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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlfunc - Perl builtin functions | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | The functions in this section can serve as terms in an expression. | |
8 | They fall into two major categories: list operators and named unary | |
9 | operators. These differ in their precedence relationship with a | |
10 | following comma. (See the precedence table in L<perlop>.) List | |
11 | operators take more than one argument, while unary operators can never | |
12 | take more than one argument. Thus, a comma terminates the argument of | |
13 | a unary operator, but merely separates the arguments of a list | |
14 | operator. A unary operator generally provides a scalar context to its | |
15 | argument, while a list operator may provide either scalar and list | |
16 | contexts for its arguments. If it does both, the scalar arguments will | |
5f05dabc | 17 | be first, and the list argument will follow. (Note that there can ever |
18 | be only one list argument.) For instance, splice() has three scalar | |
a0d0e21e LW |
19 | arguments followed by a list. |
20 | ||
21 | In the syntax descriptions that follow, list operators that expect a | |
22 | list (and provide list context for the elements of the list) are shown | |
23 | with LIST as an argument. Such a list may consist of any combination | |
24 | of scalar arguments or list values; the list values will be included | |
25 | in the list as if each individual element were interpolated at that | |
26 | point in the list, forming a longer single-dimensional list value. | |
27 | Elements of the LIST should be separated by commas. | |
28 | ||
29 | Any function in the list below may be used either with or without | |
30 | parentheses around its arguments. (The syntax descriptions omit the | |
5f05dabc | 31 | parentheses.) If you use the parentheses, the simple (but occasionally |
a0d0e21e LW |
32 | surprising) rule is this: It I<LOOKS> like a function, therefore it I<IS> a |
33 | function, and precedence doesn't matter. Otherwise it's a list | |
34 | operator or unary operator, and precedence does matter. And whitespace | |
35 | between the function and left parenthesis doesn't count--so you need to | |
36 | be careful sometimes: | |
37 | ||
68dc0745 | 38 | print 1+2+4; # Prints 7. |
39 | print(1+2) + 4; # Prints 3. | |
40 | print (1+2)+4; # Also prints 3! | |
41 | print +(1+2)+4; # Prints 7. | |
42 | print ((1+2)+4); # Prints 7. | |
a0d0e21e LW |
43 | |
44 | If you run Perl with the B<-w> switch it can warn you about this. For | |
45 | example, the third line above produces: | |
46 | ||
47 | print (...) interpreted as function at - line 1. | |
48 | Useless use of integer addition in void context at - line 1. | |
49 | ||
50 | For functions that can be used in either a scalar or list context, | |
54310121 | 51 | nonabortive failure is generally indicated in a scalar context by |
a0d0e21e LW |
52 | returning the undefined value, and in a list context by returning the |
53 | null list. | |
54 | ||
5a964f20 TC |
55 | Remember the following important rule: There is B<no rule> that relates |
56 | the behavior of an expression in list context to its behavior in scalar | |
57 | context, or vice versa. It might do two totally different things. | |
a0d0e21e LW |
58 | Each operator and function decides which sort of value it would be most |
59 | appropriate to return in a scalar context. Some operators return the | |
5a964f20 | 60 | length of the list that would have been returned in list context. Some |
a0d0e21e LW |
61 | operators return the first value in the list. Some operators return the |
62 | last value in the list. Some operators return a count of successful | |
63 | operations. In general, they do what you want, unless you want | |
64 | consistency. | |
65 | ||
5a964f20 TC |
66 | An named array in scalar context is quite different from what would at |
67 | first glance appear to be a list in scalar context. You can't get a list | |
68 | like C<(1,2,3)> into being in scalar context, because the compiler knows | |
69 | the context at compile time. It would generate the scalar comma operator | |
70 | there, not the list construction version of the comma. That means it | |
71 | was never a list to start with. | |
72 | ||
73 | In general, functions in Perl that serve as wrappers for system calls | |
f86cebdf | 74 | of the same name (like chown(2), fork(2), closedir(2), etc.) all return |
5a964f20 TC |
75 | true when they succeed and C<undef> otherwise, as is usually mentioned |
76 | in the descriptions below. This is different from the C interfaces, | |
7660c0ab A |
77 | which return C<-1> on failure. Exceptions to this rule are C<wait()>, |
78 | C<waitpid()>, and C<syscall()>. System calls also set the special C<$!> | |
5a964f20 TC |
79 | variable on failure. Other functions do not, except accidentally. |
80 | ||
cb1a09d0 AD |
81 | =head2 Perl Functions by Category |
82 | ||
83 | Here are Perl's functions (including things that look like | |
5a964f20 | 84 | functions, like some keywords and named operators) |
cb1a09d0 AD |
85 | arranged by category. Some functions appear in more |
86 | than one place. | |
87 | ||
88 | =over | |
89 | ||
90 | =item Functions for SCALARs or strings | |
91 | ||
22fae026 | 92 | C<chomp>, C<chop>, C<chr>, C<crypt>, C<hex>, C<index>, C<lc>, C<lcfirst>, |
ab4f32c2 A |
93 | C<length>, C<oct>, C<ord>, C<pack>, C<q/STRING/>, C<qq/STRING/>, C<reverse>, |
94 | C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///> | |
cb1a09d0 AD |
95 | |
96 | =item Regular expressions and pattern matching | |
97 | ||
ab4f32c2 | 98 | C<m//>, C<pos>, C<quotemeta>, C<s///>, C<split>, C<study>, C<qr//> |
cb1a09d0 AD |
99 | |
100 | =item Numeric functions | |
101 | ||
22fae026 TM |
102 | C<abs>, C<atan2>, C<cos>, C<exp>, C<hex>, C<int>, C<log>, C<oct>, C<rand>, |
103 | C<sin>, C<sqrt>, C<srand> | |
cb1a09d0 AD |
104 | |
105 | =item Functions for real @ARRAYs | |
106 | ||
22fae026 | 107 | C<pop>, C<push>, C<shift>, C<splice>, C<unshift> |
cb1a09d0 AD |
108 | |
109 | =item Functions for list data | |
110 | ||
ab4f32c2 | 111 | C<grep>, C<join>, C<map>, C<qw/STRING/>, C<reverse>, C<sort>, C<unpack> |
cb1a09d0 AD |
112 | |
113 | =item Functions for real %HASHes | |
114 | ||
22fae026 | 115 | C<delete>, C<each>, C<exists>, C<keys>, C<values> |
cb1a09d0 AD |
116 | |
117 | =item Input and output functions | |
118 | ||
22fae026 TM |
119 | C<binmode>, C<close>, C<closedir>, C<dbmclose>, C<dbmopen>, C<die>, C<eof>, |
120 | C<fileno>, C<flock>, C<format>, C<getc>, C<print>, C<printf>, C<read>, | |
121 | C<readdir>, C<rewinddir>, C<seek>, C<seekdir>, C<select>, C<syscall>, | |
122 | C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>, C<truncate>, | |
123 | C<warn>, C<write> | |
cb1a09d0 AD |
124 | |
125 | =item Functions for fixed length data or records | |
126 | ||
22fae026 | 127 | C<pack>, C<read>, C<syscall>, C<sysread>, C<syswrite>, C<unpack>, C<vec> |
cb1a09d0 AD |
128 | |
129 | =item Functions for filehandles, files, or directories | |
130 | ||
22fae026 | 131 | C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>, |
5ff3f7a4 GS |
132 | C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>, |
133 | C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<umask>, | |
134 | C<unlink>, C<utime> | |
cb1a09d0 AD |
135 | |
136 | =item Keywords related to the control flow of your perl program | |
137 | ||
a189bff9 JH |
138 | C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<else>, C<elsif>, |
139 | C<eval>, C<exit>, C<for>, C<foreach>, C<goto>, C<if>, C<last>, | |
140 | C<next>, C<redo>, C<return>, C<sub>, C<unless>, C<wantarray>, | |
141 | C<while>, C<until> | |
cb1a09d0 | 142 | |
54310121 | 143 | =item Keywords related to scoping |
cb1a09d0 | 144 | |
22fae026 | 145 | C<caller>, C<import>, C<local>, C<my>, C<package>, C<use> |
cb1a09d0 AD |
146 | |
147 | =item Miscellaneous functions | |
148 | ||
22fae026 TM |
149 | C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<reset>, |
150 | C<scalar>, C<undef>, C<wantarray> | |
cb1a09d0 AD |
151 | |
152 | =item Functions for processes and process groups | |
153 | ||
22fae026 | 154 | C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>, |
ab4f32c2 | 155 | C<pipe>, C<qx/STRING/>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>, |
22fae026 | 156 | C<times>, C<wait>, C<waitpid> |
cb1a09d0 AD |
157 | |
158 | =item Keywords related to perl modules | |
159 | ||
22fae026 | 160 | C<do>, C<import>, C<no>, C<package>, C<require>, C<use> |
cb1a09d0 AD |
161 | |
162 | =item Keywords related to classes and object-orientedness | |
163 | ||
22fae026 TM |
164 | C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>, |
165 | C<untie>, C<use> | |
cb1a09d0 AD |
166 | |
167 | =item Low-level socket functions | |
168 | ||
22fae026 TM |
169 | C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>, |
170 | C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>, | |
171 | C<socket>, C<socketpair> | |
cb1a09d0 AD |
172 | |
173 | =item System V interprocess communication functions | |
174 | ||
22fae026 TM |
175 | C<msgctl>, C<msgget>, C<msgrcv>, C<msgsnd>, C<semctl>, C<semget>, C<semop>, |
176 | C<shmctl>, C<shmget>, C<shmread>, C<shmwrite> | |
cb1a09d0 AD |
177 | |
178 | =item Fetching user and group info | |
179 | ||
22fae026 TM |
180 | C<endgrent>, C<endhostent>, C<endnetent>, C<endpwent>, C<getgrent>, |
181 | C<getgrgid>, C<getgrnam>, C<getlogin>, C<getpwent>, C<getpwnam>, | |
182 | C<getpwuid>, C<setgrent>, C<setpwent> | |
cb1a09d0 AD |
183 | |
184 | =item Fetching network info | |
185 | ||
22fae026 TM |
186 | C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>, |
187 | C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>, | |
188 | C<getprotobyname>, C<getprotobynumber>, C<getprotoent>, | |
189 | C<getservbyname>, C<getservbyport>, C<getservent>, C<sethostent>, | |
190 | C<setnetent>, C<setprotoent>, C<setservent> | |
cb1a09d0 AD |
191 | |
192 | =item Time-related functions | |
193 | ||
22fae026 | 194 | C<gmtime>, C<localtime>, C<time>, C<times> |
cb1a09d0 | 195 | |
37798a01 | 196 | =item Functions new in perl5 |
197 | ||
22fae026 TM |
198 | C<abs>, C<bless>, C<chomp>, C<chr>, C<exists>, C<formline>, C<glob>, |
199 | C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<prototype>, C<qx>, | |
200 | C<qw>, C<readline>, C<readpipe>, C<ref>, C<sub*>, C<sysopen>, C<tie>, | |
201 | C<tied>, C<uc>, C<ucfirst>, C<untie>, C<use> | |
37798a01 | 202 | |
203 | * - C<sub> was a keyword in perl4, but in perl5 it is an | |
5a964f20 | 204 | operator, which can be used in expressions. |
37798a01 | 205 | |
206 | =item Functions obsoleted in perl5 | |
207 | ||
22fae026 | 208 | C<dbmclose>, C<dbmopen> |
37798a01 | 209 | |
cb1a09d0 AD |
210 | =back |
211 | ||
60f9f73c JH |
212 | =head2 Portability |
213 | ||
214 | Perl was born in UNIX and therefore it can access all the common UNIX | |
215 | system calls. In non-UNIX environments the functionality of many | |
216 | UNIX system calls may not be available or the details of the available | |
217 | functionality may be slightly different. The Perl functions affected | |
218 | by this are: | |
219 | ||
220 | C<-X>, C<binmode>, C<chmod>, C<chown>, C<chroot>, C<crypt>, | |
221 | C<dbmclose>, C<dbmopen>, C<dump>, C<endgrent>, C<endhostent>, | |
222 | C<endnetent>, C<endprotoent>, C<endpwent>, C<endservent>, C<exec>, | |
223 | C<fcntl>, C<flock>, C<fork>, C<getgrent>, C<getgrgid>, C<gethostent>, | |
224 | C<getlogin>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>, | |
225 | C<getppid>, C<getprgp>, C<getpriority>, C<getprotobynumber>, | |
226 | C<getprotoent>, C<getpwent>, C<getpwnam>, C<getpwuid>, | |
227 | C<getservbyport>, C<getservent>, C<getsockopt>, C<glob>, C<ioctl>, | |
228 | C<kill>, C<link>, C<lstat>, C<msgctl>, C<msgget>, C<msgrcv>, | |
229 | C<msgsnd>, C<open>, C<pipe>, C<readlink>, C<select>, C<semctl>, | |
230 | C<semget>, C<semop>, C<setgrent>, C<sethostent>, C<setnetent>, | |
231 | C<setpgrp>, C<setpriority>, C<setprotoent>, C<setpwent>, | |
232 | C<setservent>, C<setsockopt>, C<shmctl>, C<shmget>, C<shmread>, | |
233 | C<shmwrite>, C<socketpair>, C<stat>, C<symlink>, C<syscall>, | |
234 | C<sysopen>, C<system>, C<times>, C<truncate>, C<umask>, C<utime>, | |
235 | C<wait>, C<waitpid> | |
236 | ||
237 | For more information about the portability of these functions, see | |
238 | L<perlport> and other available platform-specific documentation. | |
239 | ||
cb1a09d0 AD |
240 | =head2 Alphabetical Listing of Perl Functions |
241 | ||
a0d0e21e LW |
242 | =over 8 |
243 | ||
22fae026 | 244 | =item I<-X> FILEHANDLE |
a0d0e21e | 245 | |
22fae026 | 246 | =item I<-X> EXPR |
a0d0e21e | 247 | |
22fae026 | 248 | =item I<-X> |
a0d0e21e LW |
249 | |
250 | A file test, where X is one of the letters listed below. This unary | |
251 | operator takes one argument, either a filename or a filehandle, and | |
252 | tests the associated file to see if something is true about it. If the | |
7660c0ab | 253 | argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN. |
a0d0e21e LW |
254 | Unless otherwise documented, it returns C<1> for TRUE and C<''> for FALSE, or |
255 | the undefined value if the file doesn't exist. Despite the funny | |
256 | names, precedence is the same as any other named unary operator, and | |
257 | the argument may be parenthesized like any other unary operator. The | |
258 | operator may be any of: | |
7e778d91 IZ |
259 | 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> |
260 | 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 LW |
261 | |
262 | -r File is readable by effective uid/gid. | |
263 | -w File is writable by effective uid/gid. | |
264 | -x File is executable by effective uid/gid. | |
265 | -o File is owned by effective uid. | |
266 | ||
267 | -R File is readable by real uid/gid. | |
268 | -W File is writable by real uid/gid. | |
269 | -X File is executable by real uid/gid. | |
270 | -O File is owned by real uid. | |
271 | ||
272 | -e File exists. | |
273 | -z File has zero size. | |
54310121 | 274 | -s File has nonzero size (returns size). |
a0d0e21e LW |
275 | |
276 | -f File is a plain file. | |
277 | -d File is a directory. | |
278 | -l File is a symbolic link. | |
9c4d0f16 | 279 | -p File is a named pipe (FIFO), or Filehandle is a pipe. |
a0d0e21e LW |
280 | -S File is a socket. |
281 | -b File is a block special file. | |
282 | -c File is a character special file. | |
283 | -t Filehandle is opened to a tty. | |
284 | ||
285 | -u File has setuid bit set. | |
286 | -g File has setgid bit set. | |
287 | -k File has sticky bit set. | |
288 | ||
289 | -T File is a text file. | |
290 | -B File is a binary file (opposite of -T). | |
291 | ||
292 | -M Age of file in days when script started. | |
293 | -A Same for access time. | |
294 | -C Same for inode change time. | |
295 | ||
a0d0e21e LW |
296 | Example: |
297 | ||
298 | while (<>) { | |
299 | chop; | |
300 | next unless -f $_; # ignore specials | |
5a964f20 | 301 | #... |
a0d0e21e LW |
302 | } |
303 | ||
5ff3f7a4 GS |
304 | The interpretation of the file permission operators C<-r>, C<-R>, |
305 | C<-w>, C<-W>, C<-x>, and C<-X> is by default based solely on the mode | |
306 | of the file and the uids and gids of the user. There may be other | |
307 | reasons you can't actually read, write, or execute the file. Such | |
308 | reasons may be for example network filesystem access controls, ACLs | |
309 | (access control lists), read-only filesystems, and unrecognized | |
310 | executable formats. | |
311 | ||
312 | Also note that, for the superuser on the local filesystems, C<-r>, | |
313 | C<-R>, C<-w>, and C<-W> always return 1, and C<-x> and C<-X> return 1 | |
314 | if any execute bit is set in the mode. Scripts run by the superuser | |
315 | may thus need to do a stat() to determine the actual mode of the file, | |
316 | or temporarily set the uid to something else. | |
317 | ||
318 | If you are using ACLs, there is a pragma called C<filetest> that may | |
319 | produce more accurate results than the bare stat() mode bits. | |
320 | ||
321 | When under the C<use filetest 'access'> the above-mentioned filetests | |
322 | will test whether the permission can (not) be granted using the | |
468541a8 | 323 | access() family of system calls. Also note that the C<-x> and C<-X> may |
5ff3f7a4 GS |
324 | under this pragma return true even if there are no execute permission |
325 | bits set (nor any extra execute permission ACLs). This strangeness is | |
326 | due to the underlying system calls' definitions. Read the | |
327 | documentation for the C<filetest> pragma for more information. | |
328 | ||
a0d0e21e LW |
329 | Note that C<-s/a/b/> does not do a negated substitution. Saying |
330 | C<-exp($foo)> still works as expected, however--only single letters | |
331 | following a minus are interpreted as file tests. | |
332 | ||
333 | The C<-T> and C<-B> switches work as follows. The first block or so of the | |
334 | file is examined for odd characters such as strange control codes or | |
5a964f20 | 335 | characters with the high bit set. If too many strange characters (E<gt>30%) |
a0d0e21e LW |
336 | are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file |
337 | containing null in the first block is considered a binary file. If C<-T> | |
338 | or C<-B> is used on a filehandle, the current stdio buffer is examined | |
339 | rather than the first block. Both C<-T> and C<-B> return TRUE on a null | |
54310121 | 340 | file, or a file at EOF when testing a filehandle. Because you have to |
4633a7c4 LW |
341 | read a file to do the C<-T> test, on most occasions you want to use a C<-f> |
342 | against the file first, as in C<next unless -f $file && -T $file>. | |
a0d0e21e | 343 | |
7660c0ab | 344 | If any of the file tests (or either the C<stat()> or C<lstat()> operators) are given |
28757baa | 345 | the special filehandle consisting of a solitary underline, then the stat |
a0d0e21e LW |
346 | structure of the previous file test (or stat operator) is used, saving |
347 | a system call. (This doesn't work with C<-t>, and you need to remember | |
348 | that lstat() and C<-l> will leave values in the stat structure for the | |
349 | symbolic link, not the real file.) Example: | |
350 | ||
351 | print "Can do.\n" if -r $a || -w _ || -x _; | |
352 | ||
353 | stat($filename); | |
354 | print "Readable\n" if -r _; | |
355 | print "Writable\n" if -w _; | |
356 | print "Executable\n" if -x _; | |
357 | print "Setuid\n" if -u _; | |
358 | print "Setgid\n" if -g _; | |
359 | print "Sticky\n" if -k _; | |
360 | print "Text\n" if -T _; | |
361 | print "Binary\n" if -B _; | |
362 | ||
363 | =item abs VALUE | |
364 | ||
54310121 | 365 | =item abs |
bbce6d69 | 366 | |
a0d0e21e | 367 | Returns the absolute value of its argument. |
7660c0ab | 368 | If VALUE is omitted, uses C<$_>. |
a0d0e21e LW |
369 | |
370 | =item accept NEWSOCKET,GENERICSOCKET | |
371 | ||
f86cebdf | 372 | Accepts an incoming socket connect, just as the accept(2) system call |
a0d0e21e | 373 | does. Returns the packed address if it succeeded, FALSE otherwise. |
4633a7c4 | 374 | See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
375 | |
376 | =item alarm SECONDS | |
377 | ||
54310121 | 378 | =item alarm |
bbce6d69 | 379 | |
a0d0e21e | 380 | Arranges to have a SIGALRM delivered to this process after the |
bbce6d69 | 381 | specified number of seconds have elapsed. If SECONDS is not specified, |
7660c0ab | 382 | the value stored in C<$_> is used. (On some machines, |
a0d0e21e LW |
383 | unfortunately, the elapsed time may be up to one second less than you |
384 | specified because of how seconds are counted.) Only one timer may be | |
385 | counting at once. Each call disables the previous timer, and an | |
7660c0ab | 386 | argument of C<0> may be supplied to cancel the previous timer without |
a0d0e21e LW |
387 | starting a new one. The returned value is the amount of time remaining |
388 | on the previous timer. | |
389 | ||
4633a7c4 | 390 | For delays of finer granularity than one second, you may use Perl's |
f86cebdf | 391 | C<syscall()> interface to access setitimer(2) if your system supports it, |
7660c0ab A |
392 | or else see L</select()>. It is usually a mistake to intermix C<alarm()> |
393 | and C<sleep()> calls. | |
a0d0e21e | 394 | |
7660c0ab | 395 | If you want to use C<alarm()> to time out a system call you need to use an |
ab4f32c2 | 396 | C<eval()>/C<die()> pair. You can't rely on the alarm causing the system call to |
f86cebdf | 397 | fail with C<$!> set to C<EINTR> because Perl sets up signal handlers to |
ab4f32c2 | 398 | restart system calls on some systems. Using C<eval()>/C<die()> always works, |
5a964f20 | 399 | modulo the caveats given in L<perlipc/"Signals">. |
ff68c719 | 400 | |
401 | eval { | |
f86cebdf | 402 | local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required |
36477c24 | 403 | alarm $timeout; |
ff68c719 | 404 | $nread = sysread SOCKET, $buffer, $size; |
36477c24 | 405 | alarm 0; |
ff68c719 | 406 | }; |
ff68c719 | 407 | if ($@) { |
f86cebdf | 408 | die unless $@ eq "alarm\n"; # propagate unexpected errors |
ff68c719 | 409 | # timed out |
410 | } | |
411 | else { | |
412 | # didn't | |
413 | } | |
414 | ||
a0d0e21e LW |
415 | =item atan2 Y,X |
416 | ||
417 | Returns the arctangent of Y/X in the range -PI to PI. | |
418 | ||
7660c0ab | 419 | For the tangent operation, you may use the C<POSIX::tan()> |
28757baa | 420 | function, or use the familiar relation: |
421 | ||
422 | sub tan { sin($_[0]) / cos($_[0]) } | |
423 | ||
a0d0e21e LW |
424 | =item bind SOCKET,NAME |
425 | ||
426 | Binds a network address to a socket, just as the bind system call | |
427 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a | |
4633a7c4 LW |
428 | packed address of the appropriate type for the socket. See the examples in |
429 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e LW |
430 | |
431 | =item binmode FILEHANDLE | |
432 | ||
cb1a09d0 AD |
433 | Arranges for the file to be read or written in "binary" mode in operating |
434 | systems that distinguish between binary and text files. Files that are | |
435 | not in binary mode have CR LF sequences translated to LF on input and LF | |
54310121 | 436 | translated to CR LF on output. Binmode has no effect under Unix; in MS-DOS |
cb1a09d0 | 437 | and similarly archaic systems, it may be imperative--otherwise your |
54310121 | 438 | MS-DOS-damaged C library may mangle your file. The key distinction between |
ab4f32c2 | 439 | systems that need C<binmode()> and those that don't is their text file |
5a964f20 | 440 | formats. Systems like Unix, MacOS, and Plan9 that delimit lines with a single |
7660c0ab | 441 | character, and that encode that character in C as C<"\n">, do not need |
ab4f32c2 | 442 | C<binmode()>. The rest need it. If FILEHANDLE is an expression, the value |
cb1a09d0 | 443 | is taken as the name of the filehandle. |
a0d0e21e | 444 | |
4633a7c4 | 445 | =item bless REF,CLASSNAME |
a0d0e21e LW |
446 | |
447 | =item bless REF | |
448 | ||
28757baa | 449 | This function tells the thingy referenced by REF that it is now |
4633a7c4 LW |
450 | an object in the CLASSNAME package--or the current package if no CLASSNAME |
451 | is specified, which is often the case. It returns the reference for | |
7660c0ab | 452 | convenience, because a C<bless()> is often the last thing in a constructor. |
4633a7c4 | 453 | Always use the two-argument version if the function doing the blessing |
5a964f20 TC |
454 | might be inherited by a derived class. See L<perltoot> and L<perlobj> |
455 | for more about the blessing (and blessings) of objects. | |
a0d0e21e | 456 | |
57668c4d GS |
457 | Consider always blessing objects in CLASSNAMEs that are mixed case. |
458 | Namespaces with all lowercase names are considered reserved for Perl | |
459 | pragmata. Builtin types have all uppercase names, so to prevent confusion, | |
460 | it is best to avoid such package names as well. | |
60ad88b8 GS |
461 | |
462 | See L<perlmod/"Perl Modules">. | |
463 | ||
a0d0e21e LW |
464 | =item caller EXPR |
465 | ||
466 | =item caller | |
467 | ||
5a964f20 | 468 | Returns the context of the current subroutine call. In scalar context, |
28757baa | 469 | returns the caller's package name if there is a caller, that is, if |
7660c0ab | 470 | we're in a subroutine or C<eval()> or C<require()>, and the undefined value |
5a964f20 | 471 | otherwise. In list context, returns |
a0d0e21e | 472 | |
748a9306 | 473 | ($package, $filename, $line) = caller; |
a0d0e21e LW |
474 | |
475 | With EXPR, it returns some extra information that the debugger uses to | |
476 | print a stack trace. The value of EXPR indicates how many call frames | |
477 | to go back before the current one. | |
478 | ||
54310121 | 479 | ($package, $filename, $line, $subroutine, |
e7ea3e70 IZ |
480 | $hasargs, $wantarray, $evaltext, $is_require) = caller($i); |
481 | ||
7660c0ab | 482 | Here C<$subroutine> may be C<"(eval)"> if the frame is not a subroutine |
ab4f32c2 | 483 | call, but an C<eval()>. In such a case additional elements C<$evaltext> and |
7660c0ab A |
484 | C<$is_require> are set: C<$is_require> is true if the frame is created by a |
485 | C<require> or C<use> statement, C<$evaltext> contains the text of the | |
dc848c6f | 486 | C<eval EXPR> statement. In particular, for a C<eval BLOCK> statement, |
7660c0ab | 487 | C<$filename> is C<"(eval)">, but C<$evaltext> is undefined. (Note also that |
dc848c6f | 488 | each C<use> statement creates a C<require> frame inside an C<eval EXPR>) |
489 | frame. | |
748a9306 LW |
490 | |
491 | Furthermore, when called from within the DB package, caller returns more | |
7660c0ab | 492 | detailed information: it sets the list variable C<@DB::args> to be the |
54310121 | 493 | arguments with which the subroutine was invoked. |
748a9306 | 494 | |
7660c0ab | 495 | Be aware that the optimizer might have optimized call frames away before |
ab4f32c2 | 496 | C<caller()> had a chance to get the information. That means that C<caller(N)> |
7660c0ab A |
497 | might not return information about the call frame you expect it do, for |
498 | C<N E<gt> 1>. In particular, C<@DB::args> might have information from the | |
499 | previous time C<caller()> was called. | |
500 | ||
a0d0e21e LW |
501 | =item chdir EXPR |
502 | ||
503 | Changes the working directory to EXPR, if possible. If EXPR is | |
504 | omitted, changes to home directory. Returns TRUE upon success, FALSE | |
7660c0ab | 505 | otherwise. See example under C<die()>. |
a0d0e21e LW |
506 | |
507 | =item chmod LIST | |
508 | ||
509 | Changes the permissions of a list of files. The first element of the | |
4633a7c4 | 510 | list must be the numerical mode, which should probably be an octal |
2f9daede TP |
511 | number, and which definitely should I<not> a string of octal digits: |
512 | C<0644> is okay, C<'0644'> is not. Returns the number of files | |
dc848c6f | 513 | successfully changed. See also L</oct>, if all you have is a string. |
a0d0e21e LW |
514 | |
515 | $cnt = chmod 0755, 'foo', 'bar'; | |
516 | chmod 0755, @executables; | |
f86cebdf GS |
517 | $mode = '0644'; chmod $mode, 'foo'; # !!! sets mode to |
518 | # --w----r-T | |
2f9daede TP |
519 | $mode = '0644'; chmod oct($mode), 'foo'; # this is better |
520 | $mode = 0644; chmod $mode, 'foo'; # this is best | |
a0d0e21e LW |
521 | |
522 | =item chomp VARIABLE | |
523 | ||
524 | =item chomp LIST | |
525 | ||
526 | =item chomp | |
527 | ||
3e3baf6d | 528 | This is a slightly safer version of L</chop>. It removes any |
a0d0e21e | 529 | line ending that corresponds to the current value of C<$/> (also known as |
28757baa | 530 | $INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total |
531 | number of characters removed from all its arguments. It's often used to | |
532 | remove the newline from the end of an input record when you're worried | |
533 | that the final record may be missing its newline. When in paragraph mode | |
534 | (C<$/ = "">), it removes all trailing newlines from the string. If | |
7660c0ab | 535 | VARIABLE is omitted, it chomps C<$_>. Example: |
a0d0e21e LW |
536 | |
537 | while (<>) { | |
538 | chomp; # avoid \n on last field | |
539 | @array = split(/:/); | |
5a964f20 | 540 | # ... |
a0d0e21e LW |
541 | } |
542 | ||
543 | You can actually chomp anything that's an lvalue, including an assignment: | |
544 | ||
545 | chomp($cwd = `pwd`); | |
546 | chomp($answer = <STDIN>); | |
547 | ||
548 | If you chomp a list, each element is chomped, and the total number of | |
549 | characters removed is returned. | |
550 | ||
551 | =item chop VARIABLE | |
552 | ||
553 | =item chop LIST | |
554 | ||
555 | =item chop | |
556 | ||
557 | Chops off the last character of a string and returns the character | |
558 | chopped. It's used primarily to remove the newline from the end of an | |
559 | input record, but is much more efficient than C<s/\n//> because it neither | |
7660c0ab | 560 | scans nor copies the string. If VARIABLE is omitted, chops C<$_>. |
a0d0e21e LW |
561 | Example: |
562 | ||
563 | while (<>) { | |
564 | chop; # avoid \n on last field | |
565 | @array = split(/:/); | |
5a964f20 | 566 | #... |
a0d0e21e LW |
567 | } |
568 | ||
569 | You can actually chop anything that's an lvalue, including an assignment: | |
570 | ||
571 | chop($cwd = `pwd`); | |
572 | chop($answer = <STDIN>); | |
573 | ||
574 | If you chop a list, each element is chopped. Only the value of the | |
ab4f32c2 | 575 | last C<chop()> is returned. |
a0d0e21e | 576 | |
ab4f32c2 | 577 | Note that C<chop()> returns the last character. To return all but the last |
748a9306 LW |
578 | character, use C<substr($string, 0, -1)>. |
579 | ||
a0d0e21e LW |
580 | =item chown LIST |
581 | ||
582 | Changes the owner (and group) of a list of files. The first two | |
583 | elements of the list must be the I<NUMERICAL> uid and gid, in that order. | |
584 | Returns the number of files successfully changed. | |
585 | ||
586 | $cnt = chown $uid, $gid, 'foo', 'bar'; | |
587 | chown $uid, $gid, @filenames; | |
588 | ||
54310121 | 589 | Here's an example that looks up nonnumeric uids in the passwd file: |
a0d0e21e LW |
590 | |
591 | print "User: "; | |
592 | chop($user = <STDIN>); | |
5a964f20 | 593 | print "Files: "; |
a0d0e21e LW |
594 | chop($pattern = <STDIN>); |
595 | ||
596 | ($login,$pass,$uid,$gid) = getpwnam($user) | |
597 | or die "$user not in passwd file"; | |
598 | ||
5a964f20 | 599 | @ary = glob($pattern); # expand filenames |
a0d0e21e LW |
600 | chown $uid, $gid, @ary; |
601 | ||
54310121 | 602 | On most systems, you are not allowed to change the ownership of the |
4633a7c4 LW |
603 | file unless you're the superuser, although you should be able to change |
604 | the group to any of your secondary groups. On insecure systems, these | |
605 | restrictions may be relaxed, but this is not a portable assumption. | |
606 | ||
a0d0e21e LW |
607 | =item chr NUMBER |
608 | ||
54310121 | 609 | =item chr |
bbce6d69 | 610 | |
a0d0e21e | 611 | Returns the character represented by that NUMBER in the character set. |
a0ed51b3 LW |
612 | For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and |
613 | chr(0x263a) is a Unicode smiley face (but only within the scope of a | |
614 | C<use utf8>). For the reverse, use L</ord>. | |
a0d0e21e | 615 | |
7660c0ab | 616 | If NUMBER is omitted, uses C<$_>. |
bbce6d69 | 617 | |
a0d0e21e LW |
618 | =item chroot FILENAME |
619 | ||
54310121 | 620 | =item chroot |
bbce6d69 | 621 | |
5a964f20 | 622 | This function works like the system call by the same name: it makes the |
4633a7c4 | 623 | named directory the new root directory for all further pathnames that |
7660c0ab | 624 | begin with a C<"/"> by your process and all its children. (It doesn't |
28757baa | 625 | change your current working directory, which is unaffected.) For security |
4633a7c4 | 626 | reasons, this call is restricted to the superuser. If FILENAME is |
ab4f32c2 | 627 | omitted, does a C<chroot()> to C<$_>. |
a0d0e21e LW |
628 | |
629 | =item close FILEHANDLE | |
630 | ||
6a518fbc TP |
631 | =item close |
632 | ||
a0d0e21e LW |
633 | Closes the file or pipe associated with the file handle, returning TRUE |
634 | only if stdio successfully flushes buffers and closes the system file | |
6a518fbc TP |
635 | descriptor. Closes the currently selected filehandle if the argument |
636 | is omitted. | |
fb73857a | 637 | |
638 | You don't have to close FILEHANDLE if you are immediately going to do | |
7660c0ab | 639 | another C<open()> on it, because C<open()> will close it for you. (See |
ab4f32c2 | 640 | C<open()>.) However, an explicit C<close()> on an input file resets the line |
7660c0ab | 641 | counter (C<$.>), while the implicit close done by C<open()> does not. |
fb73857a | 642 | |
ab4f32c2 | 643 | If the file handle came from a piped open C<close()> will additionally |
fb73857a | 644 | return FALSE if one of the other system calls involved fails or if the |
645 | program exits with non-zero status. (If the only problem was that the | |
7660c0ab | 646 | program exited non-zero C<$!> will be set to C<0>.) Also, closing a pipe |
5a964f20 | 647 | waits for the process executing on the pipe to complete, in case you |
fb73857a | 648 | want to look at the output of the pipe afterwards. Closing a pipe |
649 | explicitly also puts the exit status value of the command into C<$?>. | |
5a964f20 | 650 | |
fb73857a | 651 | Example: |
a0d0e21e | 652 | |
fb73857a | 653 | open(OUTPUT, '|sort >foo') # pipe to sort |
654 | or die "Can't start sort: $!"; | |
5a964f20 | 655 | #... # print stuff to output |
fb73857a | 656 | close OUTPUT # wait for sort to finish |
657 | or warn $! ? "Error closing sort pipe: $!" | |
658 | : "Exit status $? from sort"; | |
659 | open(INPUT, 'foo') # get sort's results | |
660 | or die "Can't open 'foo' for input: $!"; | |
a0d0e21e | 661 | |
5a964f20 TC |
662 | FILEHANDLE may be an expression whose value can be used as an indirect |
663 | filehandle, usually the real filehandle name. | |
a0d0e21e LW |
664 | |
665 | =item closedir DIRHANDLE | |
666 | ||
7660c0ab | 667 | Closes a directory opened by C<opendir()> and returns the success of that |
5a964f20 TC |
668 | system call. |
669 | ||
670 | DIRHANDLE may be an expression whose value can be used as an indirect | |
671 | dirhandle, usually the real dirhandle name. | |
a0d0e21e LW |
672 | |
673 | =item connect SOCKET,NAME | |
674 | ||
675 | Attempts to connect to a remote socket, just as the connect system call | |
676 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a | |
4633a7c4 LW |
677 | packed address of the appropriate type for the socket. See the examples in |
678 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e | 679 | |
cb1a09d0 AD |
680 | =item continue BLOCK |
681 | ||
682 | Actually a flow control statement rather than a function. If there is a | |
dc9e4912 | 683 | C<continue> BLOCK attached to a BLOCK (typically in a L</while> or |
a189bff9 JH |
684 | L</foreach>), it is always executed just before the conditional is about to |
685 | be evaluated again, just like the third part of a L</for> loop in C. Thus | |
cb1a09d0 AD |
686 | it can be used to increment a loop variable, even when the loop has been |
687 | continued via the C<next> statement (which is similar to the C C<continue> | |
688 | statement). | |
689 | ||
a189bff9 | 690 | L</last>, L</next>, or L</redo> may appear within a C<continue> |
1d2dff63 GS |
691 | block. C<last> and C<redo> will behave as if they had been executed within |
692 | the main block. So will C<next>, but since it will execute a C<continue> | |
693 | block, it may be more entertaining. | |
694 | ||
695 | while (EXPR) { | |
696 | ### redo always comes here | |
697 | do_something; | |
698 | } continue { | |
699 | ### next always comes here | |
700 | do_something_else; | |
701 | # then back the top to re-check EXPR | |
702 | } | |
703 | ### last always comes here | |
704 | ||
705 | Omitting the C<continue> section is semantically equivalent to using an | |
706 | empty one, logically enough. In that case, C<next> goes directly back | |
707 | to check the condition at the top of the loop. | |
708 | ||
a189bff9 JH |
709 | See also L<perlsyn>. |
710 | ||
a0d0e21e LW |
711 | =item cos EXPR |
712 | ||
5a964f20 | 713 | Returns the cosine of EXPR (expressed in radians). If EXPR is omitted, |
7660c0ab | 714 | takes cosine of C<$_>. |
a0d0e21e | 715 | |
7660c0ab | 716 | For the inverse cosine operation, you may use the C<POSIX::acos()> |
28757baa | 717 | function, or use this relation: |
718 | ||
719 | sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) } | |
720 | ||
a0d0e21e LW |
721 | =item crypt PLAINTEXT,SALT |
722 | ||
f86cebdf | 723 | Encrypts a string exactly like the crypt(3) function in the C library |
4633a7c4 LW |
724 | (assuming that you actually have a version there that has not been |
725 | extirpated as a potential munition). This can prove useful for checking | |
726 | the password file for lousy passwords, amongst other things. Only the | |
727 | guys wearing white hats should do this. | |
a0d0e21e | 728 | |
7660c0ab | 729 | Note that C<crypt()> is intended to be a one-way function, much like breaking |
11155c91 CS |
730 | eggs to make an omelette. There is no (known) corresponding decrypt |
731 | function. As a result, this function isn't all that useful for | |
732 | cryptography. (For that, see your nearby CPAN mirror.) | |
2f9daede | 733 | |
e71965be RS |
734 | When verifying an existing encrypted string you should use the encrypted |
735 | text as the salt (like C<crypt($plain, $crypted) eq $crypted>). This | |
736 | allows your code to work with the standard C<crypt()> and with more | |
737 | exotic implementations. When choosing a new salt create a random two | |
738 | character string whose characters come from the set C<[./0-9A-Za-z]> | |
739 | (like C<join '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]>). | |
740 | ||
a0d0e21e LW |
741 | Here's an example that makes sure that whoever runs this program knows |
742 | their own password: | |
743 | ||
744 | $pwd = (getpwuid($<))[1]; | |
a0d0e21e LW |
745 | |
746 | system "stty -echo"; | |
747 | print "Password: "; | |
e71965be | 748 | chomp($word = <STDIN>); |
a0d0e21e LW |
749 | print "\n"; |
750 | system "stty echo"; | |
751 | ||
e71965be | 752 | if (crypt($word, $pwd) ne $pwd) { |
a0d0e21e LW |
753 | die "Sorry...\n"; |
754 | } else { | |
755 | print "ok\n"; | |
54310121 | 756 | } |
a0d0e21e | 757 | |
9f8f0c9d | 758 | Of course, typing in your own password to whoever asks you |
748a9306 | 759 | for it is unwise. |
a0d0e21e | 760 | |
aa689395 | 761 | =item dbmclose HASH |
a0d0e21e | 762 | |
7660c0ab | 763 | [This function has been superseded by the C<untie()> function.] |
a0d0e21e | 764 | |
aa689395 | 765 | Breaks the binding between a DBM file and a hash. |
a0d0e21e | 766 | |
aa689395 | 767 | =item dbmopen HASH,DBNAME,MODE |
a0d0e21e | 768 | |
7660c0ab | 769 | [This function has been superseded by the C<tie()> function.] |
a0d0e21e | 770 | |
7b8d334a | 771 | This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a |
ab4f32c2 | 772 | hash. HASH is the name of the hash. (Unlike normal C<open()>, the first |
aa689395 | 773 | argument is I<NOT> a filehandle, even though it looks like one). DBNAME |
774 | is the name of the database (without the F<.dir> or F<.pag> extension if | |
775 | any). If the database does not exist, it is created with protection | |
7660c0ab A |
776 | specified by MODE (as modified by the C<umask()>). If your system supports |
777 | only the older DBM functions, you may perform only one C<dbmopen()> in your | |
aa689395 | 778 | program. In older versions of Perl, if your system had neither DBM nor |
7660c0ab | 779 | ndbm, calling C<dbmopen()> produced a fatal error; it now falls back to |
aa689395 | 780 | sdbm(3). |
781 | ||
782 | If you don't have write access to the DBM file, you can only read hash | |
783 | variables, not set them. If you want to test whether you can write, | |
7660c0ab | 784 | either use file tests or try setting a dummy hash entry inside an C<eval()>, |
aa689395 | 785 | which will trap the error. |
a0d0e21e | 786 | |
7660c0ab A |
787 | Note that functions such as C<keys()> and C<values()> may return huge lists |
788 | when used on large DBM files. You may prefer to use the C<each()> | |
a0d0e21e LW |
789 | function to iterate over large DBM files. Example: |
790 | ||
791 | # print out history file offsets | |
792 | dbmopen(%HIST,'/usr/lib/news/history',0666); | |
793 | while (($key,$val) = each %HIST) { | |
794 | print $key, ' = ', unpack('L',$val), "\n"; | |
795 | } | |
796 | dbmclose(%HIST); | |
797 | ||
cb1a09d0 | 798 | See also L<AnyDBM_File> for a more general description of the pros and |
184e9718 | 799 | cons of the various dbm approaches, as well as L<DB_File> for a particularly |
cb1a09d0 | 800 | rich implementation. |
4633a7c4 | 801 | |
a0d0e21e LW |
802 | =item defined EXPR |
803 | ||
54310121 | 804 | =item defined |
bbce6d69 | 805 | |
2f9daede TP |
806 | Returns a Boolean value telling whether EXPR has a value other than |
807 | the undefined value C<undef>. If EXPR is not present, C<$_> will be | |
808 | checked. | |
809 | ||
810 | Many operations return C<undef> to indicate failure, end of file, | |
811 | system error, uninitialized variable, and other exceptional | |
812 | conditions. This function allows you to distinguish C<undef> from | |
813 | other values. (A simple Boolean test will not distinguish among | |
7660c0ab | 814 | C<undef>, zero, the empty string, and C<"0">, which are all equally |
2f9daede | 815 | false.) Note that since C<undef> is a valid scalar, its presence |
7660c0ab | 816 | doesn't I<necessarily> indicate an exceptional condition: C<pop()> |
2f9daede TP |
817 | returns C<undef> when its argument is an empty array, I<or> when the |
818 | element to return happens to be C<undef>. | |
819 | ||
7660c0ab | 820 | You may also use C<defined()> to check whether a subroutine exists, by |
5a964f20 | 821 | saying C<defined &func> without parentheses. On the other hand, use |
7660c0ab | 822 | of C<defined()> upon aggregates (hashes and arrays) is not guaranteed to |
5a964f20 | 823 | produce intuitive results, and should probably be avoided. |
2f9daede TP |
824 | |
825 | When used on a hash element, it tells you whether the value is defined, | |
dc848c6f | 826 | not whether the key exists in the hash. Use L</exists> for the latter |
2f9daede | 827 | purpose. |
a0d0e21e LW |
828 | |
829 | Examples: | |
830 | ||
831 | print if defined $switch{'D'}; | |
832 | print "$val\n" while defined($val = pop(@ary)); | |
833 | die "Can't readlink $sym: $!" | |
834 | unless defined($value = readlink $sym); | |
a0d0e21e | 835 | sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } |
2f9daede | 836 | $debugging = 0 unless defined $debugging; |
a0d0e21e | 837 | |
7660c0ab A |
838 | Note: Many folks tend to overuse C<defined()>, and then are surprised to |
839 | discover that the number C<0> and C<""> (the zero-length string) are, in fact, | |
2f9daede | 840 | defined values. For example, if you say |
a5f75d66 AD |
841 | |
842 | "ab" =~ /a(.*)b/; | |
843 | ||
7660c0ab | 844 | The pattern match succeeds, and C<$1> is defined, despite the fact that it |
a5f75d66 | 845 | matched "nothing". But it didn't really match nothing--rather, it |
7660c0ab | 846 | matched something that happened to be C<0> characters long. This is all |
a5f75d66 | 847 | very above-board and honest. When a function returns an undefined value, |
2f9daede | 848 | it's an admission that it couldn't give you an honest answer. So you |
7660c0ab A |
849 | should use C<defined()> only when you're questioning the integrity of what |
850 | you're trying to do. At other times, a simple comparison to C<0> or C<""> is | |
2f9daede TP |
851 | what you want. |
852 | ||
7660c0ab | 853 | Currently, using C<defined()> on an entire array or hash reports whether |
2f9daede TP |
854 | memory for that aggregate has ever been allocated. So an array you set |
855 | to the empty list appears undefined initially, and one that once was full | |
856 | and that you then set to the empty list still appears defined. You | |
857 | should instead use a simple test for size: | |
28757baa | 858 | |
859 | if (@an_array) { print "has array elements\n" } | |
860 | if (%a_hash) { print "has hash members\n" } | |
861 | ||
7660c0ab | 862 | Using C<undef()> on these, however, does clear their memory and then report |
5a964f20 | 863 | them as not defined anymore, but you shouldn't do that unless you don't |
28757baa | 864 | plan to use them again, because it saves time when you load them up |
5a964f20 TC |
865 | again to have memory already ready to be filled. The normal way to |
866 | free up space used by an aggregate is to assign the empty list. | |
28757baa | 867 | |
7660c0ab | 868 | This counterintuitive behavior of C<defined()> on aggregates may be |
28757baa | 869 | changed, fixed, or broken in a future release of Perl. |
870 | ||
dc848c6f | 871 | See also L</undef>, L</exists>, L</ref>. |
2f9daede | 872 | |
a0d0e21e LW |
873 | =item delete EXPR |
874 | ||
aa689395 | 875 | Deletes the specified key(s) and their associated values from a hash. |
876 | For each key, returns the deleted value associated with that key, or | |
877 | the undefined value if there was no such key. Deleting from C<$ENV{}> | |
878 | modifies the environment. Deleting from a hash tied to a DBM file | |
7660c0ab | 879 | deletes the entry from the DBM file. (But deleting from a C<tie()>d hash |
5f05dabc | 880 | doesn't necessarily return anything.) |
a0d0e21e | 881 | |
aa689395 | 882 | The following deletes all the values of a hash: |
a0d0e21e | 883 | |
5f05dabc | 884 | foreach $key (keys %HASH) { |
885 | delete $HASH{$key}; | |
a0d0e21e LW |
886 | } |
887 | ||
5f05dabc | 888 | And so does this: |
889 | ||
890 | delete @HASH{keys %HASH} | |
891 | ||
5a964f20 | 892 | (But both of these are slower than just assigning the empty list, or |
7660c0ab | 893 | using C<undef()>.) Note that the EXPR can be arbitrarily complicated as |
5a964f20 | 894 | long as the final operation is a hash element lookup or hash slice: |
a0d0e21e LW |
895 | |
896 | delete $ref->[$x][$y]{$key}; | |
5f05dabc | 897 | delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys}; |
a0d0e21e LW |
898 | |
899 | =item die LIST | |
900 | ||
7660c0ab A |
901 | Outside an C<eval()>, prints the value of LIST to C<STDERR> and exits with |
902 | the current value of C<$!> (errno). If C<$!> is C<0>, exits with the value of | |
54310121 | 903 | C<($? E<gt>E<gt> 8)> (backtick `command` status). If C<($? E<gt>E<gt> 8)> |
7660c0ab A |
904 | is C<0>, exits with C<255>. Inside an C<eval(),> the error message is stuffed into |
905 | C<$@> and the C<eval()> is terminated with the undefined value. This makes | |
906 | C<die()> the way to raise an exception. | |
a0d0e21e LW |
907 | |
908 | Equivalent examples: | |
909 | ||
910 | die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; | |
54310121 | 911 | chdir '/usr/spool/news' or die "Can't cd to spool: $!\n" |
a0d0e21e LW |
912 | |
913 | If the value of EXPR does not end in a newline, the current script line | |
914 | number and input line number (if any) are also printed, and a newline | |
7660c0ab A |
915 | is supplied. Hint: sometimes appending C<", stopped"> to your message |
916 | will cause it to make better sense when the string C<"at foo line 123"> is | |
a0d0e21e LW |
917 | appended. Suppose you are running script "canasta". |
918 | ||
919 | die "/etc/games is no good"; | |
920 | die "/etc/games is no good, stopped"; | |
921 | ||
922 | produce, respectively | |
923 | ||
924 | /etc/games is no good at canasta line 123. | |
925 | /etc/games is no good, stopped at canasta line 123. | |
926 | ||
7660c0ab | 927 | See also C<exit()> and C<warn()>. |
a0d0e21e | 928 | |
7660c0ab A |
929 | If LIST is empty and C<$@> already contains a value (typically from a |
930 | previous eval) that value is reused after appending C<"\t...propagated">. | |
fb73857a | 931 | This is useful for propagating exceptions: |
932 | ||
933 | eval { ... }; | |
934 | die unless $@ =~ /Expected exception/; | |
935 | ||
7660c0ab | 936 | If C<$@> is empty then the string C<"Died"> is used. |
fb73857a | 937 | |
7660c0ab | 938 | You can arrange for a callback to be run just before the C<die()> does |
774d564b | 939 | its deed, by setting the C<$SIG{__DIE__}> hook. The associated handler |
940 | will be called with the error text and can change the error message, if | |
7660c0ab | 941 | it sees fit, by calling C<die()> again. See L<perlvar/$SIG{expr}> for details on |
fb73857a | 942 | setting C<%SIG> entries, and L<"eval BLOCK"> for some examples. |
943 | ||
944 | Note that the C<$SIG{__DIE__}> hook is called even inside eval()ed | |
945 | blocks/strings. If one wants the hook to do nothing in such | |
946 | situations, put | |
947 | ||
948 | die @_ if $^S; | |
949 | ||
950 | as the first line of the handler (see L<perlvar/$^S>). | |
774d564b | 951 | |
a0d0e21e LW |
952 | =item do BLOCK |
953 | ||
954 | Not really a function. Returns the value of the last command in the | |
955 | sequence of commands indicated by BLOCK. When modified by a loop | |
a189bff9 JH |
956 | modifier such as L</while> or L</until>, executes the BLOCK once |
957 | before testing the loop condition. (On other statements the loop | |
958 | modifiers test the conditional first.) | |
a0d0e21e | 959 | |
4968c1e4 | 960 | C<do BLOCK> does I<not> count as a loop, so the loop control statements |
a189bff9 | 961 | L</next>, L</last> or L</redo> cannot be used to leave or restart the block. |
4968c1e4 | 962 | |
a0d0e21e LW |
963 | =item do SUBROUTINE(LIST) |
964 | ||
965 | A deprecated form of subroutine call. See L<perlsub>. | |
966 | ||
967 | =item do EXPR | |
968 | ||
969 | Uses the value of EXPR as a filename and executes the contents of the | |
970 | file as a Perl script. Its primary use is to include subroutines | |
971 | from a Perl subroutine library. | |
972 | ||
973 | do 'stat.pl'; | |
974 | ||
975 | is just like | |
976 | ||
fb73857a | 977 | scalar eval `cat stat.pl`; |
a0d0e21e | 978 | |
5a964f20 | 979 | except that it's more efficient and concise, keeps track of the |
a0d0e21e LW |
980 | current filename for error messages, and searches all the B<-I> |
981 | libraries if the file isn't in the current directory (see also the @INC | |
dc1be6b5 GS |
982 | array in L<perlvar/Predefined Names>). It is also different in how |
983 | code evaluated with C<do FILENAME> doesn't see lexicals in the enclosing | |
984 | scope like C<eval STRING> does. It's the same, however, in that it does | |
54310121 | 985 | reparse the file every time you call it, so you probably don't want to |
a0d0e21e LW |
986 | do this inside a loop. |
987 | ||
8e30cc93 MG |
988 | If C<do> cannot read the file, it returns undef and sets C<$!> to the |
989 | error. If C<do> can read the file but cannot compile it, it | |
990 | returns undef and sets an error message in C<$@>. If the file is | |
991 | successfully compiled, C<do> returns the value of the last expression | |
992 | evaluated. | |
993 | ||
a0d0e21e | 994 | Note that inclusion of library modules is better done with the |
7660c0ab | 995 | C<use()> and C<require()> operators, which also do automatic error checking |
4633a7c4 | 996 | and raise an exception if there's a problem. |
a0d0e21e | 997 | |
5a964f20 TC |
998 | You might like to use C<do> to read in a program configuration |
999 | file. Manual error checking can be done this way: | |
1000 | ||
1001 | # read in config files: system first, then user | |
f86cebdf GS |
1002 | for $file ("/share/prog/defaults.rc", |
1003 | "$ENV{HOME}/.someprogrc") { | |
5a964f20 | 1004 | unless ($return = do $file) { |
f86cebdf GS |
1005 | warn "couldn't parse $file: $@" if $@; |
1006 | warn "couldn't do $file: $!" unless defined $return; | |
1007 | warn "couldn't run $file" unless $return; | |
5a964f20 TC |
1008 | } |
1009 | } | |
1010 | ||
a0d0e21e LW |
1011 | =item dump LABEL |
1012 | ||
1013 | This causes an immediate core dump. Primarily this is so that you can | |
1014 | use the B<undump> program to turn your core dump into an executable binary | |
1015 | after having initialized all your variables at the beginning of the | |
1016 | program. When the new binary is executed it will begin by executing a | |
1017 | C<goto LABEL> (with all the restrictions that C<goto> suffers). Think of | |
f86cebdf | 1018 | it as a goto with an intervening core dump and reincarnation. If C<LABEL> |
5a964f20 | 1019 | is omitted, restarts the program from the top. WARNING: Any files |
a0d0e21e LW |
1020 | opened at the time of the dump will NOT be open any more when the |
1021 | program is reincarnated, with possible resulting confusion on the part | |
1022 | of Perl. See also B<-u> option in L<perlrun>. | |
1023 | ||
1024 | Example: | |
1025 | ||
1026 | #!/usr/bin/perl | |
1027 | require 'getopt.pl'; | |
1028 | require 'stat.pl'; | |
1029 | %days = ( | |
1030 | 'Sun' => 1, | |
1031 | 'Mon' => 2, | |
1032 | 'Tue' => 3, | |
1033 | 'Wed' => 4, | |
1034 | 'Thu' => 5, | |
1035 | 'Fri' => 6, | |
1036 | 'Sat' => 7, | |
1037 | ); | |
1038 | ||
1039 | dump QUICKSTART if $ARGV[0] eq '-d'; | |
1040 | ||
1041 | QUICKSTART: | |
1042 | Getopt('f'); | |
1043 | ||
5a964f20 TC |
1044 | This operator is largely obsolete, partly because it's very hard to |
1045 | convert a core file into an executable, and because the real perl-to-C | |
1046 | compiler has superseded it. | |
1047 | ||
aa689395 | 1048 | =item each HASH |
1049 | ||
5a964f20 | 1050 | When called in list context, returns a 2-element list consisting of the |
aa689395 | 1051 | key and value for the next element of a hash, so that you can iterate over |
5a964f20 | 1052 | it. When called in scalar context, returns the key for only the "next" |
7660c0ab | 1053 | element in the hash. (Note: Keys may be C<"0"> or C<"">, which are logically |
2f9daede TP |
1054 | false; you may wish to avoid constructs like C<while ($k = each %foo) {}> |
1055 | for this reason.) | |
1056 | ||
ab192400 GS |
1057 | Entries are returned in an apparently random order. The actual random |
1058 | order is subject to change in future versions of perl, but it is guaranteed | |
1059 | to be in the same order as either the C<keys()> or C<values()> function | |
1060 | would produce on the same (unmodified) hash. | |
1061 | ||
1062 | When the hash is entirely read, a null array is returned in list context | |
1063 | (which when assigned produces a FALSE (C<0>) value), and C<undef> in | |
7660c0ab A |
1064 | scalar context. The next call to C<each()> after that will start iterating |
1065 | again. There is a single iterator for each hash, shared by all C<each()>, | |
1066 | C<keys()>, and C<values()> function calls in the program; it can be reset by | |
2f9daede TP |
1067 | reading all the elements from the hash, or by evaluating C<keys HASH> or |
1068 | C<values HASH>. If you add or delete elements of a hash while you're | |
1069 | iterating over it, you may get entries skipped or duplicated, so don't. | |
aa689395 | 1070 | |
f86cebdf | 1071 | The following prints out your environment like the printenv(1) program, |
aa689395 | 1072 | only in a different order: |
a0d0e21e LW |
1073 | |
1074 | while (($key,$value) = each %ENV) { | |
1075 | print "$key=$value\n"; | |
1076 | } | |
1077 | ||
ab192400 | 1078 | See also C<keys()>, C<values()> and C<sort()>. |
a0d0e21e | 1079 | |
a189bff9 JH |
1080 | =item else BLOCK |
1081 | ||
1082 | =item elsif (EXPR) BLOCK | |
1083 | ||
1084 | See L</if>. | |
1085 | ||
a0d0e21e LW |
1086 | =item eof FILEHANDLE |
1087 | ||
4633a7c4 LW |
1088 | =item eof () |
1089 | ||
a0d0e21e LW |
1090 | =item eof |
1091 | ||
1092 | Returns 1 if the next read on FILEHANDLE will return end of file, or if | |
1093 | FILEHANDLE is not open. FILEHANDLE may be an expression whose value | |
5a964f20 | 1094 | gives the real filehandle. (Note that this function actually |
7660c0ab | 1095 | reads a character and then C<ungetc()>s it, so isn't very useful in an |
748a9306 LW |
1096 | interactive context.) Do not read from a terminal file (or call |
1097 | C<eof(FILEHANDLE)> on it) after end-of-file is reached. Filetypes such | |
1098 | as terminals may lose the end-of-file condition if you do. | |
1099 | ||
1100 | An C<eof> without an argument uses the last file read as argument. | |
5a964f20 | 1101 | Using C<eof()> with empty parentheses is very different. It indicates the pseudo file formed of |
2f9daede TP |
1102 | the files listed on the command line, i.e., C<eof()> is reasonable to |
1103 | use inside a C<while (E<lt>E<gt>)> loop to detect the end of only the | |
1104 | last file. Use C<eof(ARGV)> or eof without the parentheses to test | |
1105 | I<EACH> file in a while (E<lt>E<gt>) loop. Examples: | |
a0d0e21e | 1106 | |
748a9306 LW |
1107 | # reset line numbering on each input file |
1108 | while (<>) { | |
5a964f20 | 1109 | next if /^\s*#/; # skip comments |
748a9306 | 1110 | print "$.\t$_"; |
5a964f20 TC |
1111 | } continue { |
1112 | close ARGV if eof; # Not eof()! | |
748a9306 LW |
1113 | } |
1114 | ||
a0d0e21e LW |
1115 | # insert dashes just before last line of last file |
1116 | while (<>) { | |
5a964f20 | 1117 | if (eof()) { # check for end of current file |
a0d0e21e | 1118 | print "--------------\n"; |
748a9306 LW |
1119 | close(ARGV); # close or break; is needed if we |
1120 | # are reading from the terminal | |
a0d0e21e LW |
1121 | } |
1122 | print; | |
1123 | } | |
1124 | ||
a0d0e21e | 1125 | Practical hint: you almost never need to use C<eof> in Perl, because the |
3b02c43c GS |
1126 | input operators return false values when they run out of data, or if there |
1127 | was an error. | |
a0d0e21e LW |
1128 | |
1129 | =item eval EXPR | |
1130 | ||
1131 | =item eval BLOCK | |
1132 | ||
c7cc6f1c GS |
1133 | In the first form, the return value of EXPR is parsed and executed as if it |
1134 | were a little Perl program. The value of the expression (which is itself | |
5a964f20 | 1135 | determined within scalar context) is first parsed, and if there weren't any |
c7cc6f1c | 1136 | errors, executed in the context of the current Perl program, so that any |
5f05dabc | 1137 | variable settings or subroutine and format definitions remain afterwards. |
c7cc6f1c GS |
1138 | Note that the value is parsed every time the eval executes. If EXPR is |
1139 | omitted, evaluates C<$_>. This form is typically used to delay parsing | |
1140 | and subsequent execution of the text of EXPR until run time. | |
1141 | ||
1142 | In the second form, the code within the BLOCK is parsed only once--at the | |
1143 | same time the code surrounding the eval itself was parsed--and executed | |
1144 | within the context of the current Perl program. This form is typically | |
1145 | used to trap exceptions more efficiently than the first (see below), while | |
1146 | also providing the benefit of checking the code within BLOCK at compile | |
1147 | time. | |
1148 | ||
1149 | The final semicolon, if any, may be omitted from the value of EXPR or within | |
1150 | the BLOCK. | |
1151 | ||
1152 | In both forms, the value returned is the value of the last expression | |
5a964f20 | 1153 | evaluated inside the mini-program; a return statement may be also used, just |
c7cc6f1c | 1154 | as with subroutines. The expression providing the return value is evaluated |
5a964f20 | 1155 | in void, scalar, or list context, depending on the context of the eval itself. |
c7cc6f1c | 1156 | See L</wantarray> for more on how the evaluation context can be determined. |
a0d0e21e | 1157 | |
7660c0ab A |
1158 | If there is a syntax error or runtime error, or a C<die()> statement is |
1159 | executed, an undefined value is returned by C<eval()>, and C<$@> is set to the | |
a0d0e21e | 1160 | error message. If there was no error, C<$@> is guaranteed to be a null |
7660c0ab | 1161 | string. Beware that using C<eval()> neither silences perl from printing |
c7cc6f1c GS |
1162 | warnings to STDERR, nor does it stuff the text of warning messages into C<$@>. |
1163 | To do either of those, you have to use the C<$SIG{__WARN__}> facility. See | |
1164 | L</warn> and L<perlvar>. | |
a0d0e21e | 1165 | |
7660c0ab A |
1166 | Note that, because C<eval()> traps otherwise-fatal errors, it is useful for |
1167 | determining whether a particular feature (such as C<socket()> or C<symlink()>) | |
a0d0e21e LW |
1168 | is implemented. It is also Perl's exception trapping mechanism, where |
1169 | the die operator is used to raise exceptions. | |
1170 | ||
1171 | If the code to be executed doesn't vary, you may use the eval-BLOCK | |
1172 | form to trap run-time errors without incurring the penalty of | |
1173 | recompiling each time. The error, if any, is still returned in C<$@>. | |
1174 | Examples: | |
1175 | ||
54310121 | 1176 | # make divide-by-zero nonfatal |
a0d0e21e LW |
1177 | eval { $answer = $a / $b; }; warn $@ if $@; |
1178 | ||
1179 | # same thing, but less efficient | |
1180 | eval '$answer = $a / $b'; warn $@ if $@; | |
1181 | ||
1182 | # a compile-time error | |
5a964f20 | 1183 | eval { $answer = }; # WRONG |
a0d0e21e LW |
1184 | |
1185 | # a run-time error | |
1186 | eval '$answer ='; # sets $@ | |
1187 | ||
7660c0ab | 1188 | When using the C<eval{}> form as an exception trap in libraries, you may |
774d564b | 1189 | wish not to trigger any C<__DIE__> hooks that user code may have |
1190 | installed. You can use the C<local $SIG{__DIE__}> construct for this | |
1191 | purpose, as shown in this example: | |
1192 | ||
1193 | # a very private exception trap for divide-by-zero | |
f86cebdf GS |
1194 | eval { local $SIG{'__DIE__'}; $answer = $a / $b; }; |
1195 | warn $@ if $@; | |
774d564b | 1196 | |
1197 | This is especially significant, given that C<__DIE__> hooks can call | |
7660c0ab | 1198 | C<die()> again, which has the effect of changing their error messages: |
774d564b | 1199 | |
1200 | # __DIE__ hooks may modify error messages | |
1201 | { | |
f86cebdf GS |
1202 | local $SIG{'__DIE__'} = |
1203 | sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x }; | |
c7cc6f1c GS |
1204 | eval { die "foo lives here" }; |
1205 | print $@ if $@; # prints "bar lives here" | |
774d564b | 1206 | } |
1207 | ||
7660c0ab | 1208 | With an C<eval()>, you should be especially careful to remember what's |
a0d0e21e LW |
1209 | being looked at when: |
1210 | ||
1211 | eval $x; # CASE 1 | |
1212 | eval "$x"; # CASE 2 | |
1213 | ||
1214 | eval '$x'; # CASE 3 | |
1215 | eval { $x }; # CASE 4 | |
1216 | ||
5a964f20 | 1217 | eval "\$$x++"; # CASE 5 |
a0d0e21e LW |
1218 | $$x++; # CASE 6 |
1219 | ||
2f9daede | 1220 | Cases 1 and 2 above behave identically: they run the code contained in |
7660c0ab | 1221 | the variable C<$x>. (Although case 2 has misleading double quotes making |
2f9daede | 1222 | the reader wonder what else might be happening (nothing is).) Cases 3 |
7660c0ab | 1223 | and 4 likewise behave in the same way: they run the code C<'$x'>, which |
2f9daede TP |
1224 | does nothing but return the value of C<$x>. (Case 4 is preferred for |
1225 | purely visual reasons, but it also has the advantage of compiling at | |
1226 | compile-time instead of at run-time.) Case 5 is a place where | |
54310121 | 1227 | normally you I<WOULD> like to use double quotes, except that in this |
2f9daede TP |
1228 | particular situation, you can just use symbolic references instead, as |
1229 | in case 6. | |
a0d0e21e | 1230 | |
4968c1e4 MG |
1231 | C<eval BLOCK> does I<not> count as a loop, so the loop control statements |
1232 | C<next>, C<last> or C<redo> cannot be used to leave or restart the block. | |
1233 | ||
1234 | ||
a0d0e21e LW |
1235 | =item exec LIST |
1236 | ||
8bf3b016 GS |
1237 | =item exec PROGRAM LIST |
1238 | ||
7660c0ab A |
1239 | The C<exec()> function executes a system command I<AND NEVER RETURNS> - |
1240 | use C<system()> instead of C<exec()> if you want it to return. It fails and | |
fb73857a | 1241 | returns FALSE only if the command does not exist I<and> it is executed |
1242 | directly instead of via your system's command shell (see below). | |
a0d0e21e | 1243 | |
7660c0ab A |
1244 | Since it's a common mistake to use C<exec()> instead of C<system()>, Perl |
1245 | warns you if there is a following statement which isn't C<die()>, C<warn()>, | |
1246 | or C<exit()> (if C<-w> is set - but you always do that). If you | |
1247 | I<really> want to follow an C<exec()> with some other statement, you | |
55d729e4 GS |
1248 | can use one of these styles to avoid the warning: |
1249 | ||
5a964f20 TC |
1250 | exec ('foo') or print STDERR "couldn't exec foo: $!"; |
1251 | { exec ('foo') }; print STDERR "couldn't exec foo: $!"; | |
55d729e4 | 1252 | |
5a964f20 | 1253 | If there is more than one argument in LIST, or if LIST is an array |
f86cebdf | 1254 | with more than one value, calls execvp(3) with the arguments in LIST. |
5a964f20 TC |
1255 | If there is only one scalar argument or an array with one element in it, |
1256 | the argument is checked for shell metacharacters, and if there are any, | |
1257 | the entire argument is passed to the system's command shell for parsing | |
1258 | (this is C</bin/sh -c> on Unix platforms, but varies on other platforms). | |
1259 | If there are no shell metacharacters in the argument, it is split into | |
7660c0ab A |
1260 | words and passed directly to C<execvp()>, which is more efficient. Note: |
1261 | C<exec()> and C<system()> do not flush your output buffer, so you may need to | |
5a964f20 | 1262 | set C<$|> to avoid lost output. Examples: |
a0d0e21e LW |
1263 | |
1264 | exec '/bin/echo', 'Your arguments are: ', @ARGV; | |
1265 | exec "sort $outfile | uniq"; | |
1266 | ||
1267 | If you don't really want to execute the first argument, but want to lie | |
1268 | to the program you are executing about its own name, you can specify | |
1269 | the program you actually want to run as an "indirect object" (without a | |
1270 | comma) in front of the LIST. (This always forces interpretation of the | |
54310121 | 1271 | LIST as a multivalued list, even if there is only a single scalar in |
a0d0e21e LW |
1272 | the list.) Example: |
1273 | ||
1274 | $shell = '/bin/csh'; | |
1275 | exec $shell '-sh'; # pretend it's a login shell | |
1276 | ||
1277 | or, more directly, | |
1278 | ||
1279 | exec {'/bin/csh'} '-sh'; # pretend it's a login shell | |
1280 | ||
bb32b41a GS |
1281 | When the arguments get executed via the system shell, results will |
1282 | be subject to its quirks and capabilities. See L<perlop/"`STRING`"> | |
1283 | for details. | |
1284 | ||
ab4f32c2 | 1285 | Using an indirect object with C<exec()> or C<system()> is also more secure. |
5a964f20 TC |
1286 | This usage forces interpretation of the arguments as a multivalued list, |
1287 | even if the list had just one argument. That way you're safe from the | |
1288 | shell expanding wildcards or splitting up words with whitespace in them. | |
1289 | ||
1290 | @args = ( "echo surprise" ); | |
1291 | ||
f86cebdf GS |
1292 | system @args; # subject to shell escapes |
1293 | # if @args == 1 | |
5a964f20 TC |
1294 | system { $args[0] } @args; # safe even with one-arg list |
1295 | ||
1296 | The first version, the one without the indirect object, ran the I<echo> | |
1297 | program, passing it C<"surprise"> an argument. The second version | |
1298 | didn't--it tried to run a program literally called I<"echo surprise">, | |
1299 | didn't find it, and set C<$?> to a non-zero value indicating failure. | |
1300 | ||
ab4f32c2 | 1301 | Note that C<exec()> will not call your C<END> blocks, nor will it call |
7660c0ab A |
1302 | any C<DESTROY> methods in your objects. |
1303 | ||
a0d0e21e LW |
1304 | =item exists EXPR |
1305 | ||
1306 | Returns TRUE if the specified hash key exists in its hash array, even | |
1307 | if the corresponding value is undefined. | |
1308 | ||
1309 | print "Exists\n" if exists $array{$key}; | |
1310 | print "Defined\n" if defined $array{$key}; | |
1311 | print "True\n" if $array{$key}; | |
1312 | ||
5f05dabc | 1313 | A hash element can be TRUE only if it's defined, and defined if |
a0d0e21e LW |
1314 | it exists, but the reverse doesn't necessarily hold true. |
1315 | ||
1316 | Note that the EXPR can be arbitrarily complicated as long as the final | |
1317 | operation is a hash key lookup: | |
1318 | ||
5a964f20 TC |
1319 | if (exists $ref->{"A"}{"B"}{$key}) { ... } |
1320 | ||
1321 | Although the last element will not spring into existence just because its | |
1322 | existence was tested, intervening ones will. Thus C<$ref-E<gt>{"A"}> | |
1323 | C<$ref-E<gt>{"B"}> will spring into existence due to the existence | |
1324 | test for a $key element. This autovivification may be fixed in a later | |
1325 | release. | |
a0d0e21e LW |
1326 | |
1327 | =item exit EXPR | |
1328 | ||
1329 | Evaluates EXPR and exits immediately with that value. (Actually, it | |
1330 | calls any defined C<END> routines first, but the C<END> routines may not | |
1331 | abort the exit. Likewise any object destructors that need to be called | |
1332 | are called before exit.) Example: | |
1333 | ||
1334 | $ans = <STDIN>; | |
1335 | exit 0 if $ans =~ /^[Xx]/; | |
1336 | ||
7660c0ab A |
1337 | See also C<die()>. If EXPR is omitted, exits with C<0> status. The only |
1338 | universally portable values for EXPR are C<0> for success and C<1> for error; | |
f86702cc | 1339 | all other values are subject to unpredictable interpretation depending |
1340 | on the environment in which the Perl program is running. | |
a0d0e21e | 1341 | |
7660c0ab A |
1342 | You shouldn't use C<exit()> to abort a subroutine if there's any chance that |
1343 | someone might want to trap whatever error happened. Use C<die()> instead, | |
1344 | which can be trapped by an C<eval()>. | |
28757baa | 1345 | |
5a964f20 TC |
1346 | All C<END{}> blocks are run at exit time. See L<perlsub> for details. |
1347 | ||
a0d0e21e LW |
1348 | =item exp EXPR |
1349 | ||
54310121 | 1350 | =item exp |
bbce6d69 | 1351 | |
54310121 | 1352 | Returns I<e> (the natural logarithm base) to the power of EXPR. |
a0d0e21e LW |
1353 | If EXPR is omitted, gives C<exp($_)>. |
1354 | ||
1355 | =item fcntl FILEHANDLE,FUNCTION,SCALAR | |
1356 | ||
f86cebdf | 1357 | Implements the fcntl(2) function. You'll probably have to say |
a0d0e21e LW |
1358 | |
1359 | use Fcntl; | |
1360 | ||
0ade1984 | 1361 | first to get the correct constant definitions. Argument processing and |
7660c0ab | 1362 | value return works just like C<ioctl()> below. |
a0d0e21e LW |
1363 | For example: |
1364 | ||
1365 | use Fcntl; | |
5a964f20 TC |
1366 | fcntl($filehandle, F_GETFL, $packed_return_buffer) |
1367 | or die "can't fcntl F_GETFL: $!"; | |
1368 | ||
ab4f32c2 A |
1369 | You don't have to check for C<defined()> on the return from |
1370 | C<fnctl()>. Like C<ioctl()>, it maps a C<0> return from the system | |
7660c0ab A |
1371 | call into "C<0> but true" in Perl. This string is true in |
1372 | boolean context and C<0> in numeric context. It is also | |
5a964f20 TC |
1373 | exempt from the normal B<-w> warnings on improper numeric |
1374 | conversions. | |
1375 | ||
7660c0ab | 1376 | Note that C<fcntl()> will produce a fatal error if used on a machine that |
f86cebdf | 1377 | doesn't implement fcntl(2). |
a0d0e21e LW |
1378 | |
1379 | =item fileno FILEHANDLE | |
1380 | ||
1381 | Returns the file descriptor for a filehandle. This is useful for | |
7660c0ab | 1382 | constructing bitmaps for C<select()> and low-level POSIX tty-handling |
5a964f20 TC |
1383 | operations. If FILEHANDLE is an expression, the value is taken as |
1384 | an indirect filehandle, generally its name. | |
1385 | ||
1386 | You can use this to find out whether two handles refer to the | |
1387 | same underlying descriptor: | |
1388 | ||
1389 | if (fileno(THIS) == fileno(THAT)) { | |
1390 | print "THIS and THAT are dups\n"; | |
1391 | } | |
a0d0e21e LW |
1392 | |
1393 | =item flock FILEHANDLE,OPERATION | |
1394 | ||
f86cebdf | 1395 | Calls flock(2), or an emulation of it, on FILEHANDLE. Returns TRUE for |
68dc0745 | 1396 | success, FALSE on failure. Produces a fatal error if used on a machine |
f86cebdf | 1397 | that doesn't implement flock(2), fcntl(2) locking, or lockf(3). C<flock()> |
68dc0745 | 1398 | is Perl's portable file locking interface, although it locks only entire |
1399 | files, not records. | |
8ebc5c01 | 1400 | |
a3cb178b | 1401 | On many platforms (including most versions or clones of Unix), locks |
7660c0ab | 1402 | established by C<flock()> are B<merely advisory>. Such discretionary locks |
5a964f20 | 1403 | are more flexible, but offer fewer guarantees. This means that files |
7660c0ab A |
1404 | locked with C<flock()> may be modified by programs that do not also use |
1405 | C<flock()>. Windows NT and OS/2 are among the platforms which | |
5a964f20 | 1406 | enforce mandatory locking. See your local documentation for details. |
a3cb178b | 1407 | |
8ebc5c01 | 1408 | OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with |
1409 | LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but | |
68dc0745 | 1410 | you can use the symbolic names if import them from the Fcntl module, |
1411 | either individually, or as a group using the ':flock' tag. LOCK_SH | |
1412 | requests a shared lock, LOCK_EX requests an exclusive lock, and LOCK_UN | |
1413 | releases a previously requested lock. If LOCK_NB is added to LOCK_SH or | |
7660c0ab | 1414 | LOCK_EX then C<flock()> will return immediately rather than blocking |
68dc0745 | 1415 | waiting for the lock (check the return status to see if you got it). |
1416 | ||
1417 | To avoid the possibility of mis-coordination, Perl flushes FILEHANDLE | |
1418 | before (un)locking it. | |
8ebc5c01 | 1419 | |
f86cebdf | 1420 | Note that the emulation built with lockf(3) doesn't provide shared |
8ebc5c01 | 1421 | locks, and it requires that FILEHANDLE be open with write intent. These |
f86cebdf GS |
1422 | are the semantics that lockf(3) implements. Most (all?) systems |
1423 | implement lockf(3) in terms of fcntl(2) locking, though, so the | |
8ebc5c01 | 1424 | differing semantics shouldn't bite too many people. |
1425 | ||
7660c0ab A |
1426 | Note also that some versions of C<flock()> cannot lock things over the |
1427 | network; you would need to use the more system-specific C<fcntl()> for | |
f86cebdf GS |
1428 | that. If you like you can force Perl to ignore your system's flock(2) |
1429 | function, and so provide its own fcntl(2)-based emulation, by passing | |
8ebc5c01 | 1430 | the switch C<-Ud_flock> to the F<Configure> program when you configure |
1431 | perl. | |
4633a7c4 LW |
1432 | |
1433 | Here's a mailbox appender for BSD systems. | |
a0d0e21e | 1434 | |
7e1af8bc | 1435 | use Fcntl ':flock'; # import LOCK_* constants |
a0d0e21e LW |
1436 | |
1437 | sub lock { | |
7e1af8bc | 1438 | flock(MBOX,LOCK_EX); |
a0d0e21e LW |
1439 | # and, in case someone appended |
1440 | # while we were waiting... | |
1441 | seek(MBOX, 0, 2); | |
1442 | } | |
1443 | ||
1444 | sub unlock { | |
7e1af8bc | 1445 | flock(MBOX,LOCK_UN); |
a0d0e21e LW |
1446 | } |
1447 | ||
1448 | open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}") | |
1449 | or die "Can't open mailbox: $!"; | |
1450 | ||
1451 | lock(); | |
1452 | print MBOX $msg,"\n\n"; | |
1453 | unlock(); | |
1454 | ||
cb1a09d0 | 1455 | See also L<DB_File> for other flock() examples. |
a0d0e21e | 1456 | |
a189bff9 JH |
1457 | =item for (INITIAL; WHILE; EACH) BLOCK |
1458 | ||
1459 | Do INITIAL, enter BLOCK while EXPR is true, at the end of each round | |
1460 | do EACH. For example: | |
1461 | ||
1462 | for ($i = 0, $j = 0; $i < 10; $i++) { | |
1463 | if ($i % 3 == 0) { $j++ } | |
1464 | print "i = $i, j = $j\n"; | |
1465 | } | |
1466 | ||
1467 | See L<perlsyn> for more details. See also L</foreach>, a twin of | |
1468 | C<for>, L</while> and L</until>, close cousins of L<for>, and | |
1469 | L</last>, L</next>, and L</redo> for additional control flow. | |
1470 | ||
1471 | =item foreach LOOPVAR (LIST) BLOCK | |
1472 | ||
1473 | Enter BLOCK as LOOPVAR set in turn to each element of LIST. | |
1474 | For example: | |
1475 | ||
1476 | foreach $rolling (@stones) { print "rolling $stone\n" } | |
1477 | ||
1478 | foreach my $file (@files) { print "file $file\n" } | |
1479 | ||
1480 | The LOOPVAR is optional and defaults to C<$_>. If the elements are | |
1481 | modifiable (as opposed to constants or tied variables) you can modify them. | |
1482 | ||
1483 | foreach (@words) { tr/abc/xyz/ } | |
1484 | ||
1485 | See L<perlsyn> for more details. See also L</for>, a twin of | |
1486 | C<foreach>, L</while> and L</until>, close cousins of L<for>, and | |
1487 | L</last>, L</next>, and L</redo> for additional control flow. | |
1488 | ||
a0d0e21e LW |
1489 | =item fork |
1490 | ||
f86cebdf | 1491 | Does a fork(2) system call. Returns the child pid to the parent process, |
7660c0ab | 1492 | C<0> to the child process, or C<undef> if the fork is unsuccessful. |
5a964f20 | 1493 | |
a0d0e21e | 1494 | Note: unflushed buffers remain unflushed in both processes, which means |
7660c0ab A |
1495 | you may need to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> |
1496 | method of C<IO::Handle> to avoid duplicate output. | |
a0d0e21e | 1497 | |
7660c0ab | 1498 | If you C<fork()> without ever waiting on your children, you will accumulate |
a0d0e21e LW |
1499 | zombies: |
1500 | ||
4633a7c4 | 1501 | $SIG{CHLD} = sub { wait }; |
a0d0e21e | 1502 | |
54310121 | 1503 | There's also the double-fork trick (error checking on |
7660c0ab | 1504 | C<fork()> returns omitted); |
a0d0e21e LW |
1505 | |
1506 | unless ($pid = fork) { | |
1507 | unless (fork) { | |
1508 | exec "what you really wanna do"; | |
1509 | die "no exec"; | |
1510 | # ... or ... | |
4633a7c4 | 1511 | ## (some_perl_code_here) |
a0d0e21e LW |
1512 | exit 0; |
1513 | } | |
1514 | exit 0; | |
1515 | } | |
1516 | waitpid($pid,0); | |
1517 | ||
cb1a09d0 AD |
1518 | See also L<perlipc> for more examples of forking and reaping |
1519 | moribund children. | |
1520 | ||
28757baa | 1521 | Note that if your forked child inherits system file descriptors like |
1522 | STDIN and STDOUT that are actually connected by a pipe or socket, even | |
5a964f20 | 1523 | if you exit, then the remote server (such as, say, httpd or rsh) won't think |
7660c0ab | 1524 | you're done. You should reopen those to F</dev/null> if it's any issue. |
28757baa | 1525 | |
cb1a09d0 AD |
1526 | =item format |
1527 | ||
7660c0ab | 1528 | Declare a picture format for use by the C<write()> function. For |
cb1a09d0 AD |
1529 | example: |
1530 | ||
54310121 | 1531 | format Something = |
cb1a09d0 AD |
1532 | Test: @<<<<<<<< @||||| @>>>>> |
1533 | $str, $%, '$' . int($num) | |
1534 | . | |
1535 | ||
1536 | $str = "widget"; | |
184e9718 | 1537 | $num = $cost/$quantity; |
cb1a09d0 AD |
1538 | $~ = 'Something'; |
1539 | write; | |
1540 | ||
1541 | See L<perlform> for many details and examples. | |
1542 | ||
8903cb82 | 1543 | =item formline PICTURE,LIST |
a0d0e21e | 1544 | |
5a964f20 | 1545 | This is an internal function used by C<format>s, though you may call it, |
a0d0e21e LW |
1546 | too. It formats (see L<perlform>) a list of values according to the |
1547 | contents of PICTURE, placing the output into the format output | |
7660c0ab A |
1548 | accumulator, C<$^A> (or C<$ACCUMULATOR> in English). |
1549 | Eventually, when a C<write()> is done, the contents of | |
a0d0e21e | 1550 | C<$^A> are written to some filehandle, but you could also read C<$^A> |
7660c0ab A |
1551 | yourself and then set C<$^A> back to C<"">. Note that a format typically |
1552 | does one C<formline()> per line of form, but the C<formline()> function itself | |
748a9306 | 1553 | doesn't care how many newlines are embedded in the PICTURE. This means |
4633a7c4 | 1554 | that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line. |
748a9306 LW |
1555 | You may therefore need to use multiple formlines to implement a single |
1556 | record format, just like the format compiler. | |
1557 | ||
5f05dabc | 1558 | Be careful if you put double quotes around the picture, because an "C<@>" |
748a9306 | 1559 | character may be taken to mean the beginning of an array name. |
7660c0ab | 1560 | C<formline()> always returns TRUE. See L<perlform> for other examples. |
a0d0e21e LW |
1561 | |
1562 | =item getc FILEHANDLE | |
1563 | ||
1564 | =item getc | |
1565 | ||
1566 | Returns the next character from the input file attached to FILEHANDLE, | |
9bc64814 | 1567 | or the undefined value at end of file, or if there was an error. If |
3b02c43c GS |
1568 | FILEHANDLE is omitted, reads from STDIN. This is not particularly |
1569 | efficient. It cannot be used to get unbuffered single-characters, | |
1570 | however. For that, try something more like: | |
4633a7c4 LW |
1571 | |
1572 | if ($BSD_STYLE) { | |
1573 | system "stty cbreak </dev/tty >/dev/tty 2>&1"; | |
1574 | } | |
1575 | else { | |
54310121 | 1576 | system "stty", '-icanon', 'eol', "\001"; |
4633a7c4 LW |
1577 | } |
1578 | ||
1579 | $key = getc(STDIN); | |
1580 | ||
1581 | if ($BSD_STYLE) { | |
1582 | system "stty -cbreak </dev/tty >/dev/tty 2>&1"; | |
1583 | } | |
1584 | else { | |
5f05dabc | 1585 | system "stty", 'icanon', 'eol', '^@'; # ASCII null |
4633a7c4 LW |
1586 | } |
1587 | print "\n"; | |
1588 | ||
54310121 | 1589 | Determination of whether $BSD_STYLE should be set |
1590 | is left as an exercise to the reader. | |
cb1a09d0 | 1591 | |
7660c0ab | 1592 | The C<POSIX::getattr()> function can do this more portably on systems |
5a964f20 | 1593 | purporting POSIX compliance. |
cb1a09d0 | 1594 | See also the C<Term::ReadKey> module from your nearest CPAN site; |
b687b08b | 1595 | details on CPAN can be found on L<perlmodlib/CPAN>. |
a0d0e21e LW |
1596 | |
1597 | =item getlogin | |
1598 | ||
5a964f20 TC |
1599 | Implements the C library function of the same name, which on most |
1600 | systems returns the current login from F</etc/utmp>, if any. If null, | |
7660c0ab | 1601 | use C<getpwuid()>. |
a0d0e21e | 1602 | |
f86702cc | 1603 | $login = getlogin || getpwuid($<) || "Kilroy"; |
a0d0e21e | 1604 | |
7660c0ab A |
1605 | Do not consider C<getlogin()> for authentication: it is not as |
1606 | secure as C<getpwuid()>. | |
4633a7c4 | 1607 | |
a0d0e21e LW |
1608 | =item getpeername SOCKET |
1609 | ||
1610 | Returns the packed sockaddr address of other end of the SOCKET connection. | |
1611 | ||
4633a7c4 LW |
1612 | use Socket; |
1613 | $hersockaddr = getpeername(SOCK); | |
1614 | ($port, $iaddr) = unpack_sockaddr_in($hersockaddr); | |
1615 | $herhostname = gethostbyaddr($iaddr, AF_INET); | |
1616 | $herstraddr = inet_ntoa($iaddr); | |
a0d0e21e LW |
1617 | |
1618 | =item getpgrp PID | |
1619 | ||
47e29363 | 1620 | Returns the current process group for the specified PID. Use |
7660c0ab | 1621 | a PID of C<0> to get the current process group for the |
4633a7c4 | 1622 | current process. Will raise an exception if used on a machine that |
f86cebdf | 1623 | doesn't implement getpgrp(2). If PID is omitted, returns process |
7660c0ab A |
1624 | group of current process. Note that the POSIX version of C<getpgrp()> |
1625 | does not accept a PID argument, so only C<PID==0> is truly portable. | |
a0d0e21e LW |
1626 | |
1627 | =item getppid | |
1628 | ||
1629 | Returns the process id of the parent process. | |
1630 | ||
1631 | =item getpriority WHICH,WHO | |
1632 | ||
4633a7c4 LW |
1633 | Returns the current priority for a process, a process group, or a user. |
1634 | (See L<getpriority(2)>.) Will raise a fatal exception if used on a | |
f86cebdf | 1635 | machine that doesn't implement getpriority(2). |
a0d0e21e LW |
1636 | |
1637 | =item getpwnam NAME | |
1638 | ||
1639 | =item getgrnam NAME | |
1640 | ||
1641 | =item gethostbyname NAME | |
1642 | ||
1643 | =item getnetbyname NAME | |
1644 | ||
1645 | =item getprotobyname NAME | |
1646 | ||
1647 | =item getpwuid UID | |
1648 | ||
1649 | =item getgrgid GID | |
1650 | ||
1651 | =item getservbyname NAME,PROTO | |
1652 | ||
1653 | =item gethostbyaddr ADDR,ADDRTYPE | |
1654 | ||
1655 | =item getnetbyaddr ADDR,ADDRTYPE | |
1656 | ||
1657 | =item getprotobynumber NUMBER | |
1658 | ||
1659 | =item getservbyport PORT,PROTO | |
1660 | ||
1661 | =item getpwent | |
1662 | ||
1663 | =item getgrent | |
1664 | ||
1665 | =item gethostent | |
1666 | ||
1667 | =item getnetent | |
1668 | ||
1669 | =item getprotoent | |
1670 | ||
1671 | =item getservent | |
1672 | ||
1673 | =item setpwent | |
1674 | ||
1675 | =item setgrent | |
1676 | ||
1677 | =item sethostent STAYOPEN | |
1678 | ||
1679 | =item setnetent STAYOPEN | |
1680 | ||
1681 | =item setprotoent STAYOPEN | |
1682 | ||
1683 | =item setservent STAYOPEN | |
1684 | ||
1685 | =item endpwent | |
1686 | ||
1687 | =item endgrent | |
1688 | ||
1689 | =item endhostent | |
1690 | ||
1691 | =item endnetent | |
1692 | ||
1693 | =item endprotoent | |
1694 | ||
1695 | =item endservent | |
1696 | ||
1697 | These routines perform the same functions as their counterparts in the | |
5a964f20 | 1698 | system library. In list context, the return values from the |
a0d0e21e LW |
1699 | various get routines are as follows: |
1700 | ||
1701 | ($name,$passwd,$uid,$gid, | |
6ee623d5 | 1702 | $quota,$comment,$gcos,$dir,$shell,$expire) = getpw* |
a0d0e21e LW |
1703 | ($name,$passwd,$gid,$members) = getgr* |
1704 | ($name,$aliases,$addrtype,$length,@addrs) = gethost* | |
1705 | ($name,$aliases,$addrtype,$net) = getnet* | |
1706 | ($name,$aliases,$proto) = getproto* | |
1707 | ($name,$aliases,$port,$proto) = getserv* | |
1708 | ||
1709 | (If the entry doesn't exist you get a null list.) | |
1710 | ||
5a964f20 | 1711 | In scalar context, you get the name, unless the function was a |
a0d0e21e LW |
1712 | lookup by name, in which case you get the other thing, whatever it is. |
1713 | (If the entry doesn't exist you get the undefined value.) For example: | |
1714 | ||
5a964f20 TC |
1715 | $uid = getpwnam($name); |
1716 | $name = getpwuid($num); | |
1717 | $name = getpwent(); | |
1718 | $gid = getgrnam($name); | |
1719 | $name = getgrgid($num; | |
1720 | $name = getgrent(); | |
1721 | #etc. | |
a0d0e21e | 1722 | |
7660c0ab | 1723 | In I<getpw*()> the fields C<$quota>, C<$comment>, and C<$expire> are special |
6ee623d5 | 1724 | cases in the sense that in many systems they are unsupported. If the |
7660c0ab A |
1725 | C<$quota> is unsupported, it is an empty scalar. If it is supported, it |
1726 | usually encodes the disk quota. If the C<$comment> field is unsupported, | |
6ee623d5 GS |
1727 | it is an empty scalar. If it is supported it usually encodes some |
1728 | administrative comment about the user. In some systems the $quota | |
7660c0ab A |
1729 | field may be C<$change> or C<$age>, fields that have to do with password |
1730 | aging. In some systems the C<$comment> field may be C<$class>. The C<$expire> | |
6ee623d5 GS |
1731 | field, if present, encodes the expiration period of the account or the |
1732 | password. For the availability and the exact meaning of these fields | |
f86cebdf | 1733 | in your system, please consult your getpwnam(3) documentation and your |
7660c0ab A |
1734 | F<pwd.h> file. You can also find out from within Perl which meaning |
1735 | your C<$quota> and C<$comment> fields have and whether you have the C<$expire> | |
1736 | field by using the C<Config> module and the values C<d_pwquota>, C<d_pwage>, | |
1737 | C<d_pwchange>, C<d_pwcomment>, and C<d_pwexpire>. | |
6ee623d5 | 1738 | |
7660c0ab | 1739 | The C<$members> value returned by I<getgr*()> is a space separated list of |
a0d0e21e LW |
1740 | the login names of the members of the group. |
1741 | ||
1742 | For the I<gethost*()> functions, if the C<h_errno> variable is supported in | |
1743 | C, it will be returned to you via C<$?> if the function call fails. The | |
7660c0ab | 1744 | C<@addrs> value returned by a successful call is a list of the raw |
a0d0e21e LW |
1745 | addresses returned by the corresponding system library call. In the |
1746 | Internet domain, each address is four bytes long and you can unpack it | |
1747 | by saying something like: | |
1748 | ||
1749 | ($a,$b,$c,$d) = unpack('C4',$addr[0]); | |
1750 | ||
5a964f20 TC |
1751 | If you get tired of remembering which element of the return list contains |
1752 | which return value, by-name interfaces are also provided in modules: | |
7660c0ab A |
1753 | C<File::stat>, C<Net::hostent>, C<Net::netent>, C<Net::protoent>, C<Net::servent>, |
1754 | C<Time::gmtime>, C<Time::localtime>, and C<User::grent>. These override the | |
5a964f20 TC |
1755 | normal built-in, replacing them with versions that return objects with |
1756 | the appropriate names for each field. For example: | |
1757 | ||
1758 | use File::stat; | |
1759 | use User::pwent; | |
1760 | $is_his = (stat($filename)->uid == pwent($whoever)->uid); | |
1761 | ||
1762 | Even though it looks like they're the same method calls (uid), | |
7660c0ab | 1763 | they aren't, because a C<File::stat> object is different from a C<User::pwent> object. |
5a964f20 | 1764 | |
a0d0e21e LW |
1765 | =item getsockname SOCKET |
1766 | ||
1767 | Returns the packed sockaddr address of this end of the SOCKET connection. | |
1768 | ||
4633a7c4 LW |
1769 | use Socket; |
1770 | $mysockaddr = getsockname(SOCK); | |
1771 | ($port, $myaddr) = unpack_sockaddr_in($mysockaddr); | |
a0d0e21e LW |
1772 | |
1773 | =item getsockopt SOCKET,LEVEL,OPTNAME | |
1774 | ||
5a964f20 | 1775 | Returns the socket option requested, or undef if there is an error. |
a0d0e21e LW |
1776 | |
1777 | =item glob EXPR | |
1778 | ||
0a753a76 | 1779 | =item glob |
1780 | ||
7660c0ab | 1781 | Returns the value of EXPR with filename expansions such as the standard Unix shell F</bin/sh> would |
68dc0745 | 1782 | do. This is the internal function implementing the C<E<lt>*.cE<gt>> |
7660c0ab | 1783 | operator, but you can use it directly. If EXPR is omitted, C<$_> is used. |
68dc0745 | 1784 | The C<E<lt>*.cE<gt>> operator is discussed in more detail in |
1785 | L<perlop/"I/O Operators">. | |
a0d0e21e LW |
1786 | |
1787 | =item gmtime EXPR | |
1788 | ||
1789 | Converts a time as returned by the time function to a 9-element array | |
54310121 | 1790 | with the time localized for the standard Greenwich time zone. |
4633a7c4 | 1791 | Typically used as follows: |
a0d0e21e | 1792 | |
54310121 | 1793 | # 0 1 2 3 4 5 6 7 8 |
a0d0e21e LW |
1794 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
1795 | gmtime(time); | |
1796 | ||
1797 | All array elements are numeric, and come straight out of a struct tm. | |
7660c0ab A |
1798 | In particular this means that C<$mon> has the range C<0..11> and C<$wday> has |
1799 | the range C<0..6> with sunday as day C<0>. Also, C<$year> is the number of | |
1800 | years since 1900, that is, C<$year> is C<123> in year 2023, I<not> simply the last two digits of the year. | |
2f9daede TP |
1801 | |
1802 | If EXPR is omitted, does C<gmtime(time())>. | |
a0d0e21e | 1803 | |
f86cebdf | 1804 | In scalar context, returns the ctime(3) value: |
0a753a76 | 1805 | |
1806 | $now_string = gmtime; # e.g., "Thu Oct 13 04:54:34 1994" | |
1807 | ||
7660c0ab | 1808 | Also see the C<timegm()> function provided by the C<Time::Local> module, |
f86cebdf | 1809 | and the strftime(3) function available via the POSIX module. |
7660c0ab A |
1810 | |
1811 | This scalar value is B<not> locale dependent, see L<perllocale>, but | |
1812 | instead a Perl builtin. Also see the C<Time::Local> module, and the | |
f86cebdf | 1813 | strftime(3) and mktime(3) function available via the POSIX module. To |
7660c0ab A |
1814 | get somewhat similar but locale dependent date strings, set up your |
1815 | locale environment variables appropriately (please see L<perllocale>) | |
1816 | and try for example: | |
1817 | ||
1818 | use POSIX qw(strftime); | |
1819 | $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime; | |
1820 | ||
1821 | Note that the C<%a> and C<%b>, the short forms of the day of the week | |
1822 | and the month of the year, may not necessarily be three characters wide. | |
0a753a76 | 1823 | |
a0d0e21e LW |
1824 | =item goto LABEL |
1825 | ||
748a9306 LW |
1826 | =item goto EXPR |
1827 | ||
a0d0e21e LW |
1828 | =item goto &NAME |
1829 | ||
7660c0ab | 1830 | The C<goto-LABEL> form finds the statement labeled with LABEL and resumes |
a0d0e21e | 1831 | execution there. It may not be used to go into any construct that |
7660c0ab | 1832 | requires initialization, such as a subroutine or a C<foreach> loop. It |
0a753a76 | 1833 | also can't be used to go into a construct that is optimized away, |
7660c0ab | 1834 | or to get out of a block or subroutine given to C<sort()>. |
0a753a76 | 1835 | It can be used to go almost anywhere else within the dynamic scope, |
a0d0e21e | 1836 | including out of subroutines, but it's usually better to use some other |
ab4f32c2 | 1837 | construct such as C<last> or C<die()>. The author of Perl has never felt the |
7660c0ab | 1838 | need to use this form of C<goto> (in Perl, that is--C is another matter). |
a0d0e21e | 1839 | |
7660c0ab A |
1840 | The C<goto-EXPR> form expects a label name, whose scope will be resolved |
1841 | dynamically. This allows for computed C<goto>s per FORTRAN, but isn't | |
748a9306 LW |
1842 | necessarily recommended if you're optimizing for maintainability: |
1843 | ||
1844 | goto ("FOO", "BAR", "GLARCH")[$i]; | |
1845 | ||
7660c0ab | 1846 | The C<goto-&NAME> form is highly magical, and substitutes a call to the |
a0d0e21e | 1847 | named subroutine for the currently running subroutine. This is used by |
7660c0ab | 1848 | C<AUTOLOAD> subroutines that wish to load another subroutine and then |
a0d0e21e | 1849 | pretend that the other subroutine had been called in the first place |
7660c0ab A |
1850 | (except that any modifications to C<@_> in the current subroutine are |
1851 | propagated to the other subroutine.) After the C<goto>, not even C<caller()> | |
a0d0e21e LW |
1852 | will be able to tell that this routine was called first. |
1853 | ||
1854 | =item grep BLOCK LIST | |
1855 | ||
1856 | =item grep EXPR,LIST | |
1857 | ||
f86cebdf | 1858 | This is similar in spirit to, but not the same as, grep(1) |
2f9daede TP |
1859 | and its relatives. In particular, it is not limited to using |
1860 | regular expressions. | |
1861 | ||
a0d0e21e | 1862 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
7660c0ab | 1863 | C<$_> to each element) and returns the list value consisting of those |
a0d0e21e LW |
1864 | elements for which the expression evaluated to TRUE. In a scalar |
1865 | context, returns the number of times the expression was TRUE. | |
1866 | ||
1867 | @foo = grep(!/^#/, @bar); # weed out comments | |
1868 | ||
1869 | or equivalently, | |
1870 | ||
1871 | @foo = grep {!/^#/} @bar; # weed out comments | |
1872 | ||
7660c0ab | 1873 | Note that, because C<$_> is a reference into the list value, it can be used |
a0d0e21e LW |
1874 | to modify the elements of the array. While this is useful and |
1875 | supported, it can cause bizarre results if the LIST is not a named | |
2f9daede | 1876 | array. Similarly, grep returns aliases into the original list, |
f86cebdf | 1877 | much like the way that a for loop's index variable aliases the list |
2f9daede | 1878 | elements. That is, modifying an element of a list returned by grep |
ab4f32c2 | 1879 | (for example, in a C<foreach>, C<map()> or another C<grep()>) |
2f9daede | 1880 | actually modifies the element in the original list. |
a0d0e21e | 1881 | |
fb73857a | 1882 | See also L</map> for an array composed of the results of the BLOCK or EXPR. |
38325410 | 1883 | |
a0d0e21e LW |
1884 | =item hex EXPR |
1885 | ||
54310121 | 1886 | =item hex |
bbce6d69 | 1887 | |
54310121 | 1888 | Interprets EXPR as a hex string and returns the corresponding |
2f9daede | 1889 | value. (To convert strings that might start with either 0 or 0x |
7660c0ab | 1890 | see L</oct>.) If EXPR is omitted, uses C<$_>. |
2f9daede TP |
1891 | |
1892 | print hex '0xAf'; # prints '175' | |
1893 | print hex 'aF'; # same | |
a0d0e21e | 1894 | |
a189bff9 JH |
1895 | =item if (EXPR) BLOCK |
1896 | ||
1897 | =item if (EXPR) BLOCK else BLOCK2 | |
1898 | ||
1899 | =item if (EXPR) BLOCK elsif (EXPR2) BLOCK2 | |
1900 | ||
1901 | Enter BLOCKs conditionally. The first EXPR to return true | |
1902 | causes the corresponding BLOCK to be entered, or, in the case | |
1903 | of C<else>, the fall-through default BLOCK. | |
1904 | ||
a91c35b0 JH |
1905 | Note 1: Perl wants BLOCKS, expressions won't do (like they do |
1906 | e.g. in C, C++, Java, Pascal). | |
1907 | ||
1908 | Note 2: It's C<elsif>, not C<elseif>. You can have as many | |
1909 | C<elsif>s as you want. | |
a189bff9 JH |
1910 | |
1911 | See L<perlsyn> for more details. See also C<unless>. | |
1912 | ||
a0d0e21e LW |
1913 | =item import |
1914 | ||
7660c0ab | 1915 | There is no builtin C<import()> function. It is just an ordinary |
4633a7c4 | 1916 | method (subroutine) defined (or inherited) by modules that wish to export |
7660c0ab | 1917 | names to another module. The C<use()> function calls the C<import()> method |
54310121 | 1918 | for the package used. See also L</use()>, L<perlmod>, and L<Exporter>. |
a0d0e21e LW |
1919 | |
1920 | =item index STR,SUBSTR,POSITION | |
1921 | ||
1922 | =item index STR,SUBSTR | |
1923 | ||
4633a7c4 LW |
1924 | Returns the position of the first occurrence of SUBSTR in STR at or after |
1925 | POSITION. If POSITION is omitted, starts searching from the beginning of | |
7660c0ab | 1926 | the string. The return value is based at C<0> (or whatever you've set the C<$[> |
4633a7c4 | 1927 | variable to--but don't do that). If the substring is not found, returns |
7660c0ab | 1928 | one less than the base, ordinarily C<-1>. |
a0d0e21e LW |
1929 | |
1930 | =item int EXPR | |
1931 | ||
54310121 | 1932 | =item int |
bbce6d69 | 1933 | |
7660c0ab | 1934 | Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>. |
5a964f20 | 1935 | You should not use this for rounding, because it truncates |
7660c0ab A |
1936 | towards C<0>, and because machine representations of floating point |
1937 | numbers can sometimes produce counterintuitive results. Usually C<sprintf()> or C<printf()>, | |
1938 | or the C<POSIX::floor> or C<POSIX::ceil> functions, would serve you better. | |
a0d0e21e LW |
1939 | |
1940 | =item ioctl FILEHANDLE,FUNCTION,SCALAR | |
1941 | ||
f86cebdf | 1942 | Implements the ioctl(2) function. You'll probably have to say |
a0d0e21e | 1943 | |
4633a7c4 | 1944 | require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph |
a0d0e21e | 1945 | |
4633a7c4 | 1946 | first to get the correct function definitions. If F<ioctl.ph> doesn't |
a0d0e21e | 1947 | exist or doesn't have the correct definitions you'll have to roll your |
4633a7c4 | 1948 | own, based on your C header files such as F<E<lt>sys/ioctl.hE<gt>>. |
5a964f20 | 1949 | (There is a Perl script called B<h2ph> that comes with the Perl kit that |
54310121 | 1950 | may help you in this, but it's nontrivial.) SCALAR will be read and/or |
4633a7c4 | 1951 | written depending on the FUNCTION--a pointer to the string value of SCALAR |
ab4f32c2 | 1952 | will be passed as the third argument of the actual C<ioctl()> call. (If SCALAR |
4633a7c4 LW |
1953 | has no string value but does have a numeric value, that value will be |
1954 | passed rather than a pointer to the string value. To guarantee this to be | |
7660c0ab | 1955 | TRUE, add a C<0> to the scalar before using it.) The C<pack()> and C<unpack()> |
4633a7c4 | 1956 | functions are useful for manipulating the values of structures used by |
7660c0ab | 1957 | C<ioctl()>. The following example sets the erase character to DEL. |
a0d0e21e LW |
1958 | |
1959 | require 'ioctl.ph'; | |
4633a7c4 LW |
1960 | $getp = &TIOCGETP; |
1961 | die "NO TIOCGETP" if $@ || !$getp; | |
a0d0e21e | 1962 | $sgttyb_t = "ccccs"; # 4 chars and a short |
4633a7c4 | 1963 | if (ioctl(STDIN,$getp,$sgttyb)) { |
a0d0e21e LW |
1964 | @ary = unpack($sgttyb_t,$sgttyb); |
1965 | $ary[2] = 127; | |
1966 | $sgttyb = pack($sgttyb_t,@ary); | |
4633a7c4 | 1967 | ioctl(STDIN,&TIOCSETP,$sgttyb) |
a0d0e21e LW |
1968 | || die "Can't ioctl: $!"; |
1969 | } | |
1970 | ||
ab4f32c2 | 1971 | The return value of C<ioctl()> (and C<fcntl()>) is as follows: |
a0d0e21e LW |
1972 | |
1973 | if OS returns: then Perl returns: | |
1974 | -1 undefined value | |
1975 | 0 string "0 but true" | |
1976 | anything else that number | |
1977 | ||
1978 | Thus Perl returns TRUE on success and FALSE on failure, yet you can | |
1979 | still easily determine the actual value returned by the operating | |
1980 | system: | |
1981 | ||
1982 | ($retval = ioctl(...)) || ($retval = -1); | |
1983 | printf "System returned %d\n", $retval; | |
1984 | ||
7660c0ab | 1985 | The special string "C<0> but true" is excempt from B<-w> complaints |
5a964f20 TC |
1986 | about improper numeric conversions. |
1987 | ||
a0d0e21e LW |
1988 | =item join EXPR,LIST |
1989 | ||
54310121 | 1990 | Joins the separate strings of LIST into a single string with |
a0d0e21e LW |
1991 | fields separated by the value of EXPR, and returns the string. |
1992 | Example: | |
1993 | ||
1994 | $_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); | |
1995 | ||
7660c0ab | 1996 | See L</split>. |
a0d0e21e | 1997 | |
aa689395 | 1998 | =item keys HASH |
1999 | ||
1d2dff63 GS |
2000 | Returns a list consisting of all the keys of the named hash. (In a |
2001 | scalar context, returns the number of keys.) The keys are returned in | |
ab192400 GS |
2002 | an apparently random order. The actual random order is subject to |
2003 | change in future versions of perl, but it is guaranteed to be the same | |
2004 | order as either the C<values()> or C<each()> function produces (given | |
2005 | that the hash has not been modified). As a side effect, it resets | |
2006 | HASH's iterator. | |
a0d0e21e | 2007 | |
aa689395 | 2008 | Here is yet another way to print your environment: |
a0d0e21e LW |
2009 | |
2010 | @keys = keys %ENV; | |
2011 | @values = values %ENV; | |
2012 | while ($#keys >= 0) { | |
2013 | print pop(@keys), '=', pop(@values), "\n"; | |
2014 | } | |
2015 | ||
2016 | or how about sorted by key: | |
2017 | ||
2018 | foreach $key (sort(keys %ENV)) { | |
2019 | print $key, '=', $ENV{$key}, "\n"; | |
2020 | } | |
2021 | ||
aca803df | 2022 | To sort a hash by value, you'll need to use a C<sort()> function. |
aa689395 | 2023 | Here's a descending numeric sort of a hash by its values: |
4633a7c4 | 2024 | |
5a964f20 | 2025 | foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) { |
4633a7c4 LW |
2026 | printf "%4d %s\n", $hash{$key}, $key; |
2027 | } | |
2028 | ||
ab4f32c2 | 2029 | As an lvalue C<keys()> allows you to increase the number of hash buckets |
aa689395 | 2030 | allocated for the given hash. This can gain you a measure of efficiency if |
2031 | you know the hash is going to get big. (This is similar to pre-extending | |
2032 | an array by assigning a larger number to $#array.) If you say | |
55497cff | 2033 | |
2034 | keys %hash = 200; | |
2035 | ||
ab192400 GS |
2036 | then C<%hash> will have at least 200 buckets allocated for it--256 of them, |
2037 | in fact, since it rounds up to the next power of two. These | |
55497cff | 2038 | buckets will be retained even if you do C<%hash = ()>, use C<undef |
2039 | %hash> if you want to free the storage while C<%hash> is still in scope. | |
2040 | You can't shrink the number of buckets allocated for the hash using | |
ab4f32c2 | 2041 | C<keys()> in this way (but you needn't worry about doing this by accident, |
55497cff | 2042 | as trying has no effect). |
2043 | ||
ab192400 GS |
2044 | See also C<each()>, C<values()> and C<sort()>. |
2045 | ||
a0d0e21e LW |
2046 | =item kill LIST |
2047 | ||
54310121 | 2048 | Sends a signal to a list of processes. The first element of |
2049 | the list must be the signal to send. Returns the number of | |
4633a7c4 | 2050 | processes successfully signaled. |
a0d0e21e LW |
2051 | |
2052 | $cnt = kill 1, $child1, $child2; | |
2053 | kill 9, @goners; | |
2054 | ||
4633a7c4 LW |
2055 | Unlike in the shell, in Perl if the I<SIGNAL> is negative, it kills |
2056 | process groups instead of processes. (On System V, a negative I<PROCESS> | |
2057 | number will also kill process groups, but that's not portable.) That | |
2058 | means you usually want to use positive not negative signals. You may also | |
da0045b7 | 2059 | use a signal name in quotes. See L<perlipc/"Signals"> for details. |
a0d0e21e LW |
2060 | |
2061 | =item last LABEL | |
2062 | ||
2063 | =item last | |
2064 | ||
2065 | The C<last> command is like the C<break> statement in C (as used in | |
2066 | loops); it immediately exits the loop in question. If the LABEL is | |
2067 | omitted, the command refers to the innermost enclosing loop. The | |
2068 | C<continue> block, if any, is not executed: | |
2069 | ||
4633a7c4 LW |
2070 | LINE: while (<STDIN>) { |
2071 | last LINE if /^$/; # exit when done with header | |
5a964f20 | 2072 | #... |
a0d0e21e LW |
2073 | } |
2074 | ||
4968c1e4 MG |
2075 | C<last> cannot be used to exit a block which returns a value such as |
2076 | C<eval {}>, C<sub {}> or C<do {}>. | |
2077 | ||
a189bff9 JH |
2078 | See also L</continue> for an illustration of how C<last>, L</next>, and |
2079 | L</redo> work. | |
2080 | ||
2081 | See also L<perlsyn>. | |
1d2dff63 | 2082 | |
a0d0e21e LW |
2083 | =item lc EXPR |
2084 | ||
54310121 | 2085 | =item lc |
bbce6d69 | 2086 | |
a0d0e21e | 2087 | Returns an lowercased version of EXPR. This is the internal function |
7660c0ab | 2088 | implementing the C<\L> escape in double-quoted strings. |
a0ed51b3 | 2089 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e | 2090 | |
7660c0ab | 2091 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 2092 | |
a0d0e21e LW |
2093 | =item lcfirst EXPR |
2094 | ||
54310121 | 2095 | =item lcfirst |
bbce6d69 | 2096 | |
a0d0e21e | 2097 | Returns the value of EXPR with the first character lowercased. This is |
7660c0ab | 2098 | the internal function implementing the C<\l> escape in double-quoted strings. |
a0ed51b3 | 2099 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e | 2100 | |
7660c0ab | 2101 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 2102 | |
a0d0e21e LW |
2103 | =item length EXPR |
2104 | ||
54310121 | 2105 | =item length |
bbce6d69 | 2106 | |
a0ed51b3 | 2107 | Returns the length in characters of the value of EXPR. If EXPR is |
7660c0ab | 2108 | omitted, returns length of C<$_>. |
a0d0e21e LW |
2109 | |
2110 | =item link OLDFILE,NEWFILE | |
2111 | ||
5a964f20 TC |
2112 | Creates a new filename linked to the old filename. Returns TRUE for |
2113 | success, FALSE otherwise. | |
a0d0e21e LW |
2114 | |
2115 | =item listen SOCKET,QUEUESIZE | |
2116 | ||
2117 | Does the same thing that the listen system call does. Returns TRUE if | |
4633a7c4 | 2118 | it succeeded, FALSE otherwise. See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
2119 | |
2120 | =item local EXPR | |
2121 | ||
5a964f20 TC |
2122 | A local modifies the listed variables to be local to the enclosing |
2123 | block, file, or eval. If more than one value is listed, the list must | |
2124 | be placed in parentheses. See L<perlsub/"Temporary Values via local()"> | |
2125 | for details, including issues with tied arrays and hashes. | |
a0d0e21e | 2126 | |
7660c0ab | 2127 | You really probably want to be using C<my()> instead, because C<local()> isn't |
7b8d334a | 2128 | what most people think of as "local". See L<perlsub/"Private Variables |
cb1a09d0 | 2129 | via my()"> for details. |
a0d0e21e LW |
2130 | |
2131 | =item localtime EXPR | |
2132 | ||
2133 | Converts a time as returned by the time function to a 9-element array | |
5f05dabc | 2134 | with the time analyzed for the local time zone. Typically used as |
a0d0e21e LW |
2135 | follows: |
2136 | ||
54310121 | 2137 | # 0 1 2 3 4 5 6 7 8 |
a0d0e21e LW |
2138 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
2139 | localtime(time); | |
2140 | ||
2141 | All array elements are numeric, and come straight out of a struct tm. | |
7660c0ab A |
2142 | In particular this means that C<$mon> has the range C<0..11> and C<$wday> has |
2143 | the range C<0..6> with sunday as day C<0>. Also, C<$year> is the number of | |
2144 | years since 1900, that is, C<$year> is C<123> in year 2023, and I<not> simply the last two digits of the year. | |
54310121 | 2145 | |
2146 | If EXPR is omitted, uses the current time (C<localtime(time)>). | |
a0d0e21e | 2147 | |
f86cebdf | 2148 | In scalar context, returns the ctime(3) value: |
a0d0e21e | 2149 | |
5f05dabc | 2150 | $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994" |
a0d0e21e | 2151 | |
a3cb178b | 2152 | This scalar value is B<not> locale dependent, see L<perllocale>, but |
7660c0ab | 2153 | instead a Perl builtin. Also see the C<Time::Local> module, and the |
f86cebdf | 2154 | strftime(3) and mktime(3) function available via the POSIX module. To |
a3cb178b GS |
2155 | get somewhat similar but locale dependent date strings, set up your |
2156 | locale environment variables appropriately (please see L<perllocale>) | |
5a964f20 | 2157 | and try for example: |
a3cb178b | 2158 | |
5a964f20 | 2159 | use POSIX qw(strftime); |
a3cb178b GS |
2160 | $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime; |
2161 | ||
2162 | Note that the C<%a> and C<%b>, the short forms of the day of the week | |
2163 | and the month of the year, may not necessarily be three characters wide. | |
a0d0e21e LW |
2164 | |
2165 | =item log EXPR | |
2166 | ||
54310121 | 2167 | =item log |
bbce6d69 | 2168 | |
5a964f20 | 2169 | Returns the natural logarithm (base I<e>) of EXPR. If EXPR is omitted, returns log |
7660c0ab | 2170 | of C<$_>. |
a0d0e21e LW |
2171 | |
2172 | =item lstat FILEHANDLE | |
2173 | ||
2174 | =item lstat EXPR | |
2175 | ||
54310121 | 2176 | =item lstat |
bbce6d69 | 2177 | |
7660c0ab | 2178 | Does the same thing as the C<stat()> function (including setting the |
5a964f20 TC |
2179 | special C<_> filehandle) but stats a symbolic link instead of the file |
2180 | the symbolic link points to. If symbolic links are unimplemented on | |
7660c0ab | 2181 | your system, a normal C<stat()> is done. |
a0d0e21e | 2182 | |
7660c0ab | 2183 | If EXPR is omitted, stats C<$_>. |
bbce6d69 | 2184 | |
a0d0e21e LW |
2185 | =item m// |
2186 | ||
2187 | The match operator. See L<perlop>. | |
2188 | ||
2189 | =item map BLOCK LIST | |
2190 | ||
2191 | =item map EXPR,LIST | |
2192 | ||
7660c0ab | 2193 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting C<$_> to each |
a0d0e21e LW |
2194 | element) and returns the list value composed of the results of each such |
2195 | evaluation. Evaluates BLOCK or EXPR in a list context, so each element of LIST | |
2196 | may produce zero, one, or more elements in the returned value. | |
2197 | ||
2198 | @chars = map(chr, @nums); | |
2199 | ||
2200 | translates a list of numbers to the corresponding characters. And | |
2201 | ||
4633a7c4 | 2202 | %hash = map { getkey($_) => $_ } @array; |
a0d0e21e LW |
2203 | |
2204 | is just a funny way to write | |
2205 | ||
2206 | %hash = (); | |
2207 | foreach $_ (@array) { | |
4633a7c4 | 2208 | $hash{getkey($_)} = $_; |
a0d0e21e LW |
2209 | } |
2210 | ||
7660c0ab | 2211 | Note that, because C<$_> is a reference into the list value, it can be used |
fb73857a | 2212 | to modify the elements of the array. While this is useful and |
2213 | supported, it can cause bizarre results if the LIST is not a named | |
2214 | array. See also L</grep> for an array composed of those items of the | |
2215 | original list for which the BLOCK or EXPR evaluates to true. | |
2216 | ||
a0d0e21e LW |
2217 | =item mkdir FILENAME,MODE |
2218 | ||
0591cd52 NT |
2219 | Creates the directory specified by FILENAME, with permissions |
2220 | specified by MODE (as modified by C<umask>). If it succeeds it | |
2221 | returns TRUE, otherwise it returns FALSE and sets C<$!> (errno). | |
2222 | ||
2223 | In general, it is better to create directories with permissive MODEs, | |
2224 | and let the user modify that with their C<umask>, than it is to supply | |
2225 | a restrictive MODE and give the user no way to be more permissive. | |
2226 | The exceptions to this rule are when the file or directory should be | |
2227 | kept private (mail files, for instance). The perlfunc(1) entry on | |
2228 | C<umask> discusses the choice of MODE in more detail. | |
a0d0e21e LW |
2229 | |
2230 | =item msgctl ID,CMD,ARG | |
2231 | ||
f86cebdf | 2232 | Calls the System V IPC function msgctl(2). You'll probably have to say |
0ade1984 JH |
2233 | |
2234 | use IPC::SysV; | |
2235 | ||
7660c0ab A |
2236 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
2237 | then ARG must be a variable which will hold the returned C<msqid_ds> | |
ab4f32c2 | 2238 | structure. Returns like C<ioctl()>: the undefined value for error, "C<0> but |
0ade1984 | 2239 | true" for zero, or the actual return value otherwise. See also |
7660c0ab | 2240 | C<IPC::SysV> and C<IPC::Semaphore::Msg> documentation. |
a0d0e21e LW |
2241 | |
2242 | =item msgget KEY,FLAGS | |
2243 | ||
f86cebdf | 2244 | Calls the System V IPC function msgget(2). Returns the message queue |
7660c0ab A |
2245 | id, or the undefined value if there is an error. See also C<IPC::SysV> |
2246 | and C<IPC::SysV::Msg> documentation. | |
a0d0e21e LW |
2247 | |
2248 | =item msgsnd ID,MSG,FLAGS | |
2249 | ||
2250 | Calls the System V IPC function msgsnd to send the message MSG to the | |
2251 | message queue ID. MSG must begin with the long integer message type, | |
c07a80fd | 2252 | which may be created with C<pack("l", $type)>. Returns TRUE if |
7660c0ab A |
2253 | successful, or FALSE if there is an error. See also C<IPC::SysV> |
2254 | and C<IPC::SysV::Msg> documentation. | |
a0d0e21e LW |
2255 | |
2256 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS | |
2257 | ||
2258 | Calls the System V IPC function msgrcv to receive a message from | |
2259 | message queue ID into variable VAR with a maximum message size of | |
0ade1984 JH |
2260 | SIZE. Note that if a message is received, the message type will be |
2261 | the first thing in VAR, and the maximum length of VAR is SIZE plus the | |
2262 | size of the message type. Returns TRUE if successful, or FALSE if | |
7660c0ab | 2263 | there is an error. See also C<IPC::SysV> and C<IPC::SysV::Msg> documentation. |
a0d0e21e LW |
2264 | |
2265 | =item my EXPR | |
2266 | ||
ab4f32c2 A |
2267 | A C<my()> declares the listed variables to be local (lexically) to the |
2268 | enclosing block, file, or C<eval()>. If | |
5f05dabc | 2269 | more than one value is listed, the list must be placed in parentheses. See |
cb1a09d0 | 2270 | L<perlsub/"Private Variables via my()"> for details. |
4633a7c4 | 2271 | |
a0d0e21e LW |
2272 | =item next LABEL |
2273 | ||
2274 | =item next | |
2275 | ||
2276 | The C<next> command is like the C<continue> statement in C; it starts | |
2277 | the next iteration of the loop: | |
2278 | ||
4633a7c4 LW |
2279 | LINE: while (<STDIN>) { |
2280 | next LINE if /^#/; # discard comments | |
5a964f20 | 2281 | #... |
a0d0e21e LW |
2282 | } |
2283 | ||
2284 | Note that if there were a C<continue> block on the above, it would get | |
2285 | executed even on discarded lines. If the LABEL is omitted, the command | |
2286 | refers to the innermost enclosing loop. | |
2287 | ||
4968c1e4 MG |
2288 | C<next> cannot be used to exit a block which returns a value such as |
2289 | C<eval {}>, C<sub {}> or C<do {}>. | |
2290 | ||
a189bff9 JH |
2291 | See also L</continue> for an illustration of how L</last>, C<next>, and |
2292 | L</redo> work. | |
2293 | ||
2294 | See also L<perlsyn>. | |
1d2dff63 | 2295 | |
a0d0e21e LW |
2296 | =item no Module LIST |
2297 | ||
7660c0ab | 2298 | See the L</use> function, which C<no> is the opposite of. |
a0d0e21e LW |
2299 | |
2300 | =item oct EXPR | |
2301 | ||
54310121 | 2302 | =item oct |
bbce6d69 | 2303 | |
4633a7c4 | 2304 | Interprets EXPR as an octal string and returns the corresponding |
7660c0ab | 2305 | value. (If EXPR happens to start off with C<0x>, interprets it as |
4633a7c4 LW |
2306 | a hex string instead.) The following will handle decimal, octal, and |
2307 | hex in the standard Perl or C notation: | |
a0d0e21e LW |
2308 | |
2309 | $val = oct($val) if $val =~ /^0/; | |
2310 | ||
7660c0ab A |
2311 | If EXPR is omitted, uses C<$_>. This function is commonly used when |
2312 | a string such as C<644> needs to be converted into a file mode, for | |
2f9daede TP |
2313 | example. (Although perl will automatically convert strings into |
2314 | numbers as needed, this automatic conversion assumes base 10.) | |
a0d0e21e LW |
2315 | |
2316 | =item open FILEHANDLE,EXPR | |
2317 | ||
2318 | =item open FILEHANDLE | |
2319 | ||
2320 | Opens the file whose filename is given by EXPR, and associates it with | |
5f05dabc | 2321 | FILEHANDLE. If FILEHANDLE is an expression, its value is used as the |
2322 | name of the real filehandle wanted. If EXPR is omitted, the scalar | |
2323 | variable of the same name as the FILEHANDLE contains the filename. | |
ab4f32c2 A |
2324 | (Note that lexical variables--those declared with C<my()>--will not work |
2325 | for this purpose; so if you're using C<my()>, specify EXPR in your call | |
5f05dabc | 2326 | to open.) |
2327 | ||
7660c0ab A |
2328 | If the filename begins with C<'E<lt>'> or nothing, the file is opened for input. |
2329 | If the filename begins with C<'E<gt>'>, the file is truncated and opened for | |
2330 | output, being created if necessary. If the filename begins with C<'E<gt>E<gt>'>, | |
fbb426e4 | 2331 | the file is opened for appending, again being created if necessary. |
7660c0ab A |
2332 | You can put a C<'+'> in front of the C<'E<gt>'> or C<'E<lt>'> to indicate that |
2333 | you want both read and write access to the file; thus C<'+E<lt>'> is almost | |
2334 | always preferred for read/write updates--the C<'+E<gt>'> mode would clobber the | |
5a964f20 TC |
2335 | file first. You can't usually use either read-write mode for updating |
2336 | textfiles, since they have variable length records. See the B<-i> | |
0591cd52 NT |
2337 | switch in L<perlrun> for a better approach. The file is created with |
2338 | permissions of C<0666> modified by the process' C<umask> value. | |
5a964f20 TC |
2339 | |
2340 | The prefix and the filename may be separated with spaces. | |
f86cebdf | 2341 | These various prefixes correspond to the fopen(3) modes of C<'r'>, C<'r+'>, C<'w'>, |
7660c0ab | 2342 | C<'w+'>, C<'a'>, and C<'a+'>. |
5f05dabc | 2343 | |
7660c0ab | 2344 | If the filename begins with C<'|'>, the filename is interpreted as a |
5a964f20 | 2345 | command to which output is to be piped, and if the filename ends with a |
7660c0ab A |
2346 | C<'|'>, the filename is interpreted See L<perlipc/"Using open() for IPC"> |
2347 | for more examples of this. (You are not allowed to C<open()> to a command | |
5a964f20 TC |
2348 | that pipes both in I<and> out, but see L<IPC::Open2>, L<IPC::Open3>, |
2349 | and L<perlipc/"Bidirectional Communication"> for alternatives.) | |
cb1a09d0 | 2350 | |
7660c0ab | 2351 | Opening C<'-'> opens STDIN and opening C<'E<gt>-'> opens STDOUT. Open returns |
ab4f32c2 | 2352 | nonzero upon success, the undefined value otherwise. If the C<open()> |
4633a7c4 | 2353 | involved a pipe, the return value happens to be the pid of the |
54310121 | 2354 | subprocess. |
cb1a09d0 AD |
2355 | |
2356 | If you're unfortunate enough to be running Perl on a system that | |
2357 | distinguishes between text files and binary files (modern operating | |
2358 | systems don't care), then you should check out L</binmode> for tips for | |
ab4f32c2 | 2359 | dealing with this. The key distinction between systems that need C<binmode()> |
5a964f20 TC |
2360 | and those that don't is their text file formats. Systems like Unix, MacOS, and |
2361 | Plan9, which delimit lines with a single character, and which encode that | |
ab4f32c2 | 2362 | character in C as C<"\n">, do not need C<binmode()>. The rest need it. |
cb1a09d0 | 2363 | |
fb73857a | 2364 | When opening a file, it's usually a bad idea to continue normal execution |
ab4f32c2 A |
2365 | if the request failed, so C<open()> is frequently used in connection with |
2366 | C<die()>. Even if C<die()> won't do what you want (say, in a CGI script, | |
fb73857a | 2367 | where you want to make a nicely formatted error message (but there are |
5a964f20 | 2368 | modules that can help with that problem)) you should always check |
fb73857a | 2369 | the return value from opening a file. The infrequent exception is when |
2370 | working with an unopened filehandle is actually what you want to do. | |
2371 | ||
cb1a09d0 | 2372 | Examples: |
a0d0e21e LW |
2373 | |
2374 | $ARTICLE = 100; | |
2375 | open ARTICLE or die "Can't find article $ARTICLE: $!\n"; | |
2376 | while (<ARTICLE>) {... | |
2377 | ||
2378 | open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved) | |
fb73857a | 2379 | # if the open fails, output is discarded |
a0d0e21e | 2380 | |
fb73857a | 2381 | open(DBASE, '+<dbase.mine') # open for update |
2382 | or die "Can't open 'dbase.mine' for update: $!"; | |
cb1a09d0 | 2383 | |
fb73857a | 2384 | open(ARTICLE, "caesar <$article |") # decrypt article |
2385 | or die "Can't start caesar: $!"; | |
a0d0e21e | 2386 | |
fb73857a | 2387 | open(EXTRACT, "|sort >/tmp/Tmp$$") # $$ is our process id |
2388 | or die "Can't start sort: $!"; | |
a0d0e21e LW |
2389 | |
2390 | # process argument list of files along with any includes | |
2391 | ||
2392 | foreach $file (@ARGV) { | |
2393 | process($file, 'fh00'); | |
2394 | } | |
2395 | ||
2396 | sub process { | |
5a964f20 | 2397 | my($filename, $input) = @_; |
a0d0e21e LW |
2398 | $input++; # this is a string increment |
2399 | unless (open($input, $filename)) { | |
2400 | print STDERR "Can't open $filename: $!\n"; | |
2401 | return; | |
2402 | } | |
2403 | ||
5a964f20 | 2404 | local $_; |
a0d0e21e LW |
2405 | while (<$input>) { # note use of indirection |
2406 | if (/^#include "(.*)"/) { | |
2407 | process($1, $input); | |
2408 | next; | |
2409 | } | |
5a964f20 | 2410 | #... # whatever |
a0d0e21e LW |
2411 | } |
2412 | } | |
2413 | ||
2414 | You may also, in the Bourne shell tradition, specify an EXPR beginning | |
7660c0ab | 2415 | with C<'E<gt>&'>, in which case the rest of the string is interpreted as the |
5a964f20 | 2416 | name of a filehandle (or file descriptor, if numeric) to be |
7660c0ab A |
2417 | duped and opened. You may use C<&> after C<E<gt>>, C<E<gt>E<gt>>, C<E<lt>>, C<+E<gt>>, |
2418 | C<+E<gt>E<gt>>, and C<+E<lt>>. The | |
a0d0e21e | 2419 | mode you specify should match the mode of the original filehandle. |
184e9718 | 2420 | (Duping a filehandle does not take into account any existing contents of |
cb1a09d0 | 2421 | stdio buffers.) |
a0d0e21e LW |
2422 | Here is a script that saves, redirects, and restores STDOUT and |
2423 | STDERR: | |
2424 | ||
2425 | #!/usr/bin/perl | |
5a964f20 TC |
2426 | open(OLDOUT, ">&STDOUT"); |
2427 | open(OLDERR, ">&STDERR"); | |
a0d0e21e LW |
2428 | |
2429 | open(STDOUT, ">foo.out") || die "Can't redirect stdout"; | |
2430 | open(STDERR, ">&STDOUT") || die "Can't dup stdout"; | |
2431 | ||
2432 | select(STDERR); $| = 1; # make unbuffered | |
2433 | select(STDOUT); $| = 1; # make unbuffered | |
2434 | ||
2435 | print STDOUT "stdout 1\n"; # this works for | |
2436 | print STDERR "stderr 1\n"; # subprocesses too | |
2437 | ||
2438 | close(STDOUT); | |
2439 | close(STDERR); | |
2440 | ||
5a964f20 TC |
2441 | open(STDOUT, ">&OLDOUT"); |
2442 | open(STDERR, ">&OLDERR"); | |
a0d0e21e LW |
2443 | |
2444 | print STDOUT "stdout 2\n"; | |
2445 | print STDERR "stderr 2\n"; | |
2446 | ||
2447 | ||
7660c0ab A |
2448 | If you specify C<'E<lt>&=N'>, where C<N> is a number, then Perl will do an |
2449 | equivalent of C's C<fdopen()> of that file descriptor; this is more | |
4633a7c4 | 2450 | parsimonious of file descriptors. For example: |
a0d0e21e LW |
2451 | |
2452 | open(FILEHANDLE, "<&=$fd") | |
2453 | ||
7660c0ab | 2454 | If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>, then |
a0d0e21e | 2455 | there is an implicit fork done, and the return value of open is the pid |
7660c0ab | 2456 | of the child within the parent process, and C<0> within the child |
184e9718 | 2457 | process. (Use C<defined($pid)> to determine whether the open was successful.) |
a0d0e21e LW |
2458 | The filehandle behaves normally for the parent, but i/o to that |
2459 | filehandle is piped from/to the STDOUT/STDIN of the child process. | |
2460 | In the child process the filehandle isn't opened--i/o happens from/to | |
2461 | the new STDOUT or STDIN. Typically this is used like the normal | |
2462 | piped open when you want to exercise more control over just how the | |
2463 | pipe command gets executed, such as when you are running setuid, and | |
54310121 | 2464 | don't want to have to scan shell commands for metacharacters. |
4633a7c4 | 2465 | The following pairs are more or less equivalent: |
a0d0e21e LW |
2466 | |
2467 | open(FOO, "|tr '[a-z]' '[A-Z]'"); | |
2468 | open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]'; | |
2469 | ||
2470 | open(FOO, "cat -n '$file'|"); | |
2471 | open(FOO, "-|") || exec 'cat', '-n', $file; | |
2472 | ||
4633a7c4 LW |
2473 | See L<perlipc/"Safe Pipe Opens"> for more examples of this. |
2474 | ||
5a964f20 | 2475 | NOTE: On any operation that may do a fork, any unflushed buffers remain |
184e9718 | 2476 | unflushed in both processes, which means you may need to set C<$|> to |
4771b018 GS |
2477 | avoid duplicate output. On systems that support a close-on-exec flag on |
2478 | files, the flag will be set for the newly opened file descriptor as | |
2479 | determined by the value of $^F. See L<perlvar/$^F>. | |
a0d0e21e | 2480 | |
0dccf244 CS |
2481 | Closing any piped filehandle causes the parent process to wait for the |
2482 | child to finish, and returns the status value in C<$?>. | |
2483 | ||
5a964f20 | 2484 | The filename passed to open will have leading and trailing |
f86cebdf | 2485 | whitespace deleted, and the normal redirection characters |
5a964f20 TC |
2486 | honored. This property, known as "magic open", |
2487 | can often be used to good effect. A user could specify a filename of | |
7660c0ab | 2488 | F<"rsh cat file |">, or you could change certain filenames as needed: |
5a964f20 TC |
2489 | |
2490 | $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/; | |
2491 | open(FH, $filename) or die "Can't open $filename: $!"; | |
2492 | ||
2493 | However, to open a file with arbitrary weird characters in it, it's | |
2494 | necessary to protect any leading and trailing whitespace: | |
2495 | ||
2496 | $file =~ s#^(\s)#./$1#; | |
2497 | open(FOO, "< $file\0"); | |
2498 | ||
7660c0ab A |
2499 | If you want a "real" C C<open()> (see L<open(2)> on your system), then you |
2500 | should use the C<sysopen()> function, which involves no such magic. This is | |
5a964f20 TC |
2501 | another way to protect your filenames from interpretation. For example: |
2502 | ||
2503 | use IO::Handle; | |
2504 | sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL) | |
2505 | or die "sysopen $path: $!"; | |
2506 | $oldfh = select(HANDLE); $| = 1; select($oldfh); | |
2507 | print HANDLE "stuff $$\n"); | |
2508 | seek(HANDLE, 0, 0); | |
2509 | print "File contains: ", <HANDLE>; | |
2510 | ||
7660c0ab A |
2511 | Using the constructor from the C<IO::Handle> package (or one of its |
2512 | subclasses, such as C<IO::File> or C<IO::Socket>), you can generate anonymous | |
5a964f20 TC |
2513 | filehandles that have the scope of whatever variables hold references to |
2514 | them, and automatically close whenever and however you leave that scope: | |
c07a80fd | 2515 | |
5f05dabc | 2516 | use IO::File; |
5a964f20 | 2517 | #... |
c07a80fd | 2518 | sub read_myfile_munged { |
2519 | my $ALL = shift; | |
5f05dabc | 2520 | my $handle = new IO::File; |
c07a80fd | 2521 | open($handle, "myfile") or die "myfile: $!"; |
2522 | $first = <$handle> | |
2523 | or return (); # Automatically closed here. | |
2524 | mung $first or die "mung failed"; # Or here. | |
2525 | return $first, <$handle> if $ALL; # Or here. | |
2526 | $first; # Or here. | |
2527 | } | |
2528 | ||
b687b08b | 2529 | See L</seek> for some details about mixing reading and writing. |
a0d0e21e LW |
2530 | |
2531 | =item opendir DIRHANDLE,EXPR | |
2532 | ||
7660c0ab A |
2533 | Opens a directory named EXPR for processing by C<readdir()>, C<telldir()>, |
2534 | C<seekdir()>, C<rewinddir()>, and C<closedir()>. Returns TRUE if successful. | |
a0d0e21e LW |
2535 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
2536 | ||
2537 | =item ord EXPR | |
2538 | ||
54310121 | 2539 | =item ord |
bbce6d69 | 2540 | |
a0ed51b3 | 2541 | Returns the numeric (ASCII or Unicode) value of the first character of EXPR. If |
7660c0ab | 2542 | EXPR is omitted, uses C<$_>. For the reverse, see L</chr>. |
a0d0e21e LW |
2543 | |
2544 | =item pack TEMPLATE,LIST | |
2545 | ||
2546 | Takes an array or list of values and packs it into a binary structure, | |
2547 | returning the string containing the structure. The TEMPLATE is a | |
2548 | sequence of characters that give the order and type of values, as | |
2549 | follows: | |
2550 | ||
2551 | A An ascii string, will be space padded. | |
2552 | a An ascii string, will be null padded. | |
2553 | b A bit string (ascending bit order, like vec()). | |
2554 | B A bit string (descending bit order). | |
2555 | h A hex string (low nybble first). | |
2556 | H A hex string (high nybble first). | |
2557 | ||
2558 | c A signed char value. | |
a0ed51b3 | 2559 | C An unsigned char value. Only does bytes. See U for Unicode. |
96e4d5b1 | 2560 | |
a0d0e21e LW |
2561 | s A signed short value. |
2562 | S An unsigned short value. | |
96e4d5b1 | 2563 | (This 'short' is _exactly_ 16 bits, which may differ from |
2564 | what a local C compiler calls 'short'.) | |
2565 | ||
a0d0e21e LW |
2566 | i A signed integer value. |
2567 | I An unsigned integer value. | |
f86cebdf GS |
2568 | (This 'integer' is _at_least_ 32 bits wide. Its exact |
2569 | size depends on what a local C compiler calls 'int', | |
2570 | and may even be larger than the 'long' described in | |
2571 | the next item.) | |
96e4d5b1 | 2572 | |
a0d0e21e LW |
2573 | l A signed long value. |
2574 | L An unsigned long value. | |
96e4d5b1 | 2575 | (This 'long' is _exactly_ 32 bits, which may differ from |
2576 | what a local C compiler calls 'long'.) | |
a0d0e21e | 2577 | |
96e4d5b1 | 2578 | n A short in "network" (big-endian) order. |
2579 | N A long in "network" (big-endian) order. | |
a0d0e21e LW |
2580 | v A short in "VAX" (little-endian) order. |
2581 | V A long in "VAX" (little-endian) order. | |
96e4d5b1 | 2582 | (These 'shorts' and 'longs' are _exactly_ 16 bits and |
2583 | _exactly_ 32 bits, respectively.) | |
a0d0e21e | 2584 | |
dae0da7a JH |
2585 | q A signed quad (64-bit) value. |
2586 | Q An unsigned quad value. | |
2587 | (Available only if your system supports 64-bit integer values | |
2588 | _and_ if Perl has been compiled to support those. | |
2589 | Causes a fatal error otherwise.) | |
2590 | ||
a0d0e21e LW |
2591 | f A single-precision float in the native format. |
2592 | d A double-precision float in the native format. | |
2593 | ||
2594 | p A pointer to a null-terminated string. | |
2595 | P A pointer to a structure (fixed-length string). | |
2596 | ||
2597 | u A uuencoded string. | |
a0ed51b3 LW |
2598 | U A Unicode character number. Encodes to UTF-8 internally. |
2599 | Works even if C<use utf8> is not in effect. | |
a0d0e21e | 2600 | |
96e4d5b1 | 2601 | w A BER compressed integer. Its bytes represent an unsigned |
f86cebdf GS |
2602 | integer in base 128, most significant digit first, with as |
2603 | few digits as possible. Bit eight (the high bit) is set | |
2604 | on each byte except the last. | |
def98dd4 | 2605 | |
a0d0e21e LW |
2606 | x A null byte. |
2607 | X Back up a byte. | |
2608 | @ Null fill to absolute position. | |
2609 | ||
5a964f20 | 2610 | Each letter may optionally be followed by a number giving a repeat |
7660c0ab A |
2611 | count. With all types except C<"a">, C<"A">, C<"b">, C<"B">, C<"h">, C<"H">, and C<"P"> the |
2612 | pack function will gobble up that many values from the LIST. A C<*> for the | |
2613 | repeat count means to use however many items are left. The C<"a"> and C<"A"> | |
a0d0e21e | 2614 | types gobble just one value, but pack it as a string of length count, |
7660c0ab A |
2615 | padding with nulls or spaces as necessary. (When unpacking, C<"A"> strips |
2616 | trailing spaces and nulls, but C<"a"> does not.) Likewise, the C<"b"> and C<"B"> | |
2617 | fields pack a string that many bits long. The C<"h"> and C<"H"> fields pack a | |
2618 | string that many nybbles long. The C<"p"> type packs a pointer to a null- | |
84902520 TB |
2619 | terminated string. You are responsible for ensuring the string is not a |
2620 | temporary value (which can potentially get deallocated before you get | |
7660c0ab | 2621 | around to using the packed result). The C<"P"> packs a pointer to a structure |
61167c6f | 2622 | of the size indicated by the length. A NULL pointer is created if the |
7660c0ab | 2623 | corresponding value for C<"p"> or C<"P"> is C<undef>. |
61167c6f | 2624 | Real numbers (floats and doubles) are |
a0d0e21e LW |
2625 | in the native machine format only; due to the multiplicity of floating |
2626 | formats around, and the lack of a standard "network" representation, no | |
2627 | facility for interchange has been made. This means that packed floating | |
2628 | point data written on one machine may not be readable on another - even if | |
2629 | both use IEEE floating point arithmetic (as the endian-ness of the memory | |
2630 | representation is not part of the IEEE spec). Note that Perl uses doubles | |
2631 | internally for all numeric calculation, and converting from double into | |
5f05dabc | 2632 | float and thence back to double again will lose precision (i.e., |
7660c0ab | 2633 | C<unpack("f", pack("f", $foo)>) will not in general equal C<$foo>). |
a0d0e21e LW |
2634 | |
2635 | Examples: | |
2636 | ||
a0ed51b3 | 2637 | $foo = pack("CCCC",65,66,67,68); |
a0d0e21e | 2638 | # foo eq "ABCD" |
a0ed51b3 | 2639 | $foo = pack("C4",65,66,67,68); |
a0d0e21e | 2640 | # same thing |
a0ed51b3 LW |
2641 | $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9); |
2642 | # same thing with Unicode circled letters | |
a0d0e21e LW |
2643 | |
2644 | $foo = pack("ccxxcc",65,66,67,68); | |
2645 | # foo eq "AB\0\0CD" | |
2646 | ||
2647 | $foo = pack("s2",1,2); | |
2648 | # "\1\0\2\0" on little-endian | |
2649 | # "\0\1\0\2" on big-endian | |
2650 | ||
2651 | $foo = pack("a4","abcd","x","y","z"); | |
2652 | # "abcd" | |
2653 | ||
2654 | $foo = pack("aaaa","abcd","x","y","z"); | |
2655 | # "axyz" | |
2656 | ||
2657 | $foo = pack("a14","abcdefg"); | |
2658 | # "abcdefg\0\0\0\0\0\0\0" | |
2659 | ||
2660 | $foo = pack("i9pl", gmtime); | |
2661 | # a real struct tm (on my system anyway) | |
2662 | ||
2663 | sub bintodec { | |
2664 | unpack("N", pack("B32", substr("0" x 32 . shift, -32))); | |
2665 | } | |
2666 | ||
2667 | The same template may generally also be used in the unpack function. | |
2668 | ||
5a964f20 TC |
2669 | =item package |
2670 | ||
cb1a09d0 AD |
2671 | =item package NAMESPACE |
2672 | ||
2673 | Declares the compilation unit as being in the given namespace. The scope | |
2674 | of the package declaration is from the declaration itself through the end of | |
7660c0ab | 2675 | the enclosing block (the same scope as the C<local()> operator). All further |
cb1a09d0 | 2676 | unqualified dynamic identifiers will be in this namespace. A package |
5f05dabc | 2677 | statement affects only dynamic variables--including those you've used |
7660c0ab | 2678 | C<local()> on--but I<not> lexical variables created with C<my()>. Typically it |
cb1a09d0 AD |
2679 | would be the first declaration in a file to be included by the C<require> |
2680 | or C<use> operator. You can switch into a package in more than one place; | |
5a964f20 | 2681 | it merely influences which symbol table is used by the compiler for the |
cb1a09d0 AD |
2682 | rest of that block. You can refer to variables and filehandles in other |
2683 | packages by prefixing the identifier with the package name and a double | |
2684 | colon: C<$Package::Variable>. If the package name is null, the C<main> | |
2685 | package as assumed. That is, C<$::sail> is equivalent to C<$main::sail>. | |
2686 | ||
5a964f20 TC |
2687 | If NAMESPACE is omitted, then there is no current package, and all |
2688 | identifiers must be fully qualified or lexicals. This is stricter | |
2689 | than C<use strict>, since it also extends to function names. | |
2690 | ||
cb1a09d0 AD |
2691 | See L<perlmod/"Packages"> for more information about packages, modules, |
2692 | and classes. See L<perlsub> for other scoping issues. | |
2693 | ||
a0d0e21e LW |
2694 | =item pipe READHANDLE,WRITEHANDLE |
2695 | ||
2696 | Opens a pair of connected pipes like the corresponding system call. | |
2697 | Note that if you set up a loop of piped processes, deadlock can occur | |
2698 | unless you are very careful. In addition, note that Perl's pipes use | |
184e9718 | 2699 | stdio buffering, so you may need to set C<$|> to flush your WRITEHANDLE |
a0d0e21e LW |
2700 | after each command, depending on the application. |
2701 | ||
7e1af8bc | 2702 | See L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication"> |
4633a7c4 LW |
2703 | for examples of such things. |
2704 | ||
4771b018 GS |
2705 | On systems that support a close-on-exec flag on files, the flag will be set |
2706 | for the newly opened file descriptors as determined by the value of $^F. | |
2707 | See L<perlvar/$^F>. | |
2708 | ||
a0d0e21e LW |
2709 | =item pop ARRAY |
2710 | ||
54310121 | 2711 | =item pop |
28757baa | 2712 | |
a0d0e21e LW |
2713 | Pops and returns the last value of the array, shortening the array by |
2714 | 1. Has a similar effect to | |
2715 | ||
2716 | $tmp = $ARRAY[$#ARRAY--]; | |
2717 | ||
2718 | If there are no elements in the array, returns the undefined value. | |
cb1a09d0 | 2719 | If ARRAY is omitted, pops the |
7660c0ab A |
2720 | C<@ARGV> array in the main program, and the C<@_> array in subroutines, just |
2721 | like C<shift()>. | |
a0d0e21e LW |
2722 | |
2723 | =item pos SCALAR | |
2724 | ||
54310121 | 2725 | =item pos |
bbce6d69 | 2726 | |
4633a7c4 | 2727 | Returns the offset of where the last C<m//g> search left off for the variable |
7660c0ab | 2728 | is in question (C<$_> is used when the variable is not specified). May be |
44a8e56a | 2729 | modified to change that offset. Such modification will also influence |
2730 | the C<\G> zero-width assertion in regular expressions. See L<perlre> and | |
2731 | L<perlop>. | |
a0d0e21e LW |
2732 | |
2733 | =item print FILEHANDLE LIST | |
2734 | ||
2735 | =item print LIST | |
2736 | ||
2737 | =item print | |
2738 | ||
cb1a09d0 | 2739 | Prints a string or a comma-separated list of strings. Returns TRUE |
a0d0e21e | 2740 | if successful. FILEHANDLE may be a scalar variable name, in which case |
cb1a09d0 | 2741 | the variable contains the name of or a reference to the filehandle, thus introducing one |
a0d0e21e LW |
2742 | level of indirection. (NOTE: If FILEHANDLE is a variable and the next |
2743 | token is a term, it may be misinterpreted as an operator unless you | |
7660c0ab | 2744 | interpose a C<+> or put parentheses around the arguments.) If FILEHANDLE is |
a0d0e21e | 2745 | omitted, prints by default to standard output (or to the last selected |
7660c0ab | 2746 | output channel--see L</select>). If LIST is also omitted, prints C<$_> to |
5a964f20 | 2747 | the currently selected output channel. To set the default output channel to something other than |
a0d0e21e | 2748 | STDOUT use the select operation. Note that, because print takes a |
5a964f20 | 2749 | LIST, anything in the LIST is evaluated in list context, and any |
a0d0e21e | 2750 | subroutine that you call will have one or more of its expressions |
5a964f20 | 2751 | evaluated in list context. Also be careful not to follow the print |
a0d0e21e | 2752 | keyword with a left parenthesis unless you want the corresponding right |
7660c0ab | 2753 | parenthesis to terminate the arguments to the print--interpose a C<+> or |
5f05dabc | 2754 | put parentheses around all the arguments. |
a0d0e21e | 2755 | |
4633a7c4 | 2756 | Note that if you're storing FILEHANDLES in an array or other expression, |
da0045b7 | 2757 | you will have to use a block returning its value instead: |
4633a7c4 LW |
2758 | |
2759 | print { $files[$i] } "stuff\n"; | |
2760 | print { $OK ? STDOUT : STDERR } "stuff\n"; | |
2761 | ||
5f05dabc | 2762 | =item printf FILEHANDLE FORMAT, LIST |
a0d0e21e | 2763 | |
5f05dabc | 2764 | =item printf FORMAT, LIST |
a0d0e21e | 2765 | |
7660c0ab | 2766 | Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\> |
a3cb178b | 2767 | (the output record separator) is not appended. The first argument |
ab4f32c2 | 2768 | of the list will be interpreted as the C<printf()> format. If C<use locale> is |
a034a98d DD |
2769 | in effect, the character used for the decimal point in formatted real numbers |
2770 | is affected by the LC_NUMERIC locale. See L<perllocale>. | |
a0d0e21e | 2771 | |
7660c0ab A |
2772 | Don't fall into the trap of using a C<printf()> when a simple |
2773 | C<print()> would do. The C<print()> is more efficient and less | |
28757baa | 2774 | error prone. |
2775 | ||
da0045b7 | 2776 | =item prototype FUNCTION |
2777 | ||
2778 | Returns the prototype of a function as a string (or C<undef> if the | |
5f05dabc | 2779 | function has no prototype). FUNCTION is a reference to, or the name of, |
2780 | the function whose prototype you want to retrieve. | |
da0045b7 | 2781 | |
b6c543e3 IZ |
2782 | If FUNCTION is a string starting with C<CORE::>, the rest is taken as |
2783 | a name for Perl builtin. If builtin is not I<overridable> (such as | |
ab4f32c2 A |
2784 | C<qw//>) or its arguments cannot be expressed by a prototype (such as |
2785 | C<system()>) - in other words, the builtin does not behave like a Perl | |
b6c543e3 IZ |
2786 | function - returns C<undef>. Otherwise, the string describing the |
2787 | equivalent prototype is returned. | |
2788 | ||
a0d0e21e LW |
2789 | =item push ARRAY,LIST |
2790 | ||
2791 | Treats ARRAY as a stack, and pushes the values of LIST | |
2792 | onto the end of ARRAY. The length of ARRAY increases by the length of | |
2793 | LIST. Has the same effect as | |
2794 | ||
2795 | for $value (LIST) { | |
2796 | $ARRAY[++$#ARRAY] = $value; | |
2797 | } | |
2798 | ||
2799 | but is more efficient. Returns the new number of elements in the array. | |
2800 | ||
2801 | =item q/STRING/ | |
2802 | ||
2803 | =item qq/STRING/ | |
2804 | ||
8782bef2 GB |
2805 | =item qr/STRING/ |
2806 | ||
a0d0e21e LW |
2807 | =item qx/STRING/ |
2808 | ||
2809 | =item qw/STRING/ | |
2810 | ||
4b6a7270 | 2811 | Generalized quotes. See L<perlop/"Regexp Quote-Like Operators">. |
a0d0e21e LW |
2812 | |
2813 | =item quotemeta EXPR | |
2814 | ||
54310121 | 2815 | =item quotemeta |
bbce6d69 | 2816 | |
68dc0745 | 2817 | Returns the value of EXPR with all non-alphanumeric |
a034a98d DD |
2818 | characters backslashed. (That is, all characters not matching |
2819 | C</[A-Za-z_0-9]/> will be preceded by a backslash in the | |
2820 | returned string, regardless of any locale settings.) | |
2821 | This is the internal function implementing | |
7660c0ab | 2822 | the C<\Q> escape in double-quoted strings. |
a0d0e21e | 2823 | |
7660c0ab | 2824 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 2825 | |
a0d0e21e LW |
2826 | =item rand EXPR |
2827 | ||
2828 | =item rand | |
2829 | ||
7660c0ab | 2830 | Returns a random fractional number greater than or equal to C<0> and less |
3e3baf6d | 2831 | than the value of EXPR. (EXPR should be positive.) If EXPR is |
7660c0ab A |
2832 | omitted, the value C<1> is used. Automatically calls C<srand()> unless |
2833 | C<srand()> has already been called. See also C<srand()>. | |
a0d0e21e | 2834 | |
2f9daede | 2835 | (Note: If your rand function consistently returns numbers that are too |
a0d0e21e | 2836 | large or too small, then your version of Perl was probably compiled |
2f9daede | 2837 | with the wrong number of RANDBITS.) |
a0d0e21e LW |
2838 | |
2839 | =item read FILEHANDLE,SCALAR,LENGTH,OFFSET | |
2840 | ||
2841 | =item read FILEHANDLE,SCALAR,LENGTH | |
2842 | ||
2843 | Attempts to read LENGTH bytes of data into variable SCALAR from the | |
3b02c43c GS |
2844 | specified FILEHANDLE. Returns the number of bytes actually read, |
2845 | C<0> at end of file, or undef if there was an error. SCALAR will be grown | |
2846 | or shrunk to the length actually read. An OFFSET may be specified to | |
2847 | place the read data at some other place than the beginning of the | |
f86cebdf GS |
2848 | string. This call is actually implemented in terms of stdio's fread(3) |
2849 | call. To get a true read(2) system call, see C<sysread()>. | |
a0d0e21e LW |
2850 | |
2851 | =item readdir DIRHANDLE | |
2852 | ||
7660c0ab | 2853 | Returns the next directory entry for a directory opened by C<opendir()>. |
5a964f20 | 2854 | If used in list context, returns all the rest of the entries in the |
a0d0e21e | 2855 | directory. If there are no more entries, returns an undefined value in |
5a964f20 | 2856 | scalar context or a null list in list context. |
a0d0e21e | 2857 | |
7660c0ab | 2858 | If you're planning to filetest the return values out of a C<readdir()>, you'd |
5f05dabc | 2859 | better prepend the directory in question. Otherwise, because we didn't |
7660c0ab | 2860 | C<chdir()> there, it would have been testing the wrong file. |
cb1a09d0 AD |
2861 | |
2862 | opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!"; | |
2863 | @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR); | |
2864 | closedir DIR; | |
2865 | ||
84902520 TB |
2866 | =item readline EXPR |
2867 | ||
5a964f20 | 2868 | Reads from the filehandle whose typeglob is contained in EXPR. In scalar context, a single line |
84902520 TB |
2869 | is read and returned. In list context, reads until end-of-file is |
2870 | reached and returns a list of lines (however you've defined lines | |
7660c0ab | 2871 | with C<$/> or C<$INPUT_RECORD_SEPARATOR>). |
84902520 TB |
2872 | This is the internal function implementing the C<E<lt>EXPRE<gt>> |
2873 | operator, but you can use it directly. The C<E<lt>EXPRE<gt>> | |
2874 | operator is discussed in more detail in L<perlop/"I/O Operators">. | |
2875 | ||
5a964f20 TC |
2876 | $line = <STDIN>; |
2877 | $line = readline(*STDIN); # same thing | |
2878 | ||
a0d0e21e LW |
2879 | =item readlink EXPR |
2880 | ||
54310121 | 2881 | =item readlink |
bbce6d69 | 2882 | |
a0d0e21e LW |
2883 | Returns the value of a symbolic link, if symbolic links are |
2884 | implemented. If not, gives a fatal error. If there is some system | |
184e9718 | 2885 | error, returns the undefined value and sets C<$!> (errno). If EXPR is |
7660c0ab | 2886 | omitted, uses C<$_>. |
a0d0e21e | 2887 | |
84902520 TB |
2888 | =item readpipe EXPR |
2889 | ||
5a964f20 | 2890 | EXPR is executed as a system command. |
84902520 TB |
2891 | The collected standard output of the command is returned. |
2892 | In scalar context, it comes back as a single (potentially | |
2893 | multi-line) string. In list context, returns a list of lines | |
7660c0ab | 2894 | (however you've defined lines with C<$/> or C<$INPUT_RECORD_SEPARATOR>). |
84902520 TB |
2895 | This is the internal function implementing the C<qx/EXPR/> |
2896 | operator, but you can use it directly. The C<qx/EXPR/> | |
2897 | operator is discussed in more detail in L<perlop/"I/O Operators">. | |
2898 | ||
a0d0e21e LW |
2899 | =item recv SOCKET,SCALAR,LEN,FLAGS |
2900 | ||
2901 | Receives a message on a socket. Attempts to receive LENGTH bytes of | |
2902 | data into variable SCALAR from the specified SOCKET filehandle. | |
7660c0ab | 2903 | Actually does a C C<recvfrom()>, so that it can return the address of the |
a0d0e21e LW |
2904 | sender. Returns the undefined value if there's an error. SCALAR will |
2905 | be grown or shrunk to the length actually read. Takes the same flags | |
54310121 | 2906 | as the system call of the same name. |
4633a7c4 | 2907 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e LW |
2908 | |
2909 | =item redo LABEL | |
2910 | ||
2911 | =item redo | |
2912 | ||
2913 | The C<redo> command restarts the loop block without evaluating the | |
a189bff9 | 2914 | conditional again. The L</continue> block, if any, is not executed. If |
a0d0e21e LW |
2915 | the LABEL is omitted, the command refers to the innermost enclosing |
2916 | loop. This command is normally used by programs that want to lie to | |
2917 | themselves about what was just input: | |
2918 | ||
2919 | # a simpleminded Pascal comment stripper | |
2920 | # (warning: assumes no { or } in strings) | |
4633a7c4 | 2921 | LINE: while (<STDIN>) { |
a0d0e21e LW |
2922 | while (s|({.*}.*){.*}|$1 |) {} |
2923 | s|{.*}| |; | |
2924 | if (s|{.*| |) { | |
2925 | $front = $_; | |
2926 | while (<STDIN>) { | |
2927 | if (/}/) { # end of comment? | |
5a964f20 | 2928 | s|^|$front\{|; |
4633a7c4 | 2929 | redo LINE; |
a0d0e21e LW |
2930 | } |
2931 | } | |
2932 | } | |
2933 | print; | |
2934 | } | |
2935 | ||
4968c1e4 MG |
2936 | C<redo> cannot be used to retry a block which returns a value such as |
2937 | C<eval {}>, C<sub {}> or C<do {}>. | |
2938 | ||
a189bff9 | 2939 | See also L</continue> for an illustration of how L</last>, L</next>, and |
1d2dff63 GS |
2940 | C<redo> work. |
2941 | ||
a189bff9 JH |
2942 | See also L<perlsyn>. |
2943 | ||
a0d0e21e LW |
2944 | =item ref EXPR |
2945 | ||
54310121 | 2946 | =item ref |
bbce6d69 | 2947 | |
2f9daede | 2948 | Returns a TRUE value if EXPR is a reference, FALSE otherwise. If EXPR |
7660c0ab | 2949 | is not specified, C<$_> will be used. The value returned depends on the |
bbce6d69 | 2950 | type of thing the reference is a reference to. |
a0d0e21e LW |
2951 | Builtin types include: |
2952 | ||
2953 | REF | |
2954 | SCALAR | |
2955 | ARRAY | |
2956 | HASH | |
2957 | CODE | |
2958 | GLOB | |
2959 | ||
54310121 | 2960 | If the referenced object has been blessed into a package, then that package |
7660c0ab | 2961 | name is returned instead. You can think of C<ref()> as a C<typeof()> operator. |
a0d0e21e LW |
2962 | |
2963 | if (ref($r) eq "HASH") { | |
aa689395 | 2964 | print "r is a reference to a hash.\n"; |
54310121 | 2965 | } |
5a964f20 | 2966 | if (!ref($r)) { |
a0d0e21e | 2967 | print "r is not a reference at all.\n"; |
54310121 | 2968 | } |
a0d0e21e LW |
2969 | |
2970 | See also L<perlref>. | |
2971 | ||
2972 | =item rename OLDNAME,NEWNAME | |
2973 | ||
7660c0ab | 2974 | Changes the name of a file. Returns C<1> for success, C<0> otherwise. Will |
5f05dabc | 2975 | not work across file system boundaries. |
a0d0e21e LW |
2976 | |
2977 | =item require EXPR | |
2978 | ||
2979 | =item require | |
2980 | ||
7660c0ab | 2981 | Demands some semantics specified by EXPR, or by C<$_> if EXPR is not |
a0d0e21e | 2982 | supplied. If EXPR is numeric, demands that the current version of Perl |
184e9718 | 2983 | (C<$]> or $PERL_VERSION) be equal or greater than EXPR. |
a0d0e21e LW |
2984 | |
2985 | Otherwise, demands that a library file be included if it hasn't already | |
2986 | been included. The file is included via the do-FILE mechanism, which is | |
7660c0ab | 2987 | essentially just a variety of C<eval()>. Has semantics similar to the following |
a0d0e21e LW |
2988 | subroutine: |
2989 | ||
2990 | sub require { | |
5a964f20 | 2991 | my($filename) = @_; |
a0d0e21e | 2992 | return 1 if $INC{$filename}; |
5a964f20 | 2993 | my($realfilename,$result); |
a0d0e21e LW |
2994 | ITER: { |
2995 | foreach $prefix (@INC) { | |
2996 | $realfilename = "$prefix/$filename"; | |
2997 | if (-f $realfilename) { | |
2998 | $result = do $realfilename; | |
2999 | last ITER; | |
3000 | } | |
3001 | } | |
3002 | die "Can't find $filename in \@INC"; | |
3003 | } | |
3004 | die $@ if $@; | |
3005 | die "$filename did not return true value" unless $result; | |
3006 | $INC{$filename} = $realfilename; | |
5a964f20 | 3007 | return $result; |
a0d0e21e LW |
3008 | } |
3009 | ||
3010 | Note that the file will not be included twice under the same specified | |
3011 | name. The file must return TRUE as the last statement to indicate | |
3012 | successful execution of any initialization code, so it's customary to | |
7660c0ab | 3013 | end such a file with "C<1;>" unless you're sure it'll return TRUE |
a0d0e21e LW |
3014 | otherwise. But it's better just to put the "C<1;>", in case you add more |
3015 | statements. | |
3016 | ||
54310121 | 3017 | If EXPR is a bareword, the require assumes a "F<.pm>" extension and |
da0045b7 | 3018 | replaces "F<::>" with "F</>" in the filename for you, |
54310121 | 3019 | to make it easy to load standard modules. This form of loading of |
a0d0e21e LW |
3020 | modules does not risk altering your namespace. |
3021 | ||
ee580363 GS |
3022 | In other words, if you try this: |
3023 | ||
f86cebdf | 3024 | require Foo::Bar; # a splendid bareword |
ee580363 | 3025 | |
7660c0ab A |
3026 | The require function will actually look for the "F<Foo/Bar.pm>" file in the |
3027 | directories specified in the C<@INC> array. | |
ee580363 | 3028 | |
5a964f20 | 3029 | But if you try this: |
ee580363 GS |
3030 | |
3031 | $class = 'Foo::Bar'; | |
f86cebdf | 3032 | require $class; # $class is not a bareword |
5a964f20 | 3033 | #or |
f86cebdf | 3034 | require "Foo::Bar"; # not a bareword because of the "" |
ee580363 | 3035 | |
7660c0ab A |
3036 | The require function will look for the "F<Foo::Bar>" file in the @INC array and |
3037 | will complain about not finding "F<Foo::Bar>" there. In this case you can do: | |
ee580363 GS |
3038 | |
3039 | eval "require $class"; | |
3040 | ||
3041 | For a yet-more-powerful import facility, see L</use> and L<perlmod>. | |
a0d0e21e LW |
3042 | |
3043 | =item reset EXPR | |
3044 | ||
3045 | =item reset | |
3046 | ||
3047 | Generally used in a C<continue> block at the end of a loop to clear | |
7660c0ab | 3048 | variables and reset C<??> searches so that they work again. The |
a0d0e21e LW |
3049 | expression is interpreted as a list of single characters (hyphens |
3050 | allowed for ranges). All variables and arrays beginning with one of | |
3051 | those letters are reset to their pristine state. If the expression is | |
7660c0ab | 3052 | omitted, one-match searches (C<?pattern?>) are reset to match again. Resets |
5f05dabc | 3053 | only variables or searches in the current package. Always returns |
a0d0e21e LW |
3054 | 1. Examples: |
3055 | ||
3056 | reset 'X'; # reset all X variables | |
3057 | reset 'a-z'; # reset lower case variables | |
3058 | reset; # just reset ?? searches | |
3059 | ||
7660c0ab A |
3060 | Resetting C<"A-Z"> is not recommended because you'll wipe out your |
3061 | C<@ARGV> and C<@INC> arrays and your C<%ENV> hash. Resets only package variables--lexical variables | |
a0d0e21e | 3062 | are unaffected, but they clean themselves up on scope exit anyway, |
da0045b7 | 3063 | so you'll probably want to use them instead. See L</my>. |
a0d0e21e | 3064 | |
54310121 | 3065 | =item return EXPR |
3066 | ||
3067 | =item return | |
3068 | ||
7660c0ab | 3069 | Returns from a subroutine, C<eval()>, or C<do FILE> with the value |
5a964f20 | 3070 | given in EXPR. Evaluation of EXPR may be in list, scalar, or void |
54310121 | 3071 | context, depending on how the return value will be used, and the context |
7660c0ab | 3072 | may vary from one execution to the next (see C<wantarray()>). If no EXPR |
5a964f20 TC |
3073 | is given, returns an empty list in list context, an undefined value in |
3074 | scalar context, or nothing in a void context. | |
a0d0e21e | 3075 | |
68dc0745 | 3076 | (Note that in the absence of a return, a subroutine, eval, or do FILE |
3077 | will automatically return the value of the last expression evaluated.) | |
a0d0e21e LW |
3078 | |
3079 | =item reverse LIST | |
3080 | ||
5a964f20 TC |
3081 | In list context, returns a list value consisting of the elements |
3082 | of LIST in the opposite order. In scalar context, concatenates the | |
a0ed51b3 LW |
3083 | elements of LIST, and returns a string value with all the characters |
3084 | in the opposite order. | |
4633a7c4 | 3085 | |
2f9daede | 3086 | print reverse <>; # line tac, last line first |
4633a7c4 | 3087 | |
2f9daede | 3088 | undef $/; # for efficiency of <> |
a0ed51b3 | 3089 | print scalar reverse <>; # character tac, last line tsrif |
2f9daede TP |
3090 | |
3091 | This operator is also handy for inverting a hash, although there are some | |
3092 | caveats. If a value is duplicated in the original hash, only one of those | |
3093 | can be represented as a key in the inverted hash. Also, this has to | |
3094 | unwind one hash and build a whole new one, which may take some time | |
3095 | on a large hash. | |
3096 | ||
3097 | %by_name = reverse %by_address; # Invert the hash | |
a0d0e21e LW |
3098 | |
3099 | =item rewinddir DIRHANDLE | |
3100 | ||
3101 | Sets the current position to the beginning of the directory for the | |
7660c0ab | 3102 | C<readdir()> routine on DIRHANDLE. |
a0d0e21e LW |
3103 | |
3104 | =item rindex STR,SUBSTR,POSITION | |
3105 | ||
3106 | =item rindex STR,SUBSTR | |
3107 | ||
3108 | Works just like index except that it returns the position of the LAST | |
3109 | occurrence of SUBSTR in STR. If POSITION is specified, returns the | |
3110 | last occurrence at or before that position. | |
3111 | ||
3112 | =item rmdir FILENAME | |
3113 | ||
54310121 | 3114 | =item rmdir |
bbce6d69 | 3115 | |
5a964f20 TC |
3116 | Deletes the directory specified by FILENAME if that directory is empty. If it |
3117 | succeeds it returns TRUE, otherwise it returns FALSE and sets C<$!> (errno). If | |
7660c0ab | 3118 | FILENAME is omitted, uses C<$_>. |
a0d0e21e LW |
3119 | |
3120 | =item s/// | |
3121 | ||
3122 | The substitution operator. See L<perlop>. | |
3123 | ||
3124 | =item scalar EXPR | |
3125 | ||
5a964f20 | 3126 | Forces EXPR to be interpreted in scalar context and returns the value |
54310121 | 3127 | of EXPR. |
cb1a09d0 AD |
3128 | |
3129 | @counts = ( scalar @a, scalar @b, scalar @c ); | |
3130 | ||
54310121 | 3131 | There is no equivalent operator to force an expression to |
5a964f20 | 3132 | be interpolated in list context because it's in practice never |
cb1a09d0 AD |
3133 | needed. If you really wanted to do so, however, you could use |
3134 | the construction C<@{[ (some expression) ]}>, but usually a simple | |
3135 | C<(some expression)> suffices. | |
a0d0e21e LW |
3136 | |
3137 | =item seek FILEHANDLE,POSITION,WHENCE | |
3138 | ||
ab4f32c2 | 3139 | Sets FILEHANDLE's position, just like the C<fseek()> call of C<stdio()>. |
8903cb82 | 3140 | FILEHANDLE may be an expression whose value gives the name of the |
7660c0ab A |
3141 | filehandle. The values for WHENCE are C<0> to set the new position to |
3142 | POSITION, C<1> to set it to the current position plus POSITION, and C<2> to | |
8903cb82 | 3143 | set it to EOF plus POSITION (typically negative). For WHENCE you may |
7660c0ab A |
3144 | use the constants C<SEEK_SET>, C<SEEK_CUR>, and C<SEEK_END> from either the |
3145 | C<IO::Seekable> or the POSIX module. Returns C<1> upon success, C<0> otherwise. | |
8903cb82 | 3146 | |
7660c0ab A |
3147 | If you want to position file for C<sysread()> or C<syswrite()>, don't use |
3148 | C<seek()> -- buffering makes its effect on the file's system position | |
3149 | unpredictable and non-portable. Use C<sysseek()> instead. | |
a0d0e21e | 3150 | |
cb1a09d0 AD |
3151 | On some systems you have to do a seek whenever you switch between reading |
3152 | and writing. Amongst other things, this may have the effect of calling | |
f86cebdf | 3153 | stdio's clearerr(3). A WHENCE of C<1> (C<SEEK_CUR>) is useful for not moving |
8903cb82 | 3154 | the file position: |
cb1a09d0 AD |
3155 | |
3156 | seek(TEST,0,1); | |
3157 | ||
3158 | This is also useful for applications emulating C<tail -f>. Once you hit | |
3159 | EOF on your read, and then sleep for a while, you might have to stick in a | |
7660c0ab | 3160 | seek() to reset things. The C<seek()> doesn't change the current position, |
8903cb82 | 3161 | but it I<does> clear the end-of-file condition on the handle, so that the |
3162 | next C<E<lt>FILEE<gt>> makes Perl try again to read something. We hope. | |
cb1a09d0 AD |
3163 | |
3164 | If that doesn't work (some stdios are particularly cantankerous), then | |
3165 | you may need something more like this: | |
3166 | ||
3167 | for (;;) { | |
f86cebdf GS |
3168 | for ($curpos = tell(FILE); $_ = <FILE>; |
3169 | $curpos = tell(FILE)) { | |
cb1a09d0 AD |
3170 | # search for some stuff and put it into files |
3171 | } | |
3172 | sleep($for_a_while); | |
3173 | seek(FILE, $curpos, 0); | |
3174 | } | |
3175 | ||
a0d0e21e LW |
3176 | =item seekdir DIRHANDLE,POS |
3177 | ||
7660c0ab A |
3178 | Sets the current position for the C<readdir()> routine on DIRHANDLE. POS |
3179 | must be a value returned by C<telldir()>. Has the same caveats about | |
a0d0e21e LW |
3180 | possible directory compaction as the corresponding system library |
3181 | routine. | |
3182 | ||
3183 | =item select FILEHANDLE | |
3184 | ||
3185 | =item select | |
3186 | ||
3187 | Returns the currently selected filehandle. Sets the current default | |
3188 | filehandle for output, if FILEHANDLE is supplied. This has two | |
ab4f32c2 | 3189 | effects: first, a C<write()> or a C<print()> without a filehandle will |
a0d0e21e LW |
3190 | default to this FILEHANDLE. Second, references to variables related to |
3191 | output will refer to this output channel. For example, if you have to | |
3192 | set the top of form format for more than one output channel, you might | |
3193 | do the following: | |
3194 | ||
3195 | select(REPORT1); | |
3196 | $^ = 'report1_top'; | |
3197 | select(REPORT2); | |
3198 | $^ = 'report2_top'; | |
3199 | ||
3200 | FILEHANDLE may be an expression whose value gives the name of the | |
3201 | actual filehandle. Thus: | |
3202 | ||
3203 | $oldfh = select(STDERR); $| = 1; select($oldfh); | |
3204 | ||
4633a7c4 LW |
3205 | Some programmers may prefer to think of filehandles as objects with |
3206 | methods, preferring to write the last example as: | |
a0d0e21e | 3207 | |
28757baa | 3208 | use IO::Handle; |
a0d0e21e LW |
3209 | STDERR->autoflush(1); |
3210 | ||
3211 | =item select RBITS,WBITS,EBITS,TIMEOUT | |
3212 | ||
f86cebdf | 3213 | This calls the select(2) system call with the bit masks specified, which |
7660c0ab | 3214 | can be constructed using C<fileno()> and C<vec()>, along these lines: |
a0d0e21e LW |
3215 | |
3216 | $rin = $win = $ein = ''; | |
3217 | vec($rin,fileno(STDIN),1) = 1; | |
3218 | vec($win,fileno(STDOUT),1) = 1; | |
3219 | $ein = $rin | $win; | |
3220 | ||
3221 | If you want to select on many filehandles you might wish to write a | |
3222 | subroutine: | |
3223 | ||
3224 | sub fhbits { | |
5a964f20 TC |
3225 | my(@fhlist) = split(' ',$_[0]); |
3226 | my($bits); | |
a0d0e21e LW |
3227 | for (@fhlist) { |
3228 | vec($bits,fileno($_),1) = 1; | |
3229 | } | |
3230 | $bits; | |
3231 | } | |
4633a7c4 | 3232 | $rin = fhbits('STDIN TTY SOCK'); |
a0d0e21e LW |
3233 | |
3234 | The usual idiom is: | |
3235 | ||
3236 | ($nfound,$timeleft) = | |
3237 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); | |
3238 | ||
54310121 | 3239 | or to block until something becomes ready just do this |
a0d0e21e LW |
3240 | |
3241 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); | |
3242 | ||
7660c0ab A |
3243 | Most systems do not bother to return anything useful in C<$timeleft>, so |
3244 | calling select() in scalar context just returns C<$nfound>. | |
c07a80fd | 3245 | |
5f05dabc | 3246 | Any of the bit masks can also be undef. The timeout, if specified, is |
a0d0e21e | 3247 | in seconds, which may be fractional. Note: not all implementations are |
7660c0ab A |
3248 | capable of returning theC<$timeleft>. If not, they always return |
3249 | C<$timeleft> equal to the supplied C<$timeout>. | |
a0d0e21e | 3250 | |
ff68c719 | 3251 | You can effect a sleep of 250 milliseconds this way: |
a0d0e21e LW |
3252 | |
3253 | select(undef, undef, undef, 0.25); | |
3254 | ||
7660c0ab A |
3255 | B<WARNING>: One should not attempt to mix buffered I/O (like C<read()> |
3256 | or E<lt>FHE<gt>) with C<select()>, except as permitted by POSIX, and even | |
3257 | then only on POSIX systems. You have to use C<sysread()> instead. | |
a0d0e21e LW |
3258 | |
3259 | =item semctl ID,SEMNUM,CMD,ARG | |
3260 | ||
ab4f32c2 | 3261 | Calls the System V IPC function C<semctl()>. You'll probably have to say |
0ade1984 JH |
3262 | |
3263 | use IPC::SysV; | |
3264 | ||
3265 | first to get the correct constant definitions. If CMD is IPC_STAT or | |
3266 | GETALL, then ARG must be a variable which will hold the returned | |
ab4f32c2 | 3267 | semid_ds structure or semaphore value array. Returns like C<ioctl()>: the |
7660c0ab A |
3268 | undefined value for error, "C<0> but true" for zero, or the actual return |
3269 | value otherwise. See also C<IPC::SysV> and C<IPC::Semaphore> documentation. | |
a0d0e21e LW |
3270 | |
3271 | =item semget KEY,NSEMS,FLAGS | |
3272 | ||
3273 | Calls the System V IPC function semget. Returns the semaphore id, or | |
7660c0ab A |
3274 | the undefined value if there is an error. See also C<IPC::SysV> and |
3275 | C<IPC::SysV::Semaphore> documentation. | |
a0d0e21e LW |
3276 | |
3277 | =item semop KEY,OPSTRING | |
3278 | ||
3279 | Calls the System V IPC function semop to perform semaphore operations | |
3280 | such as signaling and waiting. OPSTRING must be a packed array of | |
3281 | semop structures. Each semop structure can be generated with | |
3282 | C<pack("sss", $semnum, $semop, $semflag)>. The number of semaphore | |
3283 | operations is implied by the length of OPSTRING. Returns TRUE if | |
3284 | successful, or FALSE if there is an error. As an example, the | |
7660c0ab | 3285 | following code waits on semaphore C<$semnum> of semaphore id C<$semid>: |
a0d0e21e LW |
3286 | |
3287 | $semop = pack("sss", $semnum, -1, 0); | |
3288 | die "Semaphore trouble: $!\n" unless semop($semid, $semop); | |
3289 | ||
7660c0ab A |
3290 | To signal the semaphore, replace C<-1> with C<1>. See also C<IPC::SysV> |
3291 | and C<IPC::SysV::Semaphore> documentation. | |
a0d0e21e LW |
3292 | |
3293 | =item send SOCKET,MSG,FLAGS,TO | |
3294 | ||
3295 | =item send SOCKET,MSG,FLAGS | |
3296 | ||
3297 | Sends a message on a socket. Takes the same flags as the system call | |
3298 | of the same name. On unconnected sockets you must specify a | |
7660c0ab | 3299 | destination to send TO, in which case it does a C C<sendto()>. Returns |
a0d0e21e LW |
3300 | the number of characters sent, or the undefined value if there is an |
3301 | error. | |
4633a7c4 | 3302 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e LW |
3303 | |
3304 | =item setpgrp PID,PGRP | |
3305 | ||
7660c0ab | 3306 | Sets the current process group for the specified PID, C<0> for the current |
a0d0e21e | 3307 | process. Will produce a fatal error if used on a machine that doesn't |
f86cebdf | 3308 | implement setpgrp(2). If the arguments are omitted, it defaults to |
7660c0ab A |
3309 | C<0,0>. Note that the POSIX version of C<setpgrp()> does not accept any |
3310 | arguments, so only setpgrp C<0,0> is portable. | |
a0d0e21e LW |
3311 | |
3312 | =item setpriority WHICH,WHO,PRIORITY | |
3313 | ||
3314 | Sets the current priority for a process, a process group, or a user. | |
f86cebdf GS |
3315 | (See setpriority(2).) Will produce a fatal error if used on a machine |
3316 | that doesn't implement setpriority(2). | |
a0d0e21e LW |
3317 | |
3318 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL | |
3319 | ||
3320 | Sets the socket option requested. Returns undefined if there is an | |
7660c0ab | 3321 | error. OPTVAL may be specified as C<undef> if you don't want to pass an |
a0d0e21e LW |
3322 | argument. |
3323 | ||
3324 | =item shift ARRAY | |
3325 | ||
3326 | =item shift | |
3327 | ||
3328 | Shifts the first value of the array off and returns it, shortening the | |
3329 | array by 1 and moving everything down. If there are no elements in the | |
3330 | array, returns the undefined value. If ARRAY is omitted, shifts the | |
7660c0ab A |
3331 | C<@_> array within the lexical scope of subroutines and formats, and the |
3332 | C<@ARGV> array at file scopes or within the lexical scopes established by | |
977336f5 | 3333 | the C<eval ''>, C<BEGIN {}>, C<END {}>, and C<INIT {}> constructs. |
7660c0ab A |
3334 | See also C<unshift()>, C<push()>, and C<pop()>. C<Shift()> and C<unshift()> do the |
3335 | same thing to the left end of an array that C<pop()> and C<push()> do to the | |
977336f5 | 3336 | right end. |
a0d0e21e LW |
3337 | |
3338 | =item shmctl ID,CMD,ARG | |
3339 | ||
0ade1984 JH |
3340 | Calls the System V IPC function shmctl. You'll probably have to say |
3341 | ||
3342 | use IPC::SysV; | |
3343 | ||
7660c0ab A |
3344 | first to get the correct constant definitions. If CMD is C<IPC_STAT>, |
3345 | then ARG must be a variable which will hold the returned C<shmid_ds> | |
3346 | structure. Returns like ioctl: the undefined value for error, "C<0> but | |
0ade1984 | 3347 | true" for zero, or the actual return value otherwise. |
7660c0ab | 3348 | See also C<IPC::SysV> documentation. |
a0d0e21e LW |
3349 | |
3350 | =item shmget KEY,SIZE,FLAGS | |
3351 | ||
3352 | Calls the System V IPC function shmget. Returns the shared memory | |
3353 | segment id, or the undefined value if there is an error. | |
7660c0ab | 3354 | See also C<IPC::SysV> documentation. |
a0d0e21e LW |
3355 | |
3356 | =item shmread ID,VAR,POS,SIZE | |
3357 | ||
3358 | =item shmwrite ID,STRING,POS,SIZE | |
3359 | ||
3360 | Reads or writes the System V shared memory segment ID starting at | |
3361 | position POS for size SIZE by attaching to it, copying in/out, and | |
5a964f20 | 3362 | detaching from it. When reading, VAR must be a variable that will |
a0d0e21e LW |
3363 | hold the data read. When writing, if STRING is too long, only SIZE |
3364 | bytes are used; if STRING is too short, nulls are written to fill out | |
3365 | SIZE bytes. Return TRUE if successful, or FALSE if there is an error. | |
7660c0ab | 3366 | See also C<IPC::SysV> documentation. |
a0d0e21e LW |
3367 | |
3368 | =item shutdown SOCKET,HOW | |
3369 | ||
3370 | Shuts down a socket connection in the manner indicated by HOW, which | |
3371 | has the same interpretation as in the system call of the same name. | |
3372 | ||
f86cebdf GS |
3373 | shutdown(SOCKET, 0); # I/we have stopped reading data |
3374 | shutdown(SOCKET, 1); # I/we have stopped writing data | |
3375 | shutdown(SOCKET, 2); # I/we have stopped using this socket | |
5a964f20 TC |
3376 | |
3377 | This is useful with sockets when you want to tell the other | |
3378 | side you're done writing but not done reading, or vice versa. | |
3379 | It's also a more insistent form of close because it also | |
3380 | disables the filedescriptor in any forked copies in other | |
3381 | processes. | |
3382 | ||
a0d0e21e LW |
3383 | =item sin EXPR |
3384 | ||
54310121 | 3385 | =item sin |
bbce6d69 | 3386 | |
a0d0e21e | 3387 | Returns the sine of EXPR (expressed in radians). If EXPR is omitted, |
7660c0ab | 3388 | returns sine of C<$_>. |
a0d0e21e | 3389 | |
7660c0ab | 3390 | For the inverse sine operation, you may use the C<POSIX::asin()> |
28757baa | 3391 | function, or use this relation: |
3392 | ||
3393 | sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) } | |
3394 | ||
a0d0e21e LW |
3395 | =item sleep EXPR |
3396 | ||
3397 | =item sleep | |
3398 | ||
3399 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. | |
7660c0ab | 3400 | May be interrupted if the process receives a signal such as C<SIGALRM>. |
1d3434b8 | 3401 | Returns the number of seconds actually slept. You probably cannot |
7660c0ab A |
3402 | mix C<alarm()> and C<sleep()> calls, because C<sleep()> is often implemented |
3403 | using C<alarm()>. | |
a0d0e21e LW |
3404 | |
3405 | On some older systems, it may sleep up to a full second less than what | |
3406 | you requested, depending on how it counts seconds. Most modern systems | |
5a964f20 TC |
3407 | always sleep the full amount. They may appear to sleep longer than that, |
3408 | however, because your process might not be scheduled right away in a | |
3409 | busy multitasking system. | |
a0d0e21e | 3410 | |
cb1a09d0 | 3411 | For delays of finer granularity than one second, you may use Perl's |
f86cebdf | 3412 | C<syscall()> interface to access setitimer(2) if your system supports it, |
b687b08b | 3413 | or else see L</select> above. |
cb1a09d0 | 3414 | |
7660c0ab | 3415 | See also the POSIX module's C<sigpause()> function. |
5f05dabc | 3416 | |
a0d0e21e LW |
3417 | =item socket SOCKET,DOMAIN,TYPE,PROTOCOL |
3418 | ||
3419 | Opens a socket of the specified kind and attaches it to filehandle | |
5f05dabc | 3420 | SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for the |
7660c0ab | 3421 | system call of the same name. You should "C<use Socket;>" first to get |
4633a7c4 | 3422 | the proper definitions imported. See the example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
3423 | |
3424 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL | |
3425 | ||
3426 | Creates an unnamed pair of sockets in the specified domain, of the | |
5f05dabc | 3427 | specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as |
a0d0e21e LW |
3428 | for the system call of the same name. If unimplemented, yields a fatal |
3429 | error. Returns TRUE if successful. | |
3430 | ||
ab4f32c2 | 3431 | Some systems defined C<pipe()> in terms of C<socketpair()>, in which a call |
5a964f20 TC |
3432 | to C<pipe(Rdr, Wtr)> is essentially: |
3433 | ||
3434 | use Socket; | |
3435 | socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC); | |
3436 | shutdown(Rdr, 1); # no more writing for reader | |
3437 | shutdown(Wtr, 0); # no more reading for writer | |
3438 | ||
3439 | See L<perlipc> for an example of socketpair use. | |
3440 | ||
a0d0e21e LW |
3441 | =item sort SUBNAME LIST |
3442 | ||
3443 | =item sort BLOCK LIST | |
3444 | ||
3445 | =item sort LIST | |
3446 | ||
2f9daede | 3447 | Sorts the LIST and returns the sorted list value. If SUBNAME or BLOCK |
ab4f32c2 | 3448 | is omitted, C<sort()>s in standard string comparison order. If SUBNAME is |
2f9daede | 3449 | specified, it gives the name of a subroutine that returns an integer |
7660c0ab | 3450 | less than, equal to, or greater than C<0>, depending on how the elements |
2f9daede TP |
3451 | of the array are to be ordered. (The C<E<lt>=E<gt>> and C<cmp> |
3452 | operators are extremely useful in such routines.) SUBNAME may be a | |
1d3434b8 GS |
3453 | scalar variable name (unsubscripted), in which case the value provides |
3454 | the name of (or a reference to) the actual subroutine to use. In place | |
3455 | of a SUBNAME, you can provide a BLOCK as an anonymous, in-line sort | |
3456 | subroutine. | |
a0d0e21e | 3457 | |
cb1a09d0 AD |
3458 | In the interests of efficiency the normal calling code for subroutines is |
3459 | bypassed, with the following effects: the subroutine may not be a | |
3460 | recursive subroutine, and the two elements to be compared are passed into | |
7660c0ab A |
3461 | the subroutine not via C<@_> but as the package global variables C<$a> and |
3462 | C<$b> (see example below). They are passed by reference, so don't | |
3463 | modify C<$a> and C<$b>. And don't try to declare them as lexicals either. | |
a0d0e21e | 3464 | |
0a753a76 | 3465 | You also cannot exit out of the sort block or subroutine using any of the |
7660c0ab | 3466 | loop control operators described in L<perlsyn> or with C<goto()>. |
0a753a76 | 3467 | |
a034a98d DD |
3468 | When C<use locale> is in effect, C<sort LIST> sorts LIST according to the |
3469 | current collation locale. See L<perllocale>. | |
3470 | ||
a0d0e21e LW |
3471 | Examples: |
3472 | ||
3473 | # sort lexically | |
3474 | @articles = sort @files; | |
3475 | ||
3476 | # same thing, but with explicit sort routine | |
3477 | @articles = sort {$a cmp $b} @files; | |
3478 | ||
cb1a09d0 | 3479 | # now case-insensitively |
54310121 | 3480 | @articles = sort {uc($a) cmp uc($b)} @files; |
cb1a09d0 | 3481 | |
a0d0e21e LW |
3482 | # same thing in reversed order |
3483 | @articles = sort {$b cmp $a} @files; | |
3484 | ||
3485 | # sort numerically ascending | |
3486 | @articles = sort {$a <=> $b} @files; | |
3487 | ||
3488 | # sort numerically descending | |
3489 | @articles = sort {$b <=> $a} @files; | |
3490 | ||
3491 | # sort using explicit subroutine name | |
3492 | sub byage { | |
2f9daede | 3493 | $age{$a} <=> $age{$b}; # presuming numeric |
a0d0e21e LW |
3494 | } |
3495 | @sortedclass = sort byage @class; | |
3496 | ||
aa689395 | 3497 | # this sorts the %age hash by value instead of key |
3498 | # using an in-line function | |
c07a80fd | 3499 | @eldest = sort { $age{$b} <=> $age{$a} } keys %age; |
3500 | ||
a0d0e21e LW |
3501 | sub backwards { $b cmp $a; } |
3502 | @harry = ('dog','cat','x','Cain','Abel'); | |
3503 | @george = ('gone','chased','yz','Punished','Axed'); | |
3504 | print sort @harry; | |
3505 | # prints AbelCaincatdogx | |
3506 | print sort backwards @harry; | |
3507 | # prints xdogcatCainAbel | |
3508 | print sort @george, 'to', @harry; | |
3509 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz | |
3510 | ||
54310121 | 3511 | # inefficiently sort by descending numeric compare using |
3512 | # the first integer after the first = sign, or the | |
cb1a09d0 AD |
3513 | # whole record case-insensitively otherwise |
3514 | ||
3515 | @new = sort { | |
3516 | ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0] | |
3517 | || | |
3518 | uc($a) cmp uc($b) | |
3519 | } @old; | |
3520 | ||
3521 | # same thing, but much more efficiently; | |
3522 | # we'll build auxiliary indices instead | |
3523 | # for speed | |
3524 | @nums = @caps = (); | |
54310121 | 3525 | for (@old) { |
cb1a09d0 AD |
3526 | push @nums, /=(\d+)/; |
3527 | push @caps, uc($_); | |
54310121 | 3528 | } |
cb1a09d0 AD |
3529 | |
3530 | @new = @old[ sort { | |
3531 | $nums[$b] <=> $nums[$a] | |
3532 | || | |
3533 | $caps[$a] cmp $caps[$b] | |
3534 | } 0..$#old | |
3535 | ]; | |
3536 | ||
3537 | # same thing using a Schwartzian Transform (no temps) | |
3538 | @new = map { $_->[0] } | |
3539 | sort { $b->[1] <=> $a->[1] | |
3540 | || | |
3541 | $a->[2] cmp $b->[2] | |
3542 | } map { [$_, /=(\d+)/, uc($_)] } @old; | |
3543 | ||
7660c0ab A |
3544 | If you're using strict, you I<MUST NOT> declare C<$a> |
3545 | and C<$b> as lexicals. They are package globals. That means | |
cb1a09d0 AD |
3546 | if you're in the C<main> package, it's |
3547 | ||
3548 | @articles = sort {$main::b <=> $main::a} @files; | |
3549 | ||
3550 | or just | |
3551 | ||
3552 | @articles = sort {$::b <=> $::a} @files; | |
3553 | ||
3554 | but if you're in the C<FooPack> package, it's | |
3555 | ||
3556 | @articles = sort {$FooPack::b <=> $FooPack::a} @files; | |
3557 | ||
55497cff | 3558 | The comparison function is required to behave. If it returns |
7660c0ab A |
3559 | inconsistent results (sometimes saying C<$x[1]> is less than C<$x[2]> and |
3560 | sometimes saying the opposite, for example) the results are not | |
3561 | well-defined. | |
55497cff | 3562 | |
a0d0e21e LW |
3563 | =item splice ARRAY,OFFSET,LENGTH,LIST |
3564 | ||
3565 | =item splice ARRAY,OFFSET,LENGTH | |
3566 | ||
3567 | =item splice ARRAY,OFFSET | |
3568 | ||
3569 | Removes the elements designated by OFFSET and LENGTH from an array, and | |
5a964f20 TC |
3570 | replaces them with the elements of LIST, if any. In list context, |
3571 | returns the elements removed from the array. In scalar context, | |
43051805 | 3572 | returns the last element removed, or C<undef> if no elements are |
48cdf507 GA |
3573 | removed. The array grows or shrinks as necessary. |
3574 | If OFFSET is negative then it start that far from the end of the array. | |
3575 | If LENGTH is omitted, removes everything from OFFSET onward. | |
3576 | If LENGTH is negative, leave that many elements off the end of the array. | |
3577 | The following equivalences hold (assuming C<$[ == 0>): | |
a0d0e21e | 3578 | |
48cdf507 | 3579 | push(@a,$x,$y) splice(@a,@a,0,$x,$y) |
a0d0e21e LW |
3580 | pop(@a) splice(@a,-1) |
3581 | shift(@a) splice(@a,0,1) | |
3582 | unshift(@a,$x,$y) splice(@a,0,0,$x,$y) | |
5a964f20 | 3583 | $a[$x] = $y splice(@a,$x,1,$y) |
a0d0e21e LW |
3584 | |
3585 | Example, assuming array lengths are passed before arrays: | |
3586 | ||
3587 | sub aeq { # compare two list values | |
5a964f20 TC |
3588 | my(@a) = splice(@_,0,shift); |
3589 | my(@b) = splice(@_,0,shift); | |
a0d0e21e LW |
3590 | return 0 unless @a == @b; # same len? |
3591 | while (@a) { | |
3592 | return 0 if pop(@a) ne pop(@b); | |
3593 | } | |
3594 | return 1; | |
3595 | } | |
3596 | if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... } | |
3597 | ||
3598 | =item split /PATTERN/,EXPR,LIMIT | |
3599 | ||
3600 | =item split /PATTERN/,EXPR | |
3601 | ||
3602 | =item split /PATTERN/ | |
3603 | ||
3604 | =item split | |
3605 | ||
5a964f20 TC |
3606 | Splits a string into an array of strings, and returns it. By default, |
3607 | empty leading fields are preserved, and empty trailing ones are deleted. | |
a0d0e21e | 3608 | |
5a964f20 | 3609 | If not in list context, returns the number of fields found and splits into |
7660c0ab | 3610 | the C<@_> array. (In list context, you can force the split into C<@_> by |
1d2dff63 | 3611 | using C<??> as the pattern delimiters, but it still returns the list |
7660c0ab | 3612 | value.) The use of implicit split to C<@_> is deprecated, however, because |
5a964f20 | 3613 | it clobbers your subroutine arguments. |
a0d0e21e | 3614 | |
7660c0ab | 3615 | If EXPR is omitted, splits the C<$_> string. If PATTERN is also omitted, |
4633a7c4 LW |
3616 | splits on whitespace (after skipping any leading whitespace). Anything |
3617 | matching PATTERN is taken to be a delimiter separating the fields. (Note | |
fb73857a | 3618 | that the delimiter may be longer than one character.) |
3619 | ||
5a964f20 | 3620 | If LIMIT is specified and positive, splits into no more than that |
7b8d334a GS |
3621 | many fields (though it may split into fewer). If LIMIT is unspecified |
3622 | or zero, trailing null fields are stripped (which potential users | |
7660c0ab | 3623 | of C<pop()> would do well to remember). If LIMIT is negative, it is |
fb73857a | 3624 | treated as if an arbitrarily large LIMIT had been specified. |
a0d0e21e LW |
3625 | |
3626 | A pattern matching the null string (not to be confused with | |
748a9306 | 3627 | a null pattern C<//>, which is just one member of the set of patterns |
a0d0e21e LW |
3628 | matching a null string) will split the value of EXPR into separate |
3629 | characters at each point it matches that way. For example: | |
3630 | ||
3631 | print join(':', split(/ */, 'hi there')); | |
3632 | ||
3633 | produces the output 'h:i:t:h:e:r:e'. | |
3634 | ||
5f05dabc | 3635 | The LIMIT parameter can be used to split a line partially |
a0d0e21e LW |
3636 | |
3637 | ($login, $passwd, $remainder) = split(/:/, $_, 3); | |
3638 | ||
3639 | When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT | |
3640 | one larger than the number of variables in the list, to avoid | |
3641 | unnecessary work. For the list above LIMIT would have been 4 by | |
3642 | default. In time critical applications it behooves you not to split | |
3643 | into more fields than you really need. | |
3644 | ||
3645 | If the PATTERN contains parentheses, additional array elements are | |
3646 | created from each matching substring in the delimiter. | |
3647 | ||
da0045b7 | 3648 | split(/([,-])/, "1-10,20", 3); |
a0d0e21e LW |
3649 | |
3650 | produces the list value | |
3651 | ||
3652 | (1, '-', 10, ',', 20) | |
3653 | ||
7660c0ab | 3654 | If you had the entire header of a normal Unix email message in C<$header>, |
4633a7c4 LW |
3655 | you could split it up into fields and their values this way: |
3656 | ||
3657 | $header =~ s/\n\s+/ /g; # fix continuation lines | |
fb73857a | 3658 | %hdrs = (UNIX_FROM => split /^(\S*?):\s*/m, $header); |
4633a7c4 | 3659 | |
a0d0e21e LW |
3660 | The pattern C</PATTERN/> may be replaced with an expression to specify |
3661 | patterns that vary at runtime. (To do runtime compilation only once, | |
748a9306 LW |
3662 | use C</$variable/o>.) |
3663 | ||
3664 | As a special case, specifying a PATTERN of space (C<' '>) will split on | |
ab4f32c2 | 3665 | white space just as C<split()> with no arguments does. Thus, C<split(' ')> can |
748a9306 LW |
3666 | be used to emulate B<awk>'s default behavior, whereas C<split(/ /)> |
3667 | will give you as many null initial fields as there are leading spaces. | |
ab4f32c2 A |
3668 | A C<split()> on C</\s+/> is like a C<split(' ')> except that any leading |
3669 | whitespace produces a null first field. A C<split()> with no arguments | |
748a9306 | 3670 | really does a C<split(' ', $_)> internally. |
a0d0e21e LW |
3671 | |
3672 | Example: | |
3673 | ||
5a964f20 TC |
3674 | open(PASSWD, '/etc/passwd'); |
3675 | while (<PASSWD>) { | |
f86cebdf GS |
3676 | ($login, $passwd, $uid, $gid, |
3677 | $gcos, $home, $shell) = split(/:/); | |
5a964f20 | 3678 | #... |
a0d0e21e LW |
3679 | } |
3680 | ||
7660c0ab | 3681 | (Note that C<$shell> above will still have a newline on it. See L</chop>, |
a0d0e21e LW |
3682 | L</chomp>, and L</join>.) |
3683 | ||
5f05dabc | 3684 | =item sprintf FORMAT, LIST |
a0d0e21e | 3685 | |
ab4f32c2 | 3686 | Returns a string formatted by the usual C<printf()> conventions of the |
7660c0ab | 3687 | C library function C<sprintf()>. See L<sprintf(3)> or L<printf(3)> |
74a77017 CS |
3688 | on your system for an explanation of the general principles. |
3689 | ||
7660c0ab A |
3690 | Perl does its own C<sprintf()> formatting -- it emulates the C |
3691 | function C<sprintf()>, but it doesn't use it (except for floating-point | |
74a77017 | 3692 | numbers, and even then only the standard modifiers are allowed). As a |
7660c0ab | 3693 | result, any non-standard extensions in your local C<sprintf()> are not |
74a77017 CS |
3694 | available from Perl. |
3695 | ||
7660c0ab | 3696 | Perl's C<sprintf()> permits the following universally-known conversions: |
74a77017 CS |
3697 | |
3698 | %% a percent sign | |
3699 | %c a character with the given number | |
3700 | %s a string | |
3701 | %d a signed integer, in decimal | |
3702 | %u an unsigned integer, in decimal | |
3703 | %o an unsigned integer, in octal | |
3704 | %x an unsigned integer, in hexadecimal | |
3705 | %e a floating-point number, in scientific notation | |
3706 | %f a floating-point number, in fixed decimal notation | |
3707 | %g a floating-point number, in %e or %f notation | |
3708 | ||
1b3f7d21 | 3709 | In addition, Perl permits the following widely-supported conversions: |
74a77017 | 3710 | |
74a77017 CS |
3711 | %X like %x, but using upper-case letters |
3712 | %E like %e, but using an upper-case "E" | |
3713 | %G like %g, but with an upper-case "E" (if applicable) | |
3714 | %p a pointer (outputs the Perl value's address in hexadecimal) | |
1b3f7d21 CS |
3715 | %n special: *stores* the number of characters output so far |
3716 | into the next variable in the parameter list | |
74a77017 | 3717 | |
1b3f7d21 CS |
3718 | Finally, for backward (and we do mean "backward") compatibility, Perl |
3719 | permits these unnecessary but widely-supported conversions: | |
74a77017 | 3720 | |
1b3f7d21 | 3721 | %i a synonym for %d |
74a77017 CS |
3722 | %D a synonym for %ld |
3723 | %U a synonym for %lu | |
3724 | %O a synonym for %lo | |
3725 | %F a synonym for %f | |
3726 | ||
3727 | Perl permits the following universally-known flags between the C<%> | |
3728 | and the conversion letter: | |
3729 | ||
3730 | space prefix positive number with a space | |
3731 | + prefix positive number with a plus sign | |
3732 | - left-justify within the field | |
3733 | 0 use zeros, not spaces, to right-justify | |
a3cb178b | 3734 | # prefix non-zero octal with "0", non-zero hex with "0x" |
74a77017 | 3735 | number minimum field width |
f86cebdf GS |
3736 | .number "precision": digits after decimal point for |
3737 | floating-point, max length for string, minimum length | |
3738 | for integer | |
74a77017 | 3739 | l interpret integer as C type "long" or "unsigned long" |
74a77017 CS |
3740 | h interpret integer as C type "short" or "unsigned short" |
3741 | ||
1b3f7d21 | 3742 | There is also one Perl-specific flag: |
74a77017 CS |
3743 | |
3744 | V interpret integer as Perl's standard integer type | |
3745 | ||
7660c0ab | 3746 | Where a number would appear in the flags, an asterisk ("C<*>") may be |
74a77017 CS |
3747 | used instead, in which case Perl uses the next item in the parameter |
3748 | list as the given number (that is, as the field width or precision). | |
7660c0ab A |
3749 | If a field width obtained through "C<*>" is negative, it has the same |
3750 | effect as the "C<->" flag: left-justification. | |
74a77017 CS |
3751 | |
3752 | If C<use locale> is in effect, the character used for the decimal | |
3753 | point in formatted real numbers is affected by the LC_NUMERIC locale. | |
3754 | See L<perllocale>. | |
a0d0e21e LW |
3755 | |
3756 | =item sqrt EXPR | |
3757 | ||
54310121 | 3758 | =item sqrt |
bbce6d69 | 3759 | |
a0d0e21e | 3760 | Return the square root of EXPR. If EXPR is omitted, returns square |
7660c0ab | 3761 | root of C<$_>. |
a0d0e21e LW |
3762 | |
3763 | =item srand EXPR | |
3764 | ||
93dc8474 CS |
3765 | =item srand |
3766 | ||
ab4f32c2 | 3767 | Sets the random number seed for the C<rand()> operator. If EXPR is |
73c60299 RS |
3768 | omitted, uses a semi-random value supplied by the kernel (if it supports |
3769 | the F</dev/urandom> device) or based on the current time and process | |
93dc8474 | 3770 | ID, among other things. In versions of Perl prior to 5.004 the default |
7660c0ab | 3771 | seed was just the current C<time()>. This isn't a particularly good seed, |
93dc8474 | 3772 | so many old programs supply their own seed value (often C<time ^ $$> or |
7b8d334a | 3773 | C<time ^ ($$ + ($$ E<lt>E<lt> 15))>), but that isn't necessary any more. |
93dc8474 | 3774 | |
7660c0ab | 3775 | In fact, it's usually not necessary to call C<srand()> at all, because if |
93dc8474 | 3776 | it is not called explicitly, it is called implicitly at the first use of |
ab4f32c2 | 3777 | the C<rand()> operator. However, this was not the case in version of Perl |
2f9daede | 3778 | before 5.004, so if your script will run under older Perl versions, it |
7660c0ab | 3779 | should call C<srand()>. |
93dc8474 | 3780 | |
2f9daede TP |
3781 | Note that you need something much more random than the default seed for |
3782 | cryptographic purposes. Checksumming the compressed output of one or more | |
3783 | rapidly changing operating system status programs is the usual method. For | |
3784 | example: | |
28757baa | 3785 | |
3786 | srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip`); | |
3787 | ||
7660c0ab | 3788 | If you're particularly concerned with this, see the C<Math::TrulyRandom> |
0078ec44 RS |
3789 | module in CPAN. |
3790 | ||
7660c0ab | 3791 | Do I<not> call C<srand()> multiple times in your program unless you know |
28757baa | 3792 | exactly what you're doing and why you're doing it. The point of the |
7660c0ab | 3793 | function is to "seed" the C<rand()> function so that C<rand()> can produce |
28757baa | 3794 | a different sequence each time you run your program. Just do it once at the |
7660c0ab | 3795 | top of your program, or you I<won't> get random numbers out of C<rand()>! |
28757baa | 3796 | |
54310121 | 3797 | Frequently called programs (like CGI scripts) that simply use |
28757baa | 3798 | |
3799 | time ^ $$ | |
3800 | ||
54310121 | 3801 | for a seed can fall prey to the mathematical property that |
28757baa | 3802 | |
3803 | a^b == (a+1)^(b+1) | |
3804 | ||
0078ec44 | 3805 | one-third of the time. So don't do that. |
f86702cc | 3806 | |
a0d0e21e LW |
3807 | =item stat FILEHANDLE |
3808 | ||
3809 | =item stat EXPR | |
3810 | ||
54310121 | 3811 | =item stat |
bbce6d69 | 3812 | |
1d2dff63 GS |
3813 | Returns a 13-element list giving the status info for a file, either |
3814 | the file opened via FILEHANDLE, or named by EXPR. If EXPR is omitted, | |
7660c0ab | 3815 | it stats C<$_>. Returns a null list if the stat fails. Typically used |
1d2dff63 | 3816 | as follows: |
a0d0e21e LW |
3817 | |
3818 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, | |
3819 | $atime,$mtime,$ctime,$blksize,$blocks) | |
3820 | = stat($filename); | |
3821 | ||
54310121 | 3822 | Not all fields are supported on all filesystem types. Here are the |
c07a80fd | 3823 | meaning of the fields: |
3824 | ||
54310121 | 3825 | 0 dev device number of filesystem |
3826 | 1 ino inode number | |
3827 | 2 mode file mode (type and permissions) | |
3828 | 3 nlink number of (hard) links to the file | |
3829 | 4 uid numeric user ID of file's owner | |
3830 | 5 gid numeric group ID of file's owner | |
3831 | 6 rdev the device identifier (special files only) | |
3832 | 7 size total size of file, in bytes | |
3833 | 8 atime last access time since the epoch | |
3834 | 9 mtime last modify time since the epoch | |
3835 | 10 ctime inode change time (NOT creation time!) since the epoch | |
3836 | 11 blksize preferred block size for file system I/O | |
3837 | 12 blocks actual number of blocks allocated | |
c07a80fd | 3838 | |
3839 | (The epoch was at 00:00 January 1, 1970 GMT.) | |
3840 | ||
a0d0e21e LW |
3841 | If stat is passed the special filehandle consisting of an underline, no |
3842 | stat is done, but the current contents of the stat structure from the | |
3843 | last stat or filetest are returned. Example: | |
3844 | ||
3845 | if (-x $file && (($d) = stat(_)) && $d < 0) { | |
3846 | print "$file is executable NFS file\n"; | |
3847 | } | |
3848 | ||
5f05dabc | 3849 | (This works on machines only for which the device number is negative under NFS.) |
a0d0e21e | 3850 | |
ab4f32c2 | 3851 | In scalar context, C<stat()> returns a boolean value indicating success |
1d2dff63 GS |
3852 | or failure, and, if successful, sets the information associated with |
3853 | the special filehandle C<_>. | |
3854 | ||
a0d0e21e LW |
3855 | =item study SCALAR |
3856 | ||
3857 | =item study | |
3858 | ||
184e9718 | 3859 | Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of |
a0d0e21e LW |
3860 | doing many pattern matches on the string before it is next modified. |
3861 | This may or may not save time, depending on the nature and number of | |
3862 | patterns you are searching on, and on the distribution of character | |
54310121 | 3863 | frequencies in the string to be searched -- you probably want to compare |
5f05dabc | 3864 | run times with and without it to see which runs faster. Those loops |
a0d0e21e LW |
3865 | which scan for many short constant strings (including the constant |
3866 | parts of more complex patterns) will benefit most. You may have only | |
ab4f32c2 A |
3867 | one C<study()> active at a time -- if you study a different scalar the first |
3868 | is "unstudied". (The way C<study()> works is this: a linked list of every | |
a0d0e21e | 3869 | character in the string to be searched is made, so we know, for |
7660c0ab | 3870 | example, where all the C<'k'> characters are. From each search string, |
a0d0e21e LW |
3871 | the rarest character is selected, based on some static frequency tables |
3872 | constructed from some C programs and English text. Only those places | |
3873 | that contain this "rarest" character are examined.) | |
3874 | ||
5a964f20 | 3875 | For example, here is a loop that inserts index producing entries |
a0d0e21e LW |
3876 | before any line containing a certain pattern: |
3877 | ||
3878 | while (<>) { | |
3879 | study; | |
3880 | print ".IX foo\n" if /\bfoo\b/; | |
3881 | print ".IX bar\n" if /\bbar\b/; | |
3882 | print ".IX blurfl\n" if /\bblurfl\b/; | |
5a964f20 | 3883 | # ... |
a0d0e21e LW |
3884 | print; |
3885 | } | |
3886 | ||
7660c0ab A |
3887 | In searching for C</\bfoo\b/>, only those locations in C<$_> that contain C<"f"> |
3888 | will be looked at, because C<"f"> is rarer than C<"o">. In general, this is | |
a0d0e21e LW |
3889 | a big win except in pathological cases. The only question is whether |
3890 | it saves you more time than it took to build the linked list in the | |
3891 | first place. | |
3892 | ||
3893 | Note that if you have to look for strings that you don't know till | |
ab4f32c2 | 3894 | runtime, you can build an entire loop as a string and C<eval()> that to |
a0d0e21e | 3895 | avoid recompiling all your patterns all the time. Together with |
7660c0ab | 3896 | undefining C<$/> to input entire files as one record, this can be very |
f86cebdf | 3897 | fast, often faster than specialized programs like fgrep(1). The following |
184e9718 | 3898 | scans a list of files (C<@files>) for a list of words (C<@words>), and prints |
a0d0e21e LW |
3899 | out the names of those files that contain a match: |
3900 | ||
3901 | $search = 'while (<>) { study;'; | |
3902 | foreach $word (@words) { | |
3903 | $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n"; | |
3904 | } | |
3905 | $search .= "}"; | |
3906 | @ARGV = @files; | |
3907 | undef $/; | |
3908 | eval $search; # this screams | |
5f05dabc | 3909 | $/ = "\n"; # put back to normal input delimiter |
a0d0e21e LW |
3910 | foreach $file (sort keys(%seen)) { |
3911 | print $file, "\n"; | |
3912 | } | |
3913 | ||
cb1a09d0 AD |
3914 | =item sub BLOCK |
3915 | ||
3916 | =item sub NAME | |
3917 | ||
3918 | =item sub NAME BLOCK | |
3919 | ||
3920 | This is subroutine definition, not a real function I<per se>. With just a | |
3921 | NAME (and possibly prototypes), it's just a forward declaration. Without | |
3922 | a NAME, it's an anonymous function declaration, and does actually return a | |
2f9daede | 3923 | value: the CODE ref of the closure you just created. See L<perlsub> and |
cb1a09d0 AD |
3924 | L<perlref> for details. |
3925 | ||
7b8d334a GS |
3926 | =item substr EXPR,OFFSET,LEN,REPLACEMENT |
3927 | ||
a0d0e21e LW |
3928 | =item substr EXPR,OFFSET,LEN |
3929 | ||
3930 | =item substr EXPR,OFFSET | |
3931 | ||
3932 | Extracts a substring out of EXPR and returns it. First character is at | |
7660c0ab | 3933 | offset C<0>, or whatever you've set C<$[> to (but don't do that). |
84902520 | 3934 | If OFFSET is negative (or more precisely, less than C<$[>), starts |
a0d0e21e | 3935 | that far from the end of the string. If LEN is omitted, returns |
748a9306 LW |
3936 | everything to the end of the string. If LEN is negative, leaves that |
3937 | many characters off the end of the string. | |
3938 | ||
5a964f20 | 3939 | If you specify a substring that is partly outside the string, the part |
84902520 TB |
3940 | within the string is returned. If the substring is totally outside |
3941 | the string a warning is produced. | |
3942 | ||
7660c0ab | 3943 | You can use the C<substr()> function |
a0d0e21e LW |
3944 | as an lvalue, in which case EXPR must be an lvalue. If you assign |
3945 | something shorter than LEN, the string will shrink, and if you assign | |
3946 | something longer than LEN, the string will grow to accommodate it. To | |
3947 | keep the string the same length you may need to pad or chop your value | |
7660c0ab | 3948 | using C<sprintf()>. |
a0d0e21e | 3949 | |
7660c0ab | 3950 | An alternative to using C<substr()> as an lvalue is to specify the |
7b8d334a GS |
3951 | replacement string as the 4th argument. This allows you to replace |
3952 | parts of the EXPR and return what was there before in one operation. | |
7b8d334a | 3953 | |
a0d0e21e LW |
3954 | =item symlink OLDFILE,NEWFILE |
3955 | ||
3956 | Creates a new filename symbolically linked to the old filename. | |
7660c0ab | 3957 | Returns C<1> for success, C<0> otherwise. On systems that don't support |
a0d0e21e LW |
3958 | symbolic links, produces a fatal error at run time. To check for that, |
3959 | use eval: | |
3960 | ||
5a964f20 | 3961 | $symlink_exists = eval { symlink("",""); 1 }; |
a0d0e21e LW |
3962 | |
3963 | =item syscall LIST | |
3964 | ||
3965 | Calls the system call specified as the first element of the list, | |
3966 | passing the remaining elements as arguments to the system call. If | |
3967 | unimplemented, produces a fatal error. The arguments are interpreted | |
3968 | as follows: if a given argument is numeric, the argument is passed as | |
3969 | an int. If not, the pointer to the string value is passed. You are | |
3970 | responsible to make sure a string is pre-extended long enough to | |
a3cb178b | 3971 | receive any result that might be written into a string. You can't use a |
7660c0ab | 3972 | string literal (or other read-only string) as an argument to C<syscall()> |
a3cb178b GS |
3973 | because Perl has to assume that any string pointer might be written |
3974 | through. If your | |
a0d0e21e | 3975 | integer arguments are not literals and have never been interpreted in a |
7660c0ab A |
3976 | numeric context, you may need to add C<0> to them to force them to look |
3977 | like numbers. This emulates the C<syswrite()> function (or vice versa): | |
a0d0e21e LW |
3978 | |
3979 | require 'syscall.ph'; # may need to run h2ph | |
a3cb178b GS |
3980 | $s = "hi there\n"; |
3981 | syscall(&SYS_write, fileno(STDOUT), $s, length $s); | |
a0d0e21e | 3982 | |
5f05dabc | 3983 | Note that Perl supports passing of up to only 14 arguments to your system call, |
a0d0e21e LW |
3984 | which in practice should usually suffice. |
3985 | ||
fb73857a | 3986 | Syscall returns whatever value returned by the system call it calls. |
ab4f32c2 | 3987 | If the system call fails, C<syscall()> returns C<-1> and sets C<$!> (errno). |
7660c0ab | 3988 | Note that some system calls can legitimately return C<-1>. The proper |
fb73857a | 3989 | way to handle such calls is to assign C<$!=0;> before the call and |
7660c0ab | 3990 | check the value of C<$!> if syscall returns C<-1>. |
fb73857a | 3991 | |
3992 | There's a problem with C<syscall(&SYS_pipe)>: it returns the file | |
3993 | number of the read end of the pipe it creates. There is no way | |
3994 | to retrieve the file number of the other end. You can avoid this | |
ab4f32c2 | 3995 | problem by using C<pipe()> instead. |
fb73857a | 3996 | |
c07a80fd | 3997 | =item sysopen FILEHANDLE,FILENAME,MODE |
3998 | ||
3999 | =item sysopen FILEHANDLE,FILENAME,MODE,PERMS | |
4000 | ||
4001 | Opens the file whose filename is given by FILENAME, and associates it | |
4002 | with FILEHANDLE. If FILEHANDLE is an expression, its value is used as | |
4003 | the name of the real filehandle wanted. This function calls the | |
ab4f32c2 | 4004 | underlying operating system's C<open()> function with the parameters |
c07a80fd | 4005 | FILENAME, MODE, PERMS. |
4006 | ||
4007 | The possible values and flag bits of the MODE parameter are | |
4008 | system-dependent; they are available via the standard module C<Fcntl>. | |
adf5897a DF |
4009 | For historical reasons, some values work on almost every system |
4010 | supported by perl: zero means read-only, one means write-only, and two | |
4011 | means read/write. We know that these values do I<not> work under | |
7c5ffed3 JH |
4012 | OS/390 & VM/ESA Unix and on the Macintosh; you probably don't want to |
4013 | use them in new code. | |
c07a80fd | 4014 | |
ab4f32c2 | 4015 | If the file named by FILENAME does not exist and the C<open()> call creates |
7660c0ab | 4016 | it (typically because MODE includes the C<O_CREAT> flag), then the value of |
5a964f20 | 4017 | PERMS specifies the permissions of the newly created file. If you omit |
ab4f32c2 | 4018 | the PERMS argument to C<sysopen()>, Perl uses the octal value C<0666>. |
5a964f20 | 4019 | These permission values need to be in octal, and are modified by your |
0591cd52 NT |
4020 | process's current C<umask>. |
4021 | ||
4022 | Seldom if ever use C<0644> as argument to C<sysopen()> because that | |
4023 | takes away the user's option to have a more permissive umask. Better | |
4024 | to omit it. See the perlfunc(1) entry on C<umask> for more on this. | |
c07a80fd | 4025 | |
7660c0ab | 4026 | The C<IO::File> module provides a more object-oriented approach, if you're |
28757baa | 4027 | into that kind of thing. |
4028 | ||
a0d0e21e LW |
4029 | =item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET |
4030 | ||
4031 | =item sysread FILEHANDLE,SCALAR,LENGTH | |
4032 | ||
4033 | Attempts to read LENGTH bytes of data into variable SCALAR from the | |
b43ceaf2 AB |
4034 | specified FILEHANDLE, using the system call read(2). It bypasses stdio, |
4035 | so mixing this with other kinds of reads, C<print()>, C<write()>, | |
4036 | C<seek()>, C<tell()>, or C<eof()> can cause confusion because stdio | |
4037 | usually buffers data. Returns the number of bytes actually read, C<0> | |
4038 | at end of file, or undef if there was an error. SCALAR will be grown or | |
4039 | shrunk so that the last byte actually read is the last byte of the | |
4040 | scalar after the read. | |
ff68c719 | 4041 | |
4042 | An OFFSET may be specified to place the read data at some place in the | |
4043 | string other than the beginning. A negative OFFSET specifies | |
4044 | placement at that many bytes counting backwards from the end of the | |
4045 | string. A positive OFFSET greater than the length of SCALAR results | |
7660c0ab | 4046 | in the string being padded to the required size with C<"\0"> bytes before |
ff68c719 | 4047 | the result of the read is appended. |
a0d0e21e | 4048 | |
137443ea | 4049 | =item sysseek FILEHANDLE,POSITION,WHENCE |
4050 | ||
f86cebdf | 4051 | Sets FILEHANDLE's system position using the system call lseek(2). It |
7660c0ab | 4052 | bypasses stdio, so mixing this with reads (other than C<sysread()>), |
b43ceaf2 AB |
4053 | C<print()>, C<write()>, C<seek()>, C<tell()>, or C<eof()> may cause |
4054 | confusion. FILEHANDLE may be an expression whose value gives the name | |
4055 | of the filehandle. The values for WHENCE are C<0> to set the new | |
4056 | position to POSITION, C<1> to set the it to the current position plus | |
4057 | POSITION, and C<2> to set it to EOF plus POSITION (typically negative). | |
4058 | For WHENCE, you may use the constants C<SEEK_SET>, C<SEEK_CUR>, and | |
4059 | C<SEEK_END> from either the C<IO::Seekable> or the POSIX module. | |
8903cb82 | 4060 | |
4061 | Returns the new position, or the undefined value on failure. A position | |
7660c0ab | 4062 | of zero is returned as the string "C<0> but true"; thus C<sysseek()> returns |
8903cb82 | 4063 | TRUE on success and FALSE on failure, yet you can still easily determine |
4064 | the new position. | |
137443ea | 4065 | |
a0d0e21e LW |
4066 | =item system LIST |
4067 | ||
8bf3b016 GS |
4068 | =item system PROGRAM LIST |
4069 | ||
7660c0ab | 4070 | Does exactly the same thing as "C<exec LIST>" except that a fork is done |
a0d0e21e LW |
4071 | first, and the parent process waits for the child process to complete. |
4072 | Note that argument processing varies depending on the number of | |
a2008d6d GS |
4073 | arguments. If there is more than one argument in LIST, or if LIST is |
4074 | an array with more than one value, starts the program given by the | |
4075 | first element of the list with arguments given by the rest of the list. | |
4076 | If there is only one scalar argument, the argument is | |
4077 | checked for shell metacharacters, and if there are any, the entire | |
4078 | argument is passed to the system's command shell for parsing (this is | |
4079 | C</bin/sh -c> on Unix platforms, but varies on other platforms). If | |
4080 | there are no shell metacharacters in the argument, it is split into | |
7660c0ab | 4081 | words and passed directly to C<execvp()>, which is more efficient. |
a2008d6d GS |
4082 | |
4083 | The return value is the exit status of the program as | |
7660c0ab | 4084 | returned by the C<wait()> call. To get the actual exit value divide by |
54310121 | 4085 | 256. See also L</exec>. This is I<NOT> what you want to use to capture |
4086 | the output from a command, for that you should use merely backticks or | |
7660c0ab | 4087 | C<qx//>, as described in L<perlop/"`STRING`">. |
a0d0e21e | 4088 | |
7660c0ab A |
4089 | Like C<exec()>, C<system()> allows you to lie to a program about its name if |
4090 | you use the "C<system PROGRAM LIST>" syntax. Again, see L</exec>. | |
8bf3b016 | 4091 | |
7660c0ab | 4092 | Because C<system()> and backticks block C<SIGINT> and C<SIGQUIT>, killing the |
28757baa | 4093 | program they're running doesn't actually interrupt your program. |
4094 | ||
4095 | @args = ("command", "arg1", "arg2"); | |
54310121 | 4096 | system(@args) == 0 |
4097 | or die "system @args failed: $?" | |
28757baa | 4098 | |
5a964f20 TC |
4099 | You can check all the failure possibilities by inspecting |
4100 | C<$?> like this: | |
28757baa | 4101 | |
5a964f20 TC |
4102 | $exit_value = $? >> 8; |
4103 | $signal_num = $? & 127; | |
4104 | $dumped_core = $? & 128; | |
f86702cc | 4105 | |
c8db1d39 TC |
4106 | When the arguments get executed via the system shell, results |
4107 | and return codes will be subject to its quirks and capabilities. | |
4108 | See L<perlop/"`STRING`"> and L</exec> for details. | |
bb32b41a | 4109 | |
a0d0e21e LW |
4110 | =item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET |
4111 | ||
4112 | =item syswrite FILEHANDLE,SCALAR,LENGTH | |
4113 | ||
145d37e2 GA |
4114 | =item syswrite FILEHANDLE,SCALAR |
4115 | ||
a0d0e21e | 4116 | Attempts to write LENGTH bytes of data from variable SCALAR to the |
145d37e2 GA |
4117 | specified FILEHANDLE, using the system call write(2). If LENGTH is |
4118 | not specified, writes whole SCALAR. It bypasses | |
7660c0ab | 4119 | stdio, so mixing this with reads (other than C<sysread())>, C<print()>, |
b43ceaf2 AB |
4120 | C<write()>, C<seek()>, C<tell()>, or C<eof()> may cause confusion |
4121 | because stdio usually buffers data. Returns the number of bytes | |
4122 | actually written, or C<undef> if there was an error. If the LENGTH is | |
4123 | greater than the available data in the SCALAR after the OFFSET, only as | |
4124 | much data as is available will be written. | |
ff68c719 | 4125 | |
4126 | An OFFSET may be specified to write the data from some part of the | |
4127 | string other than the beginning. A negative OFFSET specifies writing | |
fb73857a | 4128 | that many bytes counting backwards from the end of the string. In the |
4129 | case the SCALAR is empty you can use OFFSET but only zero offset. | |
a0d0e21e LW |
4130 | |
4131 | =item tell FILEHANDLE | |
4132 | ||
4133 | =item tell | |
4134 | ||
8903cb82 | 4135 | Returns the current position for FILEHANDLE. FILEHANDLE may be an |
a0d0e21e LW |
4136 | expression whose value gives the name of the actual filehandle. If |
4137 | FILEHANDLE is omitted, assumes the file last read. | |
4138 | ||
4139 | =item telldir DIRHANDLE | |
4140 | ||
7660c0ab A |
4141 | Returns the current position of the C<readdir()> routines on DIRHANDLE. |
4142 | Value may be given to C<seekdir()> to access a particular location in a | |
a0d0e21e LW |
4143 | directory. Has the same caveats about possible directory compaction as |
4144 | the corresponding system library routine. | |
4145 | ||
4633a7c4 | 4146 | =item tie VARIABLE,CLASSNAME,LIST |
a0d0e21e | 4147 | |
4633a7c4 LW |
4148 | This function binds a variable to a package class that will provide the |
4149 | implementation for the variable. VARIABLE is the name of the variable | |
4150 | to be enchanted. CLASSNAME is the name of a class implementing objects | |
ab4f32c2 | 4151 | of correct type. Any additional arguments are passed to the "C<new()>" |
8a059744 GS |
4152 | method of the class (meaning C<TIESCALAR>, C<TIEHANDLE>, C<TIEARRAY>, |
4153 | or C<TIEHASH>). Typically these are arguments such as might be passed | |
4154 | to the C<dbm_open()> function of C. The object returned by the "C<new()>" | |
4155 | method is also returned by the C<tie()> function, which would be useful | |
4156 | if you want to access other methods in CLASSNAME. | |
a0d0e21e | 4157 | |
7660c0ab | 4158 | Note that functions such as C<keys()> and C<values()> may return huge lists |
1d2dff63 | 4159 | when used on large objects, like DBM files. You may prefer to use the |
7660c0ab | 4160 | C<each()> function to iterate over such. Example: |
a0d0e21e LW |
4161 | |
4162 | # print out history file offsets | |
4633a7c4 | 4163 | use NDBM_File; |
da0045b7 | 4164 | tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0); |
a0d0e21e LW |
4165 | while (($key,$val) = each %HIST) { |
4166 | print $key, ' = ', unpack('L',$val), "\n"; | |
4167 | } | |
4168 | untie(%HIST); | |
4169 | ||
aa689395 | 4170 | A class implementing a hash should have the following methods: |
a0d0e21e | 4171 | |
4633a7c4 | 4172 | TIEHASH classname, LIST |
a0d0e21e LW |
4173 | FETCH this, key |
4174 | STORE this, key, value | |
4175 | DELETE this, key | |
8a059744 | 4176 | CLEAR this |
a0d0e21e LW |
4177 | EXISTS this, key |
4178 | FIRSTKEY this | |
4179 | NEXTKEY this, lastkey | |
8a059744 | 4180 | DESTROY this |
a0d0e21e | 4181 | |
4633a7c4 | 4182 | A class implementing an ordinary array should have the following methods: |
a0d0e21e | 4183 | |
4633a7c4 | 4184 | TIEARRAY classname, LIST |
a0d0e21e LW |
4185 | FETCH this, key |
4186 | STORE this, key, value | |
8a059744 GS |
4187 | FETCHSIZE this |
4188 | STORESIZE this, count | |
4189 | CLEAR this | |
4190 | PUSH this, LIST | |
4191 | POP this | |
4192 | SHIFT this | |
4193 | UNSHIFT this, LIST | |
4194 | SPLICE this, offset, length, LIST | |
4195 | EXTEND this, count | |
4196 | DESTROY this | |
4197 | ||
4198 | A class implementing a file handle should have the following methods: | |
4199 | ||
4200 | TIEHANDLE classname, LIST | |
4201 | READ this, scalar, length, offset | |
4202 | READLINE this | |
4203 | GETC this | |
4204 | WRITE this, scalar, length, offset | |
4205 | PRINT this, LIST | |
4206 | PRINTF this, format, LIST | |
4207 | CLOSE this | |
4208 | DESTROY this | |
a0d0e21e | 4209 | |
4633a7c4 | 4210 | A class implementing a scalar should have the following methods: |
a0d0e21e | 4211 | |
4633a7c4 | 4212 | TIESCALAR classname, LIST |
54310121 | 4213 | FETCH this, |
a0d0e21e | 4214 | STORE this, value |
8a059744 GS |
4215 | DESTROY this |
4216 | ||
4217 | Not all methods indicated above need be implemented. See L<perltie>, | |
4218 | L<Tie::Hash>, L<Tie::Array>, L<Tie::Scalar> and L<Tie::Handle>. | |
a0d0e21e | 4219 | |
7660c0ab | 4220 | Unlike C<dbmopen()>, the C<tie()> function will not use or require a module |
4633a7c4 | 4221 | for you--you need to do that explicitly yourself. See L<DB_File> |
7660c0ab | 4222 | or the F<Config> module for interesting C<tie()> implementations. |
4633a7c4 | 4223 | |
b687b08b | 4224 | For further details see L<perltie>, L<"tied VARIABLE">. |
cc6b7395 | 4225 | |
f3cbc334 RS |
4226 | =item tied VARIABLE |
4227 | ||
4228 | Returns a reference to the object underlying VARIABLE (the same value | |
7660c0ab | 4229 | that was originally returned by the C<tie()> call that bound the variable |
f3cbc334 RS |
4230 | to a package.) Returns the undefined value if VARIABLE isn't tied to a |
4231 | package. | |
4232 | ||
a0d0e21e LW |
4233 | =item time |
4234 | ||
da0045b7 | 4235 | Returns the number of non-leap seconds since whatever time the system |
4236 | considers to be the epoch (that's 00:00:00, January 1, 1904 for MacOS, | |
4237 | and 00:00:00 UTC, January 1, 1970 for most other systems). | |
7660c0ab | 4238 | Suitable for feeding to C<gmtime()> and C<localtime()>. |
a0d0e21e LW |
4239 | |
4240 | =item times | |
4241 | ||
1d2dff63 | 4242 | Returns a four-element list giving the user and system times, in |
a0d0e21e LW |
4243 | seconds, for this process and the children of this process. |
4244 | ||
4245 | ($user,$system,$cuser,$csystem) = times; | |
4246 | ||
4247 | =item tr/// | |
4248 | ||
7660c0ab | 4249 | The transliteration operator. Same as C<y///>. See L<perlop>. |
a0d0e21e LW |
4250 | |
4251 | =item truncate FILEHANDLE,LENGTH | |
4252 | ||
4253 | =item truncate EXPR,LENGTH | |
4254 | ||
4255 | Truncates the file opened on FILEHANDLE, or named by EXPR, to the | |
4256 | specified length. Produces a fatal error if truncate isn't implemented | |
a3cb178b GS |
4257 | on your system. Returns TRUE if successful, the undefined value |
4258 | otherwise. | |
a0d0e21e LW |
4259 | |
4260 | =item uc EXPR | |
4261 | ||
54310121 | 4262 | =item uc |
bbce6d69 | 4263 | |
a0d0e21e | 4264 | Returns an uppercased version of EXPR. This is the internal function |
7660c0ab | 4265 | implementing the C<\U> escape in double-quoted strings. |
a034a98d | 4266 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0ed51b3 LW |
4267 | Under Unicode (C<use utf8>) it uses the standard Unicode uppercase mappings. (It |
4268 | does not attempt to do titlecase mapping on initial letters. See C<ucfirst()> for that.) | |
a0d0e21e | 4269 | |
7660c0ab | 4270 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 4271 | |
a0d0e21e LW |
4272 | =item ucfirst EXPR |
4273 | ||
54310121 | 4274 | =item ucfirst |
bbce6d69 | 4275 | |
a0ed51b3 LW |
4276 | Returns the value of EXPR with the first character |
4277 | in uppercase (titlecase in Unicode). This is | |
7660c0ab | 4278 | the internal function implementing the C<\u> escape in double-quoted strings. |
a034a98d | 4279 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e | 4280 | |
7660c0ab | 4281 | If EXPR is omitted, uses C<$_>. |
bbce6d69 | 4282 | |
a0d0e21e LW |
4283 | =item umask EXPR |
4284 | ||
4285 | =item umask | |
4286 | ||
2f9daede | 4287 | Sets the umask for the process to EXPR and returns the previous value. |
eec2d3df GS |
4288 | If EXPR is omitted, merely returns the current umask. |
4289 | ||
0591cd52 NT |
4290 | The Unix permission C<rwxr-x---> is represented as three sets of three |
4291 | bits, or three octal digits: C<0750> (the leading 0 indicates octal | |
4292 | and isn't one of the the digits). The C<umask> value is such a number | |
4293 | representing disabled permissions bits. The permission (or "mode") | |
4294 | values you pass C<mkdir> or C<sysopen> are modified by your umask, so | |
4295 | even if you tell C<sysopen> to create a file with permissions C<0777>, | |
4296 | if your umask is C<0022> then the file will actually be created with | |
4297 | permissions C<0755>. If your C<umask> were C<0027> (group can't | |
4298 | write; others can't read, write, or execute), then passing | |
4299 | C<sysopen()> C<0666> would create a file with mode C<0640> (C<0666 &~ | |
4300 | 027> is C<0640>). | |
4301 | ||
4302 | Here's some advice: supply a creation mode of C<0666> for regular | |
4303 | files (in C<sysopen()>) and one of C<0777> for directories (in | |
4304 | C<mkdir()>) and executable files. This gives users the freedom of | |
4305 | choice: if they want protected files, they might choose process umasks | |
4306 | of C<022>, C<027>, or even the particularly antisocial mask of C<077>. | |
4307 | Programs should rarely if ever make policy decisions better left to | |
4308 | the user. The exception to this is when writing files that should be | |
4309 | kept private: mail files, web browser cookies, I<.rhosts> files, and | |
4310 | so on. | |
4311 | ||
f86cebdf | 4312 | If umask(2) is not implemented on your system and you are trying to |
eec2d3df | 4313 | restrict access for I<yourself> (i.e., (EXPR & 0700) > 0), produces a |
f86cebdf | 4314 | fatal error at run time. If umask(2) is not implemented and you are |
eec2d3df GS |
4315 | not trying to restrict access for yourself, returns C<undef>. |
4316 | ||
4317 | Remember that a umask is a number, usually given in octal; it is I<not> a | |
4318 | string of octal digits. See also L</oct>, if all you have is a string. | |
a0d0e21e LW |
4319 | |
4320 | =item undef EXPR | |
4321 | ||
4322 | =item undef | |
4323 | ||
54310121 | 4324 | Undefines the value of EXPR, which must be an lvalue. Use only on a |
7660c0ab A |
4325 | scalar value, an array (using "C<@>"), a hash (using "C<%>"), a subroutine |
4326 | (using "C<&>"), or a typeglob (using "<*>"). (Saying C<undef $hash{$key}> | |
20408e3c GS |
4327 | will probably not do what you expect on most predefined variables or |
4328 | DBM list values, so don't do that; see L<delete>.) Always returns the | |
4329 | undefined value. You can omit the EXPR, in which case nothing is | |
4330 | undefined, but you still get an undefined value that you could, for | |
4331 | instance, return from a subroutine, assign to a variable or pass as a | |
4332 | parameter. Examples: | |
a0d0e21e LW |
4333 | |
4334 | undef $foo; | |
f86cebdf | 4335 | undef $bar{'blurfl'}; # Compare to: delete $bar{'blurfl'}; |
a0d0e21e | 4336 | undef @ary; |
aa689395 | 4337 | undef %hash; |
a0d0e21e | 4338 | undef &mysub; |
20408e3c | 4339 | undef *xyz; # destroys $xyz, @xyz, %xyz, &xyz, etc. |
54310121 | 4340 | return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it; |
2f9daede TP |
4341 | select undef, undef, undef, 0.25; |
4342 | ($a, $b, undef, $c) = &foo; # Ignore third value returned | |
a0d0e21e | 4343 | |
5a964f20 TC |
4344 | Note that this is a unary operator, not a list operator. |
4345 | ||
a189bff9 JH |
4346 | =item unless (EXPR) BLOCK |
4347 | ||
4348 | The negative counterpart of L</if>. If the EXPR returns false the | |
4349 | BLOCK is entered. | |
4350 | ||
4351 | See also L<perlsyn>. | |
4352 | ||
a0d0e21e LW |
4353 | =item unlink LIST |
4354 | ||
54310121 | 4355 | =item unlink |
bbce6d69 | 4356 | |
a0d0e21e LW |
4357 | Deletes a list of files. Returns the number of files successfully |
4358 | deleted. | |
4359 | ||
4360 | $cnt = unlink 'a', 'b', 'c'; | |
4361 | unlink @goners; | |
4362 | unlink <*.bak>; | |
4363 | ||
ab4f32c2 | 4364 | Note: C<unlink()> will not delete directories unless you are superuser and |
a0d0e21e LW |
4365 | the B<-U> flag is supplied to Perl. Even if these conditions are |
4366 | met, be warned that unlinking a directory can inflict damage on your | |
ab4f32c2 | 4367 | filesystem. Use C<rmdir()> instead. |
a0d0e21e | 4368 | |
7660c0ab | 4369 | If LIST is omitted, uses C<$_>. |
bbce6d69 | 4370 | |
a0d0e21e LW |
4371 | =item unpack TEMPLATE,EXPR |
4372 | ||
ab4f32c2 | 4373 | C<Unpack()> does the reverse of C<pack()>: it takes a string representing a |
a0d0e21e | 4374 | structure and expands it out into a list value, returning the array |
5a964f20 | 4375 | value. (In scalar context, it returns merely the first value |
ab4f32c2 | 4376 | produced.) The TEMPLATE has the same format as in the C<pack()> function. |
a0d0e21e LW |
4377 | Here's a subroutine that does substring: |
4378 | ||
4379 | sub substr { | |
5a964f20 | 4380 | my($what,$where,$howmuch) = @_; |
a0d0e21e LW |
4381 | unpack("x$where a$howmuch", $what); |
4382 | } | |
4383 | ||
4384 | and then there's | |
4385 | ||
4386 | sub ordinal { unpack("c",$_[0]); } # same as ord() | |
4387 | ||
184e9718 | 4388 | In addition, you may prefix a field with a %E<lt>numberE<gt> to indicate that |
4389 | you want a E<lt>numberE<gt>-bit checksum of the items instead of the items | |
a0d0e21e LW |
4390 | themselves. Default is a 16-bit checksum. For example, the following |
4391 | computes the same number as the System V sum program: | |
4392 | ||
4393 | while (<>) { | |
4394 | $checksum += unpack("%16C*", $_); | |
4395 | } | |
4396 | $checksum %= 65536; | |
4397 | ||
4398 | The following efficiently counts the number of set bits in a bit vector: | |
4399 | ||
4400 | $setbits = unpack("%32b*", $selectmask); | |
4401 | ||
a0d0e21e LW |
4402 | =item unshift ARRAY,LIST |
4403 | ||
ab4f32c2 | 4404 | Does the opposite of a C<shift()>. Or the opposite of a C<push()>, |
a0d0e21e LW |
4405 | depending on how you look at it. Prepends list to the front of the |
4406 | array, and returns the new number of elements in the array. | |
4407 | ||
4408 | unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/; | |
4409 | ||
4410 | Note the LIST is prepended whole, not one element at a time, so the | |
ab4f32c2 | 4411 | prepended elements stay in the same order. Use C<reverse()> to do the |
a0d0e21e LW |
4412 | reverse. |
4413 | ||
a189bff9 JH |
4414 | =item until (EXPR) BLOCK |
4415 | ||
4416 | =item do BLOCK until (EXPR) | |
4417 | ||
4418 | Enter BLOCK until EXPR returns false. The first form may avoid entering | |
4419 | the BLOCK, the second form enters the BLOCK at least once. | |
4420 | ||
4421 | See L</do>, L</while>, and L</for>. | |
4422 | ||
4423 | See also L<perlsyn>. | |
4424 | ||
4425 | =item untie VARIABLE | |
4426 | ||
4427 | Breaks the binding between a variable and a package. (See C<tie()>.) | |
4428 | ||
a0d0e21e LW |
4429 | =item use Module LIST |
4430 | ||
4431 | =item use Module | |
4432 | ||
da0045b7 | 4433 | =item use Module VERSION LIST |
4434 | ||
4435 | =item use VERSION | |
4436 | ||
a0d0e21e LW |
4437 | Imports some semantics into the current package from the named module, |
4438 | generally by aliasing certain subroutine or variable names into your | |
4439 | package. It is exactly equivalent to | |
4440 | ||
4441 | BEGIN { require Module; import Module LIST; } | |
4442 | ||
54310121 | 4443 | except that Module I<must> be a bareword. |
da0045b7 | 4444 | |
4445 | If the first argument to C<use> is a number, it is treated as a version | |
4446 | number instead of a module name. If the version of the Perl interpreter | |
4447 | is less than VERSION, then an error message is printed and Perl exits | |
4448 | immediately. This is often useful if you need to check the current | |
5a964f20 | 4449 | Perl version before C<use>ing library modules that have changed in |
da0045b7 | 4450 | incompatible ways from older versions of Perl. (We try not to do |
4451 | this more than we have to.) | |
4452 | ||
ab4f32c2 | 4453 | The C<BEGIN> forces the C<require> and C<import()> to happen at compile time. The |
7660c0ab | 4454 | C<require> makes sure the module is loaded into memory if it hasn't been |
ab4f32c2 | 4455 | yet. The C<import()> is not a builtin--it's just an ordinary static method |
7660c0ab | 4456 | call into the "C<Module>" package to tell the module to import the list of |
a0d0e21e | 4457 | features back into the current package. The module can implement its |
ab4f32c2 A |
4458 | C<import()> method any way it likes, though most modules just choose to |
4459 | derive their C<import()> method via inheritance from the C<Exporter> class that | |
4460 | is defined in the C<Exporter> module. See L<Exporter>. If no C<import()> | |
2f9daede | 4461 | method can be found then the error is currently silently ignored. This |
55497cff | 4462 | may change to a fatal error in a future version. |
cb1a09d0 AD |
4463 | |
4464 | If you don't want your namespace altered, explicitly supply an empty list: | |
4465 | ||
4466 | use Module (); | |
4467 | ||
4468 | That is exactly equivalent to | |
4469 | ||
5a964f20 | 4470 | BEGIN { require Module } |
a0d0e21e | 4471 | |
da0045b7 | 4472 | If the VERSION argument is present between Module and LIST, then the |
71be2cbc | 4473 | C<use> will call the VERSION method in class Module with the given |
4474 | version as an argument. The default VERSION method, inherited from | |
4475 | the Universal class, croaks if the given version is larger than the | |
7660c0ab | 4476 | value of the variable C<$Module::VERSION>. (Note that there is not a |
71be2cbc | 4477 | comma after VERSION!) |
da0045b7 | 4478 | |
a0d0e21e LW |
4479 | Because this is a wide-open interface, pragmas (compiler directives) |
4480 | are also implemented this way. Currently implemented pragmas are: | |
4481 | ||
4482 | use integer; | |
4633a7c4 | 4483 | use diagnostics; |
a0d0e21e LW |
4484 | use sigtrap qw(SEGV BUS); |
4485 | use strict qw(subs vars refs); | |
4486 | use subs qw(afunc blurfl); | |
4487 | ||
5a964f20 TC |
4488 | Some of these these pseudo-modules import semantics into the current |
4489 | block scope (like C<strict> or C<integer>, unlike ordinary modules, | |
4490 | which import symbols into the current package (which are effective | |
4491 | through the end of the file). | |
a0d0e21e | 4492 | |
7660c0ab | 4493 | There's a corresponding "C<no>" command that unimports meanings imported |
ab4f32c2 | 4494 | by C<use>, i.e., it calls C<unimport Module LIST> instead of C<import()>. |
a0d0e21e LW |
4495 | |
4496 | no integer; | |
4497 | no strict 'refs'; | |
4498 | ||
ab4f32c2 | 4499 | If no C<unimport()> method can be found the call fails with a fatal error. |
55497cff | 4500 | |
a0d0e21e LW |
4501 | See L<perlmod> for a list of standard modules and pragmas. |
4502 | ||
4503 | =item utime LIST | |
4504 | ||
4505 | Changes the access and modification times on each file of a list of | |
4506 | files. The first two elements of the list must be the NUMERICAL access | |
4507 | and modification times, in that order. Returns the number of files | |
4508 | successfully changed. The inode modification time of each file is set | |
7660c0ab | 4509 | to the current time. This code has the same effect as the "C<touch>" |
a3cb178b | 4510 | command if the files already exist: |
a0d0e21e LW |
4511 | |
4512 | #!/usr/bin/perl | |
4513 | $now = time; | |
4514 | utime $now, $now, @ARGV; | |
4515 | ||
aa689395 | 4516 | =item values HASH |
a0d0e21e | 4517 | |
1d2dff63 GS |
4518 | Returns a list consisting of all the values of the named hash. (In a |
4519 | scalar context, returns the number of values.) The values are | |
ab192400 GS |
4520 | returned in an apparently random order. The actual random order is |
4521 | subject to change in future versions of perl, but it is guaranteed to | |
4522 | be the same order as either the C<keys()> or C<each()> function would | |
4523 | produce on the same (unmodified) hash. | |
4524 | ||
7660c0ab A |
4525 | As a side effect, it resets HASH's iterator. See also C<keys()>, C<each()>, |
4526 | and C<sort()>. | |
a0d0e21e LW |
4527 | |
4528 | =item vec EXPR,OFFSET,BITS | |
4529 | ||
22dc801b | 4530 | Treats the string in EXPR as a vector of unsigned integers, and |
5f05dabc | 4531 | returns the value of the bit field specified by OFFSET. BITS specifies |
22dc801b | 4532 | the number of bits that are reserved for each entry in the bit |
7660c0ab | 4533 | vector. This must be a power of two from 1 to 32. C<vec()> may also be |
5f05dabc | 4534 | assigned to, in which case parentheses are needed to give the expression |
22dc801b | 4535 | the correct precedence as in |
4536 | ||
4537 | vec($image, $max_x * $x + $y, 8) = 3; | |
a0d0e21e | 4538 | |
7660c0ab A |
4539 | Vectors created with C<vec()> can also be manipulated with the logical |
4540 | operators C<|>, C<&>, and C<^>, which will assume a bit vector operation is | |
a0d0e21e LW |
4541 | desired when both operands are strings. |
4542 | ||
7660c0ab | 4543 | The following code will build up an ASCII string saying C<'PerlPerlPerl'>. |
cca87523 GS |
4544 | The comments show the string after each step. Note that this code works |
4545 | in the same way on big-endian or little-endian machines. | |
4546 | ||
4547 | my $foo = ''; | |
4548 | vec($foo, 0, 32) = 0x5065726C; # 'Perl' | |
4549 | vec($foo, 2, 16) = 0x5065; # 'PerlPe' | |
4550 | vec($foo, 3, 16) = 0x726C; # 'PerlPerl' | |
4551 | vec($foo, 8, 8) = 0x50; # 'PerlPerlP' | |
4552 | vec($foo, 9, 8) = 0x65; # 'PerlPerlPe' | |
4553 | vec($foo, 20, 4) = 2; # 'PerlPerlPe' . "\x02" | |
f86cebdf GS |
4554 | vec($foo, 21, 4) = 7; # 'PerlPerlPer' |
4555 | # 'r' is "\x72" | |
cca87523 GS |
4556 | vec($foo, 45, 2) = 3; # 'PerlPerlPer' . "\x0c" |
4557 | vec($foo, 93, 1) = 1; # 'PerlPerlPer' . "\x2c" | |
f86cebdf GS |
4558 | vec($foo, 94, 1) = 1; # 'PerlPerlPerl' |
4559 | # 'l' is "\x6c" | |
cca87523 | 4560 | |
a0d0e21e LW |
4561 | To transform a bit vector into a string or array of 0's and 1's, use these: |
4562 | ||
4563 | $bits = unpack("b*", $vector); | |
4564 | @bits = split(//, unpack("b*", $vector)); | |
4565 | ||
7660c0ab | 4566 | If you know the exact length in bits, it can be used in place of the C<*>. |
a0d0e21e LW |
4567 | |
4568 | =item wait | |
4569 | ||
4570 | Waits for a child process to terminate and returns the pid of the | |
7660c0ab | 4571 | deceased process, or C<-1> if there are no child processes. The status is |
f648820c GS |
4572 | returned in C<$?>. Note that a return value of C<-1> could mean that |
4573 | child processes are being automatically reaped, as described in L<perlipc>. | |
a0d0e21e LW |
4574 | |
4575 | =item waitpid PID,FLAGS | |
4576 | ||
4577 | Waits for a particular child process to terminate and returns the pid | |
7660c0ab | 4578 | of the deceased process, or C<-1> if there is no such child process. The |
184e9718 | 4579 | status is returned in C<$?>. If you say |
a0d0e21e | 4580 | |
5f05dabc | 4581 | use POSIX ":sys_wait_h"; |
5a964f20 | 4582 | #... |
a0d0e21e LW |
4583 | waitpid(-1,&WNOHANG); |
4584 | ||
4585 | then you can do a non-blocking wait for any process. Non-blocking wait | |
f86cebdf GS |
4586 | is available on machines supporting either the waitpid(2) or |
4587 | wait4(2) system calls. However, waiting for a particular pid with | |
7660c0ab | 4588 | FLAGS of C<0> is implemented everywhere. (Perl emulates the system call |
a0d0e21e LW |
4589 | by remembering the status values of processes that have exited but have |
4590 | not been harvested by the Perl script yet.) | |
4591 | ||
f648820c GS |
4592 | Note that a return value of C<-1> could mean that child processes are being |
4593 | automatically reaped. See L<perlipc> for details, and for other examples. | |
5a964f20 | 4594 | |
a0d0e21e LW |
4595 | =item wantarray |
4596 | ||
4597 | Returns TRUE if the context of the currently executing subroutine is | |
4598 | looking for a list value. Returns FALSE if the context is looking | |
54310121 | 4599 | for a scalar. Returns the undefined value if the context is looking |
4600 | for no value (void context). | |
a0d0e21e | 4601 | |
54310121 | 4602 | return unless defined wantarray; # don't bother doing more |
4603 | my @a = complex_calculation(); | |
4604 | return wantarray ? @a : "@a"; | |
a0d0e21e LW |
4605 | |
4606 | =item warn LIST | |
4607 | ||
7660c0ab | 4608 | Produces a message on STDERR just like C<die()>, but doesn't exit or throw |
774d564b | 4609 | an exception. |
4610 | ||
7660c0ab A |
4611 | If LIST is empty and C<$@> already contains a value (typically from a |
4612 | previous eval) that value is used after appending C<"\t...caught"> | |
4613 | to C<$@>. This is useful for staying almost, but not entirely similar to | |
4614 | C<die()>. | |
43051805 | 4615 | |
7660c0ab | 4616 | If C<$@> is empty then the string C<"Warning: Something's wrong"> is used. |
43051805 | 4617 | |
774d564b | 4618 | No message is printed if there is a C<$SIG{__WARN__}> handler |
4619 | installed. It is the handler's responsibility to deal with the message | |
7660c0ab | 4620 | as it sees fit (like, for instance, converting it into a C<die()>). Most |
774d564b | 4621 | handlers must therefore make arrangements to actually display the |
7660c0ab | 4622 | warnings that they are not prepared to deal with, by calling C<warn()> |
774d564b | 4623 | again in the handler. Note that this is quite safe and will not |
4624 | produce an endless loop, since C<__WARN__> hooks are not called from | |
4625 | inside one. | |
4626 | ||
4627 | You will find this behavior is slightly different from that of | |
4628 | C<$SIG{__DIE__}> handlers (which don't suppress the error text, but can | |
7660c0ab | 4629 | instead call C<die()> again to change it). |
774d564b | 4630 | |
4631 | Using a C<__WARN__> handler provides a powerful way to silence all | |
4632 | warnings (even the so-called mandatory ones). An example: | |
4633 | ||
4634 | # wipe out *all* compile-time warnings | |
4635 | BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } } | |
4636 | my $foo = 10; | |
4637 | my $foo = 20; # no warning about duplicate my $foo, | |
4638 | # but hey, you asked for it! | |
4639 | # no compile-time or run-time warnings before here | |
4640 | $DOWARN = 1; | |
4641 | ||
4642 | # run-time warnings enabled after here | |
4643 | warn "\$foo is alive and $foo!"; # does show up | |
4644 | ||
4645 | See L<perlvar> for details on setting C<%SIG> entries, and for more | |
4646 | examples. | |
a0d0e21e | 4647 | |
a189bff9 JH |
4648 | =item while (EXPR) BLOCK |
4649 | ||
4650 | =item do BLOCK while (EXPR) | |
4651 | ||
4652 | Enter BLOCK while EXPR is true. The first form may avoid entering the | |
4653 | BLOCK, the second form enters the BLOCK at least once. | |
4654 | ||
4655 | See also L<perlsyn>, L</for>, L</until>, and L</continue>. | |
4656 | ||
a0d0e21e LW |
4657 | =item write FILEHANDLE |
4658 | ||
4659 | =item write EXPR | |
4660 | ||
4661 | =item write | |
4662 | ||
5a964f20 | 4663 | Writes a formatted record (possibly multi-line) to the specified FILEHANDLE, |
a0d0e21e | 4664 | using the format associated with that file. By default the format for |
54310121 | 4665 | a file is the one having the same name as the filehandle, but the |
7660c0ab | 4666 | format for the current output channel (see the C<select()> function) may be set |
184e9718 | 4667 | explicitly by assigning the name of the format to the C<$~> variable. |
a0d0e21e LW |
4668 | |
4669 | Top of form processing is handled automatically: if there is | |
4670 | insufficient room on the current page for the formatted record, the | |
4671 | page is advanced by writing a form feed, a special top-of-page format | |
4672 | is used to format the new page header, and then the record is written. | |
4673 | By default the top-of-page format is the name of the filehandle with | |
4674 | "_TOP" appended, but it may be dynamically set to the format of your | |
184e9718 | 4675 | choice by assigning the name to the C<$^> variable while the filehandle is |
a0d0e21e | 4676 | selected. The number of lines remaining on the current page is in |
7660c0ab | 4677 | variable C<$->, which can be set to C<0> to force a new page. |
a0d0e21e LW |
4678 | |
4679 | If FILEHANDLE is unspecified, output goes to the current default output | |
4680 | channel, which starts out as STDOUT but may be changed by the | |
ab4f32c2 | 4681 | C<select()> operator. If the FILEHANDLE is an EXPR, then the expression |
a0d0e21e LW |
4682 | is evaluated and the resulting string is used to look up the name of |
4683 | the FILEHANDLE at run time. For more on formats, see L<perlform>. | |
4684 | ||
ab4f32c2 | 4685 | Note that write is I<NOT> the opposite of C<read()>. Unfortunately. |
a0d0e21e LW |
4686 | |
4687 | =item y/// | |
4688 | ||
7660c0ab | 4689 | The transliteration operator. Same as C<tr///>. See L<perlop>. |
a0d0e21e LW |
4690 | |
4691 | =back |