ... back to | |
2789 | the integer value returned by time()), and the L<POSIX> module's strftime(3) | |
2790 | and mktime(3) functions. | |
2791 | ||
2792 | To get somewhat similar but locale dependent date strings, set up your | |
2793 | locale environment variables appropriately (please see L<perllocale>) and | |
2794 | try for example: | |
a3cb178b | 2795 | |
5a964f20 | 2796 | use POSIX qw(strftime); |
2b5ab1e7 | 2797 | $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime; |
fe86afc2 NC |
2798 | # or for GMT formatted appropriately for your locale: |
2799 | $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime; | |
a3cb178b GS |
2800 | |
2801 | Note that the C<%a> and C<%b>, the short forms of the day of the week | |
2802 | and the month of the year, may not necessarily be three characters wide. | |
a0d0e21e | 2803 | |
62aa5637 MS |
2804 | See L<perlport/localtime> for portability concerns. |
2805 | ||
435fbc73 GS |
2806 | The L<Time::gmtime> and L<Time::localtime> modules provides a convenient, |
2807 | by-name access mechanism to the gmtime() and localtime() functions, | |
2808 | respectively. | |
2809 | ||
2810 | For a comprehensive date and time representation look at the | |
2811 | L<DateTime> module on CPAN. | |
2812 | ||
07698885 | 2813 | =item lock THING |
d74e8afc | 2814 | X<lock> |
19799a22 | 2815 | |
01e6739c | 2816 | This function places an advisory lock on a shared variable, or referenced |
03730085 | 2817 | object contained in I<THING> until the lock goes out of scope. |
a6d5524e | 2818 | |
f3a23afb | 2819 | lock() is a "weak keyword" : this means that if you've defined a function |
67408cae | 2820 | by this name (before any calls to it), that function will be called |
03730085 AB |
2821 | instead. (However, if you've said C<use threads>, lock() is always a |
2822 | keyword.) See L<threads>. | |
19799a22 | 2823 | |
a0d0e21e | 2824 | =item log EXPR |
d74e8afc | 2825 | X<log> X<logarithm> X<e> X<ln> X<base> |
a0d0e21e | 2826 | |
54310121 | 2827 | =item log |
bbce6d69 | 2828 | |
2b5ab1e7 TC |
2829 | Returns the natural logarithm (base I<e>) of EXPR. If EXPR is omitted, |
2830 | returns log of C<$_>. To get the log of another base, use basic algebra: | |
19799a22 | 2831 | The base-N log of a number is equal to the natural log of that number |
2b5ab1e7 TC |
2832 | divided by the natural log of N. For example: |
2833 | ||
2834 | sub log10 { | |
2835 | my $n = shift; | |
2836 | return log($n)/log(10); | |
b76cc8ba | 2837 | } |
2b5ab1e7 TC |
2838 | |
2839 | See also L</exp> for the inverse operation. | |
a0d0e21e | 2840 | |
a0d0e21e | 2841 | =item lstat EXPR |
d74e8afc | 2842 | X<lstat> |
a0d0e21e | 2843 | |
54310121 | 2844 | =item lstat |
bbce6d69 | 2845 | |
19799a22 | 2846 | Does the same thing as the C<stat> function (including setting the |
5a964f20 TC |
2847 | special C<_> filehandle) but stats a symbolic link instead of the file |
2848 | the symbolic link points to. If symbolic links are unimplemented on | |
c837d5b4 DP |
2849 | your system, a normal C<stat> is done. For much more detailed |
2850 | information, please see the documentation for C<stat>. | |
a0d0e21e | 2851 | |
7660c0ab | 2852 | If EXPR is omitted, stats C<$_>. |
bbce6d69 | 2853 | |
a0d0e21e LW |
2854 | =item m// |
2855 | ||
2856 | The match operator. See L<perlop>. | |
2857 | ||
2858 | =item map BLOCK LIST | |
d74e8afc | 2859 | X<map> |
a0d0e21e LW |
2860 | |
2861 | =item map EXPR,LIST | |
2862 | ||
19799a22 GS |
2863 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
2864 | C<$_> to each element) and returns the list value composed of the | |
2865 | results of each such evaluation. In scalar context, returns the | |
2866 | total number of elements so generated. Evaluates BLOCK or EXPR in | |
2867 | list context, so each element of LIST may produce zero, one, or | |
2868 | more elements in the returned value. | |
dd99ebda | 2869 | |
a0d0e21e LW |
2870 | @chars = map(chr, @nums); |
2871 | ||
2872 | translates a list of numbers to the corresponding characters. And | |
2873 | ||
d8216f19 | 2874 | %hash = map { get_a_key_for($_) => $_ } @array; |
a0d0e21e LW |
2875 | |
2876 | is just a funny way to write | |
2877 | ||
2878 | %hash = (); | |
d8216f19 RGS |
2879 | foreach (@array) { |
2880 | $hash{get_a_key_for($_)} = $_; | |
a0d0e21e LW |
2881 | } |
2882 | ||
be3174d2 GS |
2883 | Note that C<$_> is an alias to the list value, so it can be used to |
2884 | modify the elements of the LIST. While this is useful and supported, | |
2885 | it can cause bizarre results if the elements of LIST are not variables. | |
2b5ab1e7 TC |
2886 | Using a regular C<foreach> loop for this purpose would be clearer in |
2887 | most cases. See also L</grep> for an array composed of those items of | |
2888 | the original list for which the BLOCK or EXPR evaluates to true. | |
fb73857a | 2889 | |
a4fb8298 | 2890 | If C<$_> is lexical in the scope where the C<map> appears (because it has |
d8216f19 RGS |
2891 | been declared with C<my $_>), then, in addition to being locally aliased to |
2892 | the list elements, C<$_> keeps being lexical inside the block; that is, it | |
a4fb8298 RGS |
2893 | can't be seen from the outside, avoiding any potential side-effects. |
2894 | ||
205fdb4d NC |
2895 | C<{> starts both hash references and blocks, so C<map { ...> could be either |
2896 | the start of map BLOCK LIST or map EXPR, LIST. Because perl doesn't look | |
2897 | ahead for the closing C<}> it has to take a guess at which its dealing with | |
2898 | based what it finds just after the C<{>. Usually it gets it right, but if it | |
2899 | doesn't it won't realize something is wrong until it gets to the C<}> and | |
2900 | encounters the missing (or unexpected) comma. The syntax error will be | |
2901 | reported close to the C<}> but you'll need to change something near the C<{> | |
2902 | such as using a unary C<+> to give perl some help: | |
2903 | ||
2904 | %hash = map { "\L$_", 1 } @array # perl guesses EXPR. wrong | |
2905 | %hash = map { +"\L$_", 1 } @array # perl guesses BLOCK. right | |
2906 | %hash = map { ("\L$_", 1) } @array # this also works | |
2907 | %hash = map { lc($_), 1 } @array # as does this. | |
2908 | %hash = map +( lc($_), 1 ), @array # this is EXPR and works! | |
cea6626f | 2909 | |
205fdb4d NC |
2910 | %hash = map ( lc($_), 1 ), @array # evaluates to (1, @array) |
2911 | ||
d8216f19 | 2912 | or to force an anon hash constructor use C<+{>: |
205fdb4d NC |
2913 | |
2914 | @hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end | |
2915 | ||
2916 | and you get list of anonymous hashes each with only 1 entry. | |
2917 | ||
19799a22 | 2918 | =item mkdir FILENAME,MASK |
d74e8afc | 2919 | X<mkdir> X<md> X<directory, create> |
a0d0e21e | 2920 | |
5a211162 GS |
2921 | =item mkdir FILENAME |
2922 | ||
491873e5 RGS |
2923 | =item mkdir |
2924 | ||
0591cd52 | 2925 | Creates the directory specified by FILENAME, with permissions |
19799a22 GS |
2926 | specified by MASK (as modified by C<umask>). If it succeeds it |
2927 | returns true, otherwise it returns false and sets C<$!> (errno). | |
491873e5 RGS |
2928 | If omitted, MASK defaults to 0777. If omitted, FILENAME defaults |
2929 | to C<$_>. | |
0591cd52 | 2930 | |
19799a22 | 2931 | In general, it is better to create directories with permissive MASK, |
0591cd52 | 2932 | and let the user modify that with their C<umask>, than it is to supply |
19799a22 | 2933 | a restrictive MASK and give the user no way to be more permissive. |
0591cd52 NT |
2934 | The exceptions to this rule are when the file or directory should be |
2935 | kept private (mail files, for instance). The perlfunc(1) entry on | |
19799a22 | 2936 | C<umask> discusses the choice of MASK in more detail. |
a0d0e21e | 2937 | |
cc1852e8 JH |
2938 | Note that according to the POSIX 1003.1-1996 the FILENAME may have any |
2939 | number of trailing slashes. Some operating and filesystems do not get | |
2940 | this right, so Perl automatically removes all trailing slashes to keep | |
2941 | everyone happy. | |
2942 | ||
dd184578 RGS |
2943 | In order to recursively create a directory structure look at |
2944 | the C<mkpath> function of the L<File::Path> module. | |
2945 | ||
a0d0e21e | 2946 | =item msgctl ID,CMD,ARG |
d74e8afc | 2947 | X<msgctl> |
a0d0e21e | 2948 | |
f86cebdf | 2949 | Calls the System V IPC function msgctl(2). You'll probably have to say |
0ade1984 JH |
2950 | |
2951 | use IPC::SysV; | |
2952 | ||
7660c0ab | 2953 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
cf264981 | 2954 | then ARG must be a variable that will hold the returned C<msqid_ds> |
951ba7fe GS |
2955 | structure. Returns like C<ioctl>: the undefined value for error, |
2956 | C<"0 but true"> for zero, or the actual return value otherwise. See also | |
4755096e | 2957 | L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::Semaphore> documentation. |
a0d0e21e LW |
2958 | |
2959 | =item msgget KEY,FLAGS | |
d74e8afc | 2960 | X<msgget> |
a0d0e21e | 2961 | |
f86cebdf | 2962 | Calls the System V IPC function msgget(2). Returns the message queue |
4755096e GS |
2963 | id, or the undefined value if there is an error. See also |
2964 | L<perlipc/"SysV IPC"> and C<IPC::SysV> and C<IPC::Msg> documentation. | |
a0d0e21e | 2965 | |
a0d0e21e | 2966 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS |
d74e8afc | 2967 | X<msgrcv> |
a0d0e21e LW |
2968 | |
2969 | Calls the System V IPC function msgrcv to receive a message from | |
2970 | message queue ID into variable VAR with a maximum message size of | |
41d6edb2 JH |
2971 | SIZE. Note that when a message is received, the message type as a |
2972 | native long integer will be the first thing in VAR, followed by the | |
2973 | actual message. This packing may be opened with C<unpack("l! a*")>. | |
2974 | Taints the variable. Returns true if successful, or false if there is | |
4755096e GS |
2975 | an error. See also L<perlipc/"SysV IPC">, C<IPC::SysV>, and |
2976 | C<IPC::SysV::Msg> documentation. | |
41d6edb2 JH |
2977 | |
2978 | =item msgsnd ID,MSG,FLAGS | |
d74e8afc | 2979 | X<msgsnd> |
41d6edb2 JH |
2980 | |
2981 | Calls the System V IPC function msgsnd to send the message MSG to the | |
2982 | message queue ID. MSG must begin with the native long integer message | |
2983 | type, and be followed by the length of the actual message, and finally | |
2984 | the message itself. This kind of packing can be achieved with | |
2985 | C<pack("l! a*", $type, $message)>. Returns true if successful, | |
2986 | or false if there is an error. See also C<IPC::SysV> | |
2987 | and C<IPC::SysV::Msg> documentation. | |
a0d0e21e LW |
2988 | |
2989 | =item my EXPR | |
d74e8afc | 2990 | X<my> |
a0d0e21e | 2991 | |
307ea6df JH |
2992 | =item my TYPE EXPR |
2993 | ||
1d2de774 | 2994 | =item my EXPR : ATTRS |
09bef843 | 2995 | |
1d2de774 | 2996 | =item my TYPE EXPR : ATTRS |
307ea6df | 2997 | |
19799a22 | 2998 | A C<my> declares the listed variables to be local (lexically) to the |
1d2de774 JH |
2999 | enclosing block, file, or C<eval>. If more than one value is listed, |
3000 | the list must be placed in parentheses. | |
307ea6df | 3001 | |
1d2de774 JH |
3002 | The exact semantics and interface of TYPE and ATTRS are still |
3003 | evolving. TYPE is currently bound to the use of C<fields> pragma, | |
307ea6df JH |
3004 | and attributes are handled using the C<attributes> pragma, or starting |
3005 | from Perl 5.8.0 also via the C<Attribute::Handlers> module. See | |
3006 | L<perlsub/"Private Variables via my()"> for details, and L<fields>, | |
3007 | L<attributes>, and L<Attribute::Handlers>. | |
4633a7c4 | 3008 | |
a0d0e21e | 3009 | =item next LABEL |
d74e8afc | 3010 | X<next> X<continue> |
a0d0e21e LW |
3011 | |
3012 | =item next | |
3013 | ||
3014 | The C<next> command is like the C<continue> statement in C; it starts | |
3015 | the next iteration of the loop: | |
3016 | ||
4633a7c4 LW |
3017 | LINE: while (<STDIN>) { |
3018 | next LINE if /^#/; # discard comments | |
5a964f20 | 3019 | #... |
a0d0e21e LW |
3020 | } |
3021 | ||
3022 | Note that if there were a C<continue> block on the above, it would get | |
3023 | executed even on discarded lines. If the LABEL is omitted, the command | |
3024 | refers to the innermost enclosing loop. | |
3025 | ||
4968c1e4 | 3026 | C<next> cannot be used to exit a block which returns a value such as |
2b5ab1e7 TC |
3027 | C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit |
3028 | a grep() or map() operation. | |
4968c1e4 | 3029 | |
6c1372ed GS |
3030 | Note that a block by itself is semantically identical to a loop |
3031 | that executes once. Thus C<next> will exit such a block early. | |
3032 | ||
98293880 JH |
3033 | See also L</continue> for an illustration of how C<last>, C<next>, and |
3034 | C<redo> work. | |
1d2dff63 | 3035 | |
4a66ea5a | 3036 | =item no Module VERSION LIST |
d74e8afc | 3037 | X<no> |
4a66ea5a RGS |
3038 | |
3039 | =item no Module VERSION | |
3040 | ||
a0d0e21e LW |
3041 | =item no Module LIST |
3042 | ||
4a66ea5a RGS |
3043 | =item no Module |
3044 | ||
c986422f RGS |
3045 | =item no VERSION |
3046 | ||
593b9c14 | 3047 | See the C<use> function, of which C<no> is the opposite. |
a0d0e21e LW |
3048 | |
3049 | =item oct EXPR | |
d74e8afc | 3050 | X<oct> X<octal> X<hex> X<hexadecimal> X<binary> X<bin> |
a0d0e21e | 3051 | |
54310121 | 3052 | =item oct |
bbce6d69 | 3053 | |
4633a7c4 | 3054 | Interprets EXPR as an octal string and returns the corresponding |
4f19785b WSI |
3055 | value. (If EXPR happens to start off with C<0x>, interprets it as a |
3056 | hex string. If EXPR starts off with C<0b>, it is interpreted as a | |
53305cf1 NC |
3057 | binary string. Leading whitespace is ignored in all three cases.) |
3058 | The following will handle decimal, binary, octal, and hex in the standard | |
3059 | Perl or C notation: | |
a0d0e21e LW |
3060 | |
3061 | $val = oct($val) if $val =~ /^0/; | |
3062 | ||
19799a22 GS |
3063 | If EXPR is omitted, uses C<$_>. To go the other way (produce a number |
3064 | in octal), use sprintf() or printf(): | |
3065 | ||
3066 | $perms = (stat("filename"))[2] & 07777; | |
3067 | $oct_perms = sprintf "%lo", $perms; | |
3068 | ||
3069 | The oct() function is commonly used when a string such as C<644> needs | |
3070 | to be converted into a file mode, for example. (Although perl will | |
3071 | automatically convert strings into numbers as needed, this automatic | |
3072 | conversion assumes base 10.) | |
a0d0e21e LW |
3073 | |
3074 | =item open FILEHANDLE,EXPR | |
d74e8afc | 3075 | X<open> X<pipe> X<file, open> X<fopen> |
a0d0e21e | 3076 | |
68bd7414 NIS |
3077 | =item open FILEHANDLE,MODE,EXPR |
3078 | ||
3079 | =item open FILEHANDLE,MODE,EXPR,LIST | |
3080 | ||
ba964c95 T |
3081 | =item open FILEHANDLE,MODE,REFERENCE |
3082 | ||
a0d0e21e LW |
3083 | =item open FILEHANDLE |
3084 | ||
3085 | Opens the file whose filename is given by EXPR, and associates it with | |
ed53a2bb JH |
3086 | FILEHANDLE. |
3087 | ||
460b70c2 GS |
3088 | Simple examples to open a file for reading: |
3089 | ||
3090 | open(my $fh, '<', "input.txt") or die $!; | |
3091 | ||
3092 | and for writing: | |
3093 | ||
3094 | open(my $fh, '>', "output.txt") or die $!; | |
3095 | ||
ed53a2bb JH |
3096 | (The following is a comprehensive reference to open(): for a gentler |
3097 | introduction you may consider L<perlopentut>.) | |
3098 | ||
a28cd5c9 NT |
3099 | If FILEHANDLE is an undefined scalar variable (or array or hash element) |
3100 | the variable is assigned a reference to a new anonymous filehandle, | |
3101 | otherwise if FILEHANDLE is an expression, its value is used as the name of | |
3102 | the real filehandle wanted. (This is considered a symbolic reference, so | |
3103 | C<use strict 'refs'> should I<not> be in effect.) | |
ed53a2bb JH |
3104 | |
3105 | If EXPR is omitted, the scalar variable of the same name as the | |
3106 | FILEHANDLE contains the filename. (Note that lexical variables--those | |
3107 | declared with C<my>--will not work for this purpose; so if you're | |
67408cae | 3108 | using C<my>, specify EXPR in your call to open.) |
ed53a2bb JH |
3109 | |
3110 | If three or more arguments are specified then the mode of opening and | |
3111 | the file name are separate. If MODE is C<< '<' >> or nothing, the file | |
3112 | is opened for input. If MODE is C<< '>' >>, the file is truncated and | |
3113 | opened for output, being created if necessary. If MODE is C<<< '>>' >>>, | |
b76cc8ba | 3114 | the file is opened for appending, again being created if necessary. |
5a964f20 | 3115 | |
ed53a2bb JH |
3116 | You can put a C<'+'> in front of the C<< '>' >> or C<< '<' >> to |
3117 | indicate that you want both read and write access to the file; thus | |
3118 | C<< '+<' >> is almost always preferred for read/write updates--the C<< | |
3119 | '+>' >> mode would clobber the file first. You can't usually use | |
3120 | either read-write mode for updating textfiles, since they have | |
3121 | variable length records. See the B<-i> switch in L<perlrun> for a | |
3122 | better approach. The file is created with permissions of C<0666> | |
3123 | modified by the process' C<umask> value. | |
3124 | ||
3125 | These various prefixes correspond to the fopen(3) modes of C<'r'>, | |
3126 | C<'r+'>, C<'w'>, C<'w+'>, C<'a'>, and C<'a+'>. | |
5f05dabc | 3127 | |
6170680b IZ |
3128 | In the 2-arguments (and 1-argument) form of the call the mode and |
3129 | filename should be concatenated (in this order), possibly separated by | |
68bd7414 NIS |
3130 | spaces. It is possible to omit the mode in these forms if the mode is |
3131 | C<< '<' >>. | |
6170680b | 3132 | |
7660c0ab | 3133 | If the filename begins with C<'|'>, the filename is interpreted as a |
5a964f20 | 3134 | command to which output is to be piped, and if the filename ends with a |
f244e06d GS |
3135 | C<'|'>, the filename is interpreted as a command which pipes output to |
3136 | us. See L<perlipc/"Using open() for IPC"> | |
19799a22 | 3137 | for more examples of this. (You are not allowed to C<open> to a command |
5a964f20 | 3138 | that pipes both in I<and> out, but see L<IPC::Open2>, L<IPC::Open3>, |
4a4eefd0 GS |
3139 | and L<perlipc/"Bidirectional Communication with Another Process"> |
3140 | for alternatives.) | |
cb1a09d0 | 3141 | |
ed53a2bb JH |
3142 | For three or more arguments if MODE is C<'|-'>, the filename is |
3143 | interpreted as a command to which output is to be piped, and if MODE | |
3144 | is C<'-|'>, the filename is interpreted as a command which pipes | |
3145 | output to us. In the 2-arguments (and 1-argument) form one should | |
3146 | replace dash (C<'-'>) with the command. | |
3147 | See L<perlipc/"Using open() for IPC"> for more examples of this. | |
3148 | (You are not allowed to C<open> to a command that pipes both in I<and> | |
3149 | out, but see L<IPC::Open2>, L<IPC::Open3>, and | |
3150 | L<perlipc/"Bidirectional Communication"> for alternatives.) | |
3151 | ||
3152 | In the three-or-more argument form of pipe opens, if LIST is specified | |
3153 | (extra arguments after the command name) then LIST becomes arguments | |
3154 | to the command invoked if the platform supports it. The meaning of | |
3155 | C<open> with more than three arguments for non-pipe modes is not yet | |
3156 | specified. Experimental "layers" may give extra LIST arguments | |
3157 | meaning. | |
6170680b IZ |
3158 | |
3159 | In the 2-arguments (and 1-argument) form opening C<'-'> opens STDIN | |
b76cc8ba | 3160 | and opening C<< '>-' >> opens STDOUT. |
6170680b | 3161 | |
fae2c0fb RGS |
3162 | You may use the three-argument form of open to specify IO "layers" |
3163 | (sometimes also referred to as "disciplines") to be applied to the handle | |
3164 | that affect how the input and output are processed (see L<open> and | |
3165 | L<PerlIO> for more details). For example | |
7207e29d | 3166 | |
460b70c2 | 3167 | open(my $fh, "<:encoding(UTF-8)", "file") |
9124316e JH |
3168 | |
3169 | will open the UTF-8 encoded file containing Unicode characters, | |
6d5e88a0 TS |
3170 | see L<perluniintro>. Note that if layers are specified in the |
3171 | three-arg form then default layers stored in ${^OPEN} (see L<perlvar>; | |
3172 | usually set by the B<open> pragma or the switch B<-CioD>) are ignored. | |
ed53a2bb JH |
3173 | |
3174 | Open returns nonzero upon success, the undefined value otherwise. If | |
3175 | the C<open> involved a pipe, the return value happens to be the pid of | |
3176 | the subprocess. | |
cb1a09d0 | 3177 | |
ed53a2bb JH |
3178 | If you're running Perl on a system that distinguishes between text |
3179 | files and binary files, then you should check out L</binmode> for tips | |
3180 | for dealing with this. The key distinction between systems that need | |
3181 | C<binmode> and those that don't is their text file formats. Systems | |
8939ba94 | 3182 | like Unix, Mac OS, and Plan 9, which delimit lines with a single |
ed53a2bb JH |
3183 | character, and which encode that character in C as C<"\n">, do not |
3184 | need C<binmode>. The rest need it. | |
cb1a09d0 | 3185 | |
fb73857a | 3186 | When opening a file, it's usually a bad idea to continue normal execution |
19799a22 GS |
3187 | if the request failed, so C<open> is frequently used in connection with |
3188 | C<die>. Even if C<die> won't do what you want (say, in a CGI script, | |
fb73857a | 3189 | where you want to make a nicely formatted error message (but there are |
5a964f20 | 3190 | modules that can help with that problem)) you should always check |
19799a22 | 3191 | the return value from opening a file. The infrequent exception is when |
fb73857a | 3192 | working with an unopened filehandle is actually what you want to do. |
3193 | ||
cf264981 | 3194 | As a special case the 3-arg form with a read/write mode and the third |
ed53a2bb | 3195 | argument being C<undef>: |
b76cc8ba | 3196 | |
460b70c2 | 3197 | open(my $tmp, "+>", undef) or die ... |
b76cc8ba | 3198 | |
f253e835 JH |
3199 | opens a filehandle to an anonymous temporary file. Also using "+<" |
3200 | works for symmetry, but you really should consider writing something | |
3201 | to the temporary file first. You will need to seek() to do the | |
3202 | reading. | |
b76cc8ba | 3203 | |
2ce64696 | 3204 | Since v5.8.0, perl has built using PerlIO by default. Unless you've |
28a5cf3b | 3205 | changed this (i.e. Configure -Uuseperlio), you can open file handles to |
2ce64696 | 3206 | "in memory" files held in Perl scalars via: |
ba964c95 | 3207 | |
b996200f SB |
3208 | open($fh, '>', \$variable) || .. |
3209 | ||
3210 | Though if you try to re-open C<STDOUT> or C<STDERR> as an "in memory" | |
3211 | file, you have to close it first: | |
3212 | ||
3213 | close STDOUT; | |
3214 | open STDOUT, '>', \$variable or die "Can't open STDOUT: $!"; | |
ba964c95 | 3215 | |
cb1a09d0 | 3216 | Examples: |
a0d0e21e LW |
3217 | |
3218 | $ARTICLE = 100; | |
3219 | open ARTICLE or die "Can't find article $ARTICLE: $!\n"; | |
3220 | while (<ARTICLE>) {... | |
3221 | ||
6170680b | 3222 | open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved) |
fb73857a | 3223 | # if the open fails, output is discarded |
a0d0e21e | 3224 | |
460b70c2 | 3225 | open(my $dbase, '+<', 'dbase.mine') # open for update |
fb73857a | 3226 | or die "Can't open 'dbase.mine' for update: $!"; |
cb1a09d0 | 3227 | |
460b70c2 | 3228 | open(my $dbase, '+<dbase.mine') # ditto |
6170680b IZ |
3229 | or die "Can't open 'dbase.mine' for update: $!"; |
3230 | ||
3231 | open(ARTICLE, '-|', "caesar <$article") # decrypt article | |
fb73857a | 3232 | or die "Can't start caesar: $!"; |
a0d0e21e | 3233 | |
6170680b IZ |
3234 | open(ARTICLE, "caesar <$article |") # ditto |
3235 | or die "Can't start caesar: $!"; | |
3236 | ||
2359510d | 3237 | open(EXTRACT, "|sort >Tmp$$") # $$ is our process id |
fb73857a | 3238 | or die "Can't start sort: $!"; |
a0d0e21e | 3239 | |
ba964c95 T |
3240 | # in memory files |
3241 | open(MEMORY,'>', \$var) | |
3242 | or die "Can't open memory file: $!"; | |
3243 | print MEMORY "foo!\n"; # output will end up in $var | |
3244 | ||
a0d0e21e LW |
3245 | # process argument list of files along with any includes |
3246 | ||
3247 | foreach $file (@ARGV) { | |
3248 | process($file, 'fh00'); | |
3249 | } | |
3250 | ||
3251 | sub process { | |
5a964f20 | 3252 | my($filename, $input) = @_; |
a0d0e21e LW |
3253 | $input++; # this is a string increment |
3254 | unless (open($input, $filename)) { | |
3255 | print STDERR "Can't open $filename: $!\n"; | |
3256 | return; | |
3257 | } | |
3258 | ||
5a964f20 | 3259 | local $_; |
a0d0e21e LW |
3260 | while (<$input>) { # note use of indirection |
3261 | if (/^#include "(.*)"/) { | |
3262 | process($1, $input); | |
3263 | next; | |
3264 | } | |
5a964f20 | 3265 | #... # whatever |
a0d0e21e LW |
3266 | } |
3267 | } | |
3268 | ||
ae4c5402 | 3269 | See L<perliol> for detailed info on PerlIO. |
2ce64696 | 3270 | |
a0d0e21e | 3271 | You may also, in the Bourne shell tradition, specify an EXPR beginning |
00cafafa JH |
3272 | with C<< '>&' >>, in which case the rest of the string is interpreted |
3273 | as the name of a filehandle (or file descriptor, if numeric) to be | |
3274 | duped (as L<dup(2)>) and opened. You may use C<&> after C<< > >>, | |
3275 | C<<< >> >>>, C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>. | |
3276 | The mode you specify should match the mode of the original filehandle. | |
3277 | (Duping a filehandle does not take into account any existing contents | |
cf264981 | 3278 | of IO buffers.) If you use the 3-arg form then you can pass either a |
00cafafa | 3279 | number, the name of a filehandle or the normal "reference to a glob". |
6170680b | 3280 | |
eae1b76b SB |
3281 | Here is a script that saves, redirects, and restores C<STDOUT> and |
3282 | C<STDERR> using various methods: | |
a0d0e21e LW |
3283 | |
3284 | #!/usr/bin/perl | |
eae1b76b SB |
3285 | open my $oldout, ">&STDOUT" or die "Can't dup STDOUT: $!"; |
3286 | open OLDERR, ">&", \*STDERR or die "Can't dup STDERR: $!"; | |
818c4caa | 3287 | |
eae1b76b SB |
3288 | open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!"; |
3289 | open STDERR, ">&STDOUT" or die "Can't dup STDOUT: $!"; | |
a0d0e21e | 3290 | |
eae1b76b SB |
3291 | select STDERR; $| = 1; # make unbuffered |
3292 | select STDOUT; $| = 1; # make unbuffered | |
a0d0e21e LW |
3293 | |
3294 | print STDOUT "stdout 1\n"; # this works for | |
3295 | print STDERR "stderr 1\n"; # subprocesses too | |
3296 | ||
eae1b76b SB |
3297 | open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!"; |
3298 | open STDERR, ">&OLDERR" or die "Can't dup OLDERR: $!"; | |
a0d0e21e LW |
3299 | |
3300 | print STDOUT "stdout 2\n"; | |
3301 | print STDERR "stderr 2\n"; | |
3302 | ||
ef8b303f JH |
3303 | If you specify C<< '<&=X' >>, where C<X> is a file descriptor number |
3304 | or a filehandle, then Perl will do an equivalent of C's C<fdopen> of | |
3305 | that file descriptor (and not call L<dup(2)>); this is more | |
3306 | parsimonious of file descriptors. For example: | |
a0d0e21e | 3307 | |
00cafafa | 3308 | # open for input, reusing the fileno of $fd |
a0d0e21e | 3309 | open(FILEHANDLE, "<&=$fd") |
df632fdf | 3310 | |
b76cc8ba | 3311 | or |
df632fdf | 3312 | |
b76cc8ba | 3313 | open(FILEHANDLE, "<&=", $fd) |
a0d0e21e | 3314 | |
00cafafa JH |
3315 | or |
3316 | ||
3317 | # open for append, using the fileno of OLDFH | |
3318 | open(FH, ">>&=", OLDFH) | |
3319 | ||
3320 | or | |
3321 | ||
3322 | open(FH, ">>&=OLDFH") | |
3323 | ||
ef8b303f JH |
3324 | Being parsimonious on filehandles is also useful (besides being |
3325 | parsimonious) for example when something is dependent on file | |
3326 | descriptors, like for example locking using flock(). If you do just | |
3327 | C<< open(A, '>>&B') >>, the filehandle A will not have the same file | |
3328 | descriptor as B, and therefore flock(A) will not flock(B), and vice | |
3329 | versa. But with C<< open(A, '>>&=B') >> the filehandles will share | |
3330 | the same file descriptor. | |
3331 | ||
3332 | Note that if you are using Perls older than 5.8.0, Perl will be using | |
3333 | the standard C libraries' fdopen() to implement the "=" functionality. | |
3334 | On many UNIX systems fdopen() fails when file descriptors exceed a | |
3335 | certain value, typically 255. For Perls 5.8.0 and later, PerlIO is | |
3336 | most often the default. | |
4af147f6 | 3337 | |
df632fdf JH |
3338 | You can see whether Perl has been compiled with PerlIO or not by |
3339 | running C<perl -V> and looking for C<useperlio=> line. If C<useperlio> | |
3340 | is C<define>, you have PerlIO, otherwise you don't. | |
3341 | ||
6170680b IZ |
3342 | If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'> |
3343 | with 2-arguments (or 1-argument) form of open(), then | |
a0d0e21e | 3344 | there is an implicit fork done, and the return value of open is the pid |
7660c0ab | 3345 | of the child within the parent process, and C<0> within the child |
184e9718 | 3346 | process. (Use C<defined($pid)> to determine whether the open was successful.) |
a0d0e21e LW |
3347 | The filehandle behaves normally for the parent, but i/o to that |
3348 | filehandle is piped from/to the STDOUT/STDIN of the child process. | |
3349 | In the child process the filehandle isn't opened--i/o happens from/to | |
3350 | the new STDOUT or STDIN. Typically this is used like the normal | |
3351 | piped open when you want to exercise more control over just how the | |
3352 | pipe command gets executed, such as when you are running setuid, and | |
54310121 | 3353 | don't want to have to scan shell commands for metacharacters. |
6170680b | 3354 | The following triples are more or less equivalent: |
a0d0e21e LW |
3355 | |
3356 | open(FOO, "|tr '[a-z]' '[A-Z]'"); | |
6170680b IZ |
3357 | open(FOO, '|-', "tr '[a-z]' '[A-Z]'"); |
3358 | open(FOO, '|-') || exec 'tr', '[a-z]', '[A-Z]'; | |
b76cc8ba | 3359 | open(FOO, '|-', "tr", '[a-z]', '[A-Z]'); |
a0d0e21e LW |
3360 | |
3361 | open(FOO, "cat -n '$file'|"); | |
6170680b IZ |
3362 | open(FOO, '-|', "cat -n '$file'"); |
3363 | open(FOO, '-|') || exec 'cat', '-n', $file; | |
b76cc8ba NIS |
3364 | open(FOO, '-|', "cat", '-n', $file); |
3365 | ||
3366 | The last example in each block shows the pipe as "list form", which is | |
64da03b2 JH |
3367 | not yet supported on all platforms. A good rule of thumb is that if |
3368 | your platform has true C<fork()> (in other words, if your platform is | |
3369 | UNIX) you can use the list form. | |
a0d0e21e | 3370 | |
4633a7c4 LW |
3371 | See L<perlipc/"Safe Pipe Opens"> for more examples of this. |
3372 | ||
0f897271 GS |
3373 | Beginning with v5.6.0, Perl will attempt to flush all files opened for |
3374 | output before any operation that may do a fork, but this may not be | |
3375 | supported on some platforms (see L<perlport>). To be safe, you may need | |
3376 | to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method | |
3377 | of C<IO::Handle> on any open handles. | |
3378 | ||
ed53a2bb JH |
3379 | On systems that support a close-on-exec flag on files, the flag will |
3380 | be set for the newly opened file descriptor as determined by the value | |
3381 | of $^F. See L<perlvar/$^F>. | |
a0d0e21e | 3382 | |
0dccf244 | 3383 | Closing any piped filehandle causes the parent process to wait for the |
e5218da5 GA |
3384 | child to finish, and returns the status value in C<$?> and |
3385 | C<${^CHILD_ERROR_NATIVE}>. | |
0dccf244 | 3386 | |
ed53a2bb JH |
3387 | The filename passed to 2-argument (or 1-argument) form of open() will |
3388 | have leading and trailing whitespace deleted, and the normal | |
3389 | redirection characters honored. This property, known as "magic open", | |
5a964f20 | 3390 | can often be used to good effect. A user could specify a filename of |
7660c0ab | 3391 | F<"rsh cat file |">, or you could change certain filenames as needed: |
5a964f20 TC |
3392 | |
3393 | $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/; | |
3394 | open(FH, $filename) or die "Can't open $filename: $!"; | |
3395 | ||
6170680b IZ |
3396 | Use 3-argument form to open a file with arbitrary weird characters in it, |
3397 | ||
3398 | open(FOO, '<', $file); | |
3399 | ||
3400 | otherwise it's necessary to protect any leading and trailing whitespace: | |
5a964f20 TC |
3401 | |
3402 | $file =~ s#^(\s)#./$1#; | |
3403 | open(FOO, "< $file\0"); | |
3404 | ||
a31a806a | 3405 | (this may not work on some bizarre filesystems). One should |
106325ad | 3406 | conscientiously choose between the I<magic> and 3-arguments form |
6170680b IZ |
3407 | of open(): |
3408 | ||
3409 | open IN, $ARGV[0]; | |
3410 | ||
3411 | will allow the user to specify an argument of the form C<"rsh cat file |">, | |
3412 | but will not work on a filename which happens to have a trailing space, while | |
3413 | ||
3414 | open IN, '<', $ARGV[0]; | |
3415 | ||
3416 | will have exactly the opposite restrictions. | |
3417 | ||
19799a22 | 3418 | If you want a "real" C C<open> (see L<open(2)> on your system), then you |
6170680b IZ |
3419 | should use the C<sysopen> function, which involves no such magic (but |
3420 | may use subtly different filemodes than Perl open(), which is mapped | |
3421 | to C fopen()). This is | |
5a964f20 TC |
3422 | another way to protect your filenames from interpretation. For example: |
3423 | ||
3424 | use IO::Handle; | |
3425 | sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL) | |
3426 | or die "sysopen $path: $!"; | |
3427 | $oldfh = select(HANDLE); $| = 1; select($oldfh); | |
38762f02 | 3428 | print HANDLE "stuff $$\n"; |
5a964f20 TC |
3429 | seek(HANDLE, 0, 0); |
3430 | print "File contains: ", <HANDLE>; | |
3431 | ||
7660c0ab A |
3432 | Using the constructor from the C<IO::Handle> package (or one of its |
3433 | subclasses, such as C<IO::File> or C<IO::Socket>), you can generate anonymous | |
5a964f20 TC |
3434 | filehandles that have the scope of whatever variables hold references to |
3435 | them, and automatically close whenever and however you leave that scope: | |
c07a80fd | 3436 | |
5f05dabc | 3437 | use IO::File; |
5a964f20 | 3438 | #... |
c07a80fd | 3439 | sub read_myfile_munged { |
3440 | my $ALL = shift; | |
b0169937 | 3441 | my $handle = IO::File->new; |
c07a80fd | 3442 | open($handle, "myfile") or die "myfile: $!"; |
3443 | $first = <$handle> | |
3444 | or return (); # Automatically closed here. | |
3445 | mung $first or die "mung failed"; # Or here. | |
3446 | return $first, <$handle> if $ALL; # Or here. | |
3447 | $first; # Or here. | |
3448 | } | |
3449 | ||
b687b08b | 3450 | See L</seek> for some details about mixing reading and writing. |
a0d0e21e LW |
3451 | |
3452 | =item opendir DIRHANDLE,EXPR | |
d74e8afc | 3453 | X<opendir> |
a0d0e21e | 3454 | |
19799a22 GS |
3455 | Opens a directory named EXPR for processing by C<readdir>, C<telldir>, |
3456 | C<seekdir>, C<rewinddir>, and C<closedir>. Returns true if successful. | |
a28cd5c9 NT |
3457 | DIRHANDLE may be an expression whose value can be used as an indirect |
3458 | dirhandle, usually the real dirhandle name. If DIRHANDLE is an undefined | |
3459 | scalar variable (or array or hash element), the variable is assigned a | |
3460 | reference to a new anonymous dirhandle. | |
a0d0e21e LW |
3461 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
3462 | ||
b0169937 GS |
3463 | See example at C<readdir>. |
3464 | ||
a0d0e21e | 3465 | =item ord EXPR |
d74e8afc | 3466 | X<ord> X<encoding> |
a0d0e21e | 3467 | |
54310121 | 3468 | =item ord |
bbce6d69 | 3469 | |
121910a4 JH |
3470 | Returns the numeric (the native 8-bit encoding, like ASCII or EBCDIC, |
3471 | or Unicode) value of the first character of EXPR. If EXPR is omitted, | |
3472 | uses C<$_>. | |
3473 | ||
3474 | For the reverse, see L</chr>. | |
2575c402 | 3475 | See L<perlunicode> for more about Unicode. |
a0d0e21e | 3476 | |
77ca0c92 | 3477 | =item our EXPR |
d74e8afc | 3478 | X<our> X<global> |
77ca0c92 | 3479 | |
36fb85f3 | 3480 | =item our TYPE EXPR |
307ea6df | 3481 | |
1d2de774 | 3482 | =item our EXPR : ATTRS |
9969eac4 | 3483 | |
1d2de774 | 3484 | =item our TYPE EXPR : ATTRS |
307ea6df | 3485 | |
85d8b7d5 | 3486 | C<our> associates a simple name with a package variable in the current |
65c680eb MS |
3487 | package for use within the current scope. When C<use strict 'vars'> is in |
3488 | effect, C<our> lets you use declared global variables without qualifying | |
3489 | them with package names, within the lexical scope of the C<our> declaration. | |
3490 | In this way C<our> differs from C<use vars>, which is package scoped. | |
3491 | ||
cf264981 | 3492 | Unlike C<my>, which both allocates storage for a variable and associates |
65c680eb MS |
3493 | a simple name with that storage for use within the current scope, C<our> |
3494 | associates a simple name with a package variable in the current package, | |
3495 | for use within the current scope. In other words, C<our> has the same | |
3496 | scoping rules as C<my>, but does not necessarily create a | |
3497 | variable. | |
3498 | ||
3499 | If more than one value is listed, the list must be placed | |
3500 | in parentheses. | |
85d8b7d5 MS |
3501 | |
3502 | our $foo; | |
3503 | our($bar, $baz); | |
77ca0c92 | 3504 | |
f472eb5c GS |
3505 | An C<our> declaration declares a global variable that will be visible |
3506 | across its entire lexical scope, even across package boundaries. The | |
3507 | package in which the variable is entered is determined at the point | |
3508 | of the declaration, not at the point of use. This means the following | |
3509 | behavior holds: | |
3510 | ||
3511 | package Foo; | |
3512 | our $bar; # declares $Foo::bar for rest of lexical scope | |
3513 | $bar = 20; | |
3514 | ||
3515 | package Bar; | |
65c680eb | 3516 | print $bar; # prints 20, as it refers to $Foo::bar |
f472eb5c | 3517 | |
65c680eb MS |
3518 | Multiple C<our> declarations with the same name in the same lexical |
3519 | scope are allowed if they are in different packages. If they happen | |
3520 | to be in the same package, Perl will emit warnings if you have asked | |
3521 | for them, just like multiple C<my> declarations. Unlike a second | |
3522 | C<my> declaration, which will bind the name to a fresh variable, a | |
3523 | second C<our> declaration in the same package, in the same scope, is | |
3524 | merely redundant. | |
f472eb5c GS |
3525 | |
3526 | use warnings; | |
3527 | package Foo; | |
3528 | our $bar; # declares $Foo::bar for rest of lexical scope | |
3529 | $bar = 20; | |
3530 | ||
3531 | package Bar; | |
3532 | our $bar = 30; # declares $Bar::bar for rest of lexical scope | |
3533 | print $bar; # prints 30 | |
3534 | ||
65c680eb MS |
3535 | our $bar; # emits warning but has no other effect |
3536 | print $bar; # still prints 30 | |
f472eb5c | 3537 | |
9969eac4 | 3538 | An C<our> declaration may also have a list of attributes associated |
307ea6df JH |
3539 | with it. |
3540 | ||
1d2de774 JH |
3541 | The exact semantics and interface of TYPE and ATTRS are still |
3542 | evolving. TYPE is currently bound to the use of C<fields> pragma, | |
307ea6df JH |
3543 | and attributes are handled using the C<attributes> pragma, or starting |
3544 | from Perl 5.8.0 also via the C<Attribute::Handlers> module. See | |
3545 | L<perlsub/"Private Variables via my()"> for details, and L<fields>, | |
3546 | L<attributes>, and L<Attribute::Handlers>. | |
3547 | ||
a0d0e21e | 3548 | =item pack TEMPLATE,LIST |
d74e8afc | 3549 | X<pack> |
a0d0e21e | 3550 | |
2b6c5635 GS |
3551 | Takes a LIST of values and converts it into a string using the rules |
3552 | given by the TEMPLATE. The resulting string is the concatenation of | |
3553 | the converted values. Typically, each converted value looks | |
3554 | like its machine-level representation. For example, on 32-bit machines | |
cf264981 | 3555 | an integer may be represented by a sequence of 4 bytes that will be |
f337b084 | 3556 | converted to a sequence of 4 characters. |
2b6c5635 | 3557 | |
18529408 IZ |
3558 | The TEMPLATE is a sequence of characters that give the order and type |
3559 | of values, as follows: | |
a0d0e21e | 3560 | |
5a929a98 | 3561 | a A string with arbitrary binary data, will be null padded. |
121910a4 | 3562 | A A text (ASCII) string, will be space padded. |
299600f4 | 3563 | Z A null terminated (ASCIZ) string, will be null padded. |
5a929a98 | 3564 | |
2b6c5635 GS |
3565 | b A bit string (ascending bit order inside each byte, like vec()). |
3566 | B A bit string (descending bit order inside each byte). | |
a0d0e21e LW |
3567 | h A hex string (low nybble first). |
3568 | H A hex string (high nybble first). | |
3569 | ||
1109a392 | 3570 | c A signed char (8-bit) value. |
1651fc44 | 3571 | C An unsigned char (octet) value. |
f337b084 | 3572 | W An unsigned char value (can be greater than 255). |
96e4d5b1 | 3573 | |
1109a392 | 3574 | s A signed short (16-bit) value. |
a0d0e21e | 3575 | S An unsigned short value. |
96e4d5b1 | 3576 | |
1109a392 | 3577 | l A signed long (32-bit) value. |
a0d0e21e | 3578 | L An unsigned long value. |
a0d0e21e | 3579 | |
dae0da7a JH |
3580 | q A signed quad (64-bit) value. |
3581 | Q An unsigned quad value. | |
851646ae JH |
3582 | (Quads are available only if your system supports 64-bit |
3583 | integer values _and_ if Perl has been compiled to support those. | |
dae0da7a JH |
3584 | Causes a fatal error otherwise.) |
3585 | ||
1109a392 MHM |
3586 | i A signed integer value. |
3587 | I A unsigned integer value. | |
3588 | (This 'integer' is _at_least_ 32 bits wide. Its exact | |
3589 | size depends on what a local C compiler calls 'int'.) | |
2b191d53 | 3590 | |
1109a392 MHM |
3591 | n An unsigned short (16-bit) in "network" (big-endian) order. |
3592 | N An unsigned long (32-bit) in "network" (big-endian) order. | |
3593 | v An unsigned short (16-bit) in "VAX" (little-endian) order. | |
3594 | V An unsigned long (32-bit) in "VAX" (little-endian) order. | |
3595 | ||
3596 | j A Perl internal signed integer value (IV). | |
3597 | J A Perl internal unsigned integer value (UV). | |
92d41999 | 3598 | |
a0d0e21e LW |
3599 | f A single-precision float in the native format. |
3600 | d A double-precision float in the native format. | |
3601 | ||
1109a392 | 3602 | F A Perl internal floating point value (NV) in the native format |
92d41999 JH |
3603 | D A long double-precision float in the native format. |
3604 | (Long doubles are available only if your system supports long | |
3605 | double values _and_ if Perl has been compiled to support those. | |
3606 | Causes a fatal error otherwise.) | |
3607 | ||
a0d0e21e LW |
3608 | p A pointer to a null-terminated string. |
3609 | P A pointer to a structure (fixed-length string). | |
3610 | ||
3611 | u A uuencoded string. | |
1651fc44 ML |
3612 | U A Unicode character number. Encodes to a character in character mode |
3613 | and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in byte mode. | |
a0d0e21e | 3614 | |
24436e9a RGS |
3615 | w A BER compressed integer (not an ASN.1 BER, see perlpacktut for |
3616 | details). Its bytes represent an unsigned integer in base 128, | |
3617 | most significant digit first, with as few digits as possible. Bit | |
3618 | eight (the high bit) is set on each byte except the last. | |
def98dd4 | 3619 | |
a0d0e21e LW |
3620 | x A null byte. |
3621 | X Back up a byte. | |
28be1210 TH |
3622 | @ Null fill or truncate to absolute position, counted from the |
3623 | start of the innermost ()-group. | |
3624 | . Null fill or truncate to absolute position specified by value. | |
206947d2 | 3625 | ( Start of a ()-group. |
a0d0e21e | 3626 | |
cf264981 SP |
3627 | One or more of the modifiers below may optionally follow some letters in the |
3628 | TEMPLATE (the second column lists the letters for which the modifier is | |
3629 | valid): | |
1109a392 MHM |
3630 | |
3631 | ! sSlLiI Forces native (short, long, int) sizes instead | |
3632 | of fixed (16-/32-bit) sizes. | |
3633 | ||
3634 | xX Make x and X act as alignment commands. | |
3635 | ||
3636 | nNvV Treat integers as signed instead of unsigned. | |
3637 | ||
28be1210 TH |
3638 | @. Specify position as byte offset in the internal |
3639 | representation of the packed string. Efficient but | |
3640 | dangerous. | |
3641 | ||
1109a392 MHM |
3642 | > sSiIlLqQ Force big-endian byte-order on the type. |
3643 | jJfFdDpP (The "big end" touches the construct.) | |
3644 | ||
3645 | < sSiIlLqQ Force little-endian byte-order on the type. | |
3646 | jJfFdDpP (The "little end" touches the construct.) | |
3647 | ||
66c611c5 MHM |
3648 | The C<E<gt>> and C<E<lt>> modifiers can also be used on C<()>-groups, |
3649 | in which case they force a certain byte-order on all components of | |
3650 | that group, including subgroups. | |
3651 | ||
5a929a98 VU |
3652 | The following rules apply: |
3653 | ||
3654 | =over 8 | |
3655 | ||
3656 | =item * | |
3657 | ||
5a964f20 | 3658 | Each letter may optionally be followed by a number giving a repeat |
951ba7fe | 3659 | count. With all types except C<a>, C<A>, C<Z>, C<b>, C<B>, C<h>, |
28be1210 TH |
3660 | C<H>, C<@>, C<.>, C<x>, C<X> and C<P> the pack function will gobble up |
3661 | that many values from the LIST. A C<*> for the repeat count means to | |
3662 | use however many items are left, except for C<@>, C<x>, C<X>, where it | |
3663 | is equivalent to C<0>, for <.> where it means relative to string start | |
3664 | and C<u>, where it is equivalent to 1 (or 45, which is the same). | |
3665 | A numeric repeat count may optionally be enclosed in brackets, as in | |
3666 | C<pack 'C[80]', @arr>. | |
206947d2 IZ |
3667 | |
3668 | One can replace the numeric repeat count by a template enclosed in brackets; | |
3669 | then the packed length of this template in bytes is used as a count. | |
62f95557 IZ |
3670 | For example, C<x[L]> skips a long (it skips the number of bytes in a long); |
3671 | the template C<$t X[$t] $t> unpack()s twice what $t unpacks. | |
3672 | If the template in brackets contains alignment commands (such as C<x![d]>), | |
3673 | its packed length is calculated as if the start of the template has the maximal | |
3674 | possible alignment. | |
2b6c5635 | 3675 | |
951ba7fe | 3676 | When used with C<Z>, C<*> results in the addition of a trailing null |
2b6c5635 GS |
3677 | byte (so the packed result will be one longer than the byte C<length> |
3678 | of the item). | |
3679 | ||
28be1210 TH |
3680 | When used with C<@>, the repeat count represents an offset from the start |
3681 | of the innermost () group. | |
3682 | ||
3683 | When used with C<.>, the repeat count is used to determine the starting | |
3684 | position from where the value offset is calculated. If the repeat count | |
3685 | is 0, it's relative to the current position. If the repeat count is C<*>, | |
3686 | the offset is relative to the start of the packed string. And if its an | |
3687 | integer C<n> the offset is relative to the start of the n-th innermost | |
3688 | () group (or the start of the string if C<n> is bigger then the group | |
3689 | level). | |
3690 | ||
951ba7fe | 3691 | The repeat count for C<u> is interpreted as the maximal number of bytes |
f337b084 TH |
3692 | to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat |
3693 | count should not be more than 65. | |
5a929a98 VU |
3694 | |
3695 | =item * | |
3696 | ||
951ba7fe | 3697 | The C<a>, C<A>, and C<Z> types gobble just one value, but pack it as a |
5a929a98 | 3698 | string of length count, padding with nulls or spaces as necessary. When |
18bdf90a | 3699 | unpacking, C<A> strips trailing whitespace and nulls, C<Z> strips everything |
f337b084 | 3700 | after the first null, and C<a> returns data verbatim. |
2b6c5635 GS |
3701 | |
3702 | If the value-to-pack is too long, it is truncated. If too long and an | |
951ba7fe | 3703 | explicit count is provided, C<Z> packs only C<$count-1> bytes, followed |
f337b084 TH |
3704 | by a null byte. Thus C<Z> always packs a trailing null (except when the |
3705 | count is 0). | |
5a929a98 VU |
3706 | |
3707 | =item * | |
3708 | ||
951ba7fe | 3709 | Likewise, the C<b> and C<B> fields pack a string that many bits long. |
f337b084 | 3710 | Each character of the input field of pack() generates 1 bit of the result. |
c73032f5 | 3711 | Each result bit is based on the least-significant bit of the corresponding |
f337b084 TH |
3712 | input character, i.e., on C<ord($char)%2>. In particular, characters C<"0"> |
3713 | and C<"1"> generate bits 0 and 1, as do characters C<"\0"> and C<"\1">. | |
c73032f5 IZ |
3714 | |
3715 | Starting from the beginning of the input string of pack(), each 8-tuple | |
f337b084 TH |
3716 | of characters is converted to 1 character of output. With format C<b> |
3717 | the first character of the 8-tuple determines the least-significant bit of a | |
3718 | character, and with format C<B> it determines the most-significant bit of | |
3719 | a character. | |
c73032f5 IZ |
3720 | |
3721 | If the length of the input string is not exactly divisible by 8, the | |
f337b084 | 3722 | remainder is packed as if the input string were padded by null characters |
c73032f5 IZ |
3723 | at the end. Similarly, during unpack()ing the "extra" bits are ignored. |
3724 | ||
f337b084 TH |
3725 | If the input string of pack() is longer than needed, extra characters are |
3726 | ignored. A C<*> for the repeat count of pack() means to use all the | |
3727 | characters of the input field. On unpack()ing the bits are converted to a | |
3728 | string of C<"0">s and C<"1">s. | |
5a929a98 VU |
3729 | |
3730 | =item * | |
3731 | ||
951ba7fe | 3732 | The C<h> and C<H> fields pack a string that many nybbles (4-bit groups, |
851646ae | 3733 | representable as hexadecimal digits, 0-9a-f) long. |
5a929a98 | 3734 | |
f337b084 TH |
3735 | Each character of the input field of pack() generates 4 bits of the result. |
3736 | For non-alphabetical characters the result is based on the 4 least-significant | |
3737 | bits of the input character, i.e., on C<ord($char)%16>. In particular, | |
3738 | characters C<"0"> and C<"1"> generate nybbles 0 and 1, as do bytes | |
3739 | C<"\0"> and C<"\1">. For characters C<"a".."f"> and C<"A".."F"> the result | |
c73032f5 | 3740 | is compatible with the usual hexadecimal digits, so that C<"a"> and |
f337b084 | 3741 | C<"A"> both generate the nybble C<0xa==10>. The result for characters |
c73032f5 IZ |
3742 | C<"g".."z"> and C<"G".."Z"> is not well-defined. |
3743 | ||
3744 | Starting from the beginning of the input string of pack(), each pair | |
f337b084 TH |
3745 | of characters is converted to 1 character of output. With format C<h> the |
3746 | first character of the pair determines the least-significant nybble of the | |
3747 | output character, and with format C<H> it determines the most-significant | |
c73032f5 IZ |
3748 | nybble. |
3749 | ||
3750 | If the length of the input string is not even, it behaves as if padded | |
f337b084 | 3751 | by a null character at the end. Similarly, during unpack()ing the "extra" |
c73032f5 IZ |
3752 | nybbles are ignored. |
3753 | ||
f337b084 TH |
3754 | If the input string of pack() is longer than needed, extra characters are |
3755 | ignored. | |
3756 | A C<*> for the repeat count of pack() means to use all the characters of | |
3757 | the input field. On unpack()ing the nybbles are converted to a string | |
c73032f5 IZ |
3758 | of hexadecimal digits. |
3759 | ||
5a929a98 VU |
3760 | =item * |
3761 | ||
951ba7fe | 3762 | The C<p> type packs a pointer to a null-terminated string. You are |
5a929a98 VU |
3763 | responsible for ensuring the string is not a temporary value (which can |
3764 | potentially get deallocated before you get around to using the packed result). | |
951ba7fe GS |
3765 | The C<P> type packs a pointer to a structure of the size indicated by the |
3766 | length. A NULL pointer is created if the corresponding value for C<p> or | |
3767 | C<P> is C<undef>, similarly for unpack(). | |
5a929a98 | 3768 | |
1109a392 MHM |
3769 | If your system has a strange pointer size (i.e. a pointer is neither as |
3770 | big as an int nor as big as a long), it may not be possible to pack or | |
3771 | unpack pointers in big- or little-endian byte order. Attempting to do | |
3772 | so will result in a fatal error. | |
3773 | ||
5a929a98 VU |
3774 | =item * |
3775 | ||
246f24af TH |
3776 | The C</> template character allows packing and unpacking of a sequence of |
3777 | items where the packed structure contains a packed item count followed by | |
3778 | the packed items themselves. | |
43192e07 | 3779 | |
54f961c9 PD |
3780 | For C<pack> you write I<length-item>C</>I<sequence-item> and the |
3781 | I<length-item> describes how the length value is packed. The ones likely | |
3782 | to be of most use are integer-packing ones like C<n> (for Java strings), | |
3783 | C<w> (for ASN.1 or SNMP) and C<N> (for Sun XDR). | |
43192e07 | 3784 | |
246f24af TH |
3785 | For C<pack>, the I<sequence-item> may have a repeat count, in which case |
3786 | the minimum of that and the number of available items is used as argument | |
3787 | for the I<length-item>. If it has no repeat count or uses a '*', the number | |
54f961c9 PD |
3788 | of available items is used. |
3789 | ||
3790 | For C<unpack> an internal stack of integer arguments unpacked so far is | |
3791 | used. You write C</>I<sequence-item> and the repeat count is obtained by | |
3792 | popping off the last element from the stack. The I<sequence-item> must not | |
3793 | have a repeat count. | |
246f24af TH |
3794 | |
3795 | If the I<sequence-item> refers to a string type (C<"A">, C<"a"> or C<"Z">), | |
3796 | the I<length-item> is a string length, not a number of strings. If there is | |
3797 | an explicit repeat count for pack, the packed string will be adjusted to that | |
3798 | given length. | |
3799 | ||
54f961c9 PD |
3800 | unpack 'W/a', "\04Gurusamy"; gives ('Guru') |
3801 | unpack 'a3/A A*', '007 Bond J '; gives (' Bond', 'J') | |
3802 | unpack 'a3 x2 /A A*', '007: Bond, J.'; gives ('Bond, J', '.') | |
3803 | pack 'n/a* w/a','hello,','world'; gives "\000\006hello,\005world" | |
3804 | pack 'a/W2', ord('a') .. ord('z'); gives '2ab' | |
43192e07 IP |
3805 | |
3806 | The I<length-item> is not returned explicitly from C<unpack>. | |
3807 | ||
951ba7fe GS |
3808 | Adding a count to the I<length-item> letter is unlikely to do anything |
3809 | useful, unless that letter is C<A>, C<a> or C<Z>. Packing with a | |
3810 | I<length-item> of C<a> or C<Z> may introduce C<"\000"> characters, | |
43192e07 IP |
3811 | which Perl does not regard as legal in numeric strings. |
3812 | ||
3813 | =item * | |
3814 | ||
951ba7fe | 3815 | The integer types C<s>, C<S>, C<l>, and C<L> may be |
1109a392 | 3816 | followed by a C<!> modifier to signify native shorts or |
951ba7fe | 3817 | longs--as you can see from above for example a bare C<l> does mean |
851646ae JH |
3818 | exactly 32 bits, the native C<long> (as seen by the local C compiler) |
3819 | may be larger. This is an issue mainly in 64-bit platforms. You can | |
951ba7fe | 3820 | see whether using C<!> makes any difference by |
726ea183 | 3821 | |
4d0c1c44 GS |
3822 | print length(pack("s")), " ", length(pack("s!")), "\n"; |
3823 | print length(pack("l")), " ", length(pack("l!")), "\n"; | |
ef54e1a4 | 3824 | |
951ba7fe GS |
3825 | C<i!> and C<I!> also work but only because of completeness; |
3826 | they are identical to C<i> and C<I>. | |
ef54e1a4 | 3827 | |
19799a22 GS |
3828 | The actual sizes (in bytes) of native shorts, ints, longs, and long |
3829 | longs on the platform where Perl was built are also available via | |
3830 | L<Config>: | |
3831 | ||
3832 | use Config; | |
3833 | print $Config{shortsize}, "\n"; | |
3834 | print $Config{intsize}, "\n"; | |
3835 | print $Config{longsize}, "\n"; | |
3836 | print $Config{longlongsize}, "\n"; | |
ef54e1a4 | 3837 | |
49704364 | 3838 | (The C<$Config{longlongsize}> will be undefined if your system does |
b76cc8ba | 3839 | not support long longs.) |
851646ae | 3840 | |
ef54e1a4 JH |
3841 | =item * |
3842 | ||
92d41999 | 3843 | The integer formats C<s>, C<S>, C<i>, C<I>, C<l>, C<L>, C<j>, and C<J> |
ef54e1a4 JH |
3844 | are inherently non-portable between processors and operating systems |
3845 | because they obey the native byteorder and endianness. For example a | |
82e239e7 | 3846 | 4-byte integer 0x12345678 (305419896 decimal) would be ordered natively |
ef54e1a4 | 3847 | (arranged in and handled by the CPU registers) into bytes as |
61eff3bc | 3848 | |
b35e152f JJ |
3849 | 0x12 0x34 0x56 0x78 # big-endian |
3850 | 0x78 0x56 0x34 0x12 # little-endian | |
61eff3bc | 3851 | |
b84d4f81 JH |
3852 | Basically, the Intel and VAX CPUs are little-endian, while everybody |
3853 | else, for example Motorola m68k/88k, PPC, Sparc, HP PA, Power, and | |
3854 | Cray are big-endian. Alpha and MIPS can be either: Digital/Compaq | |
82e239e7 JH |
3855 | used/uses them in little-endian mode; SGI/Cray uses them in big-endian |
3856 | mode. | |
719a3cf5 | 3857 | |
19799a22 | 3858 | The names `big-endian' and `little-endian' are comic references to |
ef54e1a4 JH |
3859 | the classic "Gulliver's Travels" (via the paper "On Holy Wars and a |
3860 | Plea for Peace" by Danny Cohen, USC/ISI IEN 137, April 1, 1980) and | |
19799a22 | 3861 | the egg-eating habits of the Lilliputians. |
61eff3bc | 3862 | |
140cb37e | 3863 | Some systems may have even weirder byte orders such as |
61eff3bc | 3864 | |
ef54e1a4 JH |
3865 | 0x56 0x78 0x12 0x34 |
3866 | 0x34 0x12 0x78 0x56 | |
61eff3bc | 3867 | |
ef54e1a4 JH |
3868 | You can see your system's preference with |
3869 | ||
3870 | print join(" ", map { sprintf "%#02x", $_ } | |
f337b084 | 3871 | unpack("W*",pack("L",0x12345678))), "\n"; |
ef54e1a4 | 3872 | |
d99ad34e | 3873 | The byteorder on the platform where Perl was built is also available |
726ea183 | 3874 | via L<Config>: |
ef54e1a4 JH |
3875 | |
3876 | use Config; | |
3877 | print $Config{byteorder}, "\n"; | |
3878 | ||
d99ad34e JH |
3879 | Byteorders C<'1234'> and C<'12345678'> are little-endian, C<'4321'> |
3880 | and C<'87654321'> are big-endian. | |
719a3cf5 | 3881 | |
1109a392 MHM |
3882 | If you want portable packed integers you can either use the formats |
3883 | C<n>, C<N>, C<v>, and C<V>, or you can use the C<E<gt>> and C<E<lt>> | |
7a4d2905 | 3884 | modifiers. These modifiers are only available as of perl 5.9.2. |
851646ae | 3885 | See also L<perlport>. |
ef54e1a4 JH |
3886 | |
3887 | =item * | |
3888 | ||
66c611c5 MHM |
3889 | All integer and floating point formats as well as C<p> and C<P> and |
3890 | C<()>-groups may be followed by the C<E<gt>> or C<E<lt>> modifiers | |
3891 | to force big- or little- endian byte-order, respectively. | |
3892 | This is especially useful, since C<n>, C<N>, C<v> and C<V> don't cover | |
3893 | signed integers, 64-bit integers and floating point values. However, | |
3894 | there are some things to keep in mind. | |
1109a392 MHM |
3895 | |
3896 | Exchanging signed integers between different platforms only works | |
3897 | if all platforms store them in the same format. Most platforms store | |
3898 | signed integers in two's complement, so usually this is not an issue. | |
3899 | ||
3900 | The C<E<gt>> or C<E<lt>> modifiers can only be used on floating point | |
3901 | formats on big- or little-endian machines. Otherwise, attempting to | |
3902 | do so will result in a fatal error. | |
3903 | ||
3904 | Forcing big- or little-endian byte-order on floating point values for | |
3905 | data exchange can only work if all platforms are using the same | |
3906 | binary representation (e.g. IEEE floating point format). Even if all | |
3907 | platforms are using IEEE, there may be subtle differences. Being able | |
3908 | to use C<E<gt>> or C<E<lt>> on floating point values can be very useful, | |
3909 | but also very dangerous if you don't know exactly what you're doing. | |
2e98ff8b | 3910 | It is definitely not a general way to portably store floating point |
1109a392 MHM |
3911 | values. |
3912 | ||
66c611c5 MHM |
3913 | When using C<E<gt>> or C<E<lt>> on an C<()>-group, this will affect |
3914 | all types inside the group that accept the byte-order modifiers, | |
3915 | including all subgroups. It will silently be ignored for all other | |
3916 | types. You are not allowed to override the byte-order within a group | |
3917 | that already has a byte-order modifier suffix. | |
3918 | ||
1109a392 MHM |
3919 | =item * |
3920 | ||
5a929a98 VU |
3921 | Real numbers (floats and doubles) are in the native machine format only; |
3922 | due to the multiplicity of floating formats around, and the lack of a | |
3923 | standard "network" representation, no facility for interchange has been | |
3924 | made. This means that packed floating point data written on one machine | |
3925 | may not be readable on another - even if both use IEEE floating point | |
3926 | arithmetic (as the endian-ness of the memory representation is not part | |
851646ae | 3927 | of the IEEE spec). See also L<perlport>. |
5a929a98 | 3928 | |
1109a392 MHM |
3929 | If you know exactly what you're doing, you can use the C<E<gt>> or C<E<lt>> |
3930 | modifiers to force big- or little-endian byte-order on floating point values. | |
3931 | ||
3932 | Note that Perl uses doubles (or long doubles, if configured) internally for | |
3933 | all numeric calculation, and converting from double into float and thence back | |
3934 | to double again will lose precision (i.e., C<unpack("f", pack("f", $foo)>) | |
3935 | will not in general equal $foo). | |
5a929a98 | 3936 | |
851646ae JH |
3937 | =item * |
3938 | ||
f337b084 TH |
3939 | Pack and unpack can operate in two modes, character mode (C<C0> mode) where |
3940 | the packed string is processed per character and UTF-8 mode (C<U0> mode) | |
3941 | where the packed string is processed in its UTF-8-encoded Unicode form on | |
3942 | a byte by byte basis. Character mode is the default unless the format string | |
3943 | starts with an C<U>. You can switch mode at any moment with an explicit | |
3944 | C<C0> or C<U0> in the format. A mode is in effect until the next mode switch | |
3945 | or until the end of the ()-group in which it was entered. | |
036b4402 GS |
3946 | |
3947 | =item * | |
3948 | ||
851646ae | 3949 | You must yourself do any alignment or padding by inserting for example |
9ccd05c0 | 3950 | enough C<'x'>es while packing. There is no way to pack() and unpack() |
f337b084 | 3951 | could know where the characters are going to or coming from. Therefore |
9ccd05c0 | 3952 | C<pack> (and C<unpack>) handle their output and input as flat |
f337b084 | 3953 | sequences of characters. |
851646ae | 3954 | |
17f4a12d IZ |
3955 | =item * |
3956 | ||
18529408 | 3957 | A ()-group is a sub-TEMPLATE enclosed in parentheses. A group may |
49704364 WL |
3958 | take a repeat count, both as postfix, and for unpack() also via the C</> |
3959 | template character. Within each repetition of a group, positioning with | |
3960 | C<@> starts again at 0. Therefore, the result of | |
3961 | ||
3962 | pack( '@1A((@2A)@3A)', 'a', 'b', 'c' ) | |
3963 | ||
3964 | is the string "\0a\0\0bc". | |
3965 | ||
18529408 IZ |
3966 | =item * |
3967 | ||
62f95557 IZ |
3968 | C<x> and C<X> accept C<!> modifier. In this case they act as |
3969 | alignment commands: they jump forward/back to the closest position | |
f337b084 | 3970 | aligned at a multiple of C<count> characters. For example, to pack() or |
62f95557 | 3971 | unpack() C's C<struct {char c; double d; char cc[2]}> one may need to |
f337b084 | 3972 | use the template C<W x![d] d W[2]>; this assumes that doubles must be |
62f95557 | 3973 | aligned on the double's size. |
666f95b9 | 3974 | |
62f95557 IZ |
3975 | For alignment commands C<count> of 0 is equivalent to C<count> of 1; |
3976 | both result in no-ops. | |
666f95b9 | 3977 | |
62f95557 IZ |
3978 | =item * |
3979 | ||
068bd2e7 MHM |
3980 | C<n>, C<N>, C<v> and C<V> accept the C<!> modifier. In this case they |
3981 | will represent signed 16-/32-bit integers in big-/little-endian order. | |
3982 | This is only portable if all platforms sharing the packed data use the | |
3983 | same binary representation for signed integers (e.g. all platforms are | |
3984 | using two's complement representation). | |
3985 | ||
3986 | =item * | |
3987 | ||
17f4a12d | 3988 | A comment in a TEMPLATE starts with C<#> and goes to the end of line. |
49704364 | 3989 | White space may be used to separate pack codes from each other, but |
1109a392 | 3990 | modifiers and a repeat count must follow immediately. |
17f4a12d | 3991 | |
2b6c5635 GS |
3992 | =item * |
3993 | ||
3994 | If TEMPLATE requires more arguments to pack() than actually given, pack() | |
cf264981 | 3995 | assumes additional C<""> arguments. If TEMPLATE requires fewer arguments |
2b6c5635 GS |
3996 | to pack() than actually given, extra arguments are ignored. |
3997 | ||
5a929a98 | 3998 | =back |
a0d0e21e LW |
3999 | |
4000 | Examples: | |
4001 | ||
f337b084 | 4002 | $foo = pack("WWWW",65,66,67,68); |
a0d0e21e | 4003 | # foo eq "ABCD" |
f337b084 | 4004 | $foo = pack("W4",65,66,67,68); |
a0d0e21e | 4005 | # same thing |
f337b084 TH |
4006 | $foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9); |
4007 | # same thing with Unicode circled letters. | |
a0ed51b3 | 4008 | $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9); |
f337b084 TH |
4009 | # same thing with Unicode circled letters. You don't get the UTF-8 |
4010 | # bytes because the U at the start of the format caused a switch to | |
4011 | # U0-mode, so the UTF-8 bytes get joined into characters | |
4012 | $foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9); | |
4013 | # foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9" | |
4014 | # This is the UTF-8 encoding of the string in the previous example | |
a0d0e21e LW |
4015 | |
4016 | $foo = pack("ccxxcc",65,66,67,68); | |
4017 | # foo eq "AB\0\0CD" | |
4018 | ||
f337b084 | 4019 | # note: the above examples featuring "W" and "c" are true |
9ccd05c0 JH |
4020 | # only on ASCII and ASCII-derived systems such as ISO Latin 1 |
4021 | # and UTF-8. In EBCDIC the first example would be | |
f337b084 | 4022 | # $foo = pack("WWWW",193,194,195,196); |
9ccd05c0 | 4023 | |
a0d0e21e LW |
4024 | $foo = pack("s2",1,2); |
4025 | # "\1\0\2\0" on little-endian | |
4026 | # "\0\1\0\2" on big-endian | |
4027 | ||
4028 | $foo = pack("a4","abcd","x","y","z"); | |
4029 | # "abcd" | |
4030 | ||
4031 | $foo = pack("aaaa","abcd","x","y","z"); | |
4032 | # "axyz" | |
4033 | ||
4034 | $foo = pack("a14","abcdefg"); | |
4035 | # "abcdefg\0\0\0\0\0\0\0" | |
4036 | ||
4037 | $foo = pack("i9pl", gmtime); | |
4038 | # a real struct tm (on my system anyway) | |
4039 | ||
5a929a98 VU |
4040 | $utmp_template = "Z8 Z8 Z16 L"; |
4041 | $utmp = pack($utmp_template, @utmp1); | |
4042 | # a struct utmp (BSDish) | |
4043 | ||
4044 | @utmp2 = unpack($utmp_template, $utmp); | |
4045 | # "@utmp1" eq "@utmp2" | |
4046 | ||
a0d0e21e LW |
4047 | sub bintodec { |
4048 | unpack("N", pack("B32", substr("0" x 32 . shift, -32))); | |
4049 | } | |
4050 | ||
851646ae JH |
4051 | $foo = pack('sx2l', 12, 34); |
4052 | # short 12, two zero bytes padding, long 34 | |
4053 | $bar = pack('s@4l', 12, 34); | |
4054 | # short 12, zero fill to position 4, long 34 | |
4055 | # $foo eq $bar | |
28be1210 TH |
4056 | $baz = pack('s.l', 12, 4, 34); |
4057 | # short 12, zero fill to position 4, long 34 | |
851646ae | 4058 | |
1109a392 MHM |
4059 | $foo = pack('nN', 42, 4711); |
4060 | # pack big-endian 16- and 32-bit unsigned integers | |
4061 | $foo = pack('S>L>', 42, 4711); | |
4062 | # exactly the same | |
4063 | $foo = pack('s<l<', -42, 4711); | |
4064 | # pack little-endian 16- and 32-bit signed integers | |
66c611c5 MHM |
4065 | $foo = pack('(sl)<', -42, 4711); |
4066 | # exactly the same | |
1109a392 | 4067 | |
5a929a98 | 4068 | The same template may generally also be used in unpack(). |
a0d0e21e | 4069 | |
cb1a09d0 | 4070 | =item package NAMESPACE |
d74e8afc | 4071 | X<package> X<module> X<namespace> |
cb1a09d0 | 4072 | |
b76cc8ba | 4073 | =item package |
d6217f1e | 4074 | |
cb1a09d0 | 4075 | Declares the compilation unit as being in the given namespace. The scope |
2b5ab1e7 | 4076 | of the package declaration is from the declaration itself through the end |
19799a22 | 4077 | of the enclosing block, file, or eval (the same as the C<my> operator). |
2b5ab1e7 TC |
4078 | All further unqualified dynamic identifiers will be in this namespace. |
4079 | A package statement affects only dynamic variables--including those | |
19799a22 GS |
4080 | you've used C<local> on--but I<not> lexical variables, which are created |
4081 | with C<my>. Typically it would be the first declaration in a file to | |
2b5ab1e7 TC |
4082 | be included by the C<require> or C<use> operator. You can switch into a |
4083 | package in more than one place; it merely influences which symbol table | |
4084 | is used by the compiler for the rest of that block. You can refer to | |
4085 | variables and filehandles in other packages by prefixing the identifier | |
4086 | with the package name and a double colon: C<$Package::Variable>. | |
4087 | If the package name is null, the C<main> package as assumed. That is, | |
4088 | C<$::sail> is equivalent to C<$main::sail> (as well as to C<$main'sail>, | |
4089 | still seen in older code). | |
cb1a09d0 AD |
4090 | |
4091 | See L<perlmod/"Packages"> for more information about packages, modules, | |
4092 | and classes. See L<perlsub> for other scoping issues. | |
4093 | ||
a0d0e21e | 4094 | =item pipe READHANDLE,WRITEHANDLE |
d74e8afc | 4095 | X<pipe> |
a0d0e21e LW |
4096 | |
4097 | Opens a pair of connected pipes like the corresponding system call. | |
4098 | Note that if you set up a loop of piped processes, deadlock can occur | |
4099 | unless you are very careful. In addition, note that Perl's pipes use | |
9124316e | 4100 | IO buffering, so you may need to set C<$|> to flush your WRITEHANDLE |
a0d0e21e LW |
4101 | after each command, depending on the application. |
4102 | ||
7e1af8bc | 4103 | See L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication"> |
4633a7c4 LW |
4104 | for examples of such things. |
4105 | ||
4771b018 GS |
4106 | On systems that support a close-on-exec flag on files, the flag will be set |
4107 | for the newly opened file descriptors as determined by the value of $^F. | |
4108 | See L<perlvar/$^F>. | |
4109 | ||
a0d0e21e | 4110 | =item pop ARRAY |
d74e8afc | 4111 | X<pop> X<stack> |
a0d0e21e | 4112 | |
54310121 | 4113 | =item pop |
28757baa | 4114 | |
a0d0e21e | 4115 | Pops and returns the last value of the array, shortening the array by |
cd7f9af7 | 4116 | one element. |
a0d0e21e | 4117 | |
19799a22 GS |
4118 | If there are no elements in the array, returns the undefined value |
4119 | (although this may happen at other times as well). If ARRAY is | |
4120 | omitted, pops the C<@ARGV> array in the main program, and the C<@_> | |
4121 | array in subroutines, just like C<shift>. | |
a0d0e21e LW |
4122 | |
4123 | =item pos SCALAR | |
d74e8afc | 4124 | X<pos> X<match, position> |
a0d0e21e | 4125 | |
54310121 | 4126 | =item pos |
bbce6d69 | 4127 | |
4633a7c4 | 4128 | Returns the offset of where the last C<m//g> search left off for the variable |
b17c04f3 | 4129 | in question (C<$_> is used when the variable is not specified). Note that |
cf264981 | 4130 | 0 is a valid match offset. C<undef> indicates that the search position |
b17c04f3 NC |
4131 | is reset (usually due to match failure, but can also be because no match has |
4132 | yet been performed on the scalar). C<pos> directly accesses the location used | |
4133 | by the regexp engine to store the offset, so assigning to C<pos> will change | |
4134 | that offset, and so will also influence the C<\G> zero-width assertion in | |
4135 | regular expressions. Because a failed C<m//gc> match doesn't reset the offset, | |
4136 | the return from C<pos> won't change either in this case. See L<perlre> and | |
44a8e56a | 4137 | L<perlop>. |
a0d0e21e LW |
4138 | |
4139 | =item print FILEHANDLE LIST | |
d74e8afc | 4140 | X<print> |
a0d0e21e LW |
4141 | |
4142 | =item print LIST | |
4143 | ||
4144 | =item print | |
4145 | ||
19799a22 GS |
4146 | Prints a string or a list of strings. Returns true if successful. |
4147 | FILEHANDLE may be a scalar variable name, in which case the variable | |
4148 | contains the name of or a reference to the filehandle, thus introducing | |
4149 | one level of indirection. (NOTE: If FILEHANDLE is a variable and | |
4150 | the next token is a term, it may be misinterpreted as an operator | |
2b5ab1e7 | 4151 | unless you interpose a C<+> or put parentheses around the arguments.) |
19799a22 GS |
4152 | If FILEHANDLE is omitted, prints by default to standard output (or |
4153 | to the last selected output channel--see L</select>). If LIST is | |
4154 | also omitted, prints C<$_> to the currently selected output channel. | |
4155 | To set the default output channel to something other than STDOUT | |
4156 | use the select operation. The current value of C<$,> (if any) is | |
4157 | printed between each LIST item. The current value of C<$\> (if | |
4158 | any) is printed after the entire LIST has been printed. Because | |
4159 | print takes a LIST, anything in the LIST is evaluated in list | |
4160 | context, and any subroutine that you call will have one or more of | |
4161 | its expressions evaluated in list context. Also be careful not to | |
4162 | follow the print keyword with a left parenthesis unless you want | |
4163 | the corresponding right parenthesis to terminate the arguments to | |
4164 | the print--interpose a C<+> or put parentheses around all the | |
4165 | arguments. | |
a0d0e21e | 4166 | |
39c9c9cd RGS |
4167 | Note that if you're storing FILEHANDLEs in an array, or if you're using |
4168 | any other expression more complex than a scalar variable to retrieve it, | |
4169 | you will have to use a block returning the filehandle value instead: | |
4633a7c4 LW |
4170 | |
4171 | print { $files[$i] } "stuff\n"; | |
4172 | print { $OK ? STDOUT : STDERR } "stuff\n"; | |
4173 | ||
5f05dabc | 4174 | =item printf FILEHANDLE FORMAT, LIST |
d74e8afc | 4175 | X<printf> |
a0d0e21e | 4176 | |
5f05dabc | 4177 | =item printf FORMAT, LIST |
a0d0e21e | 4178 | |
7660c0ab | 4179 | Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\> |
a3cb178b | 4180 | (the output record separator) is not appended. The first argument |
f39758bf | 4181 | of the list will be interpreted as the C<printf> format. See C<sprintf> |
7e4353e9 RGS |
4182 | for an explanation of the format argument. If C<use locale> is in effect, |
4183 | and POSIX::setlocale() has been called, the character used for the decimal | |
4184 | separator in formatted floating point numbers is affected by the LC_NUMERIC | |
4185 | locale. See L<perllocale> and L<POSIX>. | |
a0d0e21e | 4186 | |
19799a22 GS |
4187 | Don't fall into the trap of using a C<printf> when a simple |
4188 | C<print> would do. The C<print> is more efficient and less | |
28757baa | 4189 | error prone. |
4190 | ||
da0045b7 | 4191 | =item prototype FUNCTION |
d74e8afc | 4192 | X<prototype> |
da0045b7 | 4193 | |
4194 | Returns the prototype of a function as a string (or C<undef> if the | |
5f05dabc | 4195 | function has no prototype). FUNCTION is a reference to, or the name of, |
4196 | the function whose prototype you want to retrieve. | |
da0045b7 | 4197 | |
2b5ab1e7 TC |
4198 | If FUNCTION is a string starting with C<CORE::>, the rest is taken as a |
4199 | name for Perl builtin. If the builtin is not I<overridable> (such as | |
0a2ca743 RGS |
4200 | C<qw//>) or if its arguments cannot be adequately expressed by a prototype |
4201 | (such as C<system>), prototype() returns C<undef>, because the builtin | |
4202 | does not really behave like a Perl function. Otherwise, the string | |
4203 | describing the equivalent prototype is returned. | |
b6c543e3 | 4204 | |
a0d0e21e | 4205 | =item push ARRAY,LIST |
1dc8ecb8 | 4206 | X<push> X<stack> |
a0d0e21e LW |
4207 | |
4208 | Treats ARRAY as a stack, and pushes the values of LIST | |
4209 | onto the end of ARRAY. The length of ARRAY increases by the length of | |
4210 | LIST. Has the same effect as | |
4211 | ||
4212 | for $value (LIST) { | |
4213 | $ARRAY[++$#ARRAY] = $value; | |
4214 | } | |
4215 | ||
cde9c211 SP |
4216 | but is more efficient. Returns the number of elements in the array following |
4217 | the completed C<push>. | |
a0d0e21e LW |
4218 | |
4219 | =item q/STRING/ | |
4220 | ||
4221 | =item qq/STRING/ | |
4222 | ||
945c54fd | 4223 | =item qx/STRING/ |
a0d0e21e LW |
4224 | |
4225 | =item qw/STRING/ | |
4226 | ||
1d888ee3 MK |
4227 | Generalized quotes. See L<perlop/"Quote-Like Operators">. |
4228 | ||
4229 | =item qr/STRING/ | |
4230 | ||
4231 | Regexp-like quote. See L<perlop/"Regexp Quote-Like Operators">. | |
a0d0e21e LW |
4232 | |
4233 | =item quotemeta EXPR | |
d74e8afc | 4234 | X<quotemeta> X<metacharacter> |
a0d0e21e | 4235 | |
54310121 | 4236 | =item quotemeta |
bbce6d69 | 4237 | |
36bbe248 | 4238 | Returns the value of EXPR with all non-"word" |
a034a98d DD |
4239 | characters backslashed. (That is, all characters not matching |
4240 | C</[A-Za-z_0-9]/> will be preceded by a backslash in the | |
4241 | returned string, regardless of any locale settings.) | |
4242 | This is the internal function implementing | |
7660c0ab | 4243 | the C<\Q> escape in double-quoted strings. |
a0d0e21e | 4244 | |
7660c0ab | 4245 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 4246 | |
a0d0e21e | 4247 | =item rand EXPR |
d74e8afc | 4248 | X<rand> X<random> |
a0d0e21e LW |
4249 | |
4250 | =item rand | |
4251 | ||
7660c0ab | 4252 | Returns a random fractional number greater than or equal to C<0> and less |
3e3baf6d | 4253 | than the value of EXPR. (EXPR should be positive.) If EXPR is |
351f3254 NC |
4254 | omitted, the value C<1> is used. Currently EXPR with the value C<0> is |
4255 | also special-cased as C<1> - this has not been documented before perl 5.8.0 | |
4256 | and is subject to change in future versions of perl. Automatically calls | |
4257 | C<srand> unless C<srand> has already been called. See also C<srand>. | |
a0d0e21e | 4258 | |
6063ba18 WM |
4259 | Apply C<int()> to the value returned by C<rand()> if you want random |
4260 | integers instead of random fractional numbers. For example, | |
4261 | ||
4262 | int(rand(10)) | |
4263 | ||
4264 | returns a random integer between C<0> and C<9>, inclusive. | |
4265 | ||
2f9daede | 4266 | (Note: If your rand function consistently returns numbers that are too |
a0d0e21e | 4267 | large or too small, then your version of Perl was probably compiled |
2f9daede | 4268 | with the wrong number of RANDBITS.) |
a0d0e21e LW |
4269 | |
4270 | =item read FILEHANDLE,SCALAR,LENGTH,OFFSET | |
f723aae1 | 4271 | X<read> X<file, read> |
a0d0e21e LW |
4272 | |
4273 | =item read FILEHANDLE,SCALAR,LENGTH | |
4274 | ||
9124316e JH |
4275 | Attempts to read LENGTH I<characters> of data into variable SCALAR |
4276 | from the specified FILEHANDLE. Returns the number of characters | |
b5fe5ca2 | 4277 | actually read, C<0> at end of file, or undef if there was an error (in |
b49f3be6 SG |
4278 | the latter case C<$!> is also set). SCALAR will be grown or shrunk |
4279 | so that the last character actually read is the last character of the | |
4280 | scalar after the read. | |
4281 | ||
4282 | An OFFSET may be specified to place the read data at some place in the | |
4283 | string other than the beginning. A negative OFFSET specifies | |
4284 | placement at that many characters counting backwards from the end of | |
4285 | the string. A positive OFFSET greater than the length of SCALAR | |
4286 | results in the string being padded to the required size with C<"\0"> | |
4287 | bytes before the result of the read is appended. | |
4288 | ||
4289 | The call is actually implemented in terms of either Perl's or system's | |
4290 | fread() call. To get a true read(2) system call, see C<sysread>. | |
9124316e JH |
4291 | |
4292 | Note the I<characters>: depending on the status of the filehandle, | |
4293 | either (8-bit) bytes or characters are read. By default all | |
4294 | filehandles operate on bytes, but for example if the filehandle has | |
fae2c0fb | 4295 | been opened with the C<:utf8> I/O layer (see L</open>, and the C<open> |
1d714267 JH |
4296 | pragma, L<open>), the I/O will operate on UTF-8 encoded Unicode |
4297 | characters, not bytes. Similarly for the C<:encoding> pragma: | |
4298 | in that case pretty much any characters can be read. | |
a0d0e21e LW |
4299 | |
4300 | =item readdir DIRHANDLE | |
d74e8afc | 4301 | X<readdir> |
a0d0e21e | 4302 | |
19799a22 | 4303 | Returns the next directory entry for a directory opened by C<opendir>. |
5a964f20 | 4304 | If used in list context, returns all the rest of the entries in the |
a0d0e21e | 4305 | directory. If there are no more entries, returns an undefined value in |
5a964f20 | 4306 | scalar context or a null list in list context. |
a0d0e21e | 4307 | |
19799a22 | 4308 | If you're planning to filetest the return values out of a C<readdir>, you'd |
5f05dabc | 4309 | better prepend the directory in question. Otherwise, because we didn't |
19799a22 | 4310 | C<chdir> there, it would have been testing the wrong file. |
cb1a09d0 | 4311 | |
b0169937 GS |
4312 | opendir(my $dh, $some_dir) || die "can't opendir $some_dir: $!"; |
4313 | @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh); | |
4314 | closedir $dh; | |
cb1a09d0 | 4315 | |
84902520 | 4316 | =item readline EXPR |
e4b7ebf3 RGS |
4317 | |
4318 | =item readline | |
d74e8afc | 4319 | X<readline> X<gets> X<fgets> |
84902520 | 4320 | |
e4b7ebf3 RGS |
4321 | Reads from the filehandle whose typeglob is contained in EXPR (or from |
4322 | *ARGV if EXPR is not provided). In scalar context, each call reads and | |
4323 | returns the next line, until end-of-file is reached, whereupon the | |
4324 | subsequent call returns undef. In list context, reads until end-of-file | |
4325 | is reached and returns a list of lines. Note that the notion of "line" | |
4326 | used here is however you may have defined it with C<$/> or | |
4327 | C<$INPUT_RECORD_SEPARATOR>). See L<perlvar/"$/">. | |
fbad3eb5 | 4328 | |
2b5ab1e7 | 4329 | When C<$/> is set to C<undef>, when readline() is in scalar |
449bc448 GS |
4330 | context (i.e. file slurp mode), and when an empty file is read, it |
4331 | returns C<''> the first time, followed by C<undef> subsequently. | |
fbad3eb5 | 4332 | |
61eff3bc JH |
4333 | This is the internal function implementing the C<< <EXPR> >> |
4334 | operator, but you can use it directly. The C<< <EXPR> >> | |
84902520 TB |
4335 | operator is discussed in more detail in L<perlop/"I/O Operators">. |
4336 | ||
5a964f20 TC |
4337 | $line = <STDIN>; |
4338 | $line = readline(*STDIN); # same thing | |
4339 | ||
00cb5da1 CW |
4340 | If readline encounters an operating system error, C<$!> will be set with the |
4341 | corresponding error message. It can be helpful to check C<$!> when you are | |
4342 | reading from filehandles you don't trust, such as a tty or a socket. The | |
4343 | following example uses the operator form of C<readline>, and takes the necessary | |
4344 | steps to ensure that C<readline> was successful. | |
4345 | ||
4346 | for (;;) { | |
4347 | undef $!; | |
4348 | unless (defined( $line = <> )) { | |
4349 | die $! if $!; | |
4350 | last; # reached EOF | |
4351 | } | |
4352 | # ... | |
4353 | } | |
4354 | ||
a0d0e21e | 4355 | =item readlink EXPR |
d74e8afc | 4356 | X<readlink> |
a0d0e21e | 4357 | |
54310121 | 4358 | =item readlink |
bbce6d69 | 4359 | |
a0d0e21e LW |
4360 | Returns the value of a symbolic link, if symbolic links are |
4361 | implemented. If not, gives a fatal error. If there is some system | |
184e9718 | 4362 | error, returns the undefined value and sets C<$!> (errno). If EXPR is |
7660c0ab | 4363 | omitted, uses C<$_>. |
a0d0e21e | 4364 | |
84902520 | 4365 | =item readpipe EXPR |
8d7403e6 RGS |
4366 | |
4367 | =item readpipe | |
d74e8afc | 4368 | X<readpipe> |
84902520 | 4369 | |
5a964f20 | 4370 | EXPR is executed as a system command. |
84902520 TB |
4371 | The collected standard output of the command is returned. |
4372 | In scalar context, it comes back as a single (potentially | |
4373 | multi-line) string. In list context, returns a list of lines | |
7660c0ab | 4374 | (however you've defined lines with C<$/> or C<$INPUT_RECORD_SEPARATOR>). |
84902520 TB |
4375 | This is the internal function implementing the C<qx/EXPR/> |
4376 | operator, but you can use it directly. The C<qx/EXPR/> | |
4377 | operator is discussed in more detail in L<perlop/"I/O Operators">. | |
8d7403e6 | 4378 | If EXPR is omitted, uses C<$_>. |
84902520 | 4379 | |
399388f4 | 4380 | =item recv SOCKET,SCALAR,LENGTH,FLAGS |
d74e8afc | 4381 | X<recv> |
a0d0e21e | 4382 | |
9124316e JH |
4383 | Receives a message on a socket. Attempts to receive LENGTH characters |
4384 | of data into variable SCALAR from the specified SOCKET filehandle. | |
4385 | SCALAR will be grown or shrunk to the length actually read. Takes the | |
4386 | same flags as the system call of the same name. Returns the address | |
4387 | of the sender if SOCKET's protocol supports this; returns an empty | |
4388 | string otherwise. If there's an error, returns the undefined value. | |
4389 | This call is actually implemented in terms of recvfrom(2) system call. | |
4390 | See L<perlipc/"UDP: Message Passing"> for examples. | |
4391 | ||
4392 | Note the I<characters>: depending on the status of the socket, either | |
4393 | (8-bit) bytes or characters are received. By default all sockets | |
4394 | operate on bytes, but for example if the socket has been changed using | |
740d4bb2 JW |
4395 | binmode() to operate with the C<:encoding(utf8)> I/O layer (see the |
4396 | C<open> pragma, L<open>), the I/O will operate on UTF-8 encoded Unicode | |
4397 | characters, not bytes. Similarly for the C<:encoding> pragma: in that | |
4398 | case pretty much any characters can be read. | |
a0d0e21e LW |
4399 | |
4400 | =item redo LABEL | |
d74e8afc | 4401 | X<redo> |
a0d0e21e LW |
4402 | |
4403 | =item redo | |
4404 | ||
4405 | The C<redo> command restarts the loop block without evaluating the | |
98293880 | 4406 | conditional again. The C<continue> block, if any, is not executed. If |
a0d0e21e | 4407 | the LABEL is omitted, the command refers to the innermost enclosing |
cf264981 SP |
4408 | loop. Programs that want to lie to themselves about what was just input |
4409 | normally use this command: | |
a0d0e21e LW |
4410 | |
4411 | # a simpleminded Pascal comment stripper | |
4412 | # (warning: assumes no { or } in strings) | |
4633a7c4 | 4413 | LINE: while (<STDIN>) { |
a0d0e21e LW |
4414 | while (s|({.*}.*){.*}|$1 |) {} |
4415 | s|{.*}| |; | |
4416 | if (s|{.*| |) { | |
4417 | $front = $_; | |
4418 | while (<STDIN>) { | |
4419 | if (/}/) { # end of comment? | |
5a964f20 | 4420 | s|^|$front\{|; |
4633a7c4 | 4421 | redo LINE; |
a0d0e21e LW |
4422 | } |
4423 | } | |
4424 | } | |
4425 | print; | |
4426 | } | |
4427 | ||
4968c1e4 | 4428 | C<redo> cannot be used to retry a block which returns a value such as |
2b5ab1e7 TC |
4429 | C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit |
4430 | a grep() or map() operation. | |
4968c1e4 | 4431 | |
6c1372ed GS |
4432 | Note that a block by itself is semantically identical to a loop |
4433 | that executes once. Thus C<redo> inside such a block will effectively | |
4434 | turn it into a looping construct. | |
4435 | ||
98293880 | 4436 | See also L</continue> for an illustration of how C<last>, C<next>, and |
1d2dff63 GS |
4437 | C<redo> work. |
4438 | ||
a0d0e21e | 4439 | =item ref EXPR |
d74e8afc | 4440 | X<ref> X<reference> |
a0d0e21e | 4441 | |
54310121 | 4442 | =item ref |
bbce6d69 | 4443 | |
8a2e0804 A |
4444 | Returns a non-empty string if EXPR is a reference, the empty |
4445 | string otherwise. If EXPR | |
7660c0ab | 4446 | is not specified, C<$_> will be used. The value returned depends on the |
bbce6d69 | 4447 | type of thing the reference is a reference to. |
a0d0e21e LW |
4448 | Builtin types include: |
4449 | ||
a0d0e21e LW |
4450 | SCALAR |
4451 | ARRAY | |
4452 | HASH | |
4453 | CODE | |
19799a22 | 4454 | REF |
a0d0e21e | 4455 | GLOB |
19799a22 | 4456 | LVALUE |
cc10766d RGS |
4457 | FORMAT |
4458 | IO | |
4459 | VSTRING | |
4460 | Regexp | |
a0d0e21e | 4461 | |
54310121 | 4462 | If the referenced object has been blessed into a package, then that package |
19799a22 | 4463 | name is returned instead. You can think of C<ref> as a C<typeof> operator. |
a0d0e21e LW |
4464 | |
4465 | if (ref($r) eq "HASH") { | |
aa689395 | 4466 | print "r is a reference to a hash.\n"; |
54310121 | 4467 | } |
2b5ab1e7 | 4468 | unless (ref($r)) { |
a0d0e21e | 4469 | print "r is not a reference at all.\n"; |
54310121 | 4470 | } |
a0d0e21e | 4471 | |
85dd5c8b WL |
4472 | The return value C<LVALUE> indicates a reference to an lvalue that is not |
4473 | a variable. You get this from taking the reference of function calls like | |
4474 | C<pos()> or C<substr()>. C<VSTRING> is returned if the reference points | |
603c58be | 4475 | to a L<version string|perldata/"Version Strings">. |
85dd5c8b WL |
4476 | |
4477 | The result C<Regexp> indicates that the argument is a regular expression | |
4478 | resulting from C<qr//>. | |
4479 | ||
a0d0e21e LW |
4480 | See also L<perlref>. |
4481 | ||
4482 | =item rename OLDNAME,NEWNAME | |
d74e8afc | 4483 | X<rename> X<move> X<mv> X<ren> |
a0d0e21e | 4484 | |
19799a22 GS |
4485 | Changes the name of a file; an existing file NEWNAME will be |
4486 | clobbered. Returns true for success, false otherwise. | |
4487 | ||
2b5ab1e7 TC |
4488 | Behavior of this function varies wildly depending on your system |
4489 | implementation. For example, it will usually not work across file system | |
4490 | boundaries, even though the system I<mv> command sometimes compensates | |
4491 | for this. Other restrictions include whether it works on directories, | |
4492 | open files, or pre-existing files. Check L<perlport> and either the | |
4493 | rename(2) manpage or equivalent system documentation for details. | |
a0d0e21e | 4494 | |
dd184578 RGS |
4495 | For a platform independent C<move> function look at the L<File::Copy> |
4496 | module. | |
4497 | ||
16070b82 | 4498 | =item require VERSION |
d74e8afc | 4499 | X<require> |
16070b82 | 4500 | |
a0d0e21e LW |
4501 | =item require EXPR |
4502 | ||
4503 | =item require | |
4504 | ||
3b825e41 RK |
4505 | Demands a version of Perl specified by VERSION, or demands some semantics |
4506 | specified by EXPR or by C<$_> if EXPR is not supplied. | |
44dcb63b | 4507 | |
3b825e41 RK |
4508 | VERSION may be either a numeric argument such as 5.006, which will be |
4509 | compared to C<$]>, or a literal of the form v5.6.1, which will be compared | |
4510 | to C<$^V> (aka $PERL_VERSION). A fatal error is produced at run time if | |
4511 | VERSION is greater than the version of the current Perl interpreter. | |
4512 | Compare with L</use>, which can do a similar check at compile time. | |
4513 | ||
4514 | Specifying VERSION as a literal of the form v5.6.1 should generally be | |
4515 | avoided, because it leads to misleading error messages under earlier | |
cf264981 | 4516 | versions of Perl that do not support this syntax. The equivalent numeric |
3b825e41 | 4517 | version should be used instead. |
44dcb63b | 4518 | |
dd629d5b GS |
4519 | require v5.6.1; # run time version check |
4520 | require 5.6.1; # ditto | |
3b825e41 | 4521 | require 5.006_001; # ditto; preferred for backwards compatibility |
a0d0e21e | 4522 | |
362eead3 RGS |
4523 | Otherwise, C<require> demands that a library file be included if it |
4524 | hasn't already been included. The file is included via the do-FILE | |
73c71df6 CW |
4525 | mechanism, which is essentially just a variety of C<eval> with the |
4526 | caveat that lexical variables in the invoking script will be invisible | |
4527 | to the included code. Has semantics similar to the following subroutine: | |
a0d0e21e LW |
4528 | |
4529 | sub require { | |
20907158 AMS |
4530 | my ($filename) = @_; |
4531 | if (exists $INC{$filename}) { | |
4532 | return 1 if $INC{$filename}; | |
4533 | die "Compilation failed in require"; | |
4534 | } | |
4535 | my ($realfilename,$result); | |
4536 | ITER: { | |
4537 | foreach $prefix (@INC) { | |
4538 | $realfilename = "$prefix/$filename"; | |
4539 | if (-f $realfilename) { | |
4540 | $INC{$filename} = $realfilename; | |
4541 | $result = do $realfilename; | |
4542 | last ITER; | |
4543 | } | |
4544 | } | |
4545 | die "Can't find $filename in \@INC"; | |
4546 | } | |
4547 | if ($@) { | |
4548 | $INC{$filename} = undef; | |
4549 | die $@; | |
4550 | } elsif (!$result) { | |
4551 | delete $INC{$filename}; | |
4552 | die "$filename did not return true value"; | |
4553 | } else { | |
4554 | return $result; | |
4555 | } | |
a0d0e21e LW |
4556 | } |
4557 | ||
4558 | Note that the file will not be included twice under the same specified | |
a12755f0 SB |
4559 | name. |
4560 | ||
4561 | The file must return true as the last statement to indicate | |
a0d0e21e | 4562 | successful execution of any initialization code, so it's customary to |
19799a22 GS |
4563 | end such a file with C<1;> unless you're sure it'll return true |
4564 | otherwise. But it's better just to put the C<1;>, in case you add more | |
a0d0e21e LW |
4565 | statements. |
4566 | ||
54310121 | 4567 | If EXPR is a bareword, the require assumes a "F<.pm>" extension and |
da0045b7 | 4568 | replaces "F<::>" with "F</>" in the filename for you, |
54310121 | 4569 | to make it easy to load standard modules. This form of loading of |
a0d0e21e LW |
4570 | modules does not risk altering your namespace. |
4571 | ||
ee580363 GS |
4572 | In other words, if you try this: |
4573 | ||
b76cc8ba | 4574 | require Foo::Bar; # a splendid bareword |
ee580363 | 4575 | |
b76cc8ba | 4576 | The require function will actually look for the "F<Foo/Bar.pm>" file in the |
7660c0ab | 4577 | directories specified in the C<@INC> array. |
ee580363 | 4578 | |
5a964f20 | 4579 | But if you try this: |
ee580363 GS |
4580 | |
4581 | $class = 'Foo::Bar'; | |
f86cebdf | 4582 | require $class; # $class is not a bareword |
5a964f20 | 4583 | #or |
f86cebdf | 4584 | require "Foo::Bar"; # not a bareword because of the "" |
ee580363 | 4585 | |
b76cc8ba | 4586 | The require function will look for the "F<Foo::Bar>" file in the @INC array and |
19799a22 | 4587 | will complain about not finding "F<Foo::Bar>" there. In this case you can do: |
ee580363 GS |
4588 | |
4589 | eval "require $class"; | |
4590 | ||
a91233bf RGS |
4591 | Now that you understand how C<require> looks for files in the case of a |
4592 | bareword argument, there is a little extra functionality going on behind | |
4593 | the scenes. Before C<require> looks for a "F<.pm>" extension, it will | |
4594 | first look for a similar filename with a "F<.pmc>" extension. If this file | |
4595 | is found, it will be loaded in place of any file ending in a "F<.pm>" | |
4596 | extension. | |
662cc546 | 4597 | |
d54b56d5 RGS |
4598 | You can also insert hooks into the import facility, by putting directly |
4599 | Perl code into the @INC array. There are three forms of hooks: subroutine | |
4600 | references, array references and blessed objects. | |
4601 | ||
4602 | Subroutine references are the simplest case. When the inclusion system | |
4603 | walks through @INC and encounters a subroutine, this subroutine gets | |
4604 | called with two parameters, the first being a reference to itself, and the | |
4605 | second the name of the file to be included (e.g. "F<Foo/Bar.pm>"). The | |
cec0e1a7 | 4606 | subroutine should return nothing, or a list of up to three values in the |
1f0bdf18 NC |
4607 | following order: |
4608 | ||
4609 | =over | |
4610 | ||
4611 | =item 1 | |
4612 | ||
1f0bdf18 NC |
4613 | A filehandle, from which the file will be read. |
4614 | ||
cec0e1a7 | 4615 | =item 2 |
1f0bdf18 | 4616 | |
60d352b3 RGS |
4617 | A reference to a subroutine. If there is no filehandle (previous item), |
4618 | then this subroutine is expected to generate one line of source code per | |
4619 | call, writing the line into C<$_> and returning 1, then returning 0 at | |
4620 | "end of file". If there is a filehandle, then the subroutine will be | |
4621 | called to act a simple source filter, with the line as read in C<$_>. | |
4622 | Again, return 1 for each valid line, and 0 after all lines have been | |
4623 | returned. | |
1f0bdf18 | 4624 | |
cec0e1a7 | 4625 | =item 3 |
1f0bdf18 NC |
4626 | |
4627 | Optional state for the subroutine. The state is passed in as C<$_[1]>. A | |
4628 | reference to the subroutine itself is passed in as C<$_[0]>. | |
4629 | ||
4630 | =back | |
4631 | ||
4632 | If an empty list, C<undef>, or nothing that matches the first 3 values above | |
4633 | is returned then C<require> will look at the remaining elements of @INC. | |
903fe02a | 4634 | Note that this file handle must be a real file handle (strictly a typeglob, |
1f0bdf18 NC |
4635 | or reference to a typeglob, blessed or unblessed) - tied file handles will be |
4636 | ignored and return value processing will stop there. | |
d54b56d5 RGS |
4637 | |
4638 | If the hook is an array reference, its first element must be a subroutine | |
4639 | reference. This subroutine is called as above, but the first parameter is | |
4640 | the array reference. This enables to pass indirectly some arguments to | |
4641 | the subroutine. | |
4642 | ||
4643 | In other words, you can write: | |
4644 | ||
4645 | push @INC, \&my_sub; | |
4646 | sub my_sub { | |
4647 | my ($coderef, $filename) = @_; # $coderef is \&my_sub | |
4648 | ... | |
4649 | } | |
4650 | ||
4651 | or: | |
4652 | ||
4653 | push @INC, [ \&my_sub, $x, $y, ... ]; | |
4654 | sub my_sub { | |
4655 | my ($arrayref, $filename) = @_; | |
4656 | # Retrieve $x, $y, ... | |
4657 | my @parameters = @$arrayref[1..$#$arrayref]; | |
4658 | ... | |
4659 | } | |
4660 | ||
cf264981 | 4661 | If the hook is an object, it must provide an INC method that will be |
d54b56d5 | 4662 | called as above, the first parameter being the object itself. (Note that |
92c6daad NC |
4663 | you must fully qualify the sub's name, as unqualified C<INC> is always forced |
4664 | into package C<main>.) Here is a typical code layout: | |
d54b56d5 RGS |
4665 | |
4666 | # In Foo.pm | |
4667 | package Foo; | |
4668 | sub new { ... } | |
4669 | sub Foo::INC { | |
4670 | my ($self, $filename) = @_; | |
4671 | ... | |
4672 | } | |
4673 | ||
4674 | # In the main program | |
4675 | push @INC, new Foo(...); | |
4676 | ||
9ae8cd5b RGS |
4677 | Note that these hooks are also permitted to set the %INC entry |
4678 | corresponding to the files they have loaded. See L<perlvar/%INC>. | |
4679 | ||
ee580363 | 4680 | For a yet-more-powerful import facility, see L</use> and L<perlmod>. |
a0d0e21e LW |
4681 | |
4682 | =item reset EXPR | |
d74e8afc | 4683 | X<reset> |
a0d0e21e LW |
4684 | |
4685 | =item reset | |
4686 | ||
4687 | Generally used in a C<continue> block at the end of a loop to clear | |
7660c0ab | 4688 | variables and reset C<??> searches so that they work again. The |
a0d0e21e LW |
4689 | expression is interpreted as a list of single characters (hyphens |
4690 | allowed for ranges). All variables and arrays beginning with one of | |
4691 | those letters are reset to their pristine state. If the expression is | |
7660c0ab | 4692 | omitted, one-match searches (C<?pattern?>) are reset to match again. Resets |
5f05dabc | 4693 | only variables or searches in the current package. Always returns |
a0d0e21e LW |
4694 | 1. Examples: |
4695 | ||
4696 | reset 'X'; # reset all X variables | |
4697 | reset 'a-z'; # reset lower case variables | |
2b5ab1e7 | 4698 | reset; # just reset ?one-time? searches |
a0d0e21e | 4699 | |
7660c0ab | 4700 | Resetting C<"A-Z"> is not recommended because you'll wipe out your |
2b5ab1e7 TC |
4701 | C<@ARGV> and C<@INC> arrays and your C<%ENV> hash. Resets only package |
4702 | variables--lexical variables are unaffected, but they clean themselves | |
4703 | up on scope exit anyway, so you'll probably want to use them instead. | |
4704 | See L</my>. | |
a0d0e21e | 4705 | |
54310121 | 4706 | =item return EXPR |
d74e8afc | 4707 | X<return> |
54310121 | 4708 | |
4709 | =item return | |
4710 | ||
b76cc8ba | 4711 | Returns from a subroutine, C<eval>, or C<do FILE> with the value |
5a964f20 | 4712 | given in EXPR. Evaluation of EXPR may be in list, scalar, or void |
54310121 | 4713 | context, depending on how the return value will be used, and the context |
19799a22 | 4714 | may vary from one execution to the next (see C<wantarray>). If no EXPR |
2b5ab1e7 TC |
4715 | is given, returns an empty list in list context, the undefined value in |
4716 | scalar context, and (of course) nothing at all in a void context. | |
a0d0e21e | 4717 | |
d1be9408 | 4718 | (Note that in the absence of an explicit C<return>, a subroutine, eval, |
2b5ab1e7 TC |
4719 | or do FILE will automatically return the value of the last expression |
4720 | evaluated.) | |
a0d0e21e LW |
4721 | |
4722 | =item reverse LIST | |
d74e8afc | 4723 | X<reverse> X<rev> X<invert> |
a0d0e21e | 4724 | |
5a964f20 TC |
4725 | In list context, returns a list value consisting of the elements |
4726 | of LIST in the opposite order. In scalar context, concatenates the | |
2b5ab1e7 | 4727 | elements of LIST and returns a string value with all characters |
a0ed51b3 | 4728 | in the opposite order. |
4633a7c4 | 4729 | |
9649ed94 | 4730 | print join(", ", reverse "world", "Hello"); # Hello, world |
4633a7c4 | 4731 | |
9649ed94 | 4732 | print scalar reverse "dlrow ,", "olleH"; # Hello, world |
2f9daede | 4733 | |
2d713cbd RGS |
4734 | Used without arguments in scalar context, reverse() reverses C<$_>. |
4735 | ||
9649ed94 B |
4736 | $_ = "dlrow ,olleH"; |
4737 | print reverse; # No output, list context | |
4738 | print scalar reverse; # Hello, world | |
4739 | ||
2f9daede TP |
4740 | This operator is also handy for inverting a hash, although there are some |
4741 | caveats. If a value is duplicated in the original hash, only one of those | |
4742 | can be represented as a key in the inverted hash. Also, this has to | |
4743 | unwind one hash and build a whole new one, which may take some time | |
2b5ab1e7 | 4744 | on a large hash, such as from a DBM file. |
2f9daede TP |
4745 | |
4746 | %by_name = reverse %by_address; # Invert the hash | |
a0d0e21e LW |
4747 | |
4748 | =item rewinddir DIRHANDLE | |
d74e8afc | 4749 | X<rewinddir> |
a0d0e21e LW |
4750 | |
4751 | Sets the current position to the beginning of the directory for the | |
19799a22 | 4752 | C<readdir> routine on DIRHANDLE. |
a0d0e21e LW |
4753 | |
4754 | =item rindex STR,SUBSTR,POSITION | |
d74e8afc | 4755 | X<rindex> |
a0d0e21e LW |
4756 | |
4757 | =item rindex STR,SUBSTR | |
4758 | ||
ff551661 | 4759 | Works just like index() except that it returns the position of the I<last> |
a0d0e21e | 4760 | occurrence of SUBSTR in STR. If POSITION is specified, returns the |
ff551661 | 4761 | last occurrence beginning at or before that position. |
a0d0e21e LW |
4762 | |
4763 | =item rmdir FILENAME | |
d74e8afc | 4764 | X<rmdir> X<rd> X<directory, remove> |
a0d0e21e | 4765 | |
54310121 | 4766 | =item rmdir |
bbce6d69 | 4767 | |
974da8e5 JH |
4768 | Deletes the directory specified by FILENAME if that directory is |
4769 | empty. If it succeeds it returns true, otherwise it returns false and | |
4770 | sets C<$!> (errno). If FILENAME is omitted, uses C<$_>. | |
a0d0e21e | 4771 | |
dd184578 RGS |
4772 | To remove a directory tree recursively (C<rm -rf> on unix) look at |
4773 | the C<rmtree> function of the L<File::Path> module. | |
4774 | ||
a0d0e21e LW |
4775 | =item s/// |
4776 | ||
4777 | The substitution operator. See L<perlop>. | |
4778 | ||
0d863452 RH |
4779 | =item say FILEHANDLE LIST |
4780 | X<say> | |
4781 | ||
4782 | =item say LIST | |
4783 | ||
4784 | =item say | |
4785 | ||
4786 | Just like C<print>, but implicitly appends a newline. | |
187a5aa6 | 4787 | C<say LIST> is simply an abbreviation for C<{ local $\ = "\n"; print |
cfc4a7da | 4788 | LIST }>. |
f406c1e8 | 4789 | |
0d863452 RH |
4790 | This keyword is only available when the "say" feature is |
4791 | enabled: see L<feature>. | |
4792 | ||
a0d0e21e | 4793 | =item scalar EXPR |
d74e8afc | 4794 | X<scalar> X<context> |
a0d0e21e | 4795 | |
5a964f20 | 4796 | Forces EXPR to be interpreted in scalar context and returns the value |
54310121 | 4797 | of EXPR. |
cb1a09d0 AD |
4798 | |
4799 | @counts = ( scalar @a, scalar @b, scalar @c ); | |
4800 | ||
54310121 | 4801 | There is no equivalent operator to force an expression to |
2b5ab1e7 | 4802 | be interpolated in list context because in practice, this is never |
cb1a09d0 AD |
4803 | needed. If you really wanted to do so, however, you could use |
4804 | the construction C<@{[ (some expression) ]}>, but usually a simple | |
4805 | C<(some expression)> suffices. | |
a0d0e21e | 4806 | |
19799a22 | 4807 | Because C<scalar> is unary operator, if you accidentally use for EXPR a |
2b5ab1e7 TC |
4808 | parenthesized list, this behaves as a scalar comma expression, evaluating |
4809 | all but the last element in void context and returning the final element | |
4810 | evaluated in scalar context. This is seldom what you want. | |
62c18ce2 GS |
4811 | |
4812 | The following single statement: | |
4813 | ||
4814 | print uc(scalar(&foo,$bar)),$baz; | |
4815 | ||
4816 | is the moral equivalent of these two: | |
4817 | ||
4818 | &foo; | |
4819 | print(uc($bar),$baz); | |
4820 | ||
4821 | See L<perlop> for more details on unary operators and the comma operator. | |
4822 | ||
a0d0e21e | 4823 | =item seek FILEHANDLE,POSITION,WHENCE |
d74e8afc | 4824 | X<seek> X<fseek> X<filehandle, position> |
a0d0e21e | 4825 | |
19799a22 | 4826 | Sets FILEHANDLE's position, just like the C<fseek> call of C<stdio>. |
8903cb82 | 4827 | FILEHANDLE may be an expression whose value gives the name of the |
9124316e JH |
4828 | filehandle. The values for WHENCE are C<0> to set the new position |
4829 | I<in bytes> to POSITION, C<1> to set it to the current position plus | |
4830 | POSITION, and C<2> to set it to EOF plus POSITION (typically | |
4831 | negative). For WHENCE you may use the constants C<SEEK_SET>, | |
4832 | C<SEEK_CUR>, and C<SEEK_END> (start of the file, current position, end | |
4833 | of the file) from the Fcntl module. Returns C<1> upon success, C<0> | |
4834 | otherwise. | |
4835 | ||
4836 | Note the I<in bytes>: even if the filehandle has been set to | |
740d4bb2 | 4837 | operate on characters (for example by using the C<:encoding(utf8)> open |
fae2c0fb | 4838 | layer), tell() will return byte offsets, not character offsets |
9124316e | 4839 | (because implementing that would render seek() and tell() rather slow). |
8903cb82 | 4840 | |
19799a22 GS |
4841 | If you want to position file for C<sysread> or C<syswrite>, don't use |
4842 | C<seek>--buffering makes its effect on the file's system position | |
4843 | unpredictable and non-portable. Use C<sysseek> instead. | |
a0d0e21e | 4844 | |
2b5ab1e7 TC |
4845 | Due to the rules and rigors of ANSI C, on some systems you have to do a |
4846 | seek whenever you switch between reading and writing. Amongst other | |
4847 | things, this may have the effect of calling stdio's clearerr(3). | |
4848 | A WHENCE of C<1> (C<SEEK_CUR>) is useful for not moving the file position: | |
cb1a09d0 AD |
4849 | |
4850 | seek(TEST,0,1); | |
4851 | ||
4852 | This is also useful for applications emulating C<tail -f>. Once you hit | |
4853 | EOF on your read, and then sleep for a while, you might have to stick in a | |
19799a22 | 4854 | seek() to reset things. The C<seek> doesn't change the current position, |
8903cb82 | 4855 | but it I<does> clear the end-of-file condition on the handle, so that the |
61eff3bc | 4856 | next C<< <FILE> >> makes Perl try again to read something. We hope. |
cb1a09d0 | 4857 | |
9124316e JH |
4858 | If that doesn't work (some IO implementations are particularly |
4859 | cantankerous), then you may need something more like this: | |
cb1a09d0 AD |
4860 | |
4861 | for (;;) { | |
f86cebdf GS |
4862 | for ($curpos = tell(FILE); $_ = <FILE>; |
4863 | $curpos = tell(FILE)) { | |
cb1a09d0 AD |
4864 | # search for some stuff and put it into files |
4865 | } | |
4866 | sleep($for_a_while); | |
4867 | seek(FILE, $curpos, 0); | |
4868 | } | |
4869 | ||
a0d0e21e | 4870 | =item seekdir DIRHANDLE,POS |
d74e8afc | 4871 | X<seekdir> |
a0d0e21e | 4872 | |
19799a22 | 4873 | Sets the current position for the C<readdir> routine on DIRHANDLE. POS |
cf264981 SP |
4874 | must be a value returned by C<telldir>. C<seekdir> also has the same caveats |
4875 | about possible directory compaction as the corresponding system library | |
a0d0e21e LW |
4876 | routine. |
4877 | ||
4878 | =item select FILEHANDLE | |
d74e8afc | 4879 | X<select> X<filehandle, default> |
a0d0e21e LW |
4880 | |
4881 | =item select | |
4882 | ||
b5dffda6 RGS |
4883 | Returns the currently selected filehandle. If FILEHANDLE is supplied, |
4884 | sets the new current default filehandle for output. This has two | |
19799a22 | 4885 | effects: first, a C<write> or a C<print> without a filehandle will |
a0d0e21e LW |
4886 | default to this FILEHANDLE. Second, references to variables related to |
4887 | output will refer to this output channel. For example, if you have to | |
4888 | set the top of form format for more than one output channel, you might | |
4889 | do the following: | |
4890 | ||
4891 | select(REPORT1); | |
4892 | $^ = 'report1_top'; | |
4893 | select(REPORT2); | |
4894 | $^ = 'report2_top'; | |
4895 | ||
4896 | FILEHANDLE may be an expression whose value gives the name of the | |
4897 | actual filehandle. Thus: | |
4898 | ||
4899 | $oldfh = select(STDERR); $| = 1; select($oldfh); | |
4900 | ||
4633a7c4 LW |
4901 | Some programmers may prefer to think of filehandles as objects with |
4902 | methods, preferring to write the last example as: | |
a0d0e21e | 4903 | |
28757baa | 4904 | use IO::Handle; |
a0d0e21e LW |
4905 | STDERR->autoflush(1); |
4906 | ||
4907 | =item select RBITS,WBITS,EBITS,TIMEOUT | |
d74e8afc | 4908 | X<select> |
a0d0e21e | 4909 | |
f86cebdf | 4910 | This calls the select(2) system call with the bit masks specified, which |
19799a22 | 4911 | can be constructed using C<fileno> and C<vec>, along these lines: |
a0d0e21e LW |
4912 | |
4913 | $rin = $win = $ein = ''; | |
4914 | vec($rin,fileno(STDIN),1) = 1; | |
4915 | vec($win,fileno(STDOUT),1) = 1; | |
4916 | $ein = $rin | $win; | |
4917 | ||
4918 | If you want to select on many filehandles you might wish to write a | |
4919 | subroutine: | |
4920 | ||
4921 | sub fhbits { | |
5a964f20 TC |
4922 | my(@fhlist) = split(' ',$_[0]); |
4923 | my($bits); | |
a0d0e21e LW |
4924 | for (@fhlist) { |
4925 | vec($bits,fileno($_),1) = 1; | |
4926 | } | |
4927 | $bits; | |
4928 | } | |
4633a7c4 | 4929 | $rin = fhbits('STDIN TTY SOCK'); |
a0d0e21e LW |
4930 | |
4931 | The usual idiom is: | |
4932 | ||
4933 | ($nfound,$timeleft) = | |
4934 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); | |
4935 | ||
54310121 | 4936 | or to block until something becomes ready just do this |
a0d0e21e LW |
4937 | |
4938 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); | |
4939 | ||
19799a22 GS |
4940 | Most systems do not bother to return anything useful in $timeleft, so |
4941 | calling select() in scalar context just returns $nfound. | |
c07a80fd | 4942 | |
5f05dabc | 4943 | Any of the bit masks can also be undef. The timeout, if specified, is |
a0d0e21e | 4944 | in seconds, which may be fractional. Note: not all implementations are |
be119125 | 4945 | capable of returning the $timeleft. If not, they always return |
19799a22 | 4946 | $timeleft equal to the supplied $timeout. |
a0d0e21e | 4947 | |
ff68c719 | 4948 | You can effect a sleep of 250 milliseconds this way: |
a0d0e21e LW |
4949 | |
4950 | select(undef, undef, undef, 0.25); | |
4951 | ||
b09fc1d8 | 4952 | Note that whether C<select> gets restarted after signals (say, SIGALRM) |
8b0ac1d7 MHM |
4953 | is implementation-dependent. See also L<perlport> for notes on the |
4954 | portability of C<select>. | |
40454f26 | 4955 | |
4189264e RGS |
4956 | On error, C<select> behaves like the select(2) system call : it returns |
4957 | -1 and sets C<$!>. | |
353e5636 | 4958 | |
ec8ce15a HPM |
4959 | Note: on some Unixes, the select(2) system call may report a socket file |
4960 | descriptor as "ready for reading", when actually no data is available, | |
4961 | thus a subsequent read blocks. It can be avoided using always the | |
4962 | O_NONBLOCK flag on the socket. See select(2) and fcntl(2) for further | |
4963 | details. | |
4964 | ||
19799a22 | 4965 | B<WARNING>: One should not attempt to mix buffered I/O (like C<read> |
61eff3bc | 4966 | or <FH>) with C<select>, except as permitted by POSIX, and even |
19799a22 | 4967 | then only on POSIX systems. You have to use C<sysread> instead. |
a0d0e21e LW |
4968 | |
4969 | =item semctl ID,SEMNUM,CMD,ARG | |
d74e8afc | 4970 | X<semctl> |
a0d0e21e | 4971 | |
19799a22 | 4972 | Calls the System V IPC function C<semctl>. You'll probably have to say |
0ade1984 JH |
4973 | |
4974 | use IPC::SysV; | |
4975 | ||
4976 | first to get the correct constant definitions. If CMD is IPC_STAT or | |
cf264981 | 4977 | GETALL, then ARG must be a variable that will hold the returned |
e4038a1f MS |
4978 | semid_ds structure or semaphore value array. Returns like C<ioctl>: |
4979 | the undefined value for error, "C<0 but true>" for zero, or the actual | |
4980 | return value otherwise. The ARG must consist of a vector of native | |
106325ad | 4981 | short integers, which may be created with C<pack("s!",(0)x$nsem)>. |
4755096e GS |
4982 | See also L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::Semaphore> |
4983 | documentation. | |
a0d0e21e LW |
4984 | |
4985 | =item semget KEY,NSEMS,FLAGS | |
d74e8afc | 4986 | X<semget> |
a0d0e21e LW |
4987 | |
4988 | Calls the System V IPC function semget. Returns the semaphore id, or | |
4755096e GS |
4989 | the undefined value if there is an error. See also |
4990 | L<perlipc/"SysV IPC">, C<IPC::SysV>, C<IPC::SysV::Semaphore> | |
4991 | documentation. | |
a0d0e21e LW |
4992 | |
4993 | =item semop KEY,OPSTRING | |
d74e8afc | 4994 | X<semop> |
a0d0e21e LW |
4995 | |
4996 | Calls the System V IPC function semop to perform semaphore operations | |
5354997a | 4997 | such as signalling and waiting. OPSTRING must be a packed array of |
a0d0e21e | 4998 | semop structures. Each semop structure can be generated with |
cf264981 SP |
4999 | C<pack("s!3", $semnum, $semop, $semflag)>. The length of OPSTRING |
5000 | implies the number of semaphore operations. Returns true if | |
19799a22 GS |
5001 | successful, or false if there is an error. As an example, the |
5002 | following code waits on semaphore $semnum of semaphore id $semid: | |
a0d0e21e | 5003 | |
f878ba33 | 5004 | $semop = pack("s!3", $semnum, -1, 0); |
a0d0e21e LW |
5005 | die "Semaphore trouble: $!\n" unless semop($semid, $semop); |
5006 | ||
4755096e GS |
5007 | To signal the semaphore, replace C<-1> with C<1>. See also |
5008 | L<perlipc/"SysV IPC">, C<IPC::SysV>, and C<IPC::SysV::Semaphore> | |
5009 | documentation. | |
a0d0e21e LW |
5010 | |
5011 | =item send SOCKET,MSG,FLAGS,TO | |
d74e8afc | 5012 | X<send> |
a0d0e21e LW |
5013 | |
5014 | =item send SOCKET,MSG,FLAGS | |
5015 | ||
fe854a6f | 5016 | Sends a message on a socket. Attempts to send the scalar MSG to the |
9124316e JH |
5017 | SOCKET filehandle. Takes the same flags as the system call of the |
5018 | same name. On unconnected sockets you must specify a destination to | |
5019 | send TO, in which case it does a C C<sendto>. Returns the number of | |
5020 | characters sent, or the undefined value if there is an error. The C | |
5021 | system call sendmsg(2) is currently unimplemented. See | |
5022 | L<perlipc/"UDP: Message Passing"> for examples. | |
5023 | ||
5024 | Note the I<characters>: depending on the status of the socket, either | |
5025 | (8-bit) bytes or characters are sent. By default all sockets operate | |
5026 | on bytes, but for example if the socket has been changed using | |
740d4bb2 JW |
5027 | binmode() to operate with the C<:encoding(utf8)> I/O layer (see |
5028 | L</open>, or the C<open> pragma, L<open>), the I/O will operate on UTF-8 | |
5029 | encoded Unicode characters, not bytes. Similarly for the C<:encoding> | |
5030 | pragma: in that case pretty much any characters can be sent. | |
a0d0e21e LW |
5031 | |
5032 | =item setpgrp PID,PGRP | |
d74e8afc | 5033 | X<setpgrp> X<group> |
a0d0e21e | 5034 | |
7660c0ab | 5035 | Sets the current process group for the specified PID, C<0> for the current |
a0d0e21e | 5036 | process. Will produce a fatal error if used on a machine that doesn't |
81777298 GS |
5037 | implement POSIX setpgid(2) or BSD setpgrp(2). If the arguments are omitted, |
5038 | it defaults to C<0,0>. Note that the BSD 4.2 version of C<setpgrp> does not | |
5039 | accept any arguments, so only C<setpgrp(0,0)> is portable. See also | |
5040 | C<POSIX::setsid()>. | |
a0d0e21e LW |
5041 | |
5042 | =item setpriority WHICH,WHO,PRIORITY | |
d74e8afc | 5043 | X<setpriority> X<priority> X<nice> X<renice> |
a0d0e21e LW |
5044 | |
5045 | Sets the current priority for a process, a process group, or a user. | |
f86cebdf GS |
5046 | (See setpriority(2).) Will produce a fatal error if used on a machine |
5047 | that doesn't implement setpriority(2). | |
a0d0e21e LW |
5048 | |
5049 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL | |
d74e8afc | 5050 | X<setsockopt> |
a0d0e21e LW |
5051 | |
5052 | Sets the socket option requested. Returns undefined if there is an | |
23d0437f GA |
5053 | error. Use integer constants provided by the C<Socket> module for |
5054 | LEVEL and OPNAME. Values for LEVEL can also be obtained from | |
5055 | getprotobyname. OPTVAL might either be a packed string or an integer. | |
5056 | An integer OPTVAL is shorthand for pack("i", OPTVAL). | |
5057 | ||
5058 | An example disabling the Nagle's algorithm for a socket: | |
5059 | ||
5060 | use Socket qw(IPPROTO_TCP TCP_NODELAY); | |
5061 | setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1); | |
a0d0e21e LW |
5062 | |
5063 | =item shift ARRAY | |
d74e8afc | 5064 | X<shift> |
a0d0e21e LW |
5065 | |
5066 | =item shift | |
5067 | ||
5068 | Shifts the first value of the array off and returns it, shortening the | |
5069 | array by 1 and moving everything down. If there are no elements in the | |
5070 | array, returns the undefined value. If ARRAY is omitted, shifts the | |
7660c0ab | 5071 | C<@_> array within the lexical scope of subroutines and formats, and the |
faeb8393 | 5072 | C<@ARGV> array outside of a subroutine and also within the lexical scopes |
3c10abe3 AG |
5073 | established by the C<eval STRING>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>, |
5074 | C<UNITCHECK {}> and C<END {}> constructs. | |
4f25aa18 | 5075 | |
a1b2c429 | 5076 | See also C<unshift>, C<push>, and C<pop>. C<shift> and C<unshift> do the |
19799a22 | 5077 | same thing to the left end of an array that C<pop> and C<push> do to the |
977336f5 | 5078 | right end. |
a0d0e21e LW |
5079 | |
5080 | =item shmctl ID,CMD,ARG | |
d74e8afc | 5081 | X<shmctl> |
a0d0e21e | 5082 | |
0ade1984 JH |
5083 | Calls the System V IPC function shmctl. You'll probably have to say |
5084 | ||
5085 | use IPC::SysV; | |
5086 | ||
7660c0ab | 5087 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
cf264981 | 5088 | then ARG must be a variable that will hold the returned C<shmid_ds> |
7660c0ab | 5089 | structure. Returns like ioctl: the undefined value for error, "C<0> but |
0ade1984 | 5090 | true" for zero, or the actual return value otherwise. |
4755096e | 5091 | See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation. |
a0d0e21e LW |
5092 | |
5093 | =item shmget KEY,SIZE,FLAGS | |
d74e8afc | 5094 | X<shmget> |
a0d0e21e LW |
5095 | |
5096 | Calls the System V IPC function shmget. Returns the shared memory | |
5097 | segment id, or the undefined value if there is an error. | |
4755096e | 5098 | See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation. |
a0d0e21e LW |
5099 | |
5100 | =item shmread ID,VAR,POS,SIZE | |
d74e8afc ITB |
5101 | X<shmread> |
5102 | X<shmwrite> | |
a0d0e21e LW |
5103 | |
5104 | =item shmwrite ID,STRING,POS,SIZE | |
5105 | ||
5106 | Reads or writes the System V shared memory segment ID starting at | |
5107 | position POS for size SIZE by attaching to it, copying in/out, and | |
5a964f20 | 5108 | detaching from it. When reading, VAR must be a variable that will |
a0d0e21e LW |
5109 | hold the data read. When writing, if STRING is too long, only SIZE |
5110 | bytes are used; if STRING is too short, nulls are written to fill out | |
19799a22 | 5111 | SIZE bytes. Return true if successful, or false if there is an error. |
4755096e GS |
5112 | shmread() taints the variable. See also L<perlipc/"SysV IPC">, |
5113 | C<IPC::SysV> documentation, and the C<IPC::Shareable> module from CPAN. | |
a0d0e21e LW |
5114 | |
5115 | =item shutdown SOCKET,HOW | |
d74e8afc | 5116 | X<shutdown> |
a0d0e21e LW |
5117 | |
5118 | Shuts down a socket connection in the manner indicated by HOW, which | |
5119 | has the same interpretation as in the system call of the same name. | |
5120 | ||
f86cebdf GS |
5121 | shutdown(SOCKET, 0); # I/we have stopped reading data |
5122 | shutdown(SOCKET, 1); # I/we have stopped writing data | |
5123 | shutdown(SOCKET, 2); # I/we have stopped using this socket | |
5a964f20 TC |
5124 | |
5125 | This is useful with sockets when you want to tell the other | |
5126 | side you're done writing but not done reading, or vice versa. | |
b76cc8ba | 5127 | It's also a more insistent form of close because it also |
19799a22 | 5128 | disables the file descriptor in any forked copies in other |
5a964f20 TC |
5129 | processes. |
5130 | ||
f126b98b PF |
5131 | Returns C<1> for success. In the case of error, returns C<undef> if |
5132 | the first argument is not a valid filehandle, or returns C<0> and sets | |
5133 | C<$!> for any other failure. | |
5134 | ||
a0d0e21e | 5135 | =item sin EXPR |
d74e8afc | 5136 | X<sin> X<sine> X<asin> X<arcsine> |
a0d0e21e | 5137 | |
54310121 | 5138 | =item sin |
bbce6d69 | 5139 | |
a0d0e21e | 5140 | Returns the sine of EXPR (expressed in radians). If EXPR is omitted, |
7660c0ab | 5141 | returns sine of C<$_>. |
a0d0e21e | 5142 | |
ca6e1c26 | 5143 | For the inverse sine operation, you may use the C<Math::Trig::asin> |
28757baa | 5144 | function, or use this relation: |
5145 | ||
5146 | sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) } | |
5147 | ||
a0d0e21e | 5148 | =item sleep EXPR |
d74e8afc | 5149 | X<sleep> X<pause> |
a0d0e21e LW |
5150 | |
5151 | =item sleep | |
5152 | ||
5153 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. | |
b48653af MS |
5154 | Returns the number of seconds actually slept. |
5155 | ||
7660c0ab | 5156 | May be interrupted if the process receives a signal such as C<SIGALRM>. |
b48653af MS |
5157 | |
5158 | eval { | |
5159 | local $SIG{ALARM} = sub { die "Alarm!\n" }; | |
5160 | sleep; | |
5161 | }; | |
5162 | die $@ unless $@ eq "Alarm!\n"; | |
5163 | ||
5164 | You probably cannot mix C<alarm> and C<sleep> calls, because C<sleep> | |
5165 | is often implemented using C<alarm>. | |
a0d0e21e LW |
5166 | |
5167 | On some older systems, it may sleep up to a full second less than what | |
5168 | you requested, depending on how it counts seconds. Most modern systems | |
5a964f20 TC |
5169 | always sleep the full amount. They may appear to sleep longer than that, |
5170 | however, because your process might not be scheduled right away in a | |
5171 | busy multitasking system. | |
a0d0e21e | 5172 | |
2bc69794 BS |
5173 | For delays of finer granularity than one second, the Time::HiRes module |
5174 | (from CPAN, and starting from Perl 5.8 part of the standard | |
5175 | distribution) provides usleep(). You may also use Perl's four-argument | |
5176 | version of select() leaving the first three arguments undefined, or you | |
5177 | might be able to use the C<syscall> interface to access setitimer(2) if | |
5178 | your system supports it. See L<perlfaq8> for details. | |
cb1a09d0 | 5179 | |
b6e2112e | 5180 | See also the POSIX module's C<pause> function. |
5f05dabc | 5181 | |
a0d0e21e | 5182 | =item socket SOCKET,DOMAIN,TYPE,PROTOCOL |
d74e8afc | 5183 | X<socket> |
a0d0e21e LW |
5184 | |
5185 | Opens a socket of the specified kind and attaches it to filehandle | |
19799a22 GS |
5186 | SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for |
5187 | the system call of the same name. You should C<use Socket> first | |
5188 | to get the proper definitions imported. See the examples in | |
5189 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 5190 | |
8d2a6795 GS |
5191 | On systems that support a close-on-exec flag on files, the flag will |
5192 | be set for the newly opened file descriptor, as determined by the | |
5193 | value of $^F. See L<perlvar/$^F>. | |
5194 | ||
a0d0e21e | 5195 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL |
d74e8afc | 5196 | X<socketpair> |
a0d0e21e LW |
5197 | |
5198 | Creates an unnamed pair of sockets in the specified domain, of the | |
5f05dabc | 5199 | specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as |
a0d0e21e | 5200 | for the system call of the same name. If unimplemented, yields a fatal |
19799a22 | 5201 | error. Returns true if successful. |
a0d0e21e | 5202 | |
8d2a6795 GS |
5203 | On systems that support a close-on-exec flag on files, the flag will |
5204 | be set for the newly opened file descriptors, as determined by the value | |
5205 | of $^F. See L<perlvar/$^F>. | |
5206 | ||
19799a22 | 5207 | Some systems defined C<pipe> in terms of C<socketpair>, in which a call |
5a964f20 TC |
5208 | to C<pipe(Rdr, Wtr)> is essentially: |
5209 | ||
5210 | use Socket; | |
5211 | socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC); | |
5212 | shutdown(Rdr, 1); # no more writing for reader | |
5213 | shutdown(Wtr, 0); # no more reading for writer | |
5214 | ||
02fc2eee NC |
5215 | See L<perlipc> for an example of socketpair use. Perl 5.8 and later will |
5216 | emulate socketpair using IP sockets to localhost if your system implements | |
5217 | sockets but not socketpair. | |
5a964f20 | 5218 | |
a0d0e21e | 5219 | =item sort SUBNAME LIST |
d74e8afc | 5220 | X<sort> X<qsort> X<quicksort> X<mergesort> |
a0d0e21e LW |
5221 | |
5222 | =item sort BLOCK LIST | |
5223 | ||
5224 | =item sort LIST | |
5225 | ||
41d39f30 | 5226 | In list context, this sorts the LIST and returns the sorted list value. |
9fdc1d08 | 5227 | In scalar context, the behaviour of C<sort()> is undefined. |
41d39f30 A |
5228 | |
5229 | If SUBNAME or BLOCK is omitted, C<sort>s in standard string comparison | |
5230 | order. If SUBNAME is specified, it gives the name of a subroutine | |
5231 | that returns an integer less than, equal to, or greater than C<0>, | |
5232 | depending on how the elements of the list are to be ordered. (The C<< | |
5233 | <=> >> and C<cmp> operators are extremely useful in such routines.) | |
5234 | SUBNAME may be a scalar variable name (unsubscripted), in which case | |
5235 | the value provides the name of (or a reference to) the actual | |
5236 | subroutine to use. In place of a SUBNAME, you can provide a BLOCK as | |
5237 | an anonymous, in-line sort subroutine. | |
a0d0e21e | 5238 | |
43481408 | 5239 | If the subroutine's prototype is C<($$)>, the elements to be compared |
f9a36357 GS |
5240 | are passed by reference in C<@_>, as for a normal subroutine. This is |
5241 | slower than unprototyped subroutines, where the elements to be | |
5242 | compared are passed into the subroutine | |
43481408 GS |
5243 | as the package global variables $a and $b (see example below). Note that |
5244 | in the latter case, it is usually counter-productive to declare $a and | |
5245 | $b as lexicals. | |
5246 | ||
c106e8bb RH |
5247 | The values to be compared are always passed by reference and should not |
5248 | be modified. | |
a0d0e21e | 5249 | |
0a753a76 | 5250 | You also cannot exit out of the sort block or subroutine using any of the |
19799a22 | 5251 | loop control operators described in L<perlsyn> or with C<goto>. |
0a753a76 | 5252 | |
a034a98d DD |
5253 | When C<use locale> is in effect, C<sort LIST> sorts LIST according to the |
5254 | current collation locale. See L<perllocale>. | |
5255 | ||
db5021a3 MS |
5256 | sort() returns aliases into the original list, much as a for loop's index |
5257 | variable aliases the list elements. That is, modifying an element of a | |
5258 | list returned by sort() (for example, in a C<foreach>, C<map> or C<grep>) | |
5259 | actually modifies the element in the original list. This is usually | |
5260 | something to be avoided when writing clear code. | |
5261 | ||
58c7fc7c JH |
5262 | Perl 5.6 and earlier used a quicksort algorithm to implement sort. |
5263 | That algorithm was not stable, and I<could> go quadratic. (A I<stable> sort | |
5264 | preserves the input order of elements that compare equal. Although | |
5265 | quicksort's run time is O(NlogN) when averaged over all arrays of | |
5266 | length N, the time can be O(N**2), I<quadratic> behavior, for some | |
5267 | inputs.) In 5.7, the quicksort implementation was replaced with | |
cf264981 | 5268 | a stable mergesort algorithm whose worst-case behavior is O(NlogN). |
58c7fc7c JH |
5269 | But benchmarks indicated that for some inputs, on some platforms, |
5270 | the original quicksort was faster. 5.8 has a sort pragma for | |
5271 | limited control of the sort. Its rather blunt control of the | |
cf264981 | 5272 | underlying algorithm may not persist into future Perls, but the |
58c7fc7c | 5273 | ability to characterize the input or output in implementation |
6a30edae | 5274 | independent ways quite probably will. See L<sort>. |
c16425f1 | 5275 | |
a0d0e21e LW |
5276 | Examples: |
5277 | ||
5278 | # sort lexically | |
5279 | @articles = sort @files; | |
5280 | ||
5281 | # same thing, but with explicit sort routine | |
5282 | @articles = sort {$a cmp $b} @files; | |
5283 | ||
cb1a09d0 | 5284 | # now case-insensitively |
54310121 | 5285 | @articles = sort {uc($a) cmp uc($b)} @files; |
cb1a09d0 | 5286 | |
a0d0e21e LW |
5287 | # same thing in reversed order |
5288 | @articles = sort {$b cmp $a} @files; | |
5289 | ||
5290 | # sort numerically ascending | |
5291 | @articles = sort {$a <=> $b} @files; | |
5292 | ||
5293 | # sort numerically descending | |
5294 | @articles = sort {$b <=> $a} @files; | |
5295 | ||
19799a22 GS |
5296 | # this sorts the %age hash by value instead of key |
5297 | # using an in-line function | |
5298 | @eldest = sort { $age{$b} <=> $age{$a} } keys %age; | |
5299 | ||
a0d0e21e LW |
5300 | # sort using explicit subroutine name |
5301 | sub byage { | |
2f9daede | 5302 | $age{$a} <=> $age{$b}; # presuming numeric |
a0d0e21e LW |
5303 | } |
5304 | @sortedclass = sort byage @class; | |
5305 | ||
19799a22 GS |
5306 | sub backwards { $b cmp $a } |
5307 | @harry = qw(dog cat x Cain Abel); | |
5308 | @george = qw(gone chased yz Punished Axed); | |
a0d0e21e LW |
5309 | print sort @harry; |
5310 | # prints AbelCaincatdogx | |
5311 | print sort backwards @harry; | |
5312 | # prints xdogcatCainAbel | |
5313 | print sort @george, 'to', @harry; | |
5314 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz | |
5315 | ||
54310121 | 5316 | # inefficiently sort by descending numeric compare using |
5317 | # the first integer after the first = sign, or the | |
cb1a09d0 AD |
5318 | # whole record case-insensitively otherwise |
5319 | ||
5320 | @new = sort { | |
5321 | ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0] | |
5322 | || | |
5323 | uc($a) cmp uc($b) | |
5324 | } @old; | |
5325 | ||
5326 | # same thing, but much more efficiently; | |
5327 | # we'll build auxiliary indices instead | |
5328 | # for speed | |
5329 | @nums = @caps = (); | |
54310121 | 5330 | for (@old) { |
cb1a09d0 AD |
5331 | push @nums, /=(\d+)/; |
5332 | push @caps, uc($_); | |
54310121 | 5333 | } |
cb1a09d0 AD |
5334 | |
5335 | @new = @old[ sort { | |
5336 | $nums[$b] <=> $nums[$a] | |
5337 | || | |
5338 | $caps[$a] cmp $caps[$b] | |
5339 | } 0..$#old | |
5340 | ]; | |
5341 | ||
19799a22 | 5342 | # same thing, but without any temps |
cb1a09d0 | 5343 | @new = map { $_->[0] } |
19799a22 GS |
5344 | sort { $b->[1] <=> $a->[1] |
5345 | || | |
5346 | $a->[2] cmp $b->[2] | |
5347 | } map { [$_, /=(\d+)/, uc($_)] } @old; | |
61eff3bc | 5348 | |
43481408 GS |
5349 | # using a prototype allows you to use any comparison subroutine |
5350 | # as a sort subroutine (including other package's subroutines) | |
5351 | package other; | |
5352 | sub backwards ($$) { $_[1] cmp $_[0]; } # $a and $b are not set here | |
5353 | ||
5354 | package main; | |
5355 | @new = sort other::backwards @old; | |
cb1a09d0 | 5356 | |
58c7fc7c JH |
5357 | # guarantee stability, regardless of algorithm |
5358 | use sort 'stable'; | |
5359 | @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old; | |
5360 | ||
268e9d79 JL |
5361 | # force use of mergesort (not portable outside Perl 5.8) |
5362 | use sort '_mergesort'; # note discouraging _ | |
58c7fc7c | 5363 | @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old; |
58c7fc7c | 5364 | |
19799a22 GS |
5365 | If you're using strict, you I<must not> declare $a |
5366 | and $b as lexicals. They are package globals. That means | |
47223a36 | 5367 | if you're in the C<main> package and type |
13a2d996 | 5368 | |
47223a36 | 5369 | @articles = sort {$b <=> $a} @files; |
13a2d996 | 5370 | |
47223a36 JH |
5371 | then C<$a> and C<$b> are C<$main::a> and C<$main::b> (or C<$::a> and C<$::b>), |
5372 | but if you're in the C<FooPack> package, it's the same as typing | |
cb1a09d0 AD |
5373 | |
5374 | @articles = sort {$FooPack::b <=> $FooPack::a} @files; | |
5375 | ||
55497cff | 5376 | The comparison function is required to behave. If it returns |
7660c0ab A |
5377 | inconsistent results (sometimes saying C<$x[1]> is less than C<$x[2]> and |
5378 | sometimes saying the opposite, for example) the results are not | |
5379 | well-defined. | |
55497cff | 5380 | |
03190201 JL |
5381 | Because C<< <=> >> returns C<undef> when either operand is C<NaN> |
5382 | (not-a-number), and because C<sort> will trigger a fatal error unless the | |
5383 | result of a comparison is defined, when sorting with a comparison function | |
5384 | like C<< $a <=> $b >>, be careful about lists that might contain a C<NaN>. | |
5385 | The following example takes advantage of the fact that C<NaN != NaN> to | |
5386 | eliminate any C<NaN>s from the input. | |
5387 | ||
5388 | @result = sort { $a <=> $b } grep { $_ == $_ } @input; | |
5389 | ||
a0d0e21e | 5390 | =item splice ARRAY,OFFSET,LENGTH,LIST |
d74e8afc | 5391 | X<splice> |
a0d0e21e LW |
5392 | |
5393 | =item splice ARRAY,OFFSET,LENGTH | |
5394 | ||
5395 | =item splice ARRAY,OFFSET | |
5396 | ||
453f9044 GS |
5397 | =item splice ARRAY |
5398 | ||
a0d0e21e | 5399 | Removes the elements designated by OFFSET and LENGTH from an array, and |
5a964f20 TC |
5400 | replaces them with the elements of LIST, if any. In list context, |
5401 | returns the elements removed from the array. In scalar context, | |
43051805 | 5402 | returns the last element removed, or C<undef> if no elements are |
48cdf507 | 5403 | removed. The array grows or shrinks as necessary. |
19799a22 | 5404 | If OFFSET is negative then it starts that far from the end of the array. |
48cdf507 | 5405 | If LENGTH is omitted, removes everything from OFFSET onward. |
d0920e03 MJD |
5406 | If LENGTH is negative, removes the elements from OFFSET onward |
5407 | except for -LENGTH elements at the end of the array. | |
8cbc2e3b JH |
5408 | If both OFFSET and LENGTH are omitted, removes everything. If OFFSET is |
5409 | past the end of the array, perl issues a warning, and splices at the | |
5410 | end of the array. | |
453f9044 | 5411 | |
3272a53d | 5412 | The following equivalences hold (assuming C<< $[ == 0 and $#a >= $i >> ) |
a0d0e21e | 5413 | |
48cdf507 | 5414 | push(@a,$x,$y) splice(@a,@a,0,$x,$y) |
a0d0e21e LW |
5415 | pop(@a) splice(@a,-1) |
5416 | shift(@a) splice(@a,0,1) | |
5417 | unshift(@a,$x,$y) splice(@a,0,0,$x,$y) | |
3272a53d | 5418 | $a[$i] = $y splice(@a,$i,1,$y) |
a0d0e21e LW |
5419 | |
5420 | Example, assuming array lengths are passed before arrays: | |
5421 | ||
5422 | sub aeq { # compare two list values | |
5a964f20 TC |
5423 | my(@a) = splice(@_,0,shift); |
5424 | my(@b) = splice(@_,0,shift); | |
a0d0e21e LW |
5425 | return 0 unless @a == @b; # same len? |
5426 | while (@a) { | |
5427 | return 0 if pop(@a) ne pop(@b); | |
5428 | } | |
5429 | return 1; | |
5430 | } | |
5431 | if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... } | |
5432 | ||
5433 | =item split /PATTERN/,EXPR,LIMIT | |
d74e8afc | 5434 | X<split> |
a0d0e21e LW |
5435 | |
5436 | =item split /PATTERN/,EXPR | |
5437 | ||
5438 | =item split /PATTERN/ | |
5439 | ||
5440 | =item split | |
5441 | ||
b2e26e6e DJ |
5442 | Splits the string EXPR into a list of strings and returns that list. By |
5443 | default, empty leading fields are preserved, and empty trailing ones are | |
ab7ee80f | 5444 | deleted. (If all fields are empty, they are considered to be trailing.) |
a0d0e21e | 5445 | |
46836f5c GS |
5446 | In scalar context, returns the number of fields found and splits into |
5447 | the C<@_> array. Use of split in scalar context is deprecated, however, | |
5448 | because it clobbers your subroutine arguments. | |
a0d0e21e | 5449 | |
7660c0ab | 5450 | If EXPR is omitted, splits the C<$_> string. If PATTERN is also omitted, |
4633a7c4 LW |
5451 | splits on whitespace (after skipping any leading whitespace). Anything |
5452 | matching PATTERN is taken to be a delimiter separating the fields. (Note | |
fb73857a | 5453 | that the delimiter may be longer than one character.) |
5454 | ||
836e0ee7 | 5455 | If LIMIT is specified and positive, it represents the maximum number |
e833de1e BS |
5456 | of fields the EXPR will be split into, though the actual number of |
5457 | fields returned depends on the number of times PATTERN matches within | |
5458 | EXPR. If LIMIT is unspecified or zero, trailing null fields are | |
5459 | stripped (which potential users of C<pop> would do well to remember). | |
5460 | If LIMIT is negative, it is treated as if an arbitrarily large LIMIT | |
5461 | had been specified. Note that splitting an EXPR that evaluates to the | |
5462 | empty string always returns the empty list, regardless of the LIMIT | |
5463 | specified. | |
a0d0e21e LW |
5464 | |
5465 | A pattern matching the null string (not to be confused with | |
748a9306 | 5466 | a null pattern C<//>, which is just one member of the set of patterns |
a0d0e21e LW |
5467 | matching a null string) will split the value of EXPR into separate |
5468 | characters at each point it matches that way. For example: | |
5469 | ||
8241c1c0 | 5470 | print join(':', split(/ */, 'hi there')), "\n"; |
a0d0e21e LW |
5471 | |
5472 | produces the output 'h:i:t:h:e:r:e'. | |
5473 | ||
de5763b0 RGS |
5474 | As a special case for C<split>, using the empty pattern C<//> specifically |
5475 | matches only the null string, and is not be confused with the regular use | |
5476 | of C<//> to mean "the last successful pattern match". So, for C<split>, | |
5477 | the following: | |
6de67870 | 5478 | |
8241c1c0 | 5479 | print join(':', split(//, 'hi there')), "\n"; |
52ea55c9 | 5480 | |
de5763b0 | 5481 | produces the output 'h:i: :t:h:e:r:e'. |
52ea55c9 | 5482 | |
12977212 FC |
5483 | Empty leading fields are produced when there are positive-width matches at |
5484 | the beginning of the string; a zero-width match at the beginning of | |
5485 | the string does not produce an empty field. For example: | |
0156e0fd RB |
5486 | |
5487 | print join(':', split(/(?=\w)/, 'hi there!')); | |
5488 | ||
12977212 FC |
5489 | produces the output 'h:i :t:h:e:r:e!'. Empty trailing fields, on the other |
5490 | hand, are produced when there is a match at the end of the string (and | |
5491 | when LIMIT is given and is not 0), regardless of the length of the match. | |
5492 | For example: | |
5493 | ||
8241c1c0 B |
5494 | print join(':', split(//, 'hi there!', -1)), "\n"; |
5495 | print join(':', split(/\W/, 'hi there!', -1)), "\n"; | |
12977212 FC |
5496 | |
5497 | produce the output 'h:i: :t:h:e:r:e:!:' and 'hi:there:', respectively, | |
5498 | both with an empty trailing field. | |
0156e0fd | 5499 | |
5f05dabc | 5500 | The LIMIT parameter can be used to split a line partially |
a0d0e21e LW |
5501 | |
5502 | ($login, $passwd, $remainder) = split(/:/, $_, 3); | |
5503 | ||
b5da07fd TB |
5504 | When assigning to a list, if LIMIT is omitted, or zero, Perl supplies |
5505 | a LIMIT one larger than the number of variables in the list, to avoid | |
a0d0e21e LW |
5506 | unnecessary work. For the list above LIMIT would have been 4 by |
5507 | default. In time critical applications it behooves you not to split | |
5508 | into more fields than you really need. | |
5509 | ||
19799a22 | 5510 | If the PATTERN contains parentheses, additional list elements are |
a0d0e21e LW |
5511 | created from each matching substring in the delimiter. |
5512 | ||
da0045b7 | 5513 | split(/([,-])/, "1-10,20", 3); |
a0d0e21e LW |
5514 | |
5515 | produces the list value | |
5516 | ||
5517 | (1, '-', 10, ',', 20) | |
5518 | ||
19799a22 | 5519 | If you had the entire header of a normal Unix email message in $header, |
4633a7c4 LW |
5520 | you could split it up into fields and their values this way: |
5521 | ||
5522 | $header =~ s/\n\s+/ /g; # fix continuation lines | |
fb73857a | 5523 | %hdrs = (UNIX_FROM => split /^(\S*?):\s*/m, $header); |
4633a7c4 | 5524 | |
a0d0e21e LW |
5525 | The pattern C</PATTERN/> may be replaced with an expression to specify |
5526 | patterns that vary at runtime. (To do runtime compilation only once, | |
748a9306 LW |
5527 | use C</$variable/o>.) |
5528 | ||
5da728e2 A |
5529 | As a special case, specifying a PATTERN of space (S<C<' '>>) will split on |
5530 | white space just as C<split> with no arguments does. Thus, S<C<split(' ')>> can | |
5531 | be used to emulate B<awk>'s default behavior, whereas S<C<split(/ /)>> | |
748a9306 | 5532 | will give you as many null initial fields as there are leading spaces. |
5da728e2 | 5533 | A C<split> on C</\s+/> is like a S<C<split(' ')>> except that any leading |
19799a22 | 5534 | whitespace produces a null first field. A C<split> with no arguments |
5da728e2 | 5535 | really does a S<C<split(' ', $_)>> internally. |
a0d0e21e | 5536 | |
cc50a203 | 5537 | A PATTERN of C</^/> is treated as if it were C</^/m>, since it isn't |
1ec94568 MG |
5538 | much use otherwise. |
5539 | ||
a0d0e21e LW |
5540 | Example: |
5541 | ||
5a964f20 TC |
5542 | open(PASSWD, '/etc/passwd'); |
5543 | while (<PASSWD>) { | |
5b3eff12 MS |
5544 | chomp; |
5545 | ($login, $passwd, $uid, $gid, | |
f86cebdf | 5546 | $gcos, $home, $shell) = split(/:/); |
5a964f20 | 5547 | #... |
a0d0e21e LW |
5548 | } |
5549 | ||
6de67870 JP |
5550 | As with regular pattern matching, any capturing parentheses that are not |
5551 | matched in a C<split()> will be set to C<undef> when returned: | |
5552 | ||
5553 | @fields = split /(A)|B/, "1A2B3"; | |
5554 | # @fields is (1, 'A', 2, undef, 3) | |
a0d0e21e | 5555 | |
5f05dabc | 5556 | =item sprintf FORMAT, LIST |
d74e8afc | 5557 | X<sprintf> |
a0d0e21e | 5558 | |
6662521e GS |
5559 | Returns a string formatted by the usual C<printf> conventions of the C |
5560 | library function C<sprintf>. See below for more details | |
5561 | and see L<sprintf(3)> or L<printf(3)> on your system for an explanation of | |
5562 | the general principles. | |
5563 | ||
5564 | For example: | |
5565 | ||
5566 | # Format number with up to 8 leading zeroes | |
5567 | $result = sprintf("%08d", $number); | |
5568 | ||
5569 | # Round number to 3 digits after decimal point | |
5570 | $rounded = sprintf("%.3f", $number); | |
74a77017 | 5571 | |
19799a22 GS |
5572 | Perl does its own C<sprintf> formatting--it emulates the C |
5573 | function C<sprintf>, but it doesn't use it (except for floating-point | |
74a77017 | 5574 | numbers, and even then only the standard modifiers are allowed). As a |
19799a22 | 5575 | result, any non-standard extensions in your local C<sprintf> are not |
74a77017 CS |
5576 | available from Perl. |
5577 | ||
194e7b38 DC |
5578 | Unlike C<printf>, C<sprintf> does not do what you probably mean when you |
5579 | pass it an array as your first argument. The array is given scalar context, | |
5580 | and instead of using the 0th element of the array as the format, Perl will | |
5581 | use the count of elements in the array as the format, which is almost never | |
5582 | useful. | |
5583 | ||
19799a22 | 5584 | Perl's C<sprintf> permits the following universally-known conversions: |
74a77017 CS |
5585 | |
5586 | %% a percent sign | |
5587 | %c a character with the given number | |
5588 | %s a string | |
5589 | %d a signed integer, in decimal | |
5590 | %u an unsigned integer, in decimal | |
5591 | %o an unsigned integer, in octal | |
5592 | %x an unsigned integer, in hexadecimal | |
5593 | %e a floating-point number, in scientific notation | |
5594 | %f a floating-point number, in fixed decimal notation | |
5595 | %g a floating-point number, in %e or %f notation | |
5596 | ||
1b3f7d21 | 5597 | In addition, Perl permits the following widely-supported conversions: |
74a77017 | 5598 | |
74a77017 CS |
5599 | %X like %x, but using upper-case letters |
5600 | %E like %e, but using an upper-case "E" | |
5601 | %G like %g, but with an upper-case "E" (if applicable) | |
4f19785b | 5602 | %b an unsigned integer, in binary |
e69758a1 | 5603 | %B like %b, but using an upper-case "B" with the # flag |
74a77017 | 5604 | %p a pointer (outputs the Perl value's address in hexadecimal) |
1b3f7d21 | 5605 | %n special: *stores* the number of characters output so far |
b76cc8ba | 5606 | into the next variable in the parameter list |
74a77017 | 5607 | |
1b3f7d21 CS |
5608 | Finally, for backward (and we do mean "backward") compatibility, Perl |
5609 | permits these unnecessary but widely-supported conversions: | |
74a77017 | 5610 | |
1b3f7d21 | 5611 | %i a synonym for %d |
74a77017 CS |
5612 | %D a synonym for %ld |
5613 | %U a synonym for %lu | |
5614 | %O a synonym for %lo | |
5615 | %F a synonym for %f | |
5616 | ||
7b8dd722 HS |
5617 | Note that the number of exponent digits in the scientific notation produced |
5618 | by C<%e>, C<%E>, C<%g> and C<%G> for numbers with the modulus of the | |
b73fd64e JH |
5619 | exponent less than 100 is system-dependent: it may be three or less |
5620 | (zero-padded as necessary). In other words, 1.23 times ten to the | |
5621 | 99th may be either "1.23e99" or "1.23e099". | |
d764f01a | 5622 | |
7b8dd722 HS |
5623 | Between the C<%> and the format letter, you may specify a number of |
5624 | additional attributes controlling the interpretation of the format. | |
5625 | In order, these are: | |
74a77017 | 5626 | |
7b8dd722 HS |
5627 | =over 4 |
5628 | ||
5629 | =item format parameter index | |
5630 | ||
5631 | An explicit format parameter index, such as C<2$>. By default sprintf | |
5632 | will format the next unused argument in the list, but this allows you | |
cf264981 | 5633 | to take the arguments out of order, e.g.: |
7b8dd722 HS |
5634 | |
5635 | printf '%2$d %1$d', 12, 34; # prints "34 12" | |
5636 | printf '%3$d %d %1$d', 1, 2, 3; # prints "3 1 1" | |
5637 | ||
5638 | =item flags | |
5639 | ||
5640 | one or more of: | |
e6bb52fd | 5641 | |
7a81c58e A |
5642 | space prefix non-negative number with a space |
5643 | + prefix non-negative number with a plus sign | |
74a77017 CS |
5644 | - left-justify within the field |
5645 | 0 use zeros, not spaces, to right-justify | |
e6bb52fd TS |
5646 | # ensure the leading "0" for any octal, |
5647 | prefix non-zero hexadecimal with "0x" or "0X", | |
5648 | prefix non-zero binary with "0b" or "0B" | |
7b8dd722 HS |
5649 | |
5650 | For example: | |
5651 | ||
e6bb52fd TS |
5652 | printf '<% d>', 12; # prints "< 12>" |
5653 | printf '<%+d>', 12; # prints "<+12>" | |
5654 | printf '<%6s>', 12; # prints "< 12>" | |
5655 | printf '<%-6s>', 12; # prints "<12 >" | |
5656 | printf '<%06s>', 12; # prints "<000012>" | |
5657 | printf '<%#o>', 12; # prints "<014>" | |
5658 | printf '<%#x>', 12; # prints "<0xc>" | |
5659 | printf '<%#X>', 12; # prints "<0XC>" | |
5660 | printf '<%#b>', 12; # prints "<0b1100>" | |
5661 | printf '<%#B>', 12; # prints "<0B1100>" | |
7b8dd722 | 5662 | |
9911cee9 TS |
5663 | When a space and a plus sign are given as the flags at once, |
5664 | a plus sign is used to prefix a positive number. | |
5665 | ||
5666 | printf '<%+ d>', 12; # prints "<+12>" | |
5667 | printf '<% +d>', 12; # prints "<+12>" | |
5668 | ||
e6bb52fd TS |
5669 | When the # flag and a precision are given in the %o conversion, |
5670 | the precision is incremented if it's necessary for the leading "0". | |
5671 | ||
5672 | printf '<%#.5o>', 012; # prints "<00012>" | |
5673 | printf '<%#.5o>', 012345; # prints "<012345>" | |
5674 | printf '<%#.0o>', 0; # prints "<0>" | |
5675 | ||
7b8dd722 HS |
5676 | =item vector flag |
5677 | ||
920f3fa9 DM |
5678 | This flag tells perl to interpret the supplied string as a vector of |
5679 | integers, one for each character in the string. Perl applies the format to | |
5680 | each integer in turn, then joins the resulting strings with a separator (a | |
5681 | dot C<.> by default). This can be useful for displaying ordinal values of | |
5682 | characters in arbitrary strings: | |
7b8dd722 | 5683 | |
920f3fa9 | 5684 | printf "%vd", "AB\x{100}"; # prints "65.66.256" |
7b8dd722 HS |
5685 | printf "version is v%vd\n", $^V; # Perl's version |
5686 | ||
5687 | Put an asterisk C<*> before the C<v> to override the string to | |
5688 | use to separate the numbers: | |
5689 | ||
5690 | printf "address is %*vX\n", ":", $addr; # IPv6 address | |
5691 | printf "bits are %0*v8b\n", " ", $bits; # random bitstring | |
5692 | ||
5693 | You can also explicitly specify the argument number to use for | |
cf264981 | 5694 | the join string using e.g. C<*2$v>: |
7b8dd722 HS |
5695 | |
5696 | printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":"; # 3 IPv6 addresses | |
5697 | ||
5698 | =item (minimum) width | |
5699 | ||
5700 | Arguments are usually formatted to be only as wide as required to | |
5701 | display the given value. You can override the width by putting | |
5702 | a number here, or get the width from the next argument (with C<*>) | |
cf264981 | 5703 | or from a specified argument (with e.g. C<*2$>): |
7b8dd722 HS |
5704 | |
5705 | printf '<%s>', "a"; # prints "<a>" | |
5706 | printf '<%6s>', "a"; # prints "< a>" | |
5707 | printf '<%*s>', 6, "a"; # prints "< a>" | |
5708 | printf '<%*2$s>', "a", 6; # prints "< a>" | |
5709 | printf '<%2s>', "long"; # prints "<long>" (does not truncate) | |
5710 | ||
19799a22 GS |
5711 | If a field width obtained through C<*> is negative, it has the same |
5712 | effect as the C<-> flag: left-justification. | |
74a77017 | 5713 | |
7b8dd722 | 5714 | =item precision, or maximum width |
d74e8afc | 5715 | X<precision> |
7b8dd722 | 5716 | |
6c8c9a8e | 5717 | You can specify a precision (for numeric conversions) or a maximum |
7b8dd722 | 5718 | width (for string conversions) by specifying a C<.> followed by a number. |
1ff2d182 | 5719 | For floating point formats, with the exception of 'g' and 'G', this specifies |
cf264981 | 5720 | the number of decimal places to show (the default being 6), e.g.: |
7b8dd722 HS |
5721 | |
5722 | # these examples are subject to system-specific variation | |
5723 | printf '<%f>', 1; # prints "<1.000000>" | |
5724 | printf '<%.1f>', 1; # prints "<1.0>" | |
5725 | printf '<%.0f>', 1; # prints "<1>" | |
5726 | printf '<%e>', 10; # prints "<1.000000e+01>" | |
5727 | printf '<%.1e>', 10; # prints "<1.0e+01>" | |
5728 | ||
1ff2d182 | 5729 | For 'g' and 'G', this specifies the maximum number of digits to show, |
cf264981 | 5730 | including prior to the decimal point as well as after it, e.g.: |
1ff2d182 AS |
5731 | |
5732 | # these examples are subject to system-specific variation | |
5733 | printf '<%g>', 1; # prints "<1>" | |
5734 | printf '<%.10g>', 1; # prints "<1>" | |
5735 | printf '<%g>', 100; # prints "<100>" | |
5736 | printf '<%.1g>', 100; # prints "<1e+02>" | |
5737 | printf '<%.2g>', 100.01; # prints "<1e+02>" | |
5738 | printf '<%.5g>', 100.01; # prints "<100.01>" | |
5739 | printf '<%.4g>', 100.01; # prints "<100>" | |
5740 | ||
7b8dd722 | 5741 | For integer conversions, specifying a precision implies that the |
9911cee9 TS |
5742 | output of the number itself should be zero-padded to this width, |
5743 | where the 0 flag is ignored: | |
5744 | ||
5745 | printf '<%.6d>', 1; # prints "<000001>" | |
5746 | printf '<%+.6d>', 1; # prints "<+000001>" | |
5747 | printf '<%-10.6d>', 1; # prints "<000001 >" | |
5748 | printf '<%10.6d>', 1; # prints "< 000001>" | |
5749 | printf '<%010.6d>', 1; # prints "< 000001>" | |
5750 | printf '<%+10.6d>', 1; # prints "< +000001>" | |
7b8dd722 HS |
5751 | |
5752 | printf '<%.6x>', 1; # prints "<000001>" | |
5753 | printf '<%#.6x>', 1; # prints "<0x000001>" | |
5754 | printf '<%-10.6x>', 1; # prints "<000001 >" | |
9911cee9 TS |
5755 | printf '<%10.6x>', 1; # prints "< 000001>" |
5756 | printf '<%010.6x>', 1; # prints "< 000001>" | |
5757 | printf '<%#10.6x>', 1; # prints "< 0x000001>" | |
7b8dd722 HS |
5758 | |
5759 | For string conversions, specifying a precision truncates the string | |
5760 | to fit in the specified width: | |
5761 | ||
5762 | printf '<%.5s>', "truncated"; # prints "<trunc>" | |
5763 | printf '<%10.5s>', "truncated"; # prints "< trunc>" | |
5764 | ||
5765 | You can also get the precision from the next argument using C<.*>: | |
b22c7a20 | 5766 | |
7b8dd722 HS |
5767 | printf '<%.6x>', 1; # prints "<000001>" |
5768 | printf '<%.*x>', 6, 1; # prints "<000001>" | |
5769 | ||
9911cee9 TS |
5770 | If a precision obtained through C<*> is negative, it has the same |
5771 | effect as no precision. | |
5772 | ||
5773 | printf '<%.*s>', 7, "string"; # prints "<string>" | |
5774 | printf '<%.*s>', 3, "string"; # prints "<str>" | |
5775 | printf '<%.*s>', 0, "string"; # prints "<>" | |
5776 | printf '<%.*s>', -1, "string"; # prints "<string>" | |
5777 | ||
5778 | printf '<%.*d>', 1, 0; # prints "<0>" | |
5779 | printf '<%.*d>', 0, 0; # prints "<>" | |
5780 | printf '<%.*d>', -1, 0; # prints "<0>" | |
5781 | ||
7b8dd722 HS |
5782 | You cannot currently get the precision from a specified number, |
5783 | but it is intended that this will be possible in the future using | |
cf264981 | 5784 | e.g. C<.*2$>: |
7b8dd722 HS |
5785 | |
5786 | printf '<%.*2$x>', 1, 6; # INVALID, but in future will print "<000001>" | |
5787 | ||
5788 | =item size | |
5789 | ||
5790 | For numeric conversions, you can specify the size to interpret the | |
1ff2d182 AS |
5791 | number as using C<l>, C<h>, C<V>, C<q>, C<L>, or C<ll>. For integer |
5792 | conversions (C<d u o x X b i D U O>), numbers are usually assumed to be | |
5793 | whatever the default integer size is on your platform (usually 32 or 64 | |
5794 | bits), but you can override this to use instead one of the standard C types, | |
5795 | as supported by the compiler used to build Perl: | |
7b8dd722 HS |
5796 | |
5797 | l interpret integer as C type "long" or "unsigned long" | |
5798 | h interpret integer as C type "short" or "unsigned short" | |
1ff2d182 AS |
5799 | q, L or ll interpret integer as C type "long long", "unsigned long long". |
5800 | or "quads" (typically 64-bit integers) | |
7b8dd722 | 5801 | |
1ff2d182 AS |
5802 | The last will produce errors if Perl does not understand "quads" in your |
5803 | installation. (This requires that either the platform natively supports quads | |
5804 | or Perl was specifically compiled to support quads.) You can find out | |
5805 | whether your Perl supports quads via L<Config>: | |
7b8dd722 | 5806 | |
1ff2d182 AS |
5807 | use Config; |
5808 | ($Config{use64bitint} eq 'define' || $Config{longsize} >= 8) && | |
5809 | print "quads\n"; | |
5810 | ||
5811 | For floating point conversions (C<e f g E F G>), numbers are usually assumed | |
5812 | to be the default floating point size on your platform (double or long double), | |
5813 | but you can force 'long double' with C<q>, C<L>, or C<ll> if your | |
5814 | platform supports them. You can find out whether your Perl supports long | |
5815 | doubles via L<Config>: | |
5816 | ||
5817 | use Config; | |
5818 | $Config{d_longdbl} eq 'define' && print "long doubles\n"; | |
5819 | ||
5820 | You can find out whether Perl considers 'long double' to be the default | |
5821 | floating point size to use on your platform via L<Config>: | |
5822 | ||
5823 | use Config; | |
5824 | ($Config{uselongdouble} eq 'define') && | |
5825 | print "long doubles by default\n"; | |
5826 | ||
5827 | It can also be the case that long doubles and doubles are the same thing: | |
5828 | ||
5829 | use Config; | |
5830 | ($Config{doublesize} == $Config{longdblsize}) && | |
5831 | print "doubles are long doubles\n"; | |
5832 | ||
5833 | The size specifier C<V> has no effect for Perl code, but it is supported | |
7b8dd722 HS |
5834 | for compatibility with XS code; it means 'use the standard size for |
5835 | a Perl integer (or floating-point number)', which is already the | |
5836 | default for Perl code. | |
5837 | ||
a472f209 HS |
5838 | =item order of arguments |
5839 | ||
5840 | Normally, sprintf takes the next unused argument as the value to | |
5841 | format for each format specification. If the format specification | |
5842 | uses C<*> to require additional arguments, these are consumed from | |
5843 | the argument list in the order in which they appear in the format | |
5844 | specification I<before> the value to format. Where an argument is | |
5845 | specified using an explicit index, this does not affect the normal | |
5846 | order for the arguments (even when the explicitly specified index | |
5847 | would have been the next argument in any case). | |
5848 | ||
5849 | So: | |
5850 | ||
5851 | printf '<%*.*s>', $a, $b, $c; | |
5852 | ||
5853 | would use C<$a> for the width, C<$b> for the precision and C<$c> | |
5854 | as the value to format, while: | |
5855 | ||
d8a2d19b | 5856 | printf '<%*1$.*s>', $a, $b; |
a472f209 HS |
5857 | |
5858 | would use C<$a> for the width and the precision, and C<$b> as the | |
5859 | value to format. | |
5860 | ||
5861 | Here are some more examples - beware that when using an explicit | |
5862 | index, the C<$> may need to be escaped: | |
5863 | ||
5864 | printf "%2\$d %d\n", 12, 34; # will print "34 12\n" | |
5865 | printf "%2\$d %d %d\n", 12, 34; # will print "34 12 34\n" | |
5866 | printf "%3\$d %d %d\n", 12, 34, 56; # will print "56 12 34\n" | |
5867 | printf "%2\$*3\$d %d\n", 12, 34, 3; # will print " 34 12\n" | |
5868 | ||
7b8dd722 | 5869 | =back |
b22c7a20 | 5870 | |
7e4353e9 RGS |
5871 | If C<use locale> is in effect, and POSIX::setlocale() has been called, |
5872 | the character used for the decimal separator in formatted floating | |
5873 | point numbers is affected by the LC_NUMERIC locale. See L<perllocale> | |
5874 | and L<POSIX>. | |
a0d0e21e LW |
5875 | |
5876 | =item sqrt EXPR | |
d74e8afc | 5877 | X<sqrt> X<root> X<square root> |
a0d0e21e | 5878 | |
54310121 | 5879 | =item sqrt |
bbce6d69 | 5880 | |
a0d0e21e | 5881 | Return the square root of EXPR. If EXPR is omitted, returns square |
2b5ab1e7 TC |
5882 | root of C<$_>. Only works on non-negative operands, unless you've |
5883 | loaded the standard Math::Complex module. | |
5884 | ||
5885 | use Math::Complex; | |
5886 | print sqrt(-2); # prints 1.4142135623731i | |
a0d0e21e LW |
5887 | |
5888 | =item srand EXPR | |
d74e8afc | 5889 | X<srand> X<seed> X<randseed> |
a0d0e21e | 5890 | |
93dc8474 CS |
5891 | =item srand |
5892 | ||
0686c0b8 JH |
5893 | Sets the random number seed for the C<rand> operator. |
5894 | ||
0686c0b8 JH |
5895 | The point of the function is to "seed" the C<rand> function so that |
5896 | C<rand> can produce a different sequence each time you run your | |
e0b236fe | 5897 | program. |
0686c0b8 | 5898 | |
e0b236fe JH |
5899 | If srand() is not called explicitly, it is called implicitly at the |
5900 | first use of the C<rand> operator. However, this was not the case in | |
5901 | versions of Perl before 5.004, so if your script will run under older | |
5902 | Perl versions, it should call C<srand>. | |
93dc8474 | 5903 | |
e0b236fe JH |
5904 | Most programs won't even call srand() at all, except those that |
5905 | need a cryptographically-strong starting point rather than the | |
5906 | generally acceptable default, which is based on time of day, | |
5907 | process ID, and memory allocation, or the F</dev/urandom> device, | |
67408cae | 5908 | if available. |
9be67dbc | 5909 | |
e0b236fe JH |
5910 | You can call srand($seed) with the same $seed to reproduce the |
5911 | I<same> sequence from rand(), but this is usually reserved for | |
5912 | generating predictable results for testing or debugging. | |
5913 | Otherwise, don't call srand() more than once in your program. | |
0686c0b8 | 5914 | |
3a3e71eb JH |
5915 | Do B<not> call srand() (i.e. without an argument) more than once in |
5916 | a script. The internal state of the random number generator should | |
0686c0b8 | 5917 | contain more entropy than can be provided by any seed, so calling |
e0b236fe | 5918 | srand() again actually I<loses> randomness. |
0686c0b8 | 5919 | |
e0b236fe JH |
5920 | Most implementations of C<srand> take an integer and will silently |
5921 | truncate decimal numbers. This means C<srand(42)> will usually | |
5922 | produce the same results as C<srand(42.1)>. To be safe, always pass | |
5923 | C<srand> an integer. | |
0686c0b8 JH |
5924 | |
5925 | In versions of Perl prior to 5.004 the default seed was just the | |
5926 | current C<time>. This isn't a particularly good seed, so many old | |
5927 | programs supply their own seed value (often C<time ^ $$> or C<time ^ | |
5928 | ($$ + ($$ << 15))>), but that isn't necessary any more. | |
93dc8474 | 5929 | |
cf264981 SP |
5930 | For cryptographic purposes, however, you need something much more random |
5931 | than the default seed. Checksumming the compressed output of one or more | |
2f9daede TP |
5932 | rapidly changing operating system status programs is the usual method. For |
5933 | example: | |
28757baa | 5934 | |
784d6566 | 5935 | srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip -f`); |
28757baa | 5936 | |
7660c0ab | 5937 | If you're particularly concerned with this, see the C<Math::TrulyRandom> |
0078ec44 RS |
5938 | module in CPAN. |
5939 | ||
54310121 | 5940 | Frequently called programs (like CGI scripts) that simply use |
28757baa | 5941 | |
5942 | time ^ $$ | |
5943 | ||
54310121 | 5944 | for a seed can fall prey to the mathematical property that |
28757baa | 5945 | |
5946 | a^b == (a+1)^(b+1) | |
5947 | ||
0078ec44 | 5948 | one-third of the time. So don't do that. |
f86702cc | 5949 | |
a0d0e21e | 5950 | =item stat FILEHANDLE |
435fbc73 | 5951 | X<stat> X<file, status> X<ctime> |
a0d0e21e LW |
5952 | |
5953 | =item stat EXPR | |
5954 | ||
5228a96c SP |
5955 | =item stat DIRHANDLE |
5956 | ||
54310121 | 5957 | =item stat |
bbce6d69 | 5958 | |
1d2dff63 | 5959 | Returns a 13-element list giving the status info for a file, either |
5228a96c SP |
5960 | the file opened via FILEHANDLE or DIRHANDLE, or named by EXPR. If EXPR is |
5961 | omitted, it stats C<$_>. Returns a null list if the stat fails. Typically | |
5962 | used as follows: | |
a0d0e21e LW |
5963 | |
5964 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, | |
5965 | $atime,$mtime,$ctime,$blksize,$blocks) | |
5966 | = stat($filename); | |
5967 | ||
54310121 | 5968 | Not all fields are supported on all filesystem types. Here are the |
61967be2 | 5969 | meanings of the fields: |
c07a80fd | 5970 | |
54310121 | 5971 | 0 dev device number of filesystem |
5972 | 1 ino inode number | |
5973 | 2 mode file mode (type and permissions) | |
5974 | 3 nlink number of (hard) links to the file | |
5975 | 4 uid numeric user ID of file's owner | |
5976 | 5 gid numeric group ID of file's owner | |
5977 | 6 rdev the device identifier (special files only) | |
5978 | 7 size total size of file, in bytes | |
1c74f1bd GS |
5979 | 8 atime last access time in seconds since the epoch |
5980 | 9 mtime last modify time in seconds since the epoch | |
df2a7e48 | 5981 | 10 ctime inode change time in seconds since the epoch (*) |
54310121 | 5982 | 11 blksize preferred block size for file system I/O |
5983 | 12 blocks actual number of blocks allocated | |
c07a80fd | 5984 | |
5985 | (The epoch was at 00:00 January 1, 1970 GMT.) | |
5986 | ||
3e2557b2 RGS |
5987 | (*) Not all fields are supported on all filesystem types. Notably, the |
5988 | ctime field is non-portable. In particular, you cannot expect it to be a | |
5989 | "creation time", see L<perlport/"Files and Filesystems"> for details. | |
df2a7e48 | 5990 | |
61967be2 | 5991 | If C<stat> is passed the special filehandle consisting of an underline, no |
a0d0e21e | 5992 | stat is done, but the current contents of the stat structure from the |
61967be2 | 5993 | last C<stat>, C<lstat>, or filetest are returned. Example: |
a0d0e21e LW |
5994 | |
5995 | if (-x $file && (($d) = stat(_)) && $d < 0) { | |
5996 | print "$file is executable NFS file\n"; | |
5997 | } | |
5998 | ||
ca6e1c26 JH |
5999 | (This works on machines only for which the device number is negative |
6000 | under NFS.) | |
a0d0e21e | 6001 | |
2b5ab1e7 | 6002 | Because the mode contains both the file type and its permissions, you |
b76cc8ba | 6003 | should mask off the file type portion and (s)printf using a C<"%o"> |
2b5ab1e7 TC |
6004 | if you want to see the real permissions. |
6005 | ||
6006 | $mode = (stat($filename))[2]; | |
6007 | printf "Permissions are %04o\n", $mode & 07777; | |
6008 | ||
19799a22 | 6009 | In scalar context, C<stat> returns a boolean value indicating success |
1d2dff63 GS |
6010 | or failure, and, if successful, sets the information associated with |
6011 | the special filehandle C<_>. | |
6012 | ||
dd184578 | 6013 | The L<File::stat> module provides a convenient, by-name access mechanism: |
2b5ab1e7 TC |
6014 | |
6015 | use File::stat; | |
6016 | $sb = stat($filename); | |
b76cc8ba | 6017 | printf "File is %s, size is %s, perm %04o, mtime %s\n", |
2b5ab1e7 TC |
6018 | $filename, $sb->size, $sb->mode & 07777, |
6019 | scalar localtime $sb->mtime; | |
6020 | ||
ca6e1c26 JH |
6021 | You can import symbolic mode constants (C<S_IF*>) and functions |
6022 | (C<S_IS*>) from the Fcntl module: | |
6023 | ||
6024 | use Fcntl ':mode'; | |
6025 | ||
6026 | $mode = (stat($filename))[2]; | |
6027 | ||
6028 | $user_rwx = ($mode & S_IRWXU) >> 6; | |
6029 | $group_read = ($mode & S_IRGRP) >> 3; | |
6030 | $other_execute = $mode & S_IXOTH; | |
6031 | ||
3155e0b0 | 6032 | printf "Permissions are %04o\n", S_IMODE($mode), "\n"; |
ca6e1c26 JH |
6033 | |
6034 | $is_setuid = $mode & S_ISUID; | |
ad605d16 | 6035 | $is_directory = S_ISDIR($mode); |
ca6e1c26 JH |
6036 | |
6037 | You could write the last two using the C<-u> and C<-d> operators. | |
61967be2 | 6038 | The commonly available C<S_IF*> constants are |
ca6e1c26 JH |
6039 | |
6040 | # Permissions: read, write, execute, for user, group, others. | |
6041 | ||
6042 | S_IRWXU S_IRUSR S_IWUSR S_IXUSR | |
6043 | S_IRWXG S_IRGRP S_IWGRP S_IXGRP | |
6044 | S_IRWXO S_IROTH S_IWOTH S_IXOTH | |
61eff3bc | 6045 | |
3cee8101 RGS |
6046 | # Setuid/Setgid/Stickiness/SaveText. |
6047 | # Note that the exact meaning of these is system dependent. | |
ca6e1c26 JH |
6048 | |
6049 | S_ISUID S_ISGID S_ISVTX S_ISTXT | |
6050 | ||
6051 | # File types. Not necessarily all are available on your system. | |
6052 | ||
135ed46b | 6053 | S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR S_IFIFO S_IFSOCK S_IFWHT S_ENFMT |
ca6e1c26 JH |
6054 | |
6055 | # The following are compatibility aliases for S_IRUSR, S_IWUSR, S_IXUSR. | |
6056 | ||
6057 | S_IREAD S_IWRITE S_IEXEC | |
6058 | ||
61967be2 | 6059 | and the C<S_IF*> functions are |
ca6e1c26 | 6060 | |
3155e0b0 | 6061 | S_IMODE($mode) the part of $mode containing the permission bits |
ca6e1c26 JH |
6062 | and the setuid/setgid/sticky bits |
6063 | ||
6064 | S_IFMT($mode) the part of $mode containing the file type | |
b76cc8ba | 6065 | which can be bit-anded with e.g. S_IFREG |
ca6e1c26 JH |
6066 | or with the following functions |
6067 | ||
61967be2 | 6068 | # The operators -f, -d, -l, -b, -c, -p, and -S. |
ca6e1c26 JH |
6069 | |
6070 | S_ISREG($mode) S_ISDIR($mode) S_ISLNK($mode) | |
6071 | S_ISBLK($mode) S_ISCHR($mode) S_ISFIFO($mode) S_ISSOCK($mode) | |
6072 | ||
6073 | # No direct -X operator counterpart, but for the first one | |
6074 | # the -g operator is often equivalent. The ENFMT stands for | |
6075 | # record flocking enforcement, a platform-dependent feature. | |
6076 | ||
6077 | S_ISENFMT($mode) S_ISWHT($mode) | |
6078 | ||
6079 | See your native chmod(2) and stat(2) documentation for more details | |
61967be2 | 6080 | about the C<S_*> constants. To get status info for a symbolic link |
c837d5b4 | 6081 | instead of the target file behind the link, use the C<lstat> function. |
ca6e1c26 | 6082 | |
36fb85f3 RGS |
6083 | =item state EXPR |
6084 | X<state> | |
6085 | ||
6086 | =item state TYPE EXPR | |
6087 | ||
6088 | =item state EXPR : ATTRS | |
6089 | ||
6090 | =item state TYPE EXPR : ATTRS | |
6091 | ||
6092 | C<state> declares a lexically scoped variable, just like C<my> does. | |
b708784e | 6093 | However, those variables will never be reinitialized, contrary to |
36fb85f3 RGS |
6094 | lexical variables that are reinitialized each time their enclosing block |
6095 | is entered. | |
6096 | ||
6097 | C<state> variables are only enabled when the C<feature 'state'> pragma is | |
6098 | in effect. See L<feature>. | |
6099 | ||
a0d0e21e | 6100 | =item study SCALAR |
d74e8afc | 6101 | X<study> |
a0d0e21e LW |
6102 | |
6103 | =item study | |
6104 | ||
184e9718 | 6105 | Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of |
a0d0e21e LW |
6106 | doing many pattern matches on the string before it is next modified. |
6107 | This may or may not save time, depending on the nature and number of | |
6108 | patterns you are searching on, and on the distribution of character | |
19799a22 | 6109 | frequencies in the string to be searched--you probably want to compare |
5f05dabc | 6110 | run times with and without it to see which runs faster. Those loops |
cf264981 | 6111 | that scan for many short constant strings (including the constant |
a0d0e21e | 6112 | parts of more complex patterns) will benefit most. You may have only |
19799a22 GS |
6113 | one C<study> active at a time--if you study a different scalar the first |
6114 | is "unstudied". (The way C<study> works is this: a linked list of every | |
a0d0e21e | 6115 | character in the string to be searched is made, so we know, for |
7660c0ab | 6116 | example, where all the C<'k'> characters are. From each search string, |
a0d0e21e LW |
6117 | the rarest character is selected, based on some static frequency tables |
6118 | constructed from some C programs and English text. Only those places | |
6119 | that contain this "rarest" character are examined.) | |
6120 | ||
5a964f20 | 6121 | For example, here is a loop that inserts index producing entries |
a0d0e21e LW |
6122 | before any line containing a certain pattern: |
6123 | ||
6124 | while (<>) { | |
6125 | study; | |
2b5ab1e7 TC |
6126 | print ".IX foo\n" if /\bfoo\b/; |
6127 | print ".IX bar\n" if /\bbar\b/; | |
6128 | print ".IX blurfl\n" if /\bblurfl\b/; | |
5a964f20 | 6129 | # ... |
a0d0e21e LW |
6130 | print; |
6131 | } | |
6132 | ||
951ba7fe GS |
6133 | In searching for C</\bfoo\b/>, only those locations in C<$_> that contain C<f> |
6134 | will be looked at, because C<f> is rarer than C<o>. In general, this is | |
a0d0e21e LW |
6135 | a big win except in pathological cases. The only question is whether |
6136 | it saves you more time than it took to build the linked list in the | |
6137 | first place. | |
6138 | ||
6139 | Note that if you have to look for strings that you don't know till | |
19799a22 | 6140 | runtime, you can build an entire loop as a string and C<eval> that to |
a0d0e21e | 6141 | avoid recompiling all your patterns all the time. Together with |
7660c0ab | 6142 | undefining C<$/> to input entire files as one record, this can be very |
f86cebdf | 6143 | fast, often faster than specialized programs like fgrep(1). The following |
184e9718 | 6144 | scans a list of files (C<@files>) for a list of words (C<@words>), and prints |
a0d0e21e LW |
6145 | out the names of those files that contain a match: |
6146 | ||
6147 | $search = 'while (<>) { study;'; | |
6148 | foreach $word (@words) { | |
6149 | $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n"; | |
6150 | } | |
6151 | $search .= "}"; | |
6152 | @ARGV = @files; | |
6153 | undef $/; | |
6154 | eval $search; # this screams | |
5f05dabc | 6155 | $/ = "\n"; # put back to normal input delimiter |
a0d0e21e LW |
6156 | foreach $file (sort keys(%seen)) { |
6157 | print $file, "\n"; | |
6158 | } | |
6159 | ||
1d2de774 | 6160 | =item sub NAME BLOCK |
d74e8afc | 6161 | X<sub> |
cb1a09d0 | 6162 | |
1d2de774 | 6163 | =item sub NAME (PROTO) BLOCK |
cb1a09d0 | 6164 | |
1d2de774 JH |
6165 | =item sub NAME : ATTRS BLOCK |
6166 | ||
6167 | =item sub NAME (PROTO) : ATTRS BLOCK | |
6168 | ||
6169 | This is subroutine definition, not a real function I<per se>. | |
6170 | Without a BLOCK it's just a forward declaration. Without a NAME, | |
6171 | it's an anonymous function declaration, and does actually return | |
6172 | a value: the CODE ref of the closure you just created. | |
cb1a09d0 | 6173 | |
1d2de774 | 6174 | See L<perlsub> and L<perlref> for details about subroutines and |
0795dc2b | 6175 | references, and L<attributes> and L<Attribute::Handlers> for more |
1d2de774 | 6176 | information about attributes. |
cb1a09d0 | 6177 | |
87275199 | 6178 | =item substr EXPR,OFFSET,LENGTH,REPLACEMENT |
d74e8afc | 6179 | X<substr> X<substring> X<mid> X<left> X<right> |
7b8d334a | 6180 | |
87275199 | 6181 | =item substr EXPR,OFFSET,LENGTH |
a0d0e21e LW |
6182 | |
6183 | =item substr EXPR,OFFSET | |
6184 | ||
6185 | Extracts a substring out of EXPR and returns it. First character is at | |
7660c0ab | 6186 | offset C<0>, or whatever you've set C<$[> to (but don't do that). |
84902520 | 6187 | If OFFSET is negative (or more precisely, less than C<$[>), starts |
87275199 GS |
6188 | that far from the end of the string. If LENGTH is omitted, returns |
6189 | everything to the end of the string. If LENGTH is negative, leaves that | |
748a9306 LW |
6190 | many characters off the end of the string. |
6191 | ||
e1de3ec0 GS |
6192 | my $s = "The black cat climbed the green tree"; |
6193 | my $color = substr $s, 4, 5; # black | |
6194 | my $middle = substr $s, 4, -11; # black cat climbed the | |
6195 | my $end = substr $s, 14; # climbed the green tree | |
6196 | my $tail = substr $s, -4; # tree | |
6197 | my $z = substr $s, -4, 2; # tr | |
6198 | ||
2b5ab1e7 | 6199 | You can use the substr() function as an lvalue, in which case EXPR |
87275199 GS |
6200 | must itself be an lvalue. If you assign something shorter than LENGTH, |
6201 | the string will shrink, and if you assign something longer than LENGTH, | |
2b5ab1e7 | 6202 | the string will grow to accommodate it. To keep the string the same |
19799a22 | 6203 | length you may need to pad or chop your value using C<sprintf>. |
a0d0e21e | 6204 | |
87275199 GS |
6205 | If OFFSET and LENGTH specify a substring that is partly outside the |
6206 | string, only the part within the string is returned. If the substring | |
6207 | is beyond either end of the string, substr() returns the undefined | |
6208 | value and produces a warning. When used as an lvalue, specifying a | |
6209 | substring that is entirely outside the string is a fatal error. | |
6210 | Here's an example showing the behavior for boundary cases: | |
6211 | ||
6212 | my $name = 'fred'; | |
6213 | substr($name, 4) = 'dy'; # $name is now 'freddy' | |
6214 | my $null = substr $name, 6, 2; # returns '' (no warning) | |
6215 | my $oops = substr $name, 7; # returns undef, with warning | |
6216 | substr($name, 7) = 'gap'; # fatal error | |
6217 | ||
2b5ab1e7 | 6218 | An alternative to using substr() as an lvalue is to specify the |
7b8d334a | 6219 | replacement string as the 4th argument. This allows you to replace |
2b5ab1e7 TC |
6220 | parts of the EXPR and return what was there before in one operation, |
6221 | just as you can with splice(). | |
7b8d334a | 6222 | |
e1de3ec0 GS |
6223 | my $s = "The black cat climbed the green tree"; |
6224 | my $z = substr $s, 14, 7, "jumped from"; # climbed | |
6225 | # $s is now "The black cat jumped from the green tree" | |
6226 | ||
cf264981 | 6227 | Note that the lvalue returned by the 3-arg version of substr() acts as |
91f73676 DM |
6228 | a 'magic bullet'; each time it is assigned to, it remembers which part |
6229 | of the original string is being modified; for example: | |
6230 | ||
6231 | $x = '1234'; | |
6232 | for (substr($x,1,2)) { | |
6233 | $_ = 'a'; print $x,"\n"; # prints 1a4 | |
6234 | $_ = 'xyz'; print $x,"\n"; # prints 1xyz4 | |
6235 | $x = '56789'; | |
6236 | $_ = 'pq'; print $x,"\n"; # prints 5pq9 | |
6237 | } | |
6238 | ||
91f73676 DM |
6239 | Prior to Perl version 5.9.1, the result of using an lvalue multiple times was |
6240 | unspecified. | |
c67bbae0 | 6241 | |
a0d0e21e | 6242 | =item symlink OLDFILE,NEWFILE |
d74e8afc | 6243 | X<symlink> X<link> X<symbolic link> X<link, symbolic> |
a0d0e21e LW |
6244 | |
6245 | Creates a new filename symbolically linked to the old filename. | |
7660c0ab | 6246 | Returns C<1> for success, C<0> otherwise. On systems that don't support |
a0d0e21e LW |
6247 | symbolic links, produces a fatal error at run time. To check for that, |
6248 | use eval: | |
6249 | ||
2b5ab1e7 | 6250 | $symlink_exists = eval { symlink("",""); 1 }; |
a0d0e21e | 6251 | |
5702da47 | 6252 | =item syscall NUMBER, LIST |
d74e8afc | 6253 | X<syscall> X<system call> |
a0d0e21e LW |
6254 | |
6255 | Calls the system call specified as the first element of the list, | |
6256 | passing the remaining elements as arguments to the system call. If | |
6257 | unimplemented, produces a fatal error. The arguments are interpreted | |
6258 | as follows: if a given argument is numeric, the argument is passed as | |
6259 | an int. If not, the pointer to the string value is passed. You are | |
6260 | responsible to make sure a string is pre-extended long enough to | |
a3cb178b | 6261 | receive any result that might be written into a string. You can't use a |
19799a22 | 6262 | string literal (or other read-only string) as an argument to C<syscall> |
a3cb178b GS |
6263 | because Perl has to assume that any string pointer might be written |
6264 | through. If your | |
a0d0e21e | 6265 | integer arguments are not literals and have never been interpreted in a |
7660c0ab | 6266 | numeric context, you may need to add C<0> to them to force them to look |
19799a22 | 6267 | like numbers. This emulates the C<syswrite> function (or vice versa): |
a0d0e21e LW |
6268 | |
6269 | require 'syscall.ph'; # may need to run h2ph | |
a3cb178b GS |
6270 | $s = "hi there\n"; |
6271 | syscall(&SYS_write, fileno(STDOUT), $s, length $s); | |
a0d0e21e | 6272 | |
5f05dabc | 6273 | Note that Perl supports passing of up to only 14 arguments to your system call, |
a0d0e21e LW |
6274 | which in practice should usually suffice. |
6275 | ||
fb73857a | 6276 | Syscall returns whatever value returned by the system call it calls. |
19799a22 | 6277 | If the system call fails, C<syscall> returns C<-1> and sets C<$!> (errno). |
7660c0ab | 6278 | Note that some system calls can legitimately return C<-1>. The proper |
fb73857a | 6279 | way to handle such calls is to assign C<$!=0;> before the call and |
7660c0ab | 6280 | check the value of C<$!> if syscall returns C<-1>. |
fb73857a | 6281 | |
6282 | There's a problem with C<syscall(&SYS_pipe)>: it returns the file | |
6283 | number of the read end of the pipe it creates. There is no way | |
b76cc8ba | 6284 | to retrieve the file number of the other end. You can avoid this |
19799a22 | 6285 | problem by using C<pipe> instead. |
fb73857a | 6286 | |
c07a80fd | 6287 | =item sysopen FILEHANDLE,FILENAME,MODE |
d74e8afc | 6288 | X<sysopen> |
c07a80fd | 6289 | |
6290 | =item sysopen FILEHANDLE,FILENAME,MODE,PERMS | |
6291 | ||
6292 | Opens the file whose filename is given by FILENAME, and associates it | |
6293 | with FILEHANDLE. If FILEHANDLE is an expression, its value is used as | |
6294 | the name of the real filehandle wanted. This function calls the | |
19799a22 | 6295 | underlying operating system's C<open> function with the parameters |
c07a80fd | 6296 | FILENAME, MODE, PERMS. |
6297 | ||
6298 | The possible values and flag bits of the MODE parameter are | |
6299 | system-dependent; they are available via the standard module C<Fcntl>. | |
ea2b5ef6 JH |
6300 | See the documentation of your operating system's C<open> to see which |
6301 | values and flag bits are available. You may combine several flags | |
6302 | using the C<|>-operator. | |
6303 | ||
6304 | Some of the most common values are C<O_RDONLY> for opening the file in | |
6305 | read-only mode, C<O_WRONLY> for opening the file in write-only mode, | |
c188b257 | 6306 | and C<O_RDWR> for opening the file in read-write mode. |
d74e8afc | 6307 | X<O_RDONLY> X<O_RDWR> X<O_WRONLY> |
ea2b5ef6 | 6308 | |
adf5897a DF |
6309 | For historical reasons, some values work on almost every system |
6310 | supported by perl: zero means read-only, one means write-only, and two | |
6311 | means read/write. We know that these values do I<not> work under | |
7c5ffed3 | 6312 | OS/390 & VM/ESA Unix and on the Macintosh; you probably don't want to |
4af147f6 | 6313 | use them in new code. |
c07a80fd | 6314 | |
19799a22 | 6315 | If the file named by FILENAME does not exist and the C<open> call creates |
7660c0ab | 6316 | it (typically because MODE includes the C<O_CREAT> flag), then the value of |
5a964f20 | 6317 | PERMS specifies the permissions of the newly created file. If you omit |
19799a22 | 6318 | the PERMS argument to C<sysopen>, Perl uses the octal value C<0666>. |
5a964f20 | 6319 | These permission values need to be in octal, and are modified by your |
0591cd52 | 6320 | process's current C<umask>. |
d74e8afc | 6321 | X<O_CREAT> |
0591cd52 | 6322 | |
ea2b5ef6 JH |
6323 | In many systems the C<O_EXCL> flag is available for opening files in |
6324 | exclusive mode. This is B<not> locking: exclusiveness means here that | |
c188b257 PF |
6325 | if the file already exists, sysopen() fails. C<O_EXCL> may not work |
6326 | on network filesystems, and has no effect unless the C<O_CREAT> flag | |
6327 | is set as well. Setting C<O_CREAT|O_EXCL> prevents the file from | |
6328 | being opened if it is a symbolic link. It does not protect against | |
6329 | symbolic links in the file's path. | |
d74e8afc | 6330 | X<O_EXCL> |
c188b257 PF |
6331 | |
6332 | Sometimes you may want to truncate an already-existing file. This | |
6333 | can be done using the C<O_TRUNC> flag. The behavior of | |
6334 | C<O_TRUNC> with C<O_RDONLY> is undefined. | |
d74e8afc | 6335 | X<O_TRUNC> |
ea2b5ef6 | 6336 | |
19799a22 | 6337 | You should seldom if ever use C<0644> as argument to C<sysopen>, because |
2b5ab1e7 TC |
6338 | that takes away the user's option to have a more permissive umask. |
6339 | Better to omit it. See the perlfunc(1) entry on C<umask> for more | |
6340 | on this. | |
c07a80fd | 6341 | |
4af147f6 CS |
6342 | Note that C<sysopen> depends on the fdopen() C library function. |
6343 | On many UNIX systems, fdopen() is known to fail when file descriptors | |
6344 | exceed a certain value, typically 255. If you need more file | |
6345 | descriptors than that, consider rebuilding Perl to use the C<sfio> | |
6346 | library, or perhaps using the POSIX::open() function. | |
6347 | ||
2b5ab1e7 | 6348 | See L<perlopentut> for a kinder, gentler explanation of opening files. |
28757baa | 6349 | |
a0d0e21e | 6350 | =item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET |
d74e8afc | 6351 | X<sysread> |
a0d0e21e LW |
6352 | |
6353 | =item sysread FILEHANDLE,SCALAR,LENGTH | |
6354 | ||
3874323d JH |
6355 | Attempts to read LENGTH bytes of data into variable SCALAR from the |
6356 | specified FILEHANDLE, using the system call read(2). It bypasses | |
6357 | buffered IO, so mixing this with other kinds of reads, C<print>, | |
6358 | C<write>, C<seek>, C<tell>, or C<eof> can cause confusion because the | |
6359 | perlio or stdio layers usually buffers data. Returns the number of | |
6360 | bytes actually read, C<0> at end of file, or undef if there was an | |
6361 | error (in the latter case C<$!> is also set). SCALAR will be grown or | |
6362 | shrunk so that the last byte actually read is the last byte of the | |
6363 | scalar after the read. | |
ff68c719 | 6364 | |
6365 | An OFFSET may be specified to place the read data at some place in the | |
6366 | string other than the beginning. A negative OFFSET specifies | |
9124316e JH |
6367 | placement at that many characters counting backwards from the end of |
6368 | the string. A positive OFFSET greater than the length of SCALAR | |
6369 | results in the string being padded to the required size with C<"\0"> | |
6370 | bytes before the result of the read is appended. | |
a0d0e21e | 6371 | |
2b5ab1e7 TC |
6372 | There is no syseof() function, which is ok, since eof() doesn't work |
6373 | very well on device files (like ttys) anyway. Use sysread() and check | |
19799a22 | 6374 | for a return value for 0 to decide whether you're done. |
2b5ab1e7 | 6375 | |
3874323d JH |
6376 | Note that if the filehandle has been marked as C<:utf8> Unicode |
6377 | characters are read instead of bytes (the LENGTH, OFFSET, and the | |
5eadf7c5 | 6378 | return value of sysread() are in Unicode characters). |
3874323d JH |
6379 | The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer. |
6380 | See L</binmode>, L</open>, and the C<open> pragma, L<open>. | |
6381 | ||
137443ea | 6382 | =item sysseek FILEHANDLE,POSITION,WHENCE |
d74e8afc | 6383 | X<sysseek> X<lseek> |
137443ea | 6384 | |
3874323d | 6385 | Sets FILEHANDLE's system position in bytes using the system call |
9124316e JH |
6386 | lseek(2). FILEHANDLE may be an expression whose value gives the name |
6387 | of the filehandle. The values for WHENCE are C<0> to set the new | |
6388 | position to POSITION, C<1> to set the it to the current position plus | |
6389 | POSITION, and C<2> to set it to EOF plus POSITION (typically | |
6390 | negative). | |
6391 | ||
6392 | Note the I<in bytes>: even if the filehandle has been set to operate | |
740d4bb2 JW |
6393 | on characters (for example by using the C<:encoding(utf8)> I/O layer), |
6394 | tell() will return byte offsets, not character offsets (because | |
6395 | implementing that would render sysseek() very slow). | |
9124316e | 6396 | |
3874323d | 6397 | sysseek() bypasses normal buffered IO, so mixing this with reads (other |
aaa270e5 | 6398 | than C<sysread>, for example C<< <> >> or read()) C<print>, C<write>, |
9124316e | 6399 | C<seek>, C<tell>, or C<eof> may cause confusion. |
86989e5d JH |
6400 | |
6401 | For WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>, | |
6402 | and C<SEEK_END> (start of the file, current position, end of the file) | |
6403 | from the Fcntl module. Use of the constants is also more portable | |
6404 | than relying on 0, 1, and 2. For example to define a "systell" function: | |
6405 | ||
554ad1fc | 6406 | use Fcntl 'SEEK_CUR'; |
86989e5d | 6407 | sub systell { sysseek($_[0], 0, SEEK_CUR) } |
8903cb82 | 6408 | |
6409 | Returns the new position, or the undefined value on failure. A position | |
19799a22 GS |
6410 | of zero is returned as the string C<"0 but true">; thus C<sysseek> returns |
6411 | true on success and false on failure, yet you can still easily determine | |
8903cb82 | 6412 | the new position. |
137443ea | 6413 | |
a0d0e21e | 6414 | =item system LIST |
d74e8afc | 6415 | X<system> X<shell> |
a0d0e21e | 6416 | |
8bf3b016 GS |
6417 | =item system PROGRAM LIST |
6418 | ||
19799a22 GS |
6419 | Does exactly the same thing as C<exec LIST>, except that a fork is |
6420 | done first, and the parent process waits for the child process to | |
6421 | complete. Note that argument processing varies depending on the | |
6422 | number of arguments. If there is more than one argument in LIST, | |
6423 | or if LIST is an array with more than one value, starts the program | |
6424 | given by the first element of the list with arguments given by the | |
6425 | rest of the list. If there is only one scalar argument, the argument | |
6426 | is checked for shell metacharacters, and if there are any, the | |
6427 | entire argument is passed to the system's command shell for parsing | |
6428 | (this is C</bin/sh -c> on Unix platforms, but varies on other | |
6429 | platforms). If there are no shell metacharacters in the argument, | |
6430 | it is split into words and passed directly to C<execvp>, which is | |
6431 | more efficient. | |
6432 | ||
0f897271 GS |
6433 | Beginning with v5.6.0, Perl will attempt to flush all files opened for |
6434 | output before any operation that may do a fork, but this may not be | |
6435 | supported on some platforms (see L<perlport>). To be safe, you may need | |
6436 | to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method | |
6437 | of C<IO::Handle> on any open handles. | |
a2008d6d | 6438 | |
9d6eb86e | 6439 | The return value is the exit status of the program as returned by the |
25379e53 RGS |
6440 | C<wait> call. To get the actual exit value, shift right by eight (see |
6441 | below). See also L</exec>. This is I<not> what you want to use to capture | |
54310121 | 6442 | the output from a command, for that you should use merely backticks or |
d5a9bfb0 | 6443 | C<qx//>, as described in L<perlop/"`STRING`">. Return value of -1 |
25379e53 RGS |
6444 | indicates a failure to start the program or an error of the wait(2) system |
6445 | call (inspect $! for the reason). | |
a0d0e21e | 6446 | |
19799a22 GS |
6447 | Like C<exec>, C<system> allows you to lie to a program about its name if |
6448 | you use the C<system PROGRAM LIST> syntax. Again, see L</exec>. | |
8bf3b016 | 6449 | |
4c2e8b59 BD |
6450 | Since C<SIGINT> and C<SIGQUIT> are ignored during the execution of |
6451 | C<system>, if you expect your program to terminate on receipt of these | |
6452 | signals you will need to arrange to do so yourself based on the return | |
6453 | value. | |
28757baa | 6454 | |
6455 | @args = ("command", "arg1", "arg2"); | |
54310121 | 6456 | system(@args) == 0 |
6457 | or die "system @args failed: $?" | |
28757baa | 6458 | |
5a964f20 TC |
6459 | You can check all the failure possibilities by inspecting |
6460 | C<$?> like this: | |
28757baa | 6461 | |
4ef107a6 DM |
6462 | if ($? == -1) { |
6463 | print "failed to execute: $!\n"; | |
6464 | } | |
6465 | elsif ($? & 127) { | |
6466 | printf "child died with signal %d, %s coredump\n", | |
6467 | ($? & 127), ($? & 128) ? 'with' : 'without'; | |
6468 | } | |
6469 | else { | |
6470 | printf "child exited with value %d\n", $? >> 8; | |
6471 | } | |
6472 | ||
e5218da5 GA |
6473 | Alternatively you might inspect the value of C<${^CHILD_ERROR_NATIVE}> |
6474 | with the W*() calls of the POSIX extension. | |
9d6eb86e | 6475 | |
c8db1d39 TC |
6476 | When the arguments get executed via the system shell, results |
6477 | and return codes will be subject to its quirks and capabilities. | |
6478 | See L<perlop/"`STRING`"> and L</exec> for details. | |
bb32b41a | 6479 | |
a0d0e21e | 6480 | =item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET |
d74e8afc | 6481 | X<syswrite> |
a0d0e21e LW |
6482 | |
6483 | =item syswrite FILEHANDLE,SCALAR,LENGTH | |
6484 | ||
145d37e2 GA |
6485 | =item syswrite FILEHANDLE,SCALAR |
6486 | ||
3874323d JH |
6487 | Attempts to write LENGTH bytes of data from variable SCALAR to the |
6488 | specified FILEHANDLE, using the system call write(2). If LENGTH is | |
6489 | not specified, writes whole SCALAR. It bypasses buffered IO, so | |
9124316e | 6490 | mixing this with reads (other than C<sysread())>, C<print>, C<write>, |
3874323d JH |
6491 | C<seek>, C<tell>, or C<eof> may cause confusion because the perlio and |
6492 | stdio layers usually buffers data. Returns the number of bytes | |
6493 | actually written, or C<undef> if there was an error (in this case the | |
6494 | errno variable C<$!> is also set). If the LENGTH is greater than the | |
6495 | available data in the SCALAR after the OFFSET, only as much data as is | |
6496 | available will be written. | |
ff68c719 | 6497 | |
6498 | An OFFSET may be specified to write the data from some part of the | |
6499 | string other than the beginning. A negative OFFSET specifies writing | |
9124316e JH |
6500 | that many characters counting backwards from the end of the string. |
6501 | In the case the SCALAR is empty you can use OFFSET but only zero offset. | |
6502 | ||
1d714267 JH |
6503 | Note that if the filehandle has been marked as C<:utf8>, Unicode |
6504 | characters are written instead of bytes (the LENGTH, OFFSET, and the | |
6505 | return value of syswrite() are in UTF-8 encoded Unicode characters). | |
3874323d JH |
6506 | The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer. |
6507 | See L</binmode>, L</open>, and the C<open> pragma, L<open>. | |
a0d0e21e LW |
6508 | |
6509 | =item tell FILEHANDLE | |
d74e8afc | 6510 | X<tell> |
a0d0e21e LW |
6511 | |
6512 | =item tell | |
6513 | ||
9124316e JH |
6514 | Returns the current position I<in bytes> for FILEHANDLE, or -1 on |
6515 | error. FILEHANDLE may be an expression whose value gives the name of | |
6516 | the actual filehandle. If FILEHANDLE is omitted, assumes the file | |
6517 | last read. | |
6518 | ||
6519 | Note the I<in bytes>: even if the filehandle has been set to | |
740d4bb2 JW |
6520 | operate on characters (for example by using the C<:encoding(utf8)> open |
6521 | layer), tell() will return byte offsets, not character offsets (because | |
6522 | that would render seek() and tell() rather slow). | |
2b5ab1e7 | 6523 | |
cfd73201 JH |
6524 | The return value of tell() for the standard streams like the STDIN |
6525 | depends on the operating system: it may return -1 or something else. | |
6526 | tell() on pipes, fifos, and sockets usually returns -1. | |
6527 | ||
19799a22 | 6528 | There is no C<systell> function. Use C<sysseek(FH, 0, 1)> for that. |
a0d0e21e | 6529 | |
59c9df15 NIS |
6530 | Do not use tell() (or other buffered I/O operations) on a file handle |
6531 | that has been manipulated by sysread(), syswrite() or sysseek(). | |
6532 | Those functions ignore the buffering, while tell() does not. | |
9124316e | 6533 | |
a0d0e21e | 6534 | =item telldir DIRHANDLE |
d74e8afc | 6535 | X<telldir> |
a0d0e21e | 6536 | |
19799a22 GS |
6537 | Returns the current position of the C<readdir> routines on DIRHANDLE. |
6538 | Value may be given to C<seekdir> to access a particular location in a | |
cf264981 SP |
6539 | directory. C<telldir> has the same caveats about possible directory |
6540 | compaction as the corresponding system library routine. | |
a0d0e21e | 6541 | |
4633a7c4 | 6542 | =item tie VARIABLE,CLASSNAME,LIST |
d74e8afc | 6543 | X<tie> |
a0d0e21e | 6544 | |
4633a7c4 LW |
6545 | This function binds a variable to a package class that will provide the |
6546 | implementation for the variable. VARIABLE is the name of the variable | |
6547 | to be enchanted. CLASSNAME is the name of a class implementing objects | |
19799a22 | 6548 | of correct type. Any additional arguments are passed to the C<new> |
8a059744 GS |
6549 | method of the class (meaning C<TIESCALAR>, C<TIEHANDLE>, C<TIEARRAY>, |
6550 | or C<TIEHASH>). Typically these are arguments such as might be passed | |
19799a22 GS |
6551 | to the C<dbm_open()> function of C. The object returned by the C<new> |
6552 | method is also returned by the C<tie> function, which would be useful | |
8a059744 | 6553 | if you want to access other methods in CLASSNAME. |
a0d0e21e | 6554 | |
19799a22 | 6555 | Note that functions such as C<keys> and C<values> may return huge lists |
1d2dff63 | 6556 | when used on large objects, like DBM files. You may prefer to use the |
19799a22 | 6557 | C<each> function to iterate over such. Example: |
a0d0e21e LW |
6558 | |
6559 | # print out history file offsets | |
4633a7c4 | 6560 | use NDBM_File; |
da0045b7 | 6561 | tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0); |
a0d0e21e LW |
6562 | while (($key,$val) = each %HIST) { |
6563 | print $key, ' = ', unpack('L',$val), "\n"; | |
6564 | } | |
6565 | untie(%HIST); | |
6566 | ||
aa689395 | 6567 | A class implementing a hash should have the following methods: |
a0d0e21e | 6568 | |
4633a7c4 | 6569 | TIEHASH classname, LIST |
a0d0e21e LW |
6570 | FETCH this, key |
6571 | STORE this, key, value | |
6572 | DELETE this, key | |
8a059744 | 6573 | CLEAR this |
a0d0e21e LW |
6574 | EXISTS this, key |
6575 | FIRSTKEY this | |
6576 | NEXTKEY this, lastkey | |
a3bcc51e | 6577 | SCALAR this |
8a059744 | 6578 | DESTROY this |
d7da42b7 | 6579 | UNTIE this |
a0d0e21e | 6580 | |
4633a7c4 | 6581 | A class implementing an ordinary array should have the following methods: |
a0d0e21e | 6582 | |
4633a7c4 | 6583 | TIEARRAY classname, LIST |
a0d0e21e LW |
6584 | FETCH this, key |
6585 | STORE this, key, value | |
8a059744 GS |
6586 | FETCHSIZE this |
6587 | STORESIZE this, count | |
6588 | CLEAR this | |
6589 | PUSH this, LIST | |
6590 | POP this | |
6591 | SHIFT this | |
6592 | UNSHIFT this, LIST | |
6593 | SPLICE this, offset, length, LIST | |
6594 | EXTEND this, count | |
6595 | DESTROY this | |
d7da42b7 | 6596 | UNTIE this |
8a059744 GS |
6597 | |
6598 | A class implementing a file handle should have the following methods: | |
6599 | ||
6600 | TIEHANDLE classname, LIST | |
6601 | READ this, scalar, length, offset | |
6602 | READLINE this | |
6603 | GETC this | |
6604 | WRITE this, scalar, length, offset | |
6605 | PRINT this, LIST | |
6606 | PRINTF this, format, LIST | |
e08f2115 GA |
6607 | BINMODE this |
6608 | EOF this | |
6609 | FILENO this | |
6610 | SEEK this, position, whence | |
6611 | TELL this | |
6612 | OPEN this, mode, LIST | |
8a059744 GS |
6613 | CLOSE this |
6614 | DESTROY this | |
d7da42b7 | 6615 | UNTIE this |
a0d0e21e | 6616 | |
4633a7c4 | 6617 | A class implementing a scalar should have the following methods: |
a0d0e21e | 6618 | |
4633a7c4 | 6619 | TIESCALAR classname, LIST |
54310121 | 6620 | FETCH this, |
a0d0e21e | 6621 | STORE this, value |
8a059744 | 6622 | DESTROY this |
d7da42b7 | 6623 | UNTIE this |
8a059744 GS |
6624 | |
6625 | Not all methods indicated above need be implemented. See L<perltie>, | |
2b5ab1e7 | 6626 | L<Tie::Hash>, L<Tie::Array>, L<Tie::Scalar>, and L<Tie::Handle>. |
a0d0e21e | 6627 | |
19799a22 | 6628 | Unlike C<dbmopen>, the C<tie> function will not use or require a module |
4633a7c4 | 6629 | for you--you need to do that explicitly yourself. See L<DB_File> |
19799a22 | 6630 | or the F<Config> module for interesting C<tie> implementations. |
4633a7c4 | 6631 | |
b687b08b | 6632 | For further details see L<perltie>, L<"tied VARIABLE">. |
cc6b7395 | 6633 | |
f3cbc334 | 6634 | =item tied VARIABLE |
d74e8afc | 6635 | X<tied> |
f3cbc334 RS |
6636 | |
6637 | Returns a reference to the object underlying VARIABLE (the same value | |
19799a22 | 6638 | that was originally returned by the C<tie> call that bound the variable |
f3cbc334 RS |
6639 | to a package.) Returns the undefined value if VARIABLE isn't tied to a |
6640 | package. | |
6641 | ||
a0d0e21e | 6642 | =item time |
d74e8afc | 6643 | X<time> X<epoch> |
a0d0e21e | 6644 | |
da0045b7 | 6645 | Returns the number of non-leap seconds since whatever time the system |
ef4d88db NC |
6646 | considers to be the epoch, suitable for feeding to C<gmtime> and |
6647 | C<localtime>. On most systems the epoch is 00:00:00 UTC, January 1, 1970; | |
6648 | a prominent exception being Mac OS Classic which uses 00:00:00, January 1, | |
6649 | 1904 in the current local time zone for its epoch. | |
a0d0e21e | 6650 | |
68f8bed4 | 6651 | For measuring time in better granularity than one second, |
435fbc73 | 6652 | you may use either the L<Time::HiRes> module (from CPAN, and starting from |
c5f9c75a RGS |
6653 | Perl 5.8 part of the standard distribution), or if you have |
6654 | gettimeofday(2), you may be able to use the C<syscall> interface of Perl. | |
6655 | See L<perlfaq8> for details. | |
68f8bed4 | 6656 | |
435fbc73 GS |
6657 | For date and time processing look at the many related modules on CPAN. |
6658 | For a comprehensive date and time representation look at the | |
6659 | L<DateTime> module. | |
6660 | ||
a0d0e21e | 6661 | =item times |
d74e8afc | 6662 | X<times> |
a0d0e21e | 6663 | |
1d2dff63 | 6664 | Returns a four-element list giving the user and system times, in |
a0d0e21e LW |
6665 | seconds, for this process and the children of this process. |
6666 | ||
6667 | ($user,$system,$cuser,$csystem) = times; | |
6668 | ||
dc19f4fb MJD |
6669 | In scalar context, C<times> returns C<$user>. |
6670 | ||
2a958fe2 HS |
6671 | Note that times for children are included only after they terminate. |
6672 | ||
a0d0e21e LW |
6673 | =item tr/// |
6674 | ||
19799a22 | 6675 | The transliteration operator. Same as C<y///>. See L<perlop>. |
a0d0e21e LW |
6676 | |
6677 | =item truncate FILEHANDLE,LENGTH | |
d74e8afc | 6678 | X<truncate> |
a0d0e21e LW |
6679 | |
6680 | =item truncate EXPR,LENGTH | |
6681 | ||
6682 | Truncates the file opened on FILEHANDLE, or named by EXPR, to the | |
6683 | specified length. Produces a fatal error if truncate isn't implemented | |
19799a22 | 6684 | on your system. Returns true if successful, the undefined value |
a3cb178b | 6685 | otherwise. |
a0d0e21e | 6686 | |
90ddc76f MS |
6687 | The behavior is undefined if LENGTH is greater than the length of the |
6688 | file. | |
6689 | ||
8577f58c RK |
6690 | The position in the file of FILEHANDLE is left unchanged. You may want to |
6691 | call L<seek> before writing to the file. | |
6692 | ||
a0d0e21e | 6693 | =item uc EXPR |
d74e8afc | 6694 | X<uc> X<uppercase> X<toupper> |
a0d0e21e | 6695 | |
54310121 | 6696 | =item uc |
bbce6d69 | 6697 | |
a0d0e21e | 6698 | Returns an uppercased version of EXPR. This is the internal function |
ad0029c4 JH |
6699 | implementing the C<\U> escape in double-quoted strings. Respects |
6700 | current LC_CTYPE locale if C<use locale> in force. See L<perllocale> | |
983ffd37 JH |
6701 | and L<perlunicode> for more details about locale and Unicode support. |
6702 | It does not attempt to do titlecase mapping on initial letters. See | |
6703 | C<ucfirst> for that. | |
a0d0e21e | 6704 | |
7660c0ab | 6705 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 6706 | |
a0d0e21e | 6707 | =item ucfirst EXPR |
d74e8afc | 6708 | X<ucfirst> X<uppercase> |
a0d0e21e | 6709 | |
54310121 | 6710 | =item ucfirst |
bbce6d69 | 6711 | |
ad0029c4 JH |
6712 | Returns the value of EXPR with the first character in uppercase |
6713 | (titlecase in Unicode). This is the internal function implementing | |
6714 | the C<\u> escape in double-quoted strings. Respects current LC_CTYPE | |
983ffd37 JH |
6715 | locale if C<use locale> in force. See L<perllocale> and L<perlunicode> |
6716 | for more details about locale and Unicode support. | |
a0d0e21e | 6717 | |
7660c0ab | 6718 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 6719 | |
a0d0e21e | 6720 | =item umask EXPR |
d74e8afc | 6721 | X<umask> |
a0d0e21e LW |
6722 | |
6723 | =item umask | |
6724 | ||
2f9daede | 6725 | Sets the umask for the process to EXPR and returns the previous value. |
eec2d3df GS |
6726 | If EXPR is omitted, merely returns the current umask. |
6727 | ||
0591cd52 NT |
6728 | The Unix permission C<rwxr-x---> is represented as three sets of three |
6729 | bits, or three octal digits: C<0750> (the leading 0 indicates octal | |
b5a41e52 | 6730 | and isn't one of the digits). The C<umask> value is such a number |
0591cd52 NT |
6731 | representing disabled permissions bits. The permission (or "mode") |
6732 | values you pass C<mkdir> or C<sysopen> are modified by your umask, so | |
6733 | even if you tell C<sysopen> to create a file with permissions C<0777>, | |
6734 | if your umask is C<0022> then the file will actually be created with | |
6735 | permissions C<0755>. If your C<umask> were C<0027> (group can't | |
6736 | write; others can't read, write, or execute), then passing | |
19799a22 | 6737 | C<sysopen> C<0666> would create a file with mode C<0640> (C<0666 &~ |
0591cd52 NT |
6738 | 027> is C<0640>). |
6739 | ||
6740 | Here's some advice: supply a creation mode of C<0666> for regular | |
19799a22 GS |
6741 | files (in C<sysopen>) and one of C<0777> for directories (in |
6742 | C<mkdir>) and executable files. This gives users the freedom of | |
0591cd52 NT |
6743 | choice: if they want protected files, they might choose process umasks |
6744 | of C<022>, C<027>, or even the particularly antisocial mask of C<077>. | |
6745 | Programs should rarely if ever make policy decisions better left to | |
6746 | the user. The exception to this is when writing files that should be | |
6747 | kept private: mail files, web browser cookies, I<.rhosts> files, and | |
6748 | so on. | |
6749 | ||
f86cebdf | 6750 | If umask(2) is not implemented on your system and you are trying to |
eec2d3df | 6751 | restrict access for I<yourself> (i.e., (EXPR & 0700) > 0), produces a |
f86cebdf | 6752 | fatal error at run time. If umask(2) is not implemented and you are |
eec2d3df GS |
6753 | not trying to restrict access for yourself, returns C<undef>. |
6754 | ||
6755 | Remember that a umask is a number, usually given in octal; it is I<not> a | |
6756 | string of octal digits. See also L</oct>, if all you have is a string. | |
a0d0e21e LW |
6757 | |
6758 | =item undef EXPR | |
d74e8afc | 6759 | X<undef> X<undefine> |
a0d0e21e LW |
6760 | |
6761 | =item undef | |
6762 | ||
54310121 | 6763 | Undefines the value of EXPR, which must be an lvalue. Use only on a |
19799a22 | 6764 | scalar value, an array (using C<@>), a hash (using C<%>), a subroutine |
92d1d699 | 6765 | (using C<&>), or a typeglob (using C<*>). (Saying C<undef $hash{$key}> |
20408e3c GS |
6766 | will probably not do what you expect on most predefined variables or |
6767 | DBM list values, so don't do that; see L<delete>.) Always returns the | |
6768 | undefined value. You can omit the EXPR, in which case nothing is | |
6769 | undefined, but you still get an undefined value that you could, for | |
6770 | instance, return from a subroutine, assign to a variable or pass as a | |
6771 | parameter. Examples: | |
a0d0e21e LW |
6772 | |
6773 | undef $foo; | |
f86cebdf | 6774 | undef $bar{'blurfl'}; # Compare to: delete $bar{'blurfl'}; |
a0d0e21e | 6775 | undef @ary; |
aa689395 | 6776 | undef %hash; |
a0d0e21e | 6777 | undef &mysub; |
20408e3c | 6778 | undef *xyz; # destroys $xyz, @xyz, %xyz, &xyz, etc. |
54310121 | 6779 | return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it; |
2f9daede TP |
6780 | select undef, undef, undef, 0.25; |
6781 | ($a, $b, undef, $c) = &foo; # Ignore third value returned | |
a0d0e21e | 6782 | |
5a964f20 TC |
6783 | Note that this is a unary operator, not a list operator. |
6784 | ||
a0d0e21e | 6785 | =item unlink LIST |
dd184578 | 6786 | X<unlink> X<delete> X<remove> X<rm> X<del> |
a0d0e21e | 6787 | |
54310121 | 6788 | =item unlink |
bbce6d69 | 6789 | |
a0d0e21e LW |
6790 | Deletes a list of files. Returns the number of files successfully |
6791 | deleted. | |
6792 | ||
6793 | $cnt = unlink 'a', 'b', 'c'; | |
6794 | unlink @goners; | |
6795 | unlink <*.bak>; | |
6796 | ||
c69adce3 SP |
6797 | Note: C<unlink> will not attempt to delete directories unless you are superuser |
6798 | and the B<-U> flag is supplied to Perl. Even if these conditions are | |
a0d0e21e | 6799 | met, be warned that unlinking a directory can inflict damage on your |
c69adce3 SP |
6800 | filesystem. Finally, using C<unlink> on directories is not supported on |
6801 | many operating systems. Use C<rmdir> instead. | |
a0d0e21e | 6802 | |
7660c0ab | 6803 | If LIST is omitted, uses C<$_>. |
bbce6d69 | 6804 | |
a0d0e21e | 6805 | =item unpack TEMPLATE,EXPR |
d74e8afc | 6806 | X<unpack> |
a0d0e21e | 6807 | |
13dcffc6 CS |
6808 | =item unpack TEMPLATE |
6809 | ||
19799a22 | 6810 | C<unpack> does the reverse of C<pack>: it takes a string |
2b6c5635 | 6811 | and expands it out into a list of values. |
19799a22 | 6812 | (In scalar context, it returns merely the first value produced.) |
2b6c5635 | 6813 | |
13dcffc6 CS |
6814 | If EXPR is omitted, unpacks the C<$_> string. |
6815 | ||
2b6c5635 GS |
6816 | The string is broken into chunks described by the TEMPLATE. Each chunk |
6817 | is converted separately to a value. Typically, either the string is a result | |
f337b084 | 6818 | of C<pack>, or the characters of the string represent a C structure of some |
2b6c5635 GS |
6819 | kind. |
6820 | ||
19799a22 | 6821 | The TEMPLATE has the same format as in the C<pack> function. |
a0d0e21e LW |
6822 | Here's a subroutine that does substring: |
6823 | ||
6824 | sub substr { | |
5a964f20 | 6825 | my($what,$where,$howmuch) = @_; |
a0d0e21e LW |
6826 | unpack("x$where a$howmuch", $what); |
6827 | } | |
6828 | ||
6829 | and then there's | |
6830 | ||
f337b084 | 6831 | sub ordinal { unpack("W",$_[0]); } # same as ord() |
a0d0e21e | 6832 | |
2b6c5635 | 6833 | In addition to fields allowed in pack(), you may prefix a field with |
61eff3bc JH |
6834 | a %<number> to indicate that |
6835 | you want a <number>-bit checksum of the items instead of the items | |
2b6c5635 GS |
6836 | themselves. Default is a 16-bit checksum. Checksum is calculated by |
6837 | summing numeric values of expanded values (for string fields the sum of | |
6838 | C<ord($char)> is taken, for bit fields the sum of zeroes and ones). | |
6839 | ||
6840 | For example, the following | |
a0d0e21e LW |
6841 | computes the same number as the System V sum program: |
6842 | ||
19799a22 GS |
6843 | $checksum = do { |
6844 | local $/; # slurp! | |
f337b084 | 6845 | unpack("%32W*",<>) % 65535; |
19799a22 | 6846 | }; |
a0d0e21e LW |
6847 | |
6848 | The following efficiently counts the number of set bits in a bit vector: | |
6849 | ||
6850 | $setbits = unpack("%32b*", $selectmask); | |
6851 | ||
951ba7fe | 6852 | The C<p> and C<P> formats should be used with care. Since Perl |
3160c391 GS |
6853 | has no way of checking whether the value passed to C<unpack()> |
6854 | corresponds to a valid memory location, passing a pointer value that's | |
6855 | not known to be valid is likely to have disastrous consequences. | |
6856 | ||
49704364 WL |
6857 | If there are more pack codes or if the repeat count of a field or a group |
6858 | is larger than what the remainder of the input string allows, the result | |
6859 | is not well defined: in some cases, the repeat count is decreased, or | |
6860 | C<unpack()> will produce null strings or zeroes, or terminate with an | |
6861 | error. If the input string is longer than one described by the TEMPLATE, | |
6862 | the rest is ignored. | |
2b6c5635 | 6863 | |
851646ae | 6864 | See L</pack> for more examples and notes. |
5a929a98 | 6865 | |
98293880 | 6866 | =item untie VARIABLE |
d74e8afc | 6867 | X<untie> |
98293880 | 6868 | |
19799a22 | 6869 | Breaks the binding between a variable and a package. (See C<tie>.) |
1188453a | 6870 | Has no effect if the variable is not tied. |
98293880 | 6871 | |
a0d0e21e | 6872 | =item unshift ARRAY,LIST |
d74e8afc | 6873 | X<unshift> |
a0d0e21e | 6874 | |
19799a22 | 6875 | Does the opposite of a C<shift>. Or the opposite of a C<push>, |
a0d0e21e LW |
6876 | depending on how you look at it. Prepends list to the front of the |
6877 | array, and returns the new number of elements in the array. | |
6878 | ||
76e4c2bb | 6879 | unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/; |
a0d0e21e LW |
6880 | |
6881 | Note the LIST is prepended whole, not one element at a time, so the | |
19799a22 | 6882 | prepended elements stay in the same order. Use C<reverse> to do the |
a0d0e21e LW |
6883 | reverse. |
6884 | ||
f6c8478c | 6885 | =item use Module VERSION LIST |
d74e8afc | 6886 | X<use> X<module> X<import> |
f6c8478c GS |
6887 | |
6888 | =item use Module VERSION | |
6889 | ||
a0d0e21e LW |
6890 | =item use Module LIST |
6891 | ||
6892 | =item use Module | |
6893 | ||
da0045b7 | 6894 | =item use VERSION |
6895 | ||
a0d0e21e LW |
6896 | Imports some semantics into the current package from the named module, |
6897 | generally by aliasing certain subroutine or variable names into your | |
6898 | package. It is exactly equivalent to | |
6899 | ||
6d9d0573 | 6900 | BEGIN { require Module; Module->import( LIST ); } |
a0d0e21e | 6901 | |
54310121 | 6902 | except that Module I<must> be a bareword. |
da0045b7 | 6903 | |
c986422f RGS |
6904 | In the peculiar C<use VERSION> form, VERSION may be either a numeric |
6905 | argument such as 5.006, which will be compared to C<$]>, or a literal of | |
6906 | the form v5.6.1, which will be compared to C<$^V> (aka $PERL_VERSION). A | |
6907 | fatal error is produced if VERSION is greater than the version of the | |
6908 | current Perl interpreter; Perl will not attempt to parse the rest of the | |
6909 | file. Compare with L</require>, which can do a similar check at run time. | |
6910 | Symmetrically, C<no VERSION> allows you to specify that you want a version | |
6911 | of perl older than the specified one. | |
3b825e41 RK |
6912 | |
6913 | Specifying VERSION as a literal of the form v5.6.1 should generally be | |
6914 | avoided, because it leads to misleading error messages under earlier | |
2e8342de RGS |
6915 | versions of Perl (that is, prior to 5.6.0) that do not support this |
6916 | syntax. The equivalent numeric version should be used instead. | |
fbc891ce | 6917 | |
dd629d5b GS |
6918 | use v5.6.1; # compile time version check |
6919 | use 5.6.1; # ditto | |
3b825e41 | 6920 | use 5.006_001; # ditto; preferred for backwards compatibility |
16070b82 GS |
6921 | |
6922 | This is often useful if you need to check the current Perl version before | |
2e8342de RGS |
6923 | C<use>ing library modules that won't work with older versions of Perl. |
6924 | (We try not to do this more than we have to.) | |
da0045b7 | 6925 | |
c986422f RGS |
6926 | Also, if the specified perl version is greater than or equal to 5.9.5, |
6927 | C<use VERSION> will also load the C<feature> pragma and enable all | |
6928 | features available in the requested version. See L<feature>. | |
7dfde25d | 6929 | |
19799a22 | 6930 | The C<BEGIN> forces the C<require> and C<import> to happen at compile time. The |
7660c0ab | 6931 | C<require> makes sure the module is loaded into memory if it hasn't been |
19799a22 GS |
6932 | yet. The C<import> is not a builtin--it's just an ordinary static method |
6933 | call into the C<Module> package to tell the module to import the list of | |
a0d0e21e | 6934 | features back into the current package. The module can implement its |
19799a22 GS |
6935 | C<import> method any way it likes, though most modules just choose to |
6936 | derive their C<import> method via inheritance from the C<Exporter> class that | |
6937 | is defined in the C<Exporter> module. See L<Exporter>. If no C<import> | |
593b9c14 YST |
6938 | method can be found then the call is skipped, even if there is an AUTOLOAD |
6939 | method. | |
cb1a09d0 | 6940 | |
31686daf JP |
6941 | If you do not want to call the package's C<import> method (for instance, |
6942 | to stop your namespace from being altered), explicitly supply the empty list: | |
cb1a09d0 AD |
6943 | |
6944 | use Module (); | |
6945 | ||
6946 | That is exactly equivalent to | |
6947 | ||
5a964f20 | 6948 | BEGIN { require Module } |
a0d0e21e | 6949 | |
da0045b7 | 6950 | If the VERSION argument is present between Module and LIST, then the |
71be2cbc | 6951 | C<use> will call the VERSION method in class Module with the given |
6952 | version as an argument. The default VERSION method, inherited from | |
44dcb63b | 6953 | the UNIVERSAL class, croaks if the given version is larger than the |
b76cc8ba | 6954 | value of the variable C<$Module::VERSION>. |
f6c8478c GS |
6955 | |
6956 | Again, there is a distinction between omitting LIST (C<import> called | |
6957 | with no arguments) and an explicit empty LIST C<()> (C<import> not | |
6958 | called). Note that there is no comma after VERSION! | |
da0045b7 | 6959 | |
a0d0e21e LW |
6960 | Because this is a wide-open interface, pragmas (compiler directives) |
6961 | are also implemented this way. Currently implemented pragmas are: | |
6962 | ||
f3798619 | 6963 | use constant; |
4633a7c4 | 6964 | use diagnostics; |
f3798619 | 6965 | use integer; |
4438c4b7 JH |
6966 | use sigtrap qw(SEGV BUS); |
6967 | use strict qw(subs vars refs); | |
6968 | use subs qw(afunc blurfl); | |
6969 | use warnings qw(all); | |
58c7fc7c | 6970 | use sort qw(stable _quicksort _mergesort); |
a0d0e21e | 6971 | |
19799a22 | 6972 | Some of these pseudo-modules import semantics into the current |
5a964f20 TC |
6973 | block scope (like C<strict> or C<integer>, unlike ordinary modules, |
6974 | which import symbols into the current package (which are effective | |
6975 | through the end of the file). | |
a0d0e21e | 6976 | |
19799a22 GS |
6977 | There's a corresponding C<no> command that unimports meanings imported |
6978 | by C<use>, i.e., it calls C<unimport Module LIST> instead of C<import>. | |
593b9c14 YST |
6979 | It behaves exactly as C<import> does with respect to VERSION, an |
6980 | omitted LIST, empty LIST, or no unimport method being found. | |
a0d0e21e LW |
6981 | |
6982 | no integer; | |
6983 | no strict 'refs'; | |
4438c4b7 | 6984 | no warnings; |
a0d0e21e | 6985 | |
ac634a9a | 6986 | See L<perlmodlib> for a list of standard modules and pragmas. See L<perlrun> |
31686daf JP |
6987 | for the C<-M> and C<-m> command-line options to perl that give C<use> |
6988 | functionality from the command-line. | |
a0d0e21e LW |
6989 | |
6990 | =item utime LIST | |
d74e8afc | 6991 | X<utime> |
a0d0e21e LW |
6992 | |
6993 | Changes the access and modification times on each file of a list of | |
6994 | files. The first two elements of the list must be the NUMERICAL access | |
6995 | and modification times, in that order. Returns the number of files | |
46cdf678 | 6996 | successfully changed. The inode change time of each file is set |
4bc2a53d | 6997 | to the current time. For example, this code has the same effect as the |
a4142048 WL |
6998 | Unix touch(1) command when the files I<already exist> and belong to |
6999 | the user running the program: | |
a0d0e21e LW |
7000 | |
7001 | #!/usr/bin/perl | |
2c21a326 GA |
7002 | $atime = $mtime = time; |
7003 | utime $atime, $mtime, @ARGV; | |
4bc2a53d CW |
7004 | |
7005 | Since perl 5.7.2, if the first two elements of the list are C<undef>, then | |
7006 | the utime(2) function in the C library will be called with a null second | |
7007 | argument. On most systems, this will set the file's access and | |
7008 | modification times to the current time (i.e. equivalent to the example | |
a4142048 WL |
7009 | above) and will even work on other users' files where you have write |
7010 | permission: | |
c6f7b413 RS |
7011 | |
7012 | utime undef, undef, @ARGV; | |
7013 | ||
2c21a326 GA |
7014 | Under NFS this will use the time of the NFS server, not the time of |
7015 | the local machine. If there is a time synchronization problem, the | |
7016 | NFS server and local machine will have different times. The Unix | |
7017 | touch(1) command will in fact normally use this form instead of the | |
7018 | one shown in the first example. | |
7019 | ||
7020 | Note that only passing one of the first two elements as C<undef> will | |
7021 | be equivalent of passing it as 0 and will not have the same effect as | |
7022 | described when they are both C<undef>. This case will also trigger an | |
7023 | uninitialized warning. | |
7024 | ||
e96b369d GA |
7025 | On systems that support futimes, you might pass file handles among the |
7026 | files. On systems that don't support futimes, passing file handles | |
345da378 GA |
7027 | produces a fatal error at run time. The file handles must be passed |
7028 | as globs or references to be recognized. Barewords are considered | |
7029 | file names. | |
e96b369d | 7030 | |
aa689395 | 7031 | =item values HASH |
d74e8afc | 7032 | X<values> |
a0d0e21e | 7033 | |
aeedbbed NC |
7034 | =item values ARRAY |
7035 | ||
7036 | Returns a list consisting of all the values of the named hash, or the values | |
7037 | of an array. (In a scalar context, returns the number of values.) | |
504f80c1 JH |
7038 | |
7039 | The values are returned in an apparently random order. The actual | |
7040 | random order is subject to change in future versions of perl, but it | |
7041 | is guaranteed to be the same order as either the C<keys> or C<each> | |
4546b9e6 JH |
7042 | function would produce on the same (unmodified) hash. Since Perl |
7043 | 5.8.1 the ordering is different even between different runs of Perl | |
7044 | for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">). | |
504f80c1 | 7045 | |
aeedbbed NC |
7046 | As a side effect, calling values() resets the HASH or ARRAY's internal |
7047 | iterator, | |
2f65b2f0 | 7048 | see L</each>. (In particular, calling values() in void context resets |
aeedbbed NC |
7049 | the iterator with no other overhead. Apart from resetting the iterator, |
7050 | C<values @array> in list context is no different to plain C<@array>. | |
7051 | We recommend that you use void context C<keys @array> for this, but reasoned | |
7052 | that it taking C<values @array> out would require more documentation than | |
7053 | leaving it in.) | |
7054 | ||
ab192400 | 7055 | |
8ea1e5d4 GS |
7056 | Note that the values are not copied, which means modifying them will |
7057 | modify the contents of the hash: | |
2b5ab1e7 | 7058 | |
8ea1e5d4 GS |
7059 | for (values %hash) { s/foo/bar/g } # modifies %hash values |
7060 | for (@hash{keys %hash}) { s/foo/bar/g } # same | |
2b5ab1e7 | 7061 | |
19799a22 | 7062 | See also C<keys>, C<each>, and C<sort>. |
a0d0e21e LW |
7063 | |
7064 | =item vec EXPR,OFFSET,BITS | |
d74e8afc | 7065 | X<vec> X<bit> X<bit vector> |
a0d0e21e | 7066 | |
e69129f1 GS |
7067 | Treats the string in EXPR as a bit vector made up of elements of |
7068 | width BITS, and returns the value of the element specified by OFFSET | |
7069 | as an unsigned integer. BITS therefore specifies the number of bits | |
7070 | that are reserved for each element in the bit vector. This must | |
7071 | be a power of two from 1 to 32 (or 64, if your platform supports | |
7072 | that). | |
c5a0f51a | 7073 | |
b76cc8ba | 7074 | If BITS is 8, "elements" coincide with bytes of the input string. |
c73032f5 IZ |
7075 | |
7076 | If BITS is 16 or more, bytes of the input string are grouped into chunks | |
7077 | of size BITS/8, and each group is converted to a number as with | |
b1866b2d | 7078 | pack()/unpack() with big-endian formats C<n>/C<N> (and analogously |
c73032f5 IZ |
7079 | for BITS==64). See L<"pack"> for details. |
7080 | ||
7081 | If bits is 4 or less, the string is broken into bytes, then the bits | |
7082 | of each byte are broken into 8/BITS groups. Bits of a byte are | |
7083 | numbered in a little-endian-ish way, as in C<0x01>, C<0x02>, | |
7084 | C<0x04>, C<0x08>, C<0x10>, C<0x20>, C<0x40>, C<0x80>. For example, | |
7085 | breaking the single input byte C<chr(0x36)> into two groups gives a list | |
7086 | C<(0x6, 0x3)>; breaking it into 4 groups gives C<(0x2, 0x1, 0x3, 0x0)>. | |
7087 | ||
81e118e0 JH |
7088 | C<vec> may also be assigned to, in which case parentheses are needed |
7089 | to give the expression the correct precedence as in | |
22dc801b | 7090 | |
7091 | vec($image, $max_x * $x + $y, 8) = 3; | |
a0d0e21e | 7092 | |
fe58ced6 MG |
7093 | If the selected element is outside the string, the value 0 is returned. |
7094 | If an element off the end of the string is written to, Perl will first | |
7095 | extend the string with sufficiently many zero bytes. It is an error | |
7096 | to try to write off the beginning of the string (i.e. negative OFFSET). | |
fac70343 | 7097 | |
2575c402 JW |
7098 | If the string happens to be encoded as UTF-8 internally (and thus has |
7099 | the UTF8 flag set), this is ignored by C<vec>, and it operates on the | |
7100 | internal byte string, not the conceptual character string, even if you | |
7101 | only have characters with values less than 256. | |
246fae53 | 7102 | |
fac70343 GS |
7103 | Strings created with C<vec> can also be manipulated with the logical |
7104 | operators C<|>, C<&>, C<^>, and C<~>. These operators will assume a bit | |
7105 | vector operation is desired when both operands are strings. | |
c5a0f51a | 7106 | See L<perlop/"Bitwise String Operators">. |
a0d0e21e | 7107 | |
7660c0ab | 7108 | The following code will build up an ASCII string saying C<'PerlPerlPerl'>. |
19799a22 | 7109 | The comments show the string after each step. Note that this code works |
cca87523 GS |
7110 | in the same way on big-endian or little-endian machines. |
7111 | ||
7112 | my $foo = ''; | |
7113 | vec($foo, 0, 32) = 0x5065726C; # 'Perl' | |
e69129f1 GS |
7114 | |
7115 | # $foo eq "Perl" eq "\x50\x65\x72\x6C", 32 bits | |
7116 | print vec($foo, 0, 8); # prints 80 == 0x50 == ord('P') | |
7117 | ||
cca87523 GS |
7118 | vec($foo, 2, 16) = 0x5065; # 'PerlPe' |
7119 | vec($foo, 3, 16) = 0x726C; # 'PerlPerl' | |
7120 | vec($foo, 8, 8) = 0x50; # 'PerlPerlP' | |
7121 | vec($foo, 9, 8) = 0x65; # 'PerlPerlPe' | |
7122 | vec($foo, 20, 4) = 2; # 'PerlPerlPe' . "\x02" | |
f86cebdf GS |
7123 | vec($foo, 21, 4) = 7; # 'PerlPerlPer' |
7124 | # 'r' is "\x72" | |
cca87523 GS |
7125 | vec($foo, 45, 2) = 3; # 'PerlPerlPer' . "\x0c" |
7126 | vec($foo, 93, 1) = 1; # 'PerlPerlPer' . "\x2c" | |
f86cebdf GS |
7127 | vec($foo, 94, 1) = 1; # 'PerlPerlPerl' |
7128 | # 'l' is "\x6c" | |
cca87523 | 7129 | |
19799a22 | 7130 | To transform a bit vector into a string or list of 0's and 1's, use these: |
a0d0e21e LW |
7131 | |
7132 | $bits = unpack("b*", $vector); | |
7133 | @bits = split(//, unpack("b*", $vector)); | |
7134 | ||
7660c0ab | 7135 | If you know the exact length in bits, it can be used in place of the C<*>. |
a0d0e21e | 7136 | |
e69129f1 GS |
7137 | Here is an example to illustrate how the bits actually fall in place: |
7138 | ||
7139 | #!/usr/bin/perl -wl | |
7140 | ||
7141 | print <<'EOT'; | |
b76cc8ba | 7142 | 0 1 2 3 |
e69129f1 GS |
7143 | unpack("V",$_) 01234567890123456789012345678901 |
7144 | ------------------------------------------------------------------ | |
7145 | EOT | |
7146 | ||
7147 | for $w (0..3) { | |
7148 | $width = 2**$w; | |
7149 | for ($shift=0; $shift < $width; ++$shift) { | |
7150 | for ($off=0; $off < 32/$width; ++$off) { | |
7151 | $str = pack("B*", "0"x32); | |
7152 | $bits = (1<<$shift); | |
7153 | vec($str, $off, $width) = $bits; | |
7154 | $res = unpack("b*",$str); | |
7155 | $val = unpack("V", $str); | |
7156 | write; | |
7157 | } | |
7158 | } | |
7159 | } | |
7160 | ||
7161 | format STDOUT = | |
7162 | vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> | |
7163 | $off, $width, $bits, $val, $res | |
7164 | . | |
7165 | __END__ | |
7166 | ||
7167 | Regardless of the machine architecture on which it is run, the above | |
7168 | example should print the following table: | |
7169 | ||
b76cc8ba | 7170 | 0 1 2 3 |
e69129f1 GS |
7171 | unpack("V",$_) 01234567890123456789012345678901 |
7172 | ------------------------------------------------------------------ | |
7173 | vec($_, 0, 1) = 1 == 1 10000000000000000000000000000000 | |
7174 | vec($_, 1, 1) = 1 == 2 01000000000000000000000000000000 | |
7175 | vec($_, 2, 1) = 1 == 4 00100000000000000000000000000000 | |
7176 | vec($_, 3, 1) = 1 == 8 00010000000000000000000000000000 | |
7177 | vec($_, 4, 1) = 1 == 16 00001000000000000000000000000000 | |
7178 | vec($_, 5, 1) = 1 == 32 00000100000000000000000000000000 | |
7179 | vec($_, 6, 1) = 1 == 64 00000010000000000000000000000000 | |
7180 | vec($_, 7, 1) = 1 == 128 00000001000000000000000000000000 | |
7181 | vec($_, 8, 1) = 1 == 256 00000000100000000000000000000000 | |
7182 | vec($_, 9, 1) = 1 == 512 00000000010000000000000000000000 | |
7183 | vec($_,10, 1) = 1 == 1024 00000000001000000000000000000000 | |
7184 | vec($_,11, 1) = 1 == 2048 00000000000100000000000000000000 | |
7185 | vec($_,12, 1) = 1 == 4096 00000000000010000000000000000000 | |
7186 | vec($_,13, 1) = 1 == 8192 00000000000001000000000000000000 | |
7187 | vec($_,14, 1) = 1 == 16384 00000000000000100000000000000000 | |
7188 | vec($_,15, 1) = 1 == 32768 00000000000000010000000000000000 | |
7189 | vec($_,16, 1) = 1 == 65536 00000000000000001000000000000000 | |
7190 | vec($_,17, 1) = 1 == 131072 00000000000000000100000000000000 | |
7191 | vec($_,18, 1) = 1 == 262144 00000000000000000010000000000000 | |
7192 | vec($_,19, 1) = 1 == 524288 00000000000000000001000000000000 | |
7193 | vec($_,20, 1) = 1 == 1048576 00000000000000000000100000000000 | |
7194 | vec($_,21, 1) = 1 == 2097152 00000000000000000000010000000000 | |
7195 | vec($_,22, 1) = 1 == 4194304 00000000000000000000001000000000 | |
7196 | vec($_,23, 1) = 1 == 8388608 00000000000000000000000100000000 | |
7197 | vec($_,24, 1) = 1 == 16777216 00000000000000000000000010000000 | |
7198 | vec($_,25, 1) = 1 == 33554432 00000000000000000000000001000000 | |
7199 | vec($_,26, 1) = 1 == 67108864 00000000000000000000000000100000 | |
7200 | vec($_,27, 1) = 1 == 134217728 00000000000000000000000000010000 | |
7201 | vec($_,28, 1) = 1 == 268435456 00000000000000000000000000001000 | |
7202 | vec($_,29, 1) = 1 == 536870912 00000000000000000000000000000100 | |
7203 | vec($_,30, 1) = 1 == 1073741824 00000000000000000000000000000010 | |
7204 | vec($_,31, 1) = 1 == 2147483648 00000000000000000000000000000001 | |
7205 | vec($_, 0, 2) = 1 == 1 10000000000000000000000000000000 | |
7206 | vec($_, 1, 2) = 1 == 4 00100000000000000000000000000000 | |
7207 | vec($_, 2, 2) = 1 == 16 00001000000000000000000000000000 | |
7208 | vec($_, 3, 2) = 1 == 64 00000010000000000000000000000000 | |
7209 | vec($_, 4, 2) = 1 == 256 00000000100000000000000000000000 | |
7210 | vec($_, 5, 2) = 1 == 1024 00000000001000000000000000000000 | |
7211 | vec($_, 6, 2) = 1 == 4096 00000000000010000000000000000000 | |
7212 | vec($_, 7, 2) = 1 == 16384 00000000000000100000000000000000 | |
7213 | vec($_, 8, 2) = 1 == 65536 00000000000000001000000000000000 | |
7214 | vec($_, 9, 2) = 1 == 262144 00000000000000000010000000000000 | |
7215 | vec($_,10, 2) = 1 == 1048576 00000000000000000000100000000000 | |
7216 | vec($_,11, 2) = 1 == 4194304 00000000000000000000001000000000 | |
7217 | vec($_,12, 2) = 1 == 16777216 00000000000000000000000010000000 | |
7218 | vec($_,13, 2) = 1 == 67108864 00000000000000000000000000100000 | |
7219 | vec($_,14, 2) = 1 == 268435456 00000000000000000000000000001000 | |
7220 | vec($_,15, 2) = 1 == 1073741824 00000000000000000000000000000010 | |
7221 | vec($_, 0, 2) = 2 == 2 01000000000000000000000000000000 | |
7222 | vec($_, 1, 2) = 2 == 8 00010000000000000000000000000000 | |
7223 | vec($_, 2, 2) = 2 == 32 00000100000000000000000000000000 | |
7224 | vec($_, 3, 2) = 2 == 128 00000001000000000000000000000000 | |
7225 | vec($_, 4, 2) = 2 == 512 00000000010000000000000000000000 | |
7226 | vec($_, 5, 2) = 2 == 2048 00000000000100000000000000000000 | |
7227 | vec($_, 6, 2) = 2 == 8192 00000000000001000000000000000000 | |
7228 | vec($_, 7, 2) = 2 == 32768 00000000000000010000000000000000 | |
7229 | vec($_, 8, 2) = 2 == 131072 00000000000000000100000000000000 | |
7230 | vec($_, 9, 2) = 2 == 524288 00000000000000000001000000000000 | |
7231 | vec($_,10, 2) = 2 == 2097152 00000000000000000000010000000000 | |
7232 | vec($_,11, 2) = 2 == 8388608 00000000000000000000000100000000 | |
7233 | vec($_,12, 2) = 2 == 33554432 00000000000000000000000001000000 | |
7234 | vec($_,13, 2) = 2 == 134217728 00000000000000000000000000010000 | |
7235 | vec($_,14, 2) = 2 == 536870912 00000000000000000000000000000100 | |
7236 | vec($_,15, 2) = 2 == 2147483648 00000000000000000000000000000001 | |
7237 | vec($_, 0, 4) = 1 == 1 10000000000000000000000000000000 | |
7238 | vec($_, 1, 4) = 1 == 16 00001000000000000000000000000000 | |
7239 | vec($_, 2, 4) = 1 == 256 00000000100000000000000000000000 | |
7240 | vec($_, 3, 4) = 1 == 4096 00000000000010000000000000000000 | |
7241 | vec($_, 4, 4) = 1 == 65536 00000000000000001000000000000000 | |
7242 | vec($_, 5, 4) = 1 == 1048576 00000000000000000000100000000000 | |
7243 | vec($_, 6, 4) = 1 == 16777216 00000000000000000000000010000000 | |
7244 | vec($_, 7, 4) = 1 == 268435456 00000000000000000000000000001000 | |
7245 | vec($_, 0, 4) = 2 == 2 01000000000000000000000000000000 | |
7246 | vec($_, 1, 4) = 2 == 32 00000100000000000000000000000000 | |
7247 | vec($_, 2, 4) = 2 == 512 00000000010000000000000000000000 | |
7248 | vec($_, 3, 4) = 2 == 8192 00000000000001000000000000000000 | |
7249 | vec($_, 4, 4) = 2 == 131072 00000000000000000100000000000000 | |
7250 | vec($_, 5, 4) = 2 == 2097152 00000000000000000000010000000000 | |
7251 | vec($_, 6, 4) = 2 == 33554432 00000000000000000000000001000000 | |
7252 | vec($_, 7, 4) = 2 == 536870912 00000000000000000000000000000100 | |
7253 | vec($_, 0, 4) = 4 == 4 00100000000000000000000000000000 | |
7254 | vec($_, 1, 4) = 4 == 64 00000010000000000000000000000000 | |
7255 | vec($_, 2, 4) = 4 == 1024 00000000001000000000000000000000 | |
7256 | vec($_, 3, 4) = 4 == 16384 00000000000000100000000000000000 | |
7257 | vec($_, 4, 4) = 4 == 262144 00000000000000000010000000000000 | |
7258 | vec($_, 5, 4) = 4 == 4194304 00000000000000000000001000000000 | |
7259 | vec($_, 6, 4) = 4 == 67108864 00000000000000000000000000100000 | |
7260 | vec($_, 7, 4) = 4 == 1073741824 00000000000000000000000000000010 | |
7261 | vec($_, 0, 4) = 8 == 8 00010000000000000000000000000000 | |
7262 | vec($_, 1, 4) = 8 == 128 00000001000000000000000000000000 | |
7263 | vec($_, 2, 4) = 8 == 2048 00000000000100000000000000000000 | |
7264 | vec($_, 3, 4) = 8 == 32768 00000000000000010000000000000000 | |
7265 | vec($_, 4, 4) = 8 == 524288 00000000000000000001000000000000 | |
7266 | vec($_, 5, 4) = 8 == 8388608 00000000000000000000000100000000 | |
7267 | vec($_, 6, 4) = 8 == 134217728 00000000000000000000000000010000 | |
7268 | vec($_, 7, 4) = 8 == 2147483648 00000000000000000000000000000001 | |
7269 | vec($_, 0, 8) = 1 == 1 10000000000000000000000000000000 | |
7270 | vec($_, 1, 8) = 1 == 256 00000000100000000000000000000000 | |
7271 | vec($_, 2, 8) = 1 == 65536 00000000000000001000000000000000 | |
7272 | vec($_, 3, 8) = 1 == 16777216 00000000000000000000000010000000 | |
7273 | vec($_, 0, 8) = 2 == 2 01000000000000000000000000000000 | |
7274 | vec($_, 1, 8) = 2 == 512 00000000010000000000000000000000 | |
7275 | vec($_, 2, 8) = 2 == 131072 00000000000000000100000000000000 | |
7276 | vec($_, 3, 8) = 2 == 33554432 00000000000000000000000001000000 | |
7277 | vec($_, 0, 8) = 4 == 4 00100000000000000000000000000000 | |
7278 | vec($_, 1, 8) = 4 == 1024 00000000001000000000000000000000 | |
7279 | vec($_, 2, 8) = 4 == 262144 00000000000000000010000000000000 | |
7280 | vec($_, 3, 8) = 4 == 67108864 00000000000000000000000000100000 | |
7281 | vec($_, 0, 8) = 8 == 8 00010000000000000000000000000000 | |
7282 | vec($_, 1, 8) = 8 == 2048 00000000000100000000000000000000 | |
7283 | vec($_, 2, 8) = 8 == 524288 00000000000000000001000000000000 | |
7284 | vec($_, 3, 8) = 8 == 134217728 00000000000000000000000000010000 | |
7285 | vec($_, 0, 8) = 16 == 16 00001000000000000000000000000000 | |
7286 | vec($_, 1, 8) = 16 == 4096 00000000000010000000000000000000 | |
7287 | vec($_, 2, 8) = 16 == 1048576 00000000000000000000100000000000 | |
7288 | vec($_, 3, 8) = 16 == 268435456 00000000000000000000000000001000 | |
7289 | vec($_, 0, 8) = 32 == 32 00000100000000000000000000000000 | |
7290 | vec($_, 1, 8) = 32 == 8192 00000000000001000000000000000000 | |
7291 | vec($_, 2, 8) = 32 == 2097152 00000000000000000000010000000000 | |
7292 | vec($_, 3, 8) = 32 == 536870912 00000000000000000000000000000100 | |
7293 | vec($_, 0, 8) = 64 == 64 00000010000000000000000000000000 | |
7294 | vec($_, 1, 8) = 64 == 16384 00000000000000100000000000000000 | |
7295 | vec($_, 2, 8) = 64 == 4194304 00000000000000000000001000000000 | |
7296 | vec($_, 3, 8) = 64 == 1073741824 00000000000000000000000000000010 | |
7297 | vec($_, 0, 8) = 128 == 128 00000001000000000000000000000000 | |
7298 | vec($_, 1, 8) = 128 == 32768 00000000000000010000000000000000 | |
7299 | vec($_, 2, 8) = 128 == 8388608 00000000000000000000000100000000 | |
7300 | vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001 | |
7301 | ||
a0d0e21e | 7302 | =item wait |
d74e8afc | 7303 | X<wait> |
a0d0e21e | 7304 | |
2b5ab1e7 TC |
7305 | Behaves like the wait(2) system call on your system: it waits for a child |
7306 | process to terminate and returns the pid of the deceased process, or | |
e5218da5 | 7307 | C<-1> if there are no child processes. The status is returned in C<$?> |
eadb07ed | 7308 | and C<{^CHILD_ERROR_NATIVE}>. |
2b5ab1e7 TC |
7309 | Note that a return value of C<-1> could mean that child processes are |
7310 | being automatically reaped, as described in L<perlipc>. | |
a0d0e21e LW |
7311 | |
7312 | =item waitpid PID,FLAGS | |
d74e8afc | 7313 | X<waitpid> |
a0d0e21e | 7314 | |
2b5ab1e7 TC |
7315 | Waits for a particular child process to terminate and returns the pid of |
7316 | the deceased process, or C<-1> if there is no such child process. On some | |
7317 | systems, a value of 0 indicates that there are processes still running. | |
eadb07ed | 7318 | The status is returned in C<$?> and C<{^CHILD_ERROR_NATIVE}>. If you say |
a0d0e21e | 7319 | |
5f05dabc | 7320 | use POSIX ":sys_wait_h"; |
5a964f20 | 7321 | #... |
b76cc8ba | 7322 | do { |
2ac1ef3d | 7323 | $kid = waitpid(-1, WNOHANG); |
84b74420 | 7324 | } while $kid > 0; |
a0d0e21e | 7325 | |
2b5ab1e7 TC |
7326 | then you can do a non-blocking wait for all pending zombie processes. |
7327 | Non-blocking wait is available on machines supporting either the | |
7328 | waitpid(2) or wait4(2) system calls. However, waiting for a particular | |
7329 | pid with FLAGS of C<0> is implemented everywhere. (Perl emulates the | |
7330 | system call by remembering the status values of processes that have | |
7331 | exited but have not been harvested by the Perl script yet.) | |
a0d0e21e | 7332 | |
2b5ab1e7 TC |
7333 | Note that on some systems, a return value of C<-1> could mean that child |
7334 | processes are being automatically reaped. See L<perlipc> for details, | |
7335 | and for other examples. | |
5a964f20 | 7336 | |
a0d0e21e | 7337 | =item wantarray |
d74e8afc | 7338 | X<wantarray> X<context> |
a0d0e21e | 7339 | |
cc37eb0b | 7340 | Returns true if the context of the currently executing subroutine or |
20f13e4a | 7341 | C<eval> is looking for a list value. Returns false if the context is |
cc37eb0b RGS |
7342 | looking for a scalar. Returns the undefined value if the context is |
7343 | looking for no value (void context). | |
a0d0e21e | 7344 | |
54310121 | 7345 | return unless defined wantarray; # don't bother doing more |
7346 | my @a = complex_calculation(); | |
7347 | return wantarray ? @a : "@a"; | |
a0d0e21e | 7348 | |
20f13e4a | 7349 | C<wantarray()>'s result is unspecified in the top level of a file, |
3c10abe3 AG |
7350 | in a C<BEGIN>, C<UNITCHECK>, C<CHECK>, C<INIT> or C<END> block, or |
7351 | in a C<DESTROY> method. | |
20f13e4a | 7352 | |
19799a22 GS |
7353 | This function should have been named wantlist() instead. |
7354 | ||
a0d0e21e | 7355 | =item warn LIST |
d74e8afc | 7356 | X<warn> X<warning> X<STDERR> |
a0d0e21e | 7357 | |
2d6d0015 | 7358 | Prints the value of LIST to STDERR. If the last element of LIST does |
afd8c9c8 DM |
7359 | not end in a newline, it appends the same file/line number text as C<die> |
7360 | does. | |
774d564b | 7361 | |
7660c0ab A |
7362 | If LIST is empty and C<$@> already contains a value (typically from a |
7363 | previous eval) that value is used after appending C<"\t...caught"> | |
19799a22 GS |
7364 | to C<$@>. This is useful for staying almost, but not entirely similar to |
7365 | C<die>. | |
43051805 | 7366 | |
7660c0ab | 7367 | If C<$@> is empty then the string C<"Warning: Something's wrong"> is used. |
43051805 | 7368 | |
774d564b | 7369 | No message is printed if there is a C<$SIG{__WARN__}> handler |
7370 | installed. It is the handler's responsibility to deal with the message | |
19799a22 | 7371 | as it sees fit (like, for instance, converting it into a C<die>). Most |
774d564b | 7372 | handlers must therefore make arrangements to actually display the |
19799a22 | 7373 | warnings that they are not prepared to deal with, by calling C<warn> |
774d564b | 7374 | again in the handler. Note that this is quite safe and will not |
7375 | produce an endless loop, since C<__WARN__> hooks are not called from | |
7376 | inside one. | |
7377 | ||
7378 | You will find this behavior is slightly different from that of | |
7379 | C<$SIG{__DIE__}> handlers (which don't suppress the error text, but can | |
19799a22 | 7380 | instead call C<die> again to change it). |
774d564b | 7381 | |
7382 | Using a C<__WARN__> handler provides a powerful way to silence all | |
7383 | warnings (even the so-called mandatory ones). An example: | |
7384 | ||
7385 | # wipe out *all* compile-time warnings | |
7386 | BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } } | |
7387 | my $foo = 10; | |
7388 | my $foo = 20; # no warning about duplicate my $foo, | |
7389 | # but hey, you asked for it! | |
7390 | # no compile-time or run-time warnings before here | |
7391 | $DOWARN = 1; | |
7392 | ||
7393 | # run-time warnings enabled after here | |
7394 | warn "\$foo is alive and $foo!"; # does show up | |
7395 | ||
7396 | See L<perlvar> for details on setting C<%SIG> entries, and for more | |
2b5ab1e7 TC |
7397 | examples. See the Carp module for other kinds of warnings using its |
7398 | carp() and cluck() functions. | |
a0d0e21e LW |
7399 | |
7400 | =item write FILEHANDLE | |
d74e8afc | 7401 | X<write> |
a0d0e21e LW |
7402 | |
7403 | =item write EXPR | |
7404 | ||
7405 | =item write | |
7406 | ||
5a964f20 | 7407 | Writes a formatted record (possibly multi-line) to the specified FILEHANDLE, |
a0d0e21e | 7408 | using the format associated with that file. By default the format for |
54310121 | 7409 | a file is the one having the same name as the filehandle, but the |
19799a22 | 7410 | format for the current output channel (see the C<select> function) may be set |
184e9718 | 7411 | explicitly by assigning the name of the format to the C<$~> variable. |
a0d0e21e LW |
7412 | |
7413 | Top of form processing is handled automatically: if there is | |
7414 | insufficient room on the current page for the formatted record, the | |
7415 | page is advanced by writing a form feed, a special top-of-page format | |
7416 | is used to format the new page header, and then the record is written. | |
7417 | By default the top-of-page format is the name of the filehandle with | |
7418 | "_TOP" appended, but it may be dynamically set to the format of your | |
184e9718 | 7419 | choice by assigning the name to the C<$^> variable while the filehandle is |
a0d0e21e | 7420 | selected. The number of lines remaining on the current page is in |
7660c0ab | 7421 | variable C<$->, which can be set to C<0> to force a new page. |
a0d0e21e LW |
7422 | |
7423 | If FILEHANDLE is unspecified, output goes to the current default output | |
7424 | channel, which starts out as STDOUT but may be changed by the | |
19799a22 | 7425 | C<select> operator. If the FILEHANDLE is an EXPR, then the expression |
a0d0e21e LW |
7426 | is evaluated and the resulting string is used to look up the name of |
7427 | the FILEHANDLE at run time. For more on formats, see L<perlform>. | |
7428 | ||
19799a22 | 7429 | Note that write is I<not> the opposite of C<read>. Unfortunately. |
a0d0e21e LW |
7430 | |
7431 | =item y/// | |
7432 | ||
7660c0ab | 7433 | The transliteration operator. Same as C<tr///>. See L<perlop>. |
a0d0e21e LW |
7434 | |
7435 | =back |