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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 |
17 | be first, and the list argument will follow. (Note that there can only |
18 | ever be one list argument.) For instance, splice() has three scalar |
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 |
31 | parens.) If you use the parens, the simple (but occasionally |
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 | |
38 | print 1+2+3; # Prints 6. |
39 | print(1+2) + 3; # Prints 3. |
40 | print (1+2)+3; # Also prints 3! |
41 | print +(1+2)+3; # Prints 6. |
42 | print ((1+2)+3); # Prints 6. |
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, |
51 | non-abortive failure is generally indicated in a scalar context by |
52 | returning the undefined value, and in a list context by returning the |
53 | null list. |
54 | |
55 | Remember the following rule: |
56 | |
cb1a09d0 |
57 | =over 8 |
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58 | |
cb1a09d0 |
59 | =item |
a0d0e21e |
60 | |
61 | I<THERE IS NO GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR!> |
62 | |
63 | =back |
64 | |
65 | Each operator and function decides which sort of value it would be most |
66 | appropriate to return in a scalar context. Some operators return the |
67 | length of the list that would have been returned in a list context. Some |
68 | operators return the first value in the list. Some operators return the |
69 | last value in the list. Some operators return a count of successful |
70 | operations. In general, they do what you want, unless you want |
71 | consistency. |
72 | |
cb1a09d0 |
73 | =head2 Perl Functions by Category |
74 | |
75 | Here are Perl's functions (including things that look like |
76 | functions, like some of the keywords and named operators) |
77 | arranged by category. Some functions appear in more |
78 | than one place. |
79 | |
80 | =over |
81 | |
82 | =item Functions for SCALARs or strings |
83 | |
84 | chomp, chop, chr, crypt, hex, index, lc, lcfirst, length, |
85 | oct, ord, pack, q/STRING/, qq/STRING/, reverse, rindex, |
86 | sprintf, substr, tr///, uc, ucfirst, y/// |
87 | |
88 | =item Regular expressions and pattern matching |
89 | |
90 | m//, pos, quotemeta, s///, split, study |
91 | |
92 | =item Numeric functions |
93 | |
94 | abs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt, |
95 | srand |
96 | |
97 | =item Functions for real @ARRAYs |
98 | |
99 | pop, push, shift, splice, unshift |
100 | |
101 | =item Functions for list data |
102 | |
103 | grep, join, map, qw/STRING/, reverse, sort, unpack |
104 | |
105 | =item Functions for real %HASHes |
106 | |
107 | delete, each, exists, keys, values |
108 | |
109 | =item Input and output functions |
110 | |
111 | binmode, close, closedir, dbmclose, dbmopen, die, eof, |
112 | fileno, flock, format, getc, print, printf, read, readdir, |
113 | rewinddir, seek, seekdir, select, syscall, sysread, |
114 | syswrite, tell, telldir, truncate, warn, write |
115 | |
116 | =item Functions for fixed length data or records |
117 | |
118 | pack, read, syscall, sysread, syswrite, unpack, vec |
119 | |
120 | =item Functions for filehandles, files, or directories |
121 | |
c07a80fd |
122 | -X, chdir, chmod, chown, chroot, fcntl, glob, ioctl, link, |
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123 | lstat, mkdir, open, opendir, readlink, rename, rmdir, |
124 | stat, symlink, umask, unlink, utime |
125 | |
126 | =item Keywords related to the control flow of your perl program |
127 | |
128 | caller, continue, die, do, dump, eval, exit, goto, last, |
129 | next, redo, return, sub, wantarray |
130 | |
131 | =item Keywords related to scoping |
132 | |
133 | caller, import, local, my, package, use |
134 | |
135 | =item Miscellaneous functions |
136 | |
137 | defined, dump, eval, formline, local, my, reset, scalar, |
138 | undef, wantarray |
139 | |
140 | =item Functions for processes and process groups |
141 | |
142 | alarm, exec, fork, getpgrp, getppid, getpriority, kill, |
143 | pipe, qx/STRING/, setpgrp, setpriority, sleep, system, |
144 | times, wait, waitpid |
145 | |
146 | =item Keywords related to perl modules |
147 | |
148 | do, import, no, package, require, use |
149 | |
150 | =item Keywords related to classes and object-orientedness |
151 | |
f3cbc334 |
152 | bless, dbmclose, dbmopen, package, ref, tie, tied, untie, use |
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153 | |
154 | =item Low-level socket functions |
155 | |
156 | accept, bind, connect, getpeername, getsockname, |
157 | getsockopt, listen, recv, send, setsockopt, shutdown, |
158 | socket, socketpair |
159 | |
160 | =item System V interprocess communication functions |
161 | |
162 | msgctl, msgget, msgrcv, msgsnd, semctl, semget, semop, |
163 | shmctl, shmget, shmread, shmwrite |
164 | |
165 | =item Fetching user and group info |
166 | |
167 | endgrent, endhostent, endnetent, endpwent, getgrent, |
168 | getgrgid, getgrnam, getlogin, getpwent, getpwnam, |
169 | getpwuid, setgrent, setpwent |
170 | |
171 | =item Fetching network info |
172 | |
173 | endprotoent, endservent, gethostbyaddr, gethostbyname, |
174 | gethostent, getnetbyaddr, getnetbyname, getnetent, |
175 | getprotobyname, getprotobynumber, getprotoent, |
176 | getservbyname, getservbyport, getservent, sethostent, |
177 | setnetent, setprotoent, setservent |
178 | |
179 | =item Time-related functions |
180 | |
181 | gmtime, localtime, time, times |
182 | |
37798a01 |
183 | =item Functions new in perl5 |
184 | |
185 | abs, bless, chomp, chr, exists, formline, glob, import, lc, |
186 | lcfirst, map, my, no, qx, qw, ref, sub*, sysopen, tie, tied, uc, |
187 | ucfirst, untie, use |
188 | |
189 | * - C<sub> was a keyword in perl4, but in perl5 it is an |
190 | operator which can be used in expressions. |
191 | |
192 | =item Functions obsoleted in perl5 |
193 | |
194 | dbmclose, dbmopen |
195 | |
196 | |
cb1a09d0 |
197 | =back |
198 | |
199 | =head2 Alphabetical Listing of Perl Functions |
200 | |
201 | |
a0d0e21e |
202 | =over 8 |
203 | |
204 | =item -X FILEHANDLE |
205 | |
206 | =item -X EXPR |
207 | |
208 | =item -X |
209 | |
210 | A file test, where X is one of the letters listed below. This unary |
211 | operator takes one argument, either a filename or a filehandle, and |
212 | tests the associated file to see if something is true about it. If the |
213 | argument is omitted, tests $_, except for C<-t>, which tests STDIN. |
214 | Unless otherwise documented, it returns C<1> for TRUE and C<''> for FALSE, or |
215 | the undefined value if the file doesn't exist. Despite the funny |
216 | names, precedence is the same as any other named unary operator, and |
217 | the argument may be parenthesized like any other unary operator. The |
218 | operator may be any of: |
219 | |
220 | -r File is readable by effective uid/gid. |
221 | -w File is writable by effective uid/gid. |
222 | -x File is executable by effective uid/gid. |
223 | -o File is owned by effective uid. |
224 | |
225 | -R File is readable by real uid/gid. |
226 | -W File is writable by real uid/gid. |
227 | -X File is executable by real uid/gid. |
228 | -O File is owned by real uid. |
229 | |
230 | -e File exists. |
231 | -z File has zero size. |
232 | -s File has non-zero size (returns size). |
233 | |
234 | -f File is a plain file. |
235 | -d File is a directory. |
236 | -l File is a symbolic link. |
237 | -p File is a named pipe (FIFO). |
238 | -S File is a socket. |
239 | -b File is a block special file. |
240 | -c File is a character special file. |
241 | -t Filehandle is opened to a tty. |
242 | |
243 | -u File has setuid bit set. |
244 | -g File has setgid bit set. |
245 | -k File has sticky bit set. |
246 | |
247 | -T File is a text file. |
248 | -B File is a binary file (opposite of -T). |
249 | |
250 | -M Age of file in days when script started. |
251 | -A Same for access time. |
252 | -C Same for inode change time. |
253 | |
254 | The interpretation of the file permission operators C<-r>, C<-R>, C<-w>, |
255 | C<-W>, C<-x> and C<-X> is based solely on the mode of the file and the |
256 | uids and gids of the user. There may be other reasons you can't actually |
257 | read, write or execute the file. Also note that, for the superuser, |
258 | C<-r>, C<-R>, C<-w> and C<-W> always return 1, and C<-x> and C<-X> return |
259 | 1 if any execute bit is set in the mode. Scripts run by the superuser may |
260 | thus need to do a stat() in order to determine the actual mode of the |
261 | file, or temporarily set the uid to something else. |
262 | |
263 | Example: |
264 | |
265 | while (<>) { |
266 | chop; |
267 | next unless -f $_; # ignore specials |
268 | ... |
269 | } |
270 | |
271 | Note that C<-s/a/b/> does not do a negated substitution. Saying |
272 | C<-exp($foo)> still works as expected, however--only single letters |
273 | following a minus are interpreted as file tests. |
274 | |
275 | The C<-T> and C<-B> switches work as follows. The first block or so of the |
276 | file is examined for odd characters such as strange control codes or |
277 | characters with the high bit set. If too many odd characters (>30%) |
278 | are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file |
279 | containing null in the first block is considered a binary file. If C<-T> |
280 | or C<-B> is used on a filehandle, the current stdio buffer is examined |
281 | rather than the first block. Both C<-T> and C<-B> return TRUE on a null |
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282 | file, or a file at EOF when testing a filehandle. Because you have to |
283 | read a file to do the C<-T> test, on most occasions you want to use a C<-f> |
284 | against the file first, as in C<next unless -f $file && -T $file>. |
a0d0e21e |
285 | |
286 | If any of the file tests (or either the stat() or lstat() operators) are given the |
287 | special filehandle consisting of a solitary underline, then the stat |
288 | structure of the previous file test (or stat operator) is used, saving |
289 | a system call. (This doesn't work with C<-t>, and you need to remember |
290 | that lstat() and C<-l> will leave values in the stat structure for the |
291 | symbolic link, not the real file.) Example: |
292 | |
293 | print "Can do.\n" if -r $a || -w _ || -x _; |
294 | |
295 | stat($filename); |
296 | print "Readable\n" if -r _; |
297 | print "Writable\n" if -w _; |
298 | print "Executable\n" if -x _; |
299 | print "Setuid\n" if -u _; |
300 | print "Setgid\n" if -g _; |
301 | print "Sticky\n" if -k _; |
302 | print "Text\n" if -T _; |
303 | print "Binary\n" if -B _; |
304 | |
305 | =item abs VALUE |
306 | |
307 | Returns the absolute value of its argument. |
308 | |
309 | =item accept NEWSOCKET,GENERICSOCKET |
310 | |
311 | Accepts an incoming socket connect, just as the accept(2) system call |
312 | does. Returns the packed address if it succeeded, FALSE otherwise. |
4633a7c4 |
313 | See example in L<perlipc/"Sockets: Client/Server Communication">. |
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314 | |
315 | =item alarm SECONDS |
316 | |
317 | Arranges to have a SIGALRM delivered to this process after the |
318 | specified number of seconds have elapsed. (On some machines, |
319 | unfortunately, the elapsed time may be up to one second less than you |
320 | specified because of how seconds are counted.) Only one timer may be |
321 | counting at once. Each call disables the previous timer, and an |
322 | argument of 0 may be supplied to cancel the previous timer without |
323 | starting a new one. The returned value is the amount of time remaining |
324 | on the previous timer. |
325 | |
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326 | For delays of finer granularity than one second, you may use Perl's |
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327 | syscall() interface to access setitimer(2) if your system supports it, |
4633a7c4 |
328 | or else see L</select()> below. It is not advised to intermix alarm() |
329 | and sleep() calls. |
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330 | |
331 | =item atan2 Y,X |
332 | |
333 | Returns the arctangent of Y/X in the range -PI to PI. |
334 | |
335 | =item bind SOCKET,NAME |
336 | |
337 | Binds a network address to a socket, just as the bind system call |
338 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a |
4633a7c4 |
339 | packed address of the appropriate type for the socket. See the examples in |
340 | L<perlipc/"Sockets: Client/Server Communication">. |
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341 | |
342 | =item binmode FILEHANDLE |
343 | |
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344 | Arranges for the file to be read or written in "binary" mode in operating |
345 | systems that distinguish between binary and text files. Files that are |
346 | not in binary mode have CR LF sequences translated to LF on input and LF |
347 | translated to CR LF on output. Binmode has no effect under Unix; in DOS |
348 | and similarly archaic systems, it may be imperative--otherwise your |
349 | DOS-damaged C library may mangle your file. The key distinction between |
350 | systems that need binmode and those that don't is their text file |
351 | formats. Systems like Unix and Plan9 that delimit lines with a single |
352 | character, and that encode that character in C as '\n', do not need |
353 | C<binmode>. The rest need it. If FILEHANDLE is an expression, the value |
354 | is taken as the name of the filehandle. |
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355 | |
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356 | =item bless REF,CLASSNAME |
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357 | |
358 | =item bless REF |
359 | |
360 | This function tells the referenced object (passed as REF) that it is now |
4633a7c4 |
361 | an object in the CLASSNAME package--or the current package if no CLASSNAME |
362 | is specified, which is often the case. It returns the reference for |
363 | convenience, since a bless() is often the last thing in a constructor. |
364 | Always use the two-argument version if the function doing the blessing |
365 | might be inherited by a derived class. See L<perlobj> for more about the |
366 | blessing (and blessings) of objects. |
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367 | |
368 | =item caller EXPR |
369 | |
370 | =item caller |
371 | |
372 | Returns the context of the current subroutine call. In a scalar context, |
373 | returns TRUE if there is a caller, that is, if we're in a subroutine or |
374 | eval() or require(), and FALSE otherwise. In a list context, returns |
375 | |
748a9306 |
376 | ($package, $filename, $line) = caller; |
a0d0e21e |
377 | |
378 | With EXPR, it returns some extra information that the debugger uses to |
379 | print a stack trace. The value of EXPR indicates how many call frames |
380 | to go back before the current one. |
381 | |
748a9306 |
382 | ($package, $filename, $line, |
383 | $subroutine, $hasargs, $wantargs) = caller($i); |
384 | |
385 | Furthermore, when called from within the DB package, caller returns more |
4633a7c4 |
386 | detailed information: it sets the list variable @DB::args to be the |
748a9306 |
387 | arguments with which that subroutine was invoked. |
388 | |
a0d0e21e |
389 | =item chdir EXPR |
390 | |
391 | Changes the working directory to EXPR, if possible. If EXPR is |
392 | omitted, changes to home directory. Returns TRUE upon success, FALSE |
393 | otherwise. See example under die(). |
394 | |
395 | =item chmod LIST |
396 | |
397 | Changes the permissions of a list of files. The first element of the |
4633a7c4 |
398 | list must be the numerical mode, which should probably be an octal |
399 | number. Returns the number of files successfully changed. |
a0d0e21e |
400 | |
401 | $cnt = chmod 0755, 'foo', 'bar'; |
402 | chmod 0755, @executables; |
403 | |
404 | =item chomp VARIABLE |
405 | |
406 | =item chomp LIST |
407 | |
408 | =item chomp |
409 | |
410 | This is a slightly safer version of chop (see below). It removes any |
411 | line ending that corresponds to the current value of C<$/> (also known as |
412 | $INPUT_RECORD_SEPARATOR in the C<English> module). It returns the number |
413 | of characters removed. It's often used to remove the newline from the |
414 | end of an input record when you're worried that the final record may be |
415 | missing its newline. When in paragraph mode (C<$/ = "">), it removes all |
416 | trailing newlines from the string. If VARIABLE is omitted, it chomps |
417 | $_. Example: |
418 | |
419 | while (<>) { |
420 | chomp; # avoid \n on last field |
421 | @array = split(/:/); |
422 | ... |
423 | } |
424 | |
425 | You can actually chomp anything that's an lvalue, including an assignment: |
426 | |
427 | chomp($cwd = `pwd`); |
428 | chomp($answer = <STDIN>); |
429 | |
430 | If you chomp a list, each element is chomped, and the total number of |
431 | characters removed is returned. |
432 | |
433 | =item chop VARIABLE |
434 | |
435 | =item chop LIST |
436 | |
437 | =item chop |
438 | |
439 | Chops off the last character of a string and returns the character |
440 | chopped. It's used primarily to remove the newline from the end of an |
441 | input record, but is much more efficient than C<s/\n//> because it neither |
442 | scans nor copies the string. If VARIABLE is omitted, chops $_. |
443 | Example: |
444 | |
445 | while (<>) { |
446 | chop; # avoid \n on last field |
447 | @array = split(/:/); |
448 | ... |
449 | } |
450 | |
451 | You can actually chop anything that's an lvalue, including an assignment: |
452 | |
453 | chop($cwd = `pwd`); |
454 | chop($answer = <STDIN>); |
455 | |
456 | If you chop a list, each element is chopped. Only the value of the |
457 | last chop is returned. |
458 | |
748a9306 |
459 | Note that chop returns the last character. To return all but the last |
460 | character, use C<substr($string, 0, -1)>. |
461 | |
a0d0e21e |
462 | =item chown LIST |
463 | |
464 | Changes the owner (and group) of a list of files. The first two |
465 | elements of the list must be the I<NUMERICAL> uid and gid, in that order. |
466 | Returns the number of files successfully changed. |
467 | |
468 | $cnt = chown $uid, $gid, 'foo', 'bar'; |
469 | chown $uid, $gid, @filenames; |
470 | |
471 | Here's an example that looks up non-numeric uids in the passwd file: |
472 | |
473 | print "User: "; |
474 | chop($user = <STDIN>); |
475 | print "Files: " |
476 | chop($pattern = <STDIN>); |
477 | |
478 | ($login,$pass,$uid,$gid) = getpwnam($user) |
479 | or die "$user not in passwd file"; |
480 | |
481 | @ary = <${pattern}>; # expand filenames |
482 | chown $uid, $gid, @ary; |
483 | |
4633a7c4 |
484 | On most systems, you are not allowed to change the ownership of the |
485 | file unless you're the superuser, although you should be able to change |
486 | the group to any of your secondary groups. On insecure systems, these |
487 | restrictions may be relaxed, but this is not a portable assumption. |
488 | |
a0d0e21e |
489 | =item chr NUMBER |
490 | |
491 | Returns the character represented by that NUMBER in the character set. |
492 | For example, C<chr(65)> is "A" in ASCII. |
493 | |
494 | =item chroot FILENAME |
495 | |
4633a7c4 |
496 | This function works as the system call by the same name: it makes the |
497 | named directory the new root directory for all further pathnames that |
498 | begin with a "/" by your process and all of its children. (It doesn't |
499 | change your current working directory is unaffected.) For security |
500 | reasons, this call is restricted to the superuser. If FILENAME is |
501 | omitted, does chroot to $_. |
a0d0e21e |
502 | |
503 | =item close FILEHANDLE |
504 | |
505 | Closes the file or pipe associated with the file handle, returning TRUE |
506 | only if stdio successfully flushes buffers and closes the system file |
507 | descriptor. You don't have to close FILEHANDLE if you are immediately |
4633a7c4 |
508 | going to do another open() on it, since open() will close it for you. (See |
a0d0e21e |
509 | open().) However, an explicit close on an input file resets the line |
510 | counter ($.), while the implicit close done by open() does not. Also, |
511 | closing a pipe will wait for the process executing on the pipe to |
512 | complete, in case you want to look at the output of the pipe |
513 | afterwards. Closing a pipe explicitly also puts the status value of |
514 | the command into C<$?>. Example: |
515 | |
516 | open(OUTPUT, '|sort >foo'); # pipe to sort |
517 | ... # print stuff to output |
518 | close OUTPUT; # wait for sort to finish |
519 | open(INPUT, 'foo'); # get sort's results |
520 | |
521 | FILEHANDLE may be an expression whose value gives the real filehandle name. |
522 | |
523 | =item closedir DIRHANDLE |
524 | |
525 | Closes a directory opened by opendir(). |
526 | |
527 | =item connect SOCKET,NAME |
528 | |
529 | Attempts to connect to a remote socket, just as the connect system call |
530 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a |
4633a7c4 |
531 | packed address of the appropriate type for the socket. See the examples in |
532 | L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e |
533 | |
cb1a09d0 |
534 | =item continue BLOCK |
535 | |
536 | Actually a flow control statement rather than a function. If there is a |
537 | C<continue> BLOCK attached to a BLOCK (typically in a C<while> or |
538 | C<foreach>), it is always executed just before the conditional is about to |
539 | be evaluated again, just like the third part of a C<for> loop in C. Thus |
540 | it can be used to increment a loop variable, even when the loop has been |
541 | continued via the C<next> statement (which is similar to the C C<continue> |
542 | statement). |
543 | |
a0d0e21e |
544 | =item cos EXPR |
545 | |
546 | Returns the cosine of EXPR (expressed in radians). If EXPR is omitted |
547 | takes cosine of $_. |
548 | |
549 | =item crypt PLAINTEXT,SALT |
550 | |
4633a7c4 |
551 | Encrypts a string exactly like the crypt(3) function in the C library |
552 | (assuming that you actually have a version there that has not been |
553 | extirpated as a potential munition). This can prove useful for checking |
554 | the password file for lousy passwords, amongst other things. Only the |
555 | guys wearing white hats should do this. |
a0d0e21e |
556 | |
557 | Here's an example that makes sure that whoever runs this program knows |
558 | their own password: |
559 | |
560 | $pwd = (getpwuid($<))[1]; |
561 | $salt = substr($pwd, 0, 2); |
562 | |
563 | system "stty -echo"; |
564 | print "Password: "; |
565 | chop($word = <STDIN>); |
566 | print "\n"; |
567 | system "stty echo"; |
568 | |
569 | if (crypt($word, $salt) ne $pwd) { |
570 | die "Sorry...\n"; |
571 | } else { |
572 | print "ok\n"; |
573 | } |
574 | |
575 | Of course, typing in your own password to whoever asks you |
748a9306 |
576 | for it is unwise. |
a0d0e21e |
577 | |
578 | =item dbmclose ASSOC_ARRAY |
579 | |
580 | [This function has been superseded by the untie() function.] |
581 | |
582 | Breaks the binding between a DBM file and an associative array. |
583 | |
584 | =item dbmopen ASSOC,DBNAME,MODE |
585 | |
586 | [This function has been superseded by the tie() function.] |
587 | |
cb1a09d0 |
588 | This binds a dbm(3), ndbm(3), sdbm(3), gdbm(), or Berkeley DB file to an |
589 | associative array. ASSOC is the name of the associative array. (Unlike |
590 | normal open, the first argument is I<NOT> a filehandle, even though it |
591 | looks like one). DBNAME is the name of the database (without the F<.dir> |
592 | or F<.pag> extension if any). If the database does not exist, it is |
593 | created with protection specified by MODE (as modified by the umask()). |
594 | If your system only supports the older DBM functions, you may perform only |
595 | one dbmopen() in your program. In older versions of Perl, if your system |
596 | had neither DBM nor ndbm, calling dbmopen() produced a fatal error; it now |
597 | falls back to sdbm(3). |
a0d0e21e |
598 | |
599 | If you don't have write access to the DBM file, you can only read |
600 | associative array variables, not set them. If you want to test whether |
601 | you can write, either use file tests or try setting a dummy array entry |
602 | inside an eval(), which will trap the error. |
603 | |
604 | Note that functions such as keys() and values() may return huge array |
605 | values when used on large DBM files. You may prefer to use the each() |
606 | function to iterate over large DBM files. Example: |
607 | |
608 | # print out history file offsets |
609 | dbmopen(%HIST,'/usr/lib/news/history',0666); |
610 | while (($key,$val) = each %HIST) { |
611 | print $key, ' = ', unpack('L',$val), "\n"; |
612 | } |
613 | dbmclose(%HIST); |
614 | |
cb1a09d0 |
615 | See also L<AnyDBM_File> for a more general description of the pros and |
616 | cons of the various dbm apparoches, as well as L<DB_File> for a particularly |
617 | rich implementation. |
4633a7c4 |
618 | |
a0d0e21e |
619 | =item defined EXPR |
620 | |
cb1a09d0 |
621 | Returns a boolean value saying whether EXPR has a real value |
a0d0e21e |
622 | or not. Many operations return the undefined value under exceptional |
623 | conditions, such as end of file, uninitialized variable, system error |
624 | and such. This function allows you to distinguish between an undefined |
625 | null scalar and a defined null scalar with operations that might return |
626 | a real null string, such as referencing elements of an array. You may |
627 | also check to see if arrays or subroutines exist. Use of defined on |
628 | predefined variables is not guaranteed to produce intuitive results. |
629 | |
630 | When used on a hash array element, it tells you whether the value |
631 | is defined, not whether the key exists in the hash. Use exists() for that. |
632 | |
633 | Examples: |
634 | |
635 | print if defined $switch{'D'}; |
636 | print "$val\n" while defined($val = pop(@ary)); |
637 | die "Can't readlink $sym: $!" |
638 | unless defined($value = readlink $sym); |
639 | eval '@foo = ()' if defined(@foo); |
640 | die "No XYZ package defined" unless defined %_XYZ; |
641 | sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } |
642 | |
643 | See also undef(). |
644 | |
a5f75d66 |
645 | Note: many folks tend to overuse defined(), and then are surprised to |
646 | discover that the number 0 and the null string are, in fact, defined |
647 | concepts. For example, if you say |
648 | |
649 | "ab" =~ /a(.*)b/; |
650 | |
651 | the pattern match succeeds, and $1 is defined, despite the fact that it |
652 | matched "nothing". But it didn't really match nothing--rather, it |
653 | matched something that happened to be 0 characters long. This is all |
654 | very above-board and honest. When a function returns an undefined value, |
655 | it's an admission that it couldn't give you an honest answer. So |
656 | you should only use defined() when you're questioning the integrity |
657 | of what you're trying to do. At other times, a simple comparison to |
658 | 0 or "" is what you want. |
659 | |
a0d0e21e |
660 | =item delete EXPR |
661 | |
662 | Deletes the specified value from its hash array. Returns the deleted |
663 | value, or the undefined value if nothing was deleted. Deleting from |
664 | C<$ENV{}> modifies the environment. Deleting from an array tied to a DBM |
665 | file deletes the entry from the DBM file. (But deleting from a tie()d |
666 | hash doesn't necessarily return anything.) |
667 | |
668 | The following deletes all the values of an associative array: |
669 | |
670 | foreach $key (keys %ARRAY) { |
671 | delete $ARRAY{$key}; |
672 | } |
673 | |
674 | (But it would be faster to use the undef() command.) Note that the |
675 | EXPR can be arbitrarily complicated as long as the final operation is |
676 | a hash key lookup: |
677 | |
678 | delete $ref->[$x][$y]{$key}; |
679 | |
680 | =item die LIST |
681 | |
682 | Outside of an eval(), prints the value of LIST to C<STDERR> and exits with |
4633a7c4 |
683 | the current value of $! (errno). If $! is 0, exits with the value of |
748a9306 |
684 | C<($? E<gt>E<gt> 8)> (backtick `command` status). If C<($? E<gt>E<gt> 8)> is 0, |
685 | exits with 255. Inside an eval(), the error message is stuffed into C<$@>, |
4633a7c4 |
686 | and the eval() is terminated with the undefined value; this makes die() |
687 | the way to raise an exception. |
a0d0e21e |
688 | |
689 | Equivalent examples: |
690 | |
691 | die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; |
692 | chdir '/usr/spool/news' or die "Can't cd to spool: $!\n" |
693 | |
694 | If the value of EXPR does not end in a newline, the current script line |
695 | number and input line number (if any) are also printed, and a newline |
696 | is supplied. Hint: sometimes appending ", stopped" to your message |
697 | will cause it to make better sense when the string "at foo line 123" is |
698 | appended. Suppose you are running script "canasta". |
699 | |
700 | die "/etc/games is no good"; |
701 | die "/etc/games is no good, stopped"; |
702 | |
703 | produce, respectively |
704 | |
705 | /etc/games is no good at canasta line 123. |
706 | /etc/games is no good, stopped at canasta line 123. |
707 | |
708 | See also exit() and warn(). |
709 | |
710 | =item do BLOCK |
711 | |
712 | Not really a function. Returns the value of the last command in the |
713 | sequence of commands indicated by BLOCK. When modified by a loop |
714 | modifier, executes the BLOCK once before testing the loop condition. |
715 | (On other statements the loop modifiers test the conditional first.) |
716 | |
717 | =item do SUBROUTINE(LIST) |
718 | |
719 | A deprecated form of subroutine call. See L<perlsub>. |
720 | |
721 | =item do EXPR |
722 | |
723 | Uses the value of EXPR as a filename and executes the contents of the |
724 | file as a Perl script. Its primary use is to include subroutines |
725 | from a Perl subroutine library. |
726 | |
727 | do 'stat.pl'; |
728 | |
729 | is just like |
730 | |
731 | eval `cat stat.pl`; |
732 | |
733 | except that it's more efficient, more concise, keeps track of the |
734 | current filename for error messages, and searches all the B<-I> |
735 | libraries if the file isn't in the current directory (see also the @INC |
736 | array in L<perlvar/Predefined Names>). It's the same, however, in that it does |
737 | reparse the file every time you call it, so you probably don't want to |
738 | do this inside a loop. |
739 | |
740 | Note that inclusion of library modules is better done with the |
4633a7c4 |
741 | use() and require() operators, which also do error checking |
742 | and raise an exception if there's a problem. |
a0d0e21e |
743 | |
744 | =item dump LABEL |
745 | |
746 | This causes an immediate core dump. Primarily this is so that you can |
747 | use the B<undump> program to turn your core dump into an executable binary |
748 | after having initialized all your variables at the beginning of the |
749 | program. When the new binary is executed it will begin by executing a |
750 | C<goto LABEL> (with all the restrictions that C<goto> suffers). Think of |
751 | it as a goto with an intervening core dump and reincarnation. If LABEL |
752 | is omitted, restarts the program from the top. WARNING: any files |
753 | opened at the time of the dump will NOT be open any more when the |
754 | program is reincarnated, with possible resulting confusion on the part |
755 | of Perl. See also B<-u> option in L<perlrun>. |
756 | |
757 | Example: |
758 | |
759 | #!/usr/bin/perl |
760 | require 'getopt.pl'; |
761 | require 'stat.pl'; |
762 | %days = ( |
763 | 'Sun' => 1, |
764 | 'Mon' => 2, |
765 | 'Tue' => 3, |
766 | 'Wed' => 4, |
767 | 'Thu' => 5, |
768 | 'Fri' => 6, |
769 | 'Sat' => 7, |
770 | ); |
771 | |
772 | dump QUICKSTART if $ARGV[0] eq '-d'; |
773 | |
774 | QUICKSTART: |
775 | Getopt('f'); |
776 | |
777 | =item each ASSOC_ARRAY |
778 | |
4633a7c4 |
779 | Returns a 2-element array consisting of the key and value for the next |
a0d0e21e |
780 | value of an associative array, so that you can iterate over it. |
781 | Entries are returned in an apparently random order. When the array is |
782 | entirely read, a null array is returned (which when assigned produces a |
783 | FALSE (0) value). The next call to each() after that will start |
784 | iterating again. The iterator can be reset only by reading all the |
785 | elements from the array. You should not add elements to an array while |
786 | you're iterating over it. There is a single iterator for each |
787 | associative array, shared by all each(), keys() and values() function |
788 | calls in the program. The following prints out your environment like |
789 | the printenv(1) program, only in a different order: |
790 | |
791 | while (($key,$value) = each %ENV) { |
792 | print "$key=$value\n"; |
793 | } |
794 | |
795 | See also keys() and values(). |
796 | |
797 | =item eof FILEHANDLE |
798 | |
4633a7c4 |
799 | =item eof () |
800 | |
a0d0e21e |
801 | =item eof |
802 | |
803 | Returns 1 if the next read on FILEHANDLE will return end of file, or if |
804 | FILEHANDLE is not open. FILEHANDLE may be an expression whose value |
805 | gives the real filehandle name. (Note that this function actually |
806 | reads a character and then ungetc()s it, so it is not very useful in an |
748a9306 |
807 | interactive context.) Do not read from a terminal file (or call |
808 | C<eof(FILEHANDLE)> on it) after end-of-file is reached. Filetypes such |
809 | as terminals may lose the end-of-file condition if you do. |
810 | |
811 | An C<eof> without an argument uses the last file read as argument. |
812 | Empty parentheses () may be used to indicate |
4633a7c4 |
813 | the pseudofile formed of the files listed on the command line, i.e. |
37798a01 |
814 | C<eof()> is reasonable to use inside a while (E<lt>E<gt>) loop to detect the end |
a0d0e21e |
815 | of only the last file. Use C<eof(ARGV)> or eof without the parentheses to |
37798a01 |
816 | test I<EACH> file in a while (E<lt>E<gt>) loop. Examples: |
a0d0e21e |
817 | |
748a9306 |
818 | # reset line numbering on each input file |
819 | while (<>) { |
820 | print "$.\t$_"; |
821 | close(ARGV) if (eof); # Not eof(). |
822 | } |
823 | |
a0d0e21e |
824 | # insert dashes just before last line of last file |
825 | while (<>) { |
826 | if (eof()) { |
827 | print "--------------\n"; |
748a9306 |
828 | close(ARGV); # close or break; is needed if we |
829 | # are reading from the terminal |
a0d0e21e |
830 | } |
831 | print; |
832 | } |
833 | |
a0d0e21e |
834 | Practical hint: you almost never need to use C<eof> in Perl, because the |
37798a01 |
835 | input operators return undef when they run out of data. |
a0d0e21e |
836 | |
837 | =item eval EXPR |
838 | |
839 | =item eval BLOCK |
840 | |
841 | EXPR is parsed and executed as if it were a little Perl program. It |
842 | is executed in the context of the current Perl program, so that any |
843 | variable settings, subroutine or format definitions remain afterwards. |
844 | The value returned is the value of the last expression evaluated, or a |
845 | return statement may be used, just as with subroutines. |
846 | |
847 | If there is a syntax error or runtime error, or a die() statement is |
848 | executed, an undefined value is returned by eval(), and C<$@> is set to the |
849 | error message. If there was no error, C<$@> is guaranteed to be a null |
850 | string. If EXPR is omitted, evaluates $_. The final semicolon, if |
851 | any, may be omitted from the expression. |
852 | |
853 | Note that, since eval() traps otherwise-fatal errors, it is useful for |
4633a7c4 |
854 | determining whether a particular feature (such as socket() or symlink()) |
a0d0e21e |
855 | is implemented. It is also Perl's exception trapping mechanism, where |
856 | the die operator is used to raise exceptions. |
857 | |
858 | If the code to be executed doesn't vary, you may use the eval-BLOCK |
859 | form to trap run-time errors without incurring the penalty of |
860 | recompiling each time. The error, if any, is still returned in C<$@>. |
861 | Examples: |
862 | |
863 | # make divide-by-zero non-fatal |
864 | eval { $answer = $a / $b; }; warn $@ if $@; |
865 | |
866 | # same thing, but less efficient |
867 | eval '$answer = $a / $b'; warn $@ if $@; |
868 | |
869 | # a compile-time error |
870 | eval { $answer = }; |
871 | |
872 | # a run-time error |
873 | eval '$answer ='; # sets $@ |
874 | |
875 | With an eval(), you should be especially careful to remember what's |
876 | being looked at when: |
877 | |
878 | eval $x; # CASE 1 |
879 | eval "$x"; # CASE 2 |
880 | |
881 | eval '$x'; # CASE 3 |
882 | eval { $x }; # CASE 4 |
883 | |
884 | eval "\$$x++" # CASE 5 |
885 | $$x++; # CASE 6 |
886 | |
887 | Cases 1 and 2 above behave identically: they run the code contained in the |
888 | variable $x. (Although case 2 has misleading double quotes making the |
889 | reader wonder what else might be happening (nothing is).) Cases 3 and 4 |
890 | likewise behave in the same way: they run the code <$x>, which does |
891 | nothing at all. (Case 4 is preferred for purely visual reasons.) Case 5 |
892 | is a place where normally you I<WOULD> like to use double quotes, except |
cb1a09d0 |
893 | that in that particular situation, you can just use symbolic references |
a0d0e21e |
894 | instead, as in case 6. |
895 | |
896 | =item exec LIST |
897 | |
898 | The exec() function executes a system command I<AND NEVER RETURNS>. Use |
899 | the system() function if you want it to return. |
900 | |
901 | If there is more than one argument in LIST, or if LIST is an array with |
902 | more than one value, calls execvp(3) with the arguments in LIST. If |
903 | there is only one scalar argument, the argument is checked for shell |
904 | metacharacters. If there are any, the entire argument is passed to |
905 | C</bin/sh -c> for parsing. If there are none, the argument is split |
906 | into words and passed directly to execvp(), which is more efficient. |
37798a01 |
907 | Note: exec() and system() do not flush your output buffer, so you may |
a0d0e21e |
908 | need to set C<$|> to avoid lost output. Examples: |
909 | |
910 | exec '/bin/echo', 'Your arguments are: ', @ARGV; |
911 | exec "sort $outfile | uniq"; |
912 | |
913 | If you don't really want to execute the first argument, but want to lie |
914 | to the program you are executing about its own name, you can specify |
915 | the program you actually want to run as an "indirect object" (without a |
916 | comma) in front of the LIST. (This always forces interpretation of the |
917 | LIST as a multi-valued list, even if there is only a single scalar in |
918 | the list.) Example: |
919 | |
920 | $shell = '/bin/csh'; |
921 | exec $shell '-sh'; # pretend it's a login shell |
922 | |
923 | or, more directly, |
924 | |
925 | exec {'/bin/csh'} '-sh'; # pretend it's a login shell |
926 | |
927 | =item exists EXPR |
928 | |
929 | Returns TRUE if the specified hash key exists in its hash array, even |
930 | if the corresponding value is undefined. |
931 | |
932 | print "Exists\n" if exists $array{$key}; |
933 | print "Defined\n" if defined $array{$key}; |
934 | print "True\n" if $array{$key}; |
935 | |
936 | A hash element can only be TRUE if it's defined, and defined if |
937 | it exists, but the reverse doesn't necessarily hold true. |
938 | |
939 | Note that the EXPR can be arbitrarily complicated as long as the final |
940 | operation is a hash key lookup: |
941 | |
942 | if (exists $ref->[$x][$y]{$key}) { ... } |
943 | |
944 | =item exit EXPR |
945 | |
946 | Evaluates EXPR and exits immediately with that value. (Actually, it |
947 | calls any defined C<END> routines first, but the C<END> routines may not |
948 | abort the exit. Likewise any object destructors that need to be called |
949 | are called before exit.) Example: |
950 | |
951 | $ans = <STDIN>; |
952 | exit 0 if $ans =~ /^[Xx]/; |
953 | |
954 | See also die(). If EXPR is omitted, exits with 0 status. |
955 | |
956 | =item exp EXPR |
957 | |
958 | Returns I<e> (the natural logarithm base) to the power of EXPR. |
959 | If EXPR is omitted, gives C<exp($_)>. |
960 | |
961 | =item fcntl FILEHANDLE,FUNCTION,SCALAR |
962 | |
963 | Implements the fcntl(2) function. You'll probably have to say |
964 | |
965 | use Fcntl; |
966 | |
967 | first to get the correct function definitions. Argument processing and |
968 | value return works just like ioctl() below. Note that fcntl() will produce |
969 | a fatal error if used on a machine that doesn't implement fcntl(2). |
970 | For example: |
971 | |
972 | use Fcntl; |
973 | fcntl($filehandle, F_GETLK, $packed_return_buffer); |
974 | |
975 | =item fileno FILEHANDLE |
976 | |
977 | Returns the file descriptor for a filehandle. This is useful for |
978 | constructing bitmaps for select(). If FILEHANDLE is an expression, the |
979 | value is taken as the name of the filehandle. |
980 | |
981 | =item flock FILEHANDLE,OPERATION |
982 | |
4633a7c4 |
983 | Calls flock(2) on FILEHANDLE. See L<flock(2)> for definition of |
984 | OPERATION. Returns TRUE for success, FALSE on failure. Will produce a |
985 | fatal error if used on a machine that doesn't implement either flock(2) or |
cb1a09d0 |
986 | fcntl(2). The fcntl(2) system call will be automatically used if flock(2) |
987 | is missing from your system. This makes flock() the portable file locking |
988 | strategy, although it will only lock entire files, not records. Note also |
989 | that some versions of flock() cannot lock things over the network; you |
990 | would need to use the more system-specific fcntl() for that. |
4633a7c4 |
991 | |
992 | Here's a mailbox appender for BSD systems. |
a0d0e21e |
993 | |
994 | $LOCK_SH = 1; |
995 | $LOCK_EX = 2; |
996 | $LOCK_NB = 4; |
997 | $LOCK_UN = 8; |
998 | |
999 | sub lock { |
1000 | flock(MBOX,$LOCK_EX); |
1001 | # and, in case someone appended |
1002 | # while we were waiting... |
1003 | seek(MBOX, 0, 2); |
1004 | } |
1005 | |
1006 | sub unlock { |
1007 | flock(MBOX,$LOCK_UN); |
1008 | } |
1009 | |
1010 | open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}") |
1011 | or die "Can't open mailbox: $!"; |
1012 | |
1013 | lock(); |
1014 | print MBOX $msg,"\n\n"; |
1015 | unlock(); |
1016 | |
cb1a09d0 |
1017 | See also L<DB_File> for other flock() examples. |
a0d0e21e |
1018 | |
1019 | =item fork |
1020 | |
1021 | Does a fork(2) system call. Returns the child pid to the parent process |
4633a7c4 |
1022 | and 0 to the child process, or C<undef> if the fork is unsuccessful. |
a0d0e21e |
1023 | Note: unflushed buffers remain unflushed in both processes, which means |
1024 | you may need to set C<$|> ($AUTOFLUSH in English) or call the |
1025 | autoflush() FileHandle method to avoid duplicate output. |
1026 | |
1027 | If you fork() without ever waiting on your children, you will accumulate |
1028 | zombies: |
1029 | |
4633a7c4 |
1030 | $SIG{CHLD} = sub { wait }; |
a0d0e21e |
1031 | |
1032 | There's also the double-fork trick (error checking on |
1033 | fork() returns omitted); |
1034 | |
1035 | unless ($pid = fork) { |
1036 | unless (fork) { |
1037 | exec "what you really wanna do"; |
1038 | die "no exec"; |
1039 | # ... or ... |
4633a7c4 |
1040 | ## (some_perl_code_here) |
a0d0e21e |
1041 | exit 0; |
1042 | } |
1043 | exit 0; |
1044 | } |
1045 | waitpid($pid,0); |
1046 | |
cb1a09d0 |
1047 | See also L<perlipc> for more examples of forking and reaping |
1048 | moribund children. |
1049 | |
1050 | =item format |
1051 | |
1052 | Declare a picture format with use by the write() function. For |
1053 | example: |
1054 | |
1055 | format Something = |
1056 | Test: @<<<<<<<< @||||| @>>>>> |
1057 | $str, $%, '$' . int($num) |
1058 | . |
1059 | |
1060 | $str = "widget"; |
1061 | $num = $cost/$quantiy; |
1062 | $~ = 'Something'; |
1063 | write; |
1064 | |
1065 | See L<perlform> for many details and examples. |
1066 | |
a0d0e21e |
1067 | |
1068 | =item formline PICTURE, LIST |
1069 | |
4633a7c4 |
1070 | This is an internal function used by C<format>s, though you may call it |
a0d0e21e |
1071 | too. It formats (see L<perlform>) a list of values according to the |
1072 | contents of PICTURE, placing the output into the format output |
4633a7c4 |
1073 | accumulator, C<$^A> (or $ACCUMULATOR in English). |
1074 | Eventually, when a write() is done, the contents of |
a0d0e21e |
1075 | C<$^A> are written to some filehandle, but you could also read C<$^A> |
1076 | yourself and then set C<$^A> back to "". Note that a format typically |
1077 | does one formline() per line of form, but the formline() function itself |
748a9306 |
1078 | doesn't care how many newlines are embedded in the PICTURE. This means |
4633a7c4 |
1079 | that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line. |
748a9306 |
1080 | You may therefore need to use multiple formlines to implement a single |
1081 | record format, just like the format compiler. |
1082 | |
1083 | Be careful if you put double quotes around the picture, since an "C<@>" |
1084 | character may be taken to mean the beginning of an array name. |
4633a7c4 |
1085 | formline() always returns TRUE. See L<perlform> for other examples. |
a0d0e21e |
1086 | |
1087 | =item getc FILEHANDLE |
1088 | |
1089 | =item getc |
1090 | |
1091 | Returns the next character from the input file attached to FILEHANDLE, |
1092 | or a null string at end of file. If FILEHANDLE is omitted, reads from STDIN. |
4633a7c4 |
1093 | This is not particularly efficient. It cannot be used to get unbuffered |
cb1a09d0 |
1094 | single-characters, however. For that, try something more like: |
4633a7c4 |
1095 | |
1096 | if ($BSD_STYLE) { |
1097 | system "stty cbreak </dev/tty >/dev/tty 2>&1"; |
1098 | } |
1099 | else { |
cb1a09d0 |
1100 | system "stty", '-icanon', 'eol', "\001"; |
4633a7c4 |
1101 | } |
1102 | |
1103 | $key = getc(STDIN); |
1104 | |
1105 | if ($BSD_STYLE) { |
1106 | system "stty -cbreak </dev/tty >/dev/tty 2>&1"; |
1107 | } |
1108 | else { |
cb1a09d0 |
1109 | system "stty", 'icanon', 'eol', '^@'; # ascii null |
4633a7c4 |
1110 | } |
1111 | print "\n"; |
1112 | |
1113 | Determination of whether to whether $BSD_STYLE should be set |
cb1a09d0 |
1114 | is left as an exercise to the reader. |
1115 | |
1116 | See also the C<Term::ReadKey> module from your nearest CPAN site; |
1117 | details on CPAN can be found on L<perlmod/CPAN> |
a0d0e21e |
1118 | |
1119 | =item getlogin |
1120 | |
1121 | Returns the current login from F</etc/utmp>, if any. If null, use |
4633a7c4 |
1122 | getpwuid(). |
a0d0e21e |
1123 | |
1124 | $login = getlogin || (getpwuid($<))[0] || "Kilroy"; |
1125 | |
4633a7c4 |
1126 | Do not consider getlogin() for authorentication: it is not as |
1127 | secure as getpwuid(). |
1128 | |
a0d0e21e |
1129 | =item getpeername SOCKET |
1130 | |
1131 | Returns the packed sockaddr address of other end of the SOCKET connection. |
1132 | |
4633a7c4 |
1133 | use Socket; |
1134 | $hersockaddr = getpeername(SOCK); |
1135 | ($port, $iaddr) = unpack_sockaddr_in($hersockaddr); |
1136 | $herhostname = gethostbyaddr($iaddr, AF_INET); |
1137 | $herstraddr = inet_ntoa($iaddr); |
a0d0e21e |
1138 | |
1139 | =item getpgrp PID |
1140 | |
1141 | Returns the current process group for the specified PID, 0 for the |
4633a7c4 |
1142 | current process. Will raise an exception if used on a machine that |
a0d0e21e |
1143 | doesn't implement getpgrp(2). If PID is omitted, returns process |
1144 | group of current process. |
1145 | |
1146 | =item getppid |
1147 | |
1148 | Returns the process id of the parent process. |
1149 | |
1150 | =item getpriority WHICH,WHO |
1151 | |
4633a7c4 |
1152 | Returns the current priority for a process, a process group, or a user. |
1153 | (See L<getpriority(2)>.) Will raise a fatal exception if used on a |
a0d0e21e |
1154 | machine that doesn't implement getpriority(2). |
1155 | |
1156 | =item getpwnam NAME |
1157 | |
1158 | =item getgrnam NAME |
1159 | |
1160 | =item gethostbyname NAME |
1161 | |
1162 | =item getnetbyname NAME |
1163 | |
1164 | =item getprotobyname NAME |
1165 | |
1166 | =item getpwuid UID |
1167 | |
1168 | =item getgrgid GID |
1169 | |
1170 | =item getservbyname NAME,PROTO |
1171 | |
1172 | =item gethostbyaddr ADDR,ADDRTYPE |
1173 | |
1174 | =item getnetbyaddr ADDR,ADDRTYPE |
1175 | |
1176 | =item getprotobynumber NUMBER |
1177 | |
1178 | =item getservbyport PORT,PROTO |
1179 | |
1180 | =item getpwent |
1181 | |
1182 | =item getgrent |
1183 | |
1184 | =item gethostent |
1185 | |
1186 | =item getnetent |
1187 | |
1188 | =item getprotoent |
1189 | |
1190 | =item getservent |
1191 | |
1192 | =item setpwent |
1193 | |
1194 | =item setgrent |
1195 | |
1196 | =item sethostent STAYOPEN |
1197 | |
1198 | =item setnetent STAYOPEN |
1199 | |
1200 | =item setprotoent STAYOPEN |
1201 | |
1202 | =item setservent STAYOPEN |
1203 | |
1204 | =item endpwent |
1205 | |
1206 | =item endgrent |
1207 | |
1208 | =item endhostent |
1209 | |
1210 | =item endnetent |
1211 | |
1212 | =item endprotoent |
1213 | |
1214 | =item endservent |
1215 | |
1216 | These routines perform the same functions as their counterparts in the |
1217 | system library. Within a list context, the return values from the |
1218 | various get routines are as follows: |
1219 | |
1220 | ($name,$passwd,$uid,$gid, |
1221 | $quota,$comment,$gcos,$dir,$shell) = getpw* |
1222 | ($name,$passwd,$gid,$members) = getgr* |
1223 | ($name,$aliases,$addrtype,$length,@addrs) = gethost* |
1224 | ($name,$aliases,$addrtype,$net) = getnet* |
1225 | ($name,$aliases,$proto) = getproto* |
1226 | ($name,$aliases,$port,$proto) = getserv* |
1227 | |
1228 | (If the entry doesn't exist you get a null list.) |
1229 | |
1230 | Within a scalar context, you get the name, unless the function was a |
1231 | lookup by name, in which case you get the other thing, whatever it is. |
1232 | (If the entry doesn't exist you get the undefined value.) For example: |
1233 | |
1234 | $uid = getpwnam |
1235 | $name = getpwuid |
1236 | $name = getpwent |
1237 | $gid = getgrnam |
1238 | $name = getgrgid |
1239 | $name = getgrent |
1240 | etc. |
1241 | |
1242 | The $members value returned by I<getgr*()> is a space separated list of |
1243 | the login names of the members of the group. |
1244 | |
1245 | For the I<gethost*()> functions, if the C<h_errno> variable is supported in |
1246 | C, it will be returned to you via C<$?> if the function call fails. The |
1247 | @addrs value returned by a successful call is a list of the raw |
1248 | addresses returned by the corresponding system library call. In the |
1249 | Internet domain, each address is four bytes long and you can unpack it |
1250 | by saying something like: |
1251 | |
1252 | ($a,$b,$c,$d) = unpack('C4',$addr[0]); |
1253 | |
1254 | =item getsockname SOCKET |
1255 | |
1256 | Returns the packed sockaddr address of this end of the SOCKET connection. |
1257 | |
4633a7c4 |
1258 | use Socket; |
1259 | $mysockaddr = getsockname(SOCK); |
1260 | ($port, $myaddr) = unpack_sockaddr_in($mysockaddr); |
a0d0e21e |
1261 | |
1262 | =item getsockopt SOCKET,LEVEL,OPTNAME |
1263 | |
1264 | Returns the socket option requested, or undefined if there is an error. |
1265 | |
1266 | =item glob EXPR |
1267 | |
1268 | Returns the value of EXPR with filename expansions such as a shell |
1269 | would do. This is the internal function implementing the <*.*> |
4633a7c4 |
1270 | operator, except it's easier to use. |
a0d0e21e |
1271 | |
1272 | =item gmtime EXPR |
1273 | |
1274 | Converts a time as returned by the time function to a 9-element array |
4633a7c4 |
1275 | with the time localized for the standard Greenwich timezone. |
1276 | Typically used as follows: |
a0d0e21e |
1277 | |
1278 | |
1279 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
1280 | gmtime(time); |
1281 | |
1282 | All array elements are numeric, and come straight out of a struct tm. |
1283 | In particular this means that $mon has the range 0..11 and $wday has |
1284 | the range 0..6. If EXPR is omitted, does C<gmtime(time())>. |
1285 | |
1286 | =item goto LABEL |
1287 | |
748a9306 |
1288 | =item goto EXPR |
1289 | |
a0d0e21e |
1290 | =item goto &NAME |
1291 | |
1292 | The goto-LABEL form finds the statement labeled with LABEL and resumes |
1293 | execution there. It may not be used to go into any construct that |
1294 | requires initialization, such as a subroutine or a foreach loop. It |
1295 | also can't be used to go into a construct that is optimized away. It |
1296 | can be used to go almost anywhere else within the dynamic scope, |
1297 | including out of subroutines, but it's usually better to use some other |
1298 | construct such as last or die. The author of Perl has never felt the |
1299 | need to use this form of goto (in Perl, that is--C is another matter). |
1300 | |
748a9306 |
1301 | The goto-EXPR form expects a label name, whose scope will be resolved |
1302 | dynamically. This allows for computed gotos per FORTRAN, but isn't |
1303 | necessarily recommended if you're optimizing for maintainability: |
1304 | |
1305 | goto ("FOO", "BAR", "GLARCH")[$i]; |
1306 | |
a0d0e21e |
1307 | The goto-&NAME form is highly magical, and substitutes a call to the |
1308 | named subroutine for the currently running subroutine. This is used by |
1309 | AUTOLOAD subroutines that wish to load another subroutine and then |
1310 | pretend that the other subroutine had been called in the first place |
1311 | (except that any modifications to @_ in the current subroutine are |
1312 | propagated to the other subroutine.) After the goto, not even caller() |
1313 | will be able to tell that this routine was called first. |
1314 | |
1315 | =item grep BLOCK LIST |
1316 | |
1317 | =item grep EXPR,LIST |
1318 | |
1319 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
1320 | $_ to each element) and returns the list value consisting of those |
1321 | elements for which the expression evaluated to TRUE. In a scalar |
1322 | context, returns the number of times the expression was TRUE. |
1323 | |
1324 | @foo = grep(!/^#/, @bar); # weed out comments |
1325 | |
1326 | or equivalently, |
1327 | |
1328 | @foo = grep {!/^#/} @bar; # weed out comments |
1329 | |
1330 | Note that, since $_ is a reference into the list value, it can be used |
1331 | to modify the elements of the array. While this is useful and |
1332 | supported, it can cause bizarre results if the LIST is not a named |
1333 | array. |
1334 | |
1335 | =item hex EXPR |
1336 | |
4633a7c4 |
1337 | Interprets EXPR as a hex string and returns the corresponding decimal |
1338 | value. (To convert strings that might start with 0 or 0x see |
1339 | oct().) If EXPR is omitted, uses $_. |
a0d0e21e |
1340 | |
1341 | =item import |
1342 | |
1343 | There is no built-in import() function. It is merely an ordinary |
4633a7c4 |
1344 | method (subroutine) defined (or inherited) by modules that wish to export |
a0d0e21e |
1345 | names to another module. The use() function calls the import() method |
4633a7c4 |
1346 | for the package used. See also L</use>, L<perlmod>, and L<Exporter>. |
a0d0e21e |
1347 | |
1348 | =item index STR,SUBSTR,POSITION |
1349 | |
1350 | =item index STR,SUBSTR |
1351 | |
4633a7c4 |
1352 | Returns the position of the first occurrence of SUBSTR in STR at or after |
1353 | POSITION. If POSITION is omitted, starts searching from the beginning of |
1354 | the string. The return value is based at 0 (or whatever you've set the $[ |
1355 | variable to--but don't do that). If the substring is not found, returns |
a0d0e21e |
1356 | one less than the base, ordinarily -1. |
1357 | |
1358 | =item int EXPR |
1359 | |
1360 | Returns the integer portion of EXPR. If EXPR is omitted, uses $_. |
1361 | |
1362 | =item ioctl FILEHANDLE,FUNCTION,SCALAR |
1363 | |
1364 | Implements the ioctl(2) function. You'll probably have to say |
1365 | |
4633a7c4 |
1366 | require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph |
a0d0e21e |
1367 | |
4633a7c4 |
1368 | first to get the correct function definitions. If F<ioctl.ph> doesn't |
a0d0e21e |
1369 | exist or doesn't have the correct definitions you'll have to roll your |
4633a7c4 |
1370 | own, based on your C header files such as F<E<lt>sys/ioctl.hE<gt>>. |
1371 | (There is a Perl script called B<h2ph> that comes with the Perl kit which |
1372 | may help you in this, but it's non-trivial.) SCALAR will be read and/or |
1373 | written depending on the FUNCTION--a pointer to the string value of SCALAR |
1374 | will be passed as the third argument of the actual ioctl call. (If SCALAR |
1375 | has no string value but does have a numeric value, that value will be |
1376 | passed rather than a pointer to the string value. To guarantee this to be |
1377 | TRUE, add a 0 to the scalar before using it.) The pack() and unpack() |
1378 | functions are useful for manipulating the values of structures used by |
1379 | ioctl(). The following example sets the erase character to DEL. |
a0d0e21e |
1380 | |
1381 | require 'ioctl.ph'; |
4633a7c4 |
1382 | $getp = &TIOCGETP; |
1383 | die "NO TIOCGETP" if $@ || !$getp; |
a0d0e21e |
1384 | $sgttyb_t = "ccccs"; # 4 chars and a short |
4633a7c4 |
1385 | if (ioctl(STDIN,$getp,$sgttyb)) { |
a0d0e21e |
1386 | @ary = unpack($sgttyb_t,$sgttyb); |
1387 | $ary[2] = 127; |
1388 | $sgttyb = pack($sgttyb_t,@ary); |
4633a7c4 |
1389 | ioctl(STDIN,&TIOCSETP,$sgttyb) |
a0d0e21e |
1390 | || die "Can't ioctl: $!"; |
1391 | } |
1392 | |
1393 | The return value of ioctl (and fcntl) is as follows: |
1394 | |
1395 | if OS returns: then Perl returns: |
1396 | -1 undefined value |
1397 | 0 string "0 but true" |
1398 | anything else that number |
1399 | |
1400 | Thus Perl returns TRUE on success and FALSE on failure, yet you can |
1401 | still easily determine the actual value returned by the operating |
1402 | system: |
1403 | |
1404 | ($retval = ioctl(...)) || ($retval = -1); |
1405 | printf "System returned %d\n", $retval; |
1406 | |
1407 | =item join EXPR,LIST |
1408 | |
1409 | Joins the separate strings of LIST or ARRAY into a single string with |
1410 | fields separated by the value of EXPR, and returns the string. |
1411 | Example: |
1412 | |
1413 | $_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); |
1414 | |
1415 | See L<perlfunc/split>. |
1416 | |
1417 | =item keys ASSOC_ARRAY |
1418 | |
1419 | Returns a normal array consisting of all the keys of the named |
1420 | associative array. (In a scalar context, returns the number of keys.) |
1421 | The keys are returned in an apparently random order, but it is the same |
1422 | order as either the values() or each() function produces (given that |
1423 | the associative array has not been modified). Here is yet another way |
1424 | to print your environment: |
1425 | |
1426 | @keys = keys %ENV; |
1427 | @values = values %ENV; |
1428 | while ($#keys >= 0) { |
1429 | print pop(@keys), '=', pop(@values), "\n"; |
1430 | } |
1431 | |
1432 | or how about sorted by key: |
1433 | |
1434 | foreach $key (sort(keys %ENV)) { |
1435 | print $key, '=', $ENV{$key}, "\n"; |
1436 | } |
1437 | |
4633a7c4 |
1438 | To sort an array by value, you'll need to use a C<sort{}> |
cb1a09d0 |
1439 | function. Here's a descending numeric sort of a hash by its values: |
4633a7c4 |
1440 | |
1441 | foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash)) { |
1442 | printf "%4d %s\n", $hash{$key}, $key; |
1443 | } |
1444 | |
a0d0e21e |
1445 | =item kill LIST |
1446 | |
4633a7c4 |
1447 | Sends a signal to a list of processes. The first element of |
1448 | the list must be the signal to send. Returns the number of |
1449 | processes successfully signaled. |
a0d0e21e |
1450 | |
1451 | $cnt = kill 1, $child1, $child2; |
1452 | kill 9, @goners; |
1453 | |
4633a7c4 |
1454 | Unlike in the shell, in Perl if the I<SIGNAL> is negative, it kills |
1455 | process groups instead of processes. (On System V, a negative I<PROCESS> |
1456 | number will also kill process groups, but that's not portable.) That |
1457 | means you usually want to use positive not negative signals. You may also |
1458 | use a signal name in quotes. See the L<perlipc/"Signals"> man page for details. |
a0d0e21e |
1459 | |
1460 | =item last LABEL |
1461 | |
1462 | =item last |
1463 | |
1464 | The C<last> command is like the C<break> statement in C (as used in |
1465 | loops); it immediately exits the loop in question. If the LABEL is |
1466 | omitted, the command refers to the innermost enclosing loop. The |
1467 | C<continue> block, if any, is not executed: |
1468 | |
4633a7c4 |
1469 | LINE: while (<STDIN>) { |
1470 | last LINE if /^$/; # exit when done with header |
a0d0e21e |
1471 | ... |
1472 | } |
1473 | |
1474 | =item lc EXPR |
1475 | |
1476 | Returns an lowercased version of EXPR. This is the internal function |
4633a7c4 |
1477 | implementing the \L escape in double-quoted strings. |
1478 | Should respect any POSIX setlocale() settings. |
a0d0e21e |
1479 | |
1480 | =item lcfirst EXPR |
1481 | |
1482 | Returns the value of EXPR with the first character lowercased. This is |
1483 | the internal function implementing the \l escape in double-quoted strings. |
4633a7c4 |
1484 | Should respect any POSIX setlocale() settings. |
a0d0e21e |
1485 | |
1486 | =item length EXPR |
1487 | |
1488 | Returns the length in characters of the value of EXPR. If EXPR is |
1489 | omitted, returns length of $_. |
1490 | |
1491 | =item link OLDFILE,NEWFILE |
1492 | |
1493 | Creates a new filename linked to the old filename. Returns 1 for |
1494 | success, 0 otherwise. |
1495 | |
1496 | =item listen SOCKET,QUEUESIZE |
1497 | |
1498 | Does the same thing that the listen system call does. Returns TRUE if |
4633a7c4 |
1499 | it succeeded, FALSE otherwise. See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e |
1500 | |
1501 | =item local EXPR |
1502 | |
a0d0e21e |
1503 | A local modifies the listed variables to be local to the enclosing block, |
cb1a09d0 |
1504 | subroutine, C<eval{}> or C<do>. If more than one value is listed, the |
1505 | list must be placed in parens. See L<perlsub/"Temporary Values via |
1506 | local()"> for details. |
a0d0e21e |
1507 | |
cb1a09d0 |
1508 | But you really probably want to be using my() instead, because local() isn't |
1509 | what most people think of as "local"). See L<perlsub/"Private Variables |
1510 | via my()"> for details. |
a0d0e21e |
1511 | |
1512 | =item localtime EXPR |
1513 | |
1514 | Converts a time as returned by the time function to a 9-element array |
1515 | with the time analyzed for the local timezone. Typically used as |
1516 | follows: |
1517 | |
1518 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
1519 | localtime(time); |
1520 | |
1521 | All array elements are numeric, and come straight out of a struct tm. |
1522 | In particular this means that $mon has the range 0..11 and $wday has |
1523 | the range 0..6. If EXPR is omitted, does localtime(time). |
1524 | |
1525 | In a scalar context, prints out the ctime(3) value: |
1526 | |
1527 | $now_string = localtime; # e.g. "Thu Oct 13 04:54:34 1994" |
1528 | |
37798a01 |
1529 | Also see the F<timelocal.pl> library, and the strftime(3) function available |
a0d0e21e |
1530 | via the POSIX modulie. |
1531 | |
1532 | =item log EXPR |
1533 | |
1534 | Returns logarithm (base I<e>) of EXPR. If EXPR is omitted, returns log |
1535 | of $_. |
1536 | |
1537 | =item lstat FILEHANDLE |
1538 | |
1539 | =item lstat EXPR |
1540 | |
1541 | Does the same thing as the stat() function, but stats a symbolic link |
1542 | instead of the file the symbolic link points to. If symbolic links are |
1543 | unimplemented on your system, a normal stat() is done. |
1544 | |
1545 | =item m// |
1546 | |
1547 | The match operator. See L<perlop>. |
1548 | |
1549 | =item map BLOCK LIST |
1550 | |
1551 | =item map EXPR,LIST |
1552 | |
1553 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each |
1554 | element) and returns the list value composed of the results of each such |
1555 | evaluation. Evaluates BLOCK or EXPR in a list context, so each element of LIST |
1556 | may produce zero, one, or more elements in the returned value. |
1557 | |
1558 | @chars = map(chr, @nums); |
1559 | |
1560 | translates a list of numbers to the corresponding characters. And |
1561 | |
4633a7c4 |
1562 | %hash = map { getkey($_) => $_ } @array; |
a0d0e21e |
1563 | |
1564 | is just a funny way to write |
1565 | |
1566 | %hash = (); |
1567 | foreach $_ (@array) { |
4633a7c4 |
1568 | $hash{getkey($_)} = $_; |
a0d0e21e |
1569 | } |
1570 | |
1571 | =item mkdir FILENAME,MODE |
1572 | |
1573 | Creates the directory specified by FILENAME, with permissions specified |
1574 | by MODE (as modified by umask). If it succeeds it returns 1, otherwise |
1575 | it returns 0 and sets $! (errno). |
1576 | |
1577 | =item msgctl ID,CMD,ARG |
1578 | |
4633a7c4 |
1579 | Calls the System V IPC function msgctl(2). If CMD is &IPC_STAT, then ARG |
a0d0e21e |
1580 | must be a variable which will hold the returned msqid_ds structure. |
1581 | Returns like ioctl: the undefined value for error, "0 but true" for |
1582 | zero, or the actual return value otherwise. |
1583 | |
1584 | =item msgget KEY,FLAGS |
1585 | |
4633a7c4 |
1586 | Calls the System V IPC function msgget(2). Returns the message queue id, |
a0d0e21e |
1587 | or the undefined value if there is an error. |
1588 | |
1589 | =item msgsnd ID,MSG,FLAGS |
1590 | |
1591 | Calls the System V IPC function msgsnd to send the message MSG to the |
1592 | message queue ID. MSG must begin with the long integer message type, |
c07a80fd |
1593 | which may be created with C<pack("l", $type)>. Returns TRUE if |
a0d0e21e |
1594 | successful, or FALSE if there is an error. |
1595 | |
1596 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS |
1597 | |
1598 | Calls the System V IPC function msgrcv to receive a message from |
1599 | message queue ID into variable VAR with a maximum message size of |
1600 | SIZE. Note that if a message is received, the message type will be the |
1601 | first thing in VAR, and the maximum length of VAR is SIZE plus the size |
1602 | of the message type. Returns TRUE if successful, or FALSE if there is |
1603 | an error. |
1604 | |
1605 | =item my EXPR |
1606 | |
1607 | A "my" declares the listed variables to be local (lexically) to the |
cb1a09d0 |
1608 | enclosing block, subroutine, C<eval>, or C<do/require/use>'d file. If |
1609 | more than one value is listed, the list must be placed in parens. See |
1610 | L<perlsub/"Private Variables via my()"> for details. |
4633a7c4 |
1611 | |
a0d0e21e |
1612 | =item next LABEL |
1613 | |
1614 | =item next |
1615 | |
1616 | The C<next> command is like the C<continue> statement in C; it starts |
1617 | the next iteration of the loop: |
1618 | |
4633a7c4 |
1619 | LINE: while (<STDIN>) { |
1620 | next LINE if /^#/; # discard comments |
a0d0e21e |
1621 | ... |
1622 | } |
1623 | |
1624 | Note that if there were a C<continue> block on the above, it would get |
1625 | executed even on discarded lines. If the LABEL is omitted, the command |
1626 | refers to the innermost enclosing loop. |
1627 | |
1628 | =item no Module LIST |
1629 | |
1630 | See the "use" function, which "no" is the opposite of. |
1631 | |
1632 | =item oct EXPR |
1633 | |
4633a7c4 |
1634 | Interprets EXPR as an octal string and returns the corresponding |
1635 | decimal value. (If EXPR happens to start off with 0x, interprets it as |
1636 | a hex string instead.) The following will handle decimal, octal, and |
1637 | hex in the standard Perl or C notation: |
a0d0e21e |
1638 | |
1639 | $val = oct($val) if $val =~ /^0/; |
1640 | |
1641 | If EXPR is omitted, uses $_. |
1642 | |
1643 | =item open FILEHANDLE,EXPR |
1644 | |
1645 | =item open FILEHANDLE |
1646 | |
1647 | Opens the file whose filename is given by EXPR, and associates it with |
4633a7c4 |
1648 | FILEHANDLE. If FILEHANDLE is an expression, its value is used as the name |
1649 | of the real filehandle wanted. If EXPR is omitted, the scalar variable of |
1650 | the same name as the FILEHANDLE contains the filename. If the filename |
1651 | begins with "<" or nothing, the file is opened for input. If the filename |
1652 | begins with ">", the file is opened for output. If the filename begins |
cb1a09d0 |
1653 | with ">>", the file is opened for appending. You can put a '+' in front |
4633a7c4 |
1654 | of the '>' or '<' to indicate that you want both read and write access to |
cb1a09d0 |
1655 | the file; thus '+<' is usually preferred for read/write updates--the '+>' |
1656 | mode would clobber the file first. These correspond to the fopen(3) modes |
1657 | of 'r', 'r+', 'w', 'w+', 'a', and 'a+'. |
1658 | |
1659 | If the filename begins with "|", the filename is interpreted |
4633a7c4 |
1660 | as a command to which output is to be piped, and if the filename ends with |
1661 | a "|", the filename is interpreted See L<perlipc/"Using open() for IPC"> |
1662 | for more examples of this. as command which pipes input to us. (You may |
cb1a09d0 |
1663 | not have a raw open() to a command that pipes both in I<and> out, but see See L<open2>, |
4633a7c4 |
1664 | L<open3>, and L<perlipc/"Bidirectional Communication"> for alternatives.) |
cb1a09d0 |
1665 | |
4633a7c4 |
1666 | Opening '-' opens STDIN and opening '>-' opens STDOUT. Open returns |
1667 | non-zero upon success, the undefined value otherwise. If the open |
1668 | involved a pipe, the return value happens to be the pid of the |
cb1a09d0 |
1669 | subprocess. |
1670 | |
1671 | If you're unfortunate enough to be running Perl on a system that |
1672 | distinguishes between text files and binary files (modern operating |
1673 | systems don't care), then you should check out L</binmode> for tips for |
1674 | dealing with this. The key distinction between systems that need binmode |
1675 | and those that don't is their text file formats. Systems like Unix and |
1676 | Plan9 that delimit lines with a single character, and that encode that |
1677 | character in C as '\n', do not need C<binmode>. The rest need it. |
1678 | |
cb1a09d0 |
1679 | Examples: |
a0d0e21e |
1680 | |
1681 | $ARTICLE = 100; |
1682 | open ARTICLE or die "Can't find article $ARTICLE: $!\n"; |
1683 | while (<ARTICLE>) {... |
1684 | |
1685 | open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved) |
1686 | |
cb1a09d0 |
1687 | open(DBASE, '+<dbase.mine'); # open for update |
1688 | |
4633a7c4 |
1689 | open(ARTICLE, "caesar <$article |"); # decrypt article |
a0d0e21e |
1690 | |
4633a7c4 |
1691 | open(EXTRACT, "|sort >/tmp/Tmp$$"); # $$ is our process id |
a0d0e21e |
1692 | |
1693 | # process argument list of files along with any includes |
1694 | |
1695 | foreach $file (@ARGV) { |
1696 | process($file, 'fh00'); |
1697 | } |
1698 | |
1699 | sub process { |
1700 | local($filename, $input) = @_; |
1701 | $input++; # this is a string increment |
1702 | unless (open($input, $filename)) { |
1703 | print STDERR "Can't open $filename: $!\n"; |
1704 | return; |
1705 | } |
1706 | |
1707 | while (<$input>) { # note use of indirection |
1708 | if (/^#include "(.*)"/) { |
1709 | process($1, $input); |
1710 | next; |
1711 | } |
1712 | ... # whatever |
1713 | } |
1714 | } |
1715 | |
1716 | You may also, in the Bourne shell tradition, specify an EXPR beginning |
1717 | with ">&", in which case the rest of the string is interpreted as the |
1718 | name of a filehandle (or file descriptor, if numeric) which is to be |
1719 | duped and opened. You may use & after >, >>, <, +>, +>> and +<. The |
1720 | mode you specify should match the mode of the original filehandle. |
cb1a09d0 |
1721 | (Duping a filehandle does not take into acount any existing contents of |
1722 | stdio buffers.) |
a0d0e21e |
1723 | Here is a script that saves, redirects, and restores STDOUT and |
1724 | STDERR: |
1725 | |
1726 | #!/usr/bin/perl |
1727 | open(SAVEOUT, ">&STDOUT"); |
1728 | open(SAVEERR, ">&STDERR"); |
1729 | |
1730 | open(STDOUT, ">foo.out") || die "Can't redirect stdout"; |
1731 | open(STDERR, ">&STDOUT") || die "Can't dup stdout"; |
1732 | |
1733 | select(STDERR); $| = 1; # make unbuffered |
1734 | select(STDOUT); $| = 1; # make unbuffered |
1735 | |
1736 | print STDOUT "stdout 1\n"; # this works for |
1737 | print STDERR "stderr 1\n"; # subprocesses too |
1738 | |
1739 | close(STDOUT); |
1740 | close(STDERR); |
1741 | |
1742 | open(STDOUT, ">&SAVEOUT"); |
1743 | open(STDERR, ">&SAVEERR"); |
1744 | |
1745 | print STDOUT "stdout 2\n"; |
1746 | print STDERR "stderr 2\n"; |
1747 | |
1748 | |
1749 | If you specify "<&=N", where N is a number, then Perl will do an |
4633a7c4 |
1750 | equivalent of C's fdopen() of that file descriptor; this is more |
1751 | parsimonious of file descriptors. For example: |
a0d0e21e |
1752 | |
1753 | open(FILEHANDLE, "<&=$fd") |
1754 | |
1755 | If you open a pipe on the command "-", i.e. either "|-" or "-|", then |
1756 | there is an implicit fork done, and the return value of open is the pid |
1757 | of the child within the parent process, and 0 within the child |
1758 | process. (Use defined($pid) to determine whether the open was successful.) |
1759 | The filehandle behaves normally for the parent, but i/o to that |
1760 | filehandle is piped from/to the STDOUT/STDIN of the child process. |
1761 | In the child process the filehandle isn't opened--i/o happens from/to |
1762 | the new STDOUT or STDIN. Typically this is used like the normal |
1763 | piped open when you want to exercise more control over just how the |
1764 | pipe command gets executed, such as when you are running setuid, and |
4633a7c4 |
1765 | don't want to have to scan shell commands for metacharacters. |
1766 | The following pairs are more or less equivalent: |
a0d0e21e |
1767 | |
1768 | open(FOO, "|tr '[a-z]' '[A-Z]'"); |
1769 | open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]'; |
1770 | |
1771 | open(FOO, "cat -n '$file'|"); |
1772 | open(FOO, "-|") || exec 'cat', '-n', $file; |
1773 | |
4633a7c4 |
1774 | See L<perlipc/"Safe Pipe Opens"> for more examples of this. |
1775 | |
a0d0e21e |
1776 | Explicitly closing any piped filehandle causes the parent process to |
1777 | wait for the child to finish, and returns the status value in $?. |
1778 | Note: on any operation which may do a fork, unflushed buffers remain |
1779 | unflushed in both processes, which means you may need to set $| to |
1780 | avoid duplicate output. |
1781 | |
c07a80fd |
1782 | Using the FileHandle constructor from the FileHandle package, |
1783 | you can generate anonymous filehandles which have the scope of whatever |
1784 | variables hold references to them, and automatically close whenever |
1785 | and however you leave that scope: |
1786 | |
1787 | use FileHandle; |
1788 | ... |
1789 | sub read_myfile_munged { |
1790 | my $ALL = shift; |
1791 | my $handle = new FileHandle; |
1792 | open($handle, "myfile") or die "myfile: $!"; |
1793 | $first = <$handle> |
1794 | or return (); # Automatically closed here. |
1795 | mung $first or die "mung failed"; # Or here. |
1796 | return $first, <$handle> if $ALL; # Or here. |
1797 | $first; # Or here. |
1798 | } |
1799 | |
a0d0e21e |
1800 | The filename that is passed to open will have leading and trailing |
1801 | whitespace deleted. In order to open a file with arbitrary weird |
1802 | characters in it, it's necessary to protect any leading and trailing |
1803 | whitespace thusly: |
1804 | |
cb1a09d0 |
1805 | $file =~ s#^(\s)#./$1#; |
1806 | open(FOO, "< $file\0"); |
1807 | |
c07a80fd |
1808 | If you want a "real" C open() (see L<open(2)> on your system), then |
1809 | you should use the sysopen() function. This is another way to |
1810 | protect your filenames from interpretation. For example: |
cb1a09d0 |
1811 | |
1812 | use FileHandle; |
c07a80fd |
1813 | sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL, 0700) |
1814 | or die "sysopen $path: $!"; |
1815 | HANDLE->autoflush(1); |
1816 | HANDLE->print("stuff $$\n"); |
1817 | seek(HANDLE, 0, 0); |
1818 | print "File contains: ", <HANDLE>; |
cb1a09d0 |
1819 | |
1820 | See L</seek()> for some details about mixing reading and writing. |
a0d0e21e |
1821 | |
1822 | =item opendir DIRHANDLE,EXPR |
1823 | |
1824 | Opens a directory named EXPR for processing by readdir(), telldir(), |
1825 | seekdir(), rewinddir() and closedir(). Returns TRUE if successful. |
1826 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
1827 | |
1828 | =item ord EXPR |
1829 | |
1830 | Returns the numeric ascii value of the first character of EXPR. If |
1831 | EXPR is omitted, uses $_. |
1832 | |
1833 | =item pack TEMPLATE,LIST |
1834 | |
1835 | Takes an array or list of values and packs it into a binary structure, |
1836 | returning the string containing the structure. The TEMPLATE is a |
1837 | sequence of characters that give the order and type of values, as |
1838 | follows: |
1839 | |
1840 | A An ascii string, will be space padded. |
1841 | a An ascii string, will be null padded. |
1842 | b A bit string (ascending bit order, like vec()). |
1843 | B A bit string (descending bit order). |
1844 | h A hex string (low nybble first). |
1845 | H A hex string (high nybble first). |
1846 | |
1847 | c A signed char value. |
1848 | C An unsigned char value. |
1849 | s A signed short value. |
1850 | S An unsigned short value. |
1851 | i A signed integer value. |
1852 | I An unsigned integer value. |
1853 | l A signed long value. |
1854 | L An unsigned long value. |
1855 | |
1856 | n A short in "network" order. |
1857 | N A long in "network" order. |
1858 | v A short in "VAX" (little-endian) order. |
1859 | V A long in "VAX" (little-endian) order. |
1860 | |
1861 | f A single-precision float in the native format. |
1862 | d A double-precision float in the native format. |
1863 | |
1864 | p A pointer to a null-terminated string. |
1865 | P A pointer to a structure (fixed-length string). |
1866 | |
1867 | u A uuencoded string. |
1868 | |
1869 | x A null byte. |
1870 | X Back up a byte. |
1871 | @ Null fill to absolute position. |
1872 | |
1873 | Each letter may optionally be followed by a number which gives a repeat |
1874 | count. With all types except "a", "A", "b", "B", "h" and "H", and "P" the |
1875 | pack function will gobble up that many values from the LIST. A * for the |
1876 | repeat count means to use however many items are left. The "a" and "A" |
1877 | types gobble just one value, but pack it as a string of length count, |
1878 | padding with nulls or spaces as necessary. (When unpacking, "A" strips |
1879 | trailing spaces and nulls, but "a" does not.) Likewise, the "b" and "B" |
1880 | fields pack a string that many bits long. The "h" and "H" fields pack a |
1881 | string that many nybbles long. The "P" packs a pointer to a structure of |
1882 | the size indicated by the length. Real numbers (floats and doubles) are |
1883 | in the native machine format only; due to the multiplicity of floating |
1884 | formats around, and the lack of a standard "network" representation, no |
1885 | facility for interchange has been made. This means that packed floating |
1886 | point data written on one machine may not be readable on another - even if |
1887 | both use IEEE floating point arithmetic (as the endian-ness of the memory |
1888 | representation is not part of the IEEE spec). Note that Perl uses doubles |
1889 | internally for all numeric calculation, and converting from double into |
1890 | float and thence back to double again will lose precision (i.e. |
1891 | C<unpack("f", pack("f", $foo)>) will not in general equal $foo). |
1892 | |
1893 | Examples: |
1894 | |
1895 | $foo = pack("cccc",65,66,67,68); |
1896 | # foo eq "ABCD" |
1897 | $foo = pack("c4",65,66,67,68); |
1898 | # same thing |
1899 | |
1900 | $foo = pack("ccxxcc",65,66,67,68); |
1901 | # foo eq "AB\0\0CD" |
1902 | |
1903 | $foo = pack("s2",1,2); |
1904 | # "\1\0\2\0" on little-endian |
1905 | # "\0\1\0\2" on big-endian |
1906 | |
1907 | $foo = pack("a4","abcd","x","y","z"); |
1908 | # "abcd" |
1909 | |
1910 | $foo = pack("aaaa","abcd","x","y","z"); |
1911 | # "axyz" |
1912 | |
1913 | $foo = pack("a14","abcdefg"); |
1914 | # "abcdefg\0\0\0\0\0\0\0" |
1915 | |
1916 | $foo = pack("i9pl", gmtime); |
1917 | # a real struct tm (on my system anyway) |
1918 | |
1919 | sub bintodec { |
1920 | unpack("N", pack("B32", substr("0" x 32 . shift, -32))); |
1921 | } |
1922 | |
1923 | The same template may generally also be used in the unpack function. |
1924 | |
cb1a09d0 |
1925 | =item package NAMESPACE |
1926 | |
1927 | Declares the compilation unit as being in the given namespace. The scope |
1928 | of the package declaration is from the declaration itself through the end of |
1929 | the enclosing block (the same scope as the local() operator). All further |
1930 | unqualified dynamic identifiers will be in this namespace. A package |
1931 | statement only affects dynamic variables--including those you've used |
1932 | local() on--but I<not> lexical variables created with my(). Typically it |
1933 | would be the first declaration in a file to be included by the C<require> |
1934 | or C<use> operator. You can switch into a package in more than one place; |
1935 | it merely influences which symbol table is used by the compiler for the |
1936 | rest of that block. You can refer to variables and filehandles in other |
1937 | packages by prefixing the identifier with the package name and a double |
1938 | colon: C<$Package::Variable>. If the package name is null, the C<main> |
1939 | package as assumed. That is, C<$::sail> is equivalent to C<$main::sail>. |
1940 | |
1941 | See L<perlmod/"Packages"> for more information about packages, modules, |
1942 | and classes. See L<perlsub> for other scoping issues. |
1943 | |
a0d0e21e |
1944 | =item pipe READHANDLE,WRITEHANDLE |
1945 | |
1946 | Opens a pair of connected pipes like the corresponding system call. |
1947 | Note that if you set up a loop of piped processes, deadlock can occur |
1948 | unless you are very careful. In addition, note that Perl's pipes use |
1949 | stdio buffering, so you may need to set $| to flush your WRITEHANDLE |
1950 | after each command, depending on the application. |
1951 | |
4633a7c4 |
1952 | See L<open2>, L<open3>, and L<perlipc/"Bidirectional Communication"> |
1953 | for examples of such things. |
1954 | |
a0d0e21e |
1955 | =item pop ARRAY |
1956 | |
1957 | Pops and returns the last value of the array, shortening the array by |
1958 | 1. Has a similar effect to |
1959 | |
1960 | $tmp = $ARRAY[$#ARRAY--]; |
1961 | |
1962 | If there are no elements in the array, returns the undefined value. |
cb1a09d0 |
1963 | If ARRAY is omitted, pops the |
1964 | @ARGV array in the main program, and the @_ array in subroutines, just |
1965 | like shift(). |
a0d0e21e |
1966 | |
1967 | =item pos SCALAR |
1968 | |
4633a7c4 |
1969 | Returns the offset of where the last C<m//g> search left off for the variable |
a0d0e21e |
1970 | in question. May be modified to change that offset. |
1971 | |
1972 | =item print FILEHANDLE LIST |
1973 | |
1974 | =item print LIST |
1975 | |
1976 | =item print |
1977 | |
cb1a09d0 |
1978 | Prints a string or a comma-separated list of strings. Returns TRUE |
a0d0e21e |
1979 | if successful. FILEHANDLE may be a scalar variable name, in which case |
cb1a09d0 |
1980 | the variable contains the name of or a reference to the filehandle, thus introducing one |
a0d0e21e |
1981 | level of indirection. (NOTE: If FILEHANDLE is a variable and the next |
1982 | token is a term, it may be misinterpreted as an operator unless you |
1983 | interpose a + or put parens around the arguments.) If FILEHANDLE is |
1984 | omitted, prints by default to standard output (or to the last selected |
1985 | output channel--see select()). If LIST is also omitted, prints $_ to |
1986 | STDOUT. To set the default output channel to something other than |
1987 | STDOUT use the select operation. Note that, because print takes a |
1988 | LIST, anything in the LIST is evaluated in a list context, and any |
1989 | subroutine that you call will have one or more of its expressions |
1990 | evaluated in a list context. Also be careful not to follow the print |
1991 | keyword with a left parenthesis unless you want the corresponding right |
1992 | parenthesis to terminate the arguments to the print--interpose a + or |
1993 | put parens around all the arguments. |
1994 | |
4633a7c4 |
1995 | Note that if you're storing FILEHANDLES in an array or other expression, |
1996 | you will have to use a block returning its value instead |
1997 | |
1998 | print { $files[$i] } "stuff\n"; |
1999 | print { $OK ? STDOUT : STDERR } "stuff\n"; |
2000 | |
a0d0e21e |
2001 | =item printf FILEHANDLE LIST |
2002 | |
2003 | =item printf LIST |
2004 | |
2005 | Equivalent to a "print FILEHANDLE sprintf(LIST)". The first argument |
2006 | of the list will be interpreted as the printf format. |
2007 | |
2008 | =item push ARRAY,LIST |
2009 | |
2010 | Treats ARRAY as a stack, and pushes the values of LIST |
2011 | onto the end of ARRAY. The length of ARRAY increases by the length of |
2012 | LIST. Has the same effect as |
2013 | |
2014 | for $value (LIST) { |
2015 | $ARRAY[++$#ARRAY] = $value; |
2016 | } |
2017 | |
2018 | but is more efficient. Returns the new number of elements in the array. |
2019 | |
2020 | =item q/STRING/ |
2021 | |
2022 | =item qq/STRING/ |
2023 | |
2024 | =item qx/STRING/ |
2025 | |
2026 | =item qw/STRING/ |
2027 | |
2028 | Generalized quotes. See L<perlop>. |
2029 | |
2030 | =item quotemeta EXPR |
2031 | |
2032 | Returns the value of EXPR with with all regular expression |
2033 | metacharacters backslashed. This is the internal function implementing |
2034 | the \Q escape in double-quoted strings. |
2035 | |
2036 | =item rand EXPR |
2037 | |
2038 | =item rand |
2039 | |
2040 | Returns a random fractional number between 0 and the value of EXPR. |
2041 | (EXPR should be positive.) If EXPR is omitted, returns a value between |
2042 | 0 and 1. This function produces repeatable sequences unless srand() |
2043 | is invoked. See also srand(). |
2044 | |
2045 | (Note: if your rand function consistently returns numbers that are too |
2046 | large or too small, then your version of Perl was probably compiled |
2047 | with the wrong number of RANDBITS. As a workaround, you can usually |
2048 | multiply EXPR by the correct power of 2 to get the range you want. |
2049 | This will make your script unportable, however. It's better to recompile |
2050 | if you can.) |
2051 | |
2052 | =item read FILEHANDLE,SCALAR,LENGTH,OFFSET |
2053 | |
2054 | =item read FILEHANDLE,SCALAR,LENGTH |
2055 | |
2056 | Attempts to read LENGTH bytes of data into variable SCALAR from the |
2057 | specified FILEHANDLE. Returns the number of bytes actually read, or |
2058 | undef if there was an error. SCALAR will be grown or shrunk to the |
2059 | length actually read. An OFFSET may be specified to place the read |
2060 | data at some other place than the beginning of the string. This call |
2061 | is actually implemented in terms of stdio's fread call. To get a true |
2062 | read system call, see sysread(). |
2063 | |
2064 | =item readdir DIRHANDLE |
2065 | |
2066 | Returns the next directory entry for a directory opened by opendir(). |
2067 | If used in a list context, returns all the rest of the entries in the |
2068 | directory. If there are no more entries, returns an undefined value in |
2069 | a scalar context or a null list in a list context. |
2070 | |
cb1a09d0 |
2071 | If you're planning to filetest the return values out of a readdir(), you'd |
2072 | better prepend the directory in question. Otherwise, since we didn't |
2073 | chdir() there, it would have been testing the wrong file. |
2074 | |
2075 | opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!"; |
2076 | @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR); |
2077 | closedir DIR; |
2078 | |
a0d0e21e |
2079 | =item readlink EXPR |
2080 | |
2081 | Returns the value of a symbolic link, if symbolic links are |
2082 | implemented. If not, gives a fatal error. If there is some system |
2083 | error, returns the undefined value and sets $! (errno). If EXPR is |
2084 | omitted, uses $_. |
2085 | |
2086 | =item recv SOCKET,SCALAR,LEN,FLAGS |
2087 | |
2088 | Receives a message on a socket. Attempts to receive LENGTH bytes of |
2089 | data into variable SCALAR from the specified SOCKET filehandle. |
2090 | Actually does a C recvfrom(), so that it can returns the address of the |
2091 | sender. Returns the undefined value if there's an error. SCALAR will |
2092 | be grown or shrunk to the length actually read. Takes the same flags |
4633a7c4 |
2093 | as the system call of the same name. |
2094 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e |
2095 | |
2096 | =item redo LABEL |
2097 | |
2098 | =item redo |
2099 | |
2100 | The C<redo> command restarts the loop block without evaluating the |
2101 | conditional again. The C<continue> block, if any, is not executed. If |
2102 | the LABEL is omitted, the command refers to the innermost enclosing |
2103 | loop. This command is normally used by programs that want to lie to |
2104 | themselves about what was just input: |
2105 | |
2106 | # a simpleminded Pascal comment stripper |
2107 | # (warning: assumes no { or } in strings) |
4633a7c4 |
2108 | LINE: while (<STDIN>) { |
a0d0e21e |
2109 | while (s|({.*}.*){.*}|$1 |) {} |
2110 | s|{.*}| |; |
2111 | if (s|{.*| |) { |
2112 | $front = $_; |
2113 | while (<STDIN>) { |
2114 | if (/}/) { # end of comment? |
2115 | s|^|$front{|; |
4633a7c4 |
2116 | redo LINE; |
a0d0e21e |
2117 | } |
2118 | } |
2119 | } |
2120 | print; |
2121 | } |
2122 | |
2123 | =item ref EXPR |
2124 | |
2125 | Returns a TRUE value if EXPR is a reference, FALSE otherwise. The value |
2126 | returned depends on the type of thing the reference is a reference to. |
2127 | Builtin types include: |
2128 | |
2129 | REF |
2130 | SCALAR |
2131 | ARRAY |
2132 | HASH |
2133 | CODE |
2134 | GLOB |
2135 | |
2136 | If the referenced object has been blessed into a package, then that package |
2137 | name is returned instead. You can think of ref() as a typeof() operator. |
2138 | |
2139 | if (ref($r) eq "HASH") { |
2140 | print "r is a reference to an associative array.\n"; |
2141 | } |
2142 | if (!ref ($r) { |
2143 | print "r is not a reference at all.\n"; |
2144 | } |
2145 | |
2146 | See also L<perlref>. |
2147 | |
2148 | =item rename OLDNAME,NEWNAME |
2149 | |
2150 | Changes the name of a file. Returns 1 for success, 0 otherwise. Will |
2151 | not work across filesystem boundaries. |
2152 | |
2153 | =item require EXPR |
2154 | |
2155 | =item require |
2156 | |
2157 | Demands some semantics specified by EXPR, or by $_ if EXPR is not |
2158 | supplied. If EXPR is numeric, demands that the current version of Perl |
2159 | ($] or $PERL_VERSION) be equal or greater than EXPR. |
2160 | |
2161 | Otherwise, demands that a library file be included if it hasn't already |
2162 | been included. The file is included via the do-FILE mechanism, which is |
2163 | essentially just a variety of eval(). Has semantics similar to the following |
2164 | subroutine: |
2165 | |
2166 | sub require { |
2167 | local($filename) = @_; |
2168 | return 1 if $INC{$filename}; |
2169 | local($realfilename,$result); |
2170 | ITER: { |
2171 | foreach $prefix (@INC) { |
2172 | $realfilename = "$prefix/$filename"; |
2173 | if (-f $realfilename) { |
2174 | $result = do $realfilename; |
2175 | last ITER; |
2176 | } |
2177 | } |
2178 | die "Can't find $filename in \@INC"; |
2179 | } |
2180 | die $@ if $@; |
2181 | die "$filename did not return true value" unless $result; |
2182 | $INC{$filename} = $realfilename; |
2183 | $result; |
2184 | } |
2185 | |
2186 | Note that the file will not be included twice under the same specified |
2187 | name. The file must return TRUE as the last statement to indicate |
2188 | successful execution of any initialization code, so it's customary to |
2189 | end such a file with "1;" unless you're sure it'll return TRUE |
2190 | otherwise. But it's better just to put the "C<1;>", in case you add more |
2191 | statements. |
2192 | |
2193 | If EXPR is a bare word, the require assumes a "F<.pm>" extension for you, |
2194 | to make it easy to load standard modules. This form of loading of |
2195 | modules does not risk altering your namespace. |
2196 | |
748a9306 |
2197 | For a yet-more-powerful import facility, see the L</use()> and |
2198 | L<perlmod>. |
a0d0e21e |
2199 | |
2200 | =item reset EXPR |
2201 | |
2202 | =item reset |
2203 | |
2204 | Generally used in a C<continue> block at the end of a loop to clear |
2205 | variables and reset ?? searches so that they work again. The |
2206 | expression is interpreted as a list of single characters (hyphens |
2207 | allowed for ranges). All variables and arrays beginning with one of |
2208 | those letters are reset to their pristine state. If the expression is |
2209 | omitted, one-match searches (?pattern?) are reset to match again. Only |
2210 | resets variables or searches in the current package. Always returns |
2211 | 1. Examples: |
2212 | |
2213 | reset 'X'; # reset all X variables |
2214 | reset 'a-z'; # reset lower case variables |
2215 | reset; # just reset ?? searches |
2216 | |
2217 | Resetting "A-Z" is not recommended since you'll wipe out your |
2218 | ARGV and ENV arrays. Only resets package variables--lexical variables |
2219 | are unaffected, but they clean themselves up on scope exit anyway, |
2220 | so anymore you probably want to use them instead. See L</my>. |
2221 | |
2222 | =item return LIST |
2223 | |
2224 | Returns from a subroutine or eval with the value specified. (Note that |
4633a7c4 |
2225 | in the absence of a return a subroutine or eval() will automatically |
a0d0e21e |
2226 | return the value of the last expression evaluated.) |
2227 | |
2228 | =item reverse LIST |
2229 | |
2230 | In a list context, returns a list value consisting of the elements |
2231 | of LIST in the opposite order. In a scalar context, returns a string |
2232 | value consisting of the bytes of the first element of LIST in the |
4633a7c4 |
2233 | opposite order. |
2234 | |
2235 | print reverse <>; # line tac |
2236 | |
2237 | undef $/; |
2238 | print scalar reverse scalar <>; # byte tac |
a0d0e21e |
2239 | |
2240 | =item rewinddir DIRHANDLE |
2241 | |
2242 | Sets the current position to the beginning of the directory for the |
2243 | readdir() routine on DIRHANDLE. |
2244 | |
2245 | =item rindex STR,SUBSTR,POSITION |
2246 | |
2247 | =item rindex STR,SUBSTR |
2248 | |
2249 | Works just like index except that it returns the position of the LAST |
2250 | occurrence of SUBSTR in STR. If POSITION is specified, returns the |
2251 | last occurrence at or before that position. |
2252 | |
2253 | =item rmdir FILENAME |
2254 | |
2255 | Deletes the directory specified by FILENAME if it is empty. If it |
2256 | succeeds it returns 1, otherwise it returns 0 and sets $! (errno). If |
2257 | FILENAME is omitted, uses $_. |
2258 | |
2259 | =item s/// |
2260 | |
2261 | The substitution operator. See L<perlop>. |
2262 | |
2263 | =item scalar EXPR |
2264 | |
2265 | Forces EXPR to be interpreted in a scalar context and returns the value |
cb1a09d0 |
2266 | of EXPR. |
2267 | |
2268 | @counts = ( scalar @a, scalar @b, scalar @c ); |
2269 | |
2270 | There is no equivalent operator to force an expression to |
2271 | be interpolated in a list context because it's in practice never |
2272 | needed. If you really wanted to do so, however, you could use |
2273 | the construction C<@{[ (some expression) ]}>, but usually a simple |
2274 | C<(some expression)> suffices. |
a0d0e21e |
2275 | |
2276 | =item seek FILEHANDLE,POSITION,WHENCE |
2277 | |
2278 | Randomly positions the file pointer for FILEHANDLE, just like the fseek() |
2279 | call of stdio. FILEHANDLE may be an expression whose value gives the name |
2280 | of the filehandle. The values for WHENCE are 0 to set the file pointer to |
2281 | POSITION, 1 to set the it to current plus POSITION, and 2 to set it to EOF |
2282 | plus offset. You may use the values SEEK_SET, SEEK_CUR, and SEEK_END for |
4633a7c4 |
2283 | this from POSIX module. Returns 1 upon success, 0 otherwise. |
a0d0e21e |
2284 | |
cb1a09d0 |
2285 | On some systems you have to do a seek whenever you switch between reading |
2286 | and writing. Amongst other things, this may have the effect of calling |
2287 | stdio's clearerr(3). A "whence" of 1 (SEEK_CUR) is useful for not moving |
2288 | the file pointer: |
2289 | |
2290 | seek(TEST,0,1); |
2291 | |
2292 | This is also useful for applications emulating C<tail -f>. Once you hit |
2293 | EOF on your read, and then sleep for a while, you might have to stick in a |
2294 | seek() to reset things. First the simple trick listed above to clear the |
2295 | filepointer. The seek() doesn't change the current position, but it |
2296 | I<does> clear the end-of-file condition on the handle, so that the next |
37798a01 |
2297 | C<E<lt>FILEE<gt>> makes Perl try again to read something. Hopefully. |
cb1a09d0 |
2298 | |
2299 | If that doesn't work (some stdios are particularly cantankerous), then |
2300 | you may need something more like this: |
2301 | |
2302 | for (;;) { |
2303 | for ($curpos = tell(FILE); $_ = <FILE>; $curpos = tell(FILE)) { |
2304 | # search for some stuff and put it into files |
2305 | } |
2306 | sleep($for_a_while); |
2307 | seek(FILE, $curpos, 0); |
2308 | } |
2309 | |
a0d0e21e |
2310 | =item seekdir DIRHANDLE,POS |
2311 | |
2312 | Sets the current position for the readdir() routine on DIRHANDLE. POS |
2313 | must be a value returned by telldir(). Has the same caveats about |
2314 | possible directory compaction as the corresponding system library |
2315 | routine. |
2316 | |
2317 | =item select FILEHANDLE |
2318 | |
2319 | =item select |
2320 | |
2321 | Returns the currently selected filehandle. Sets the current default |
2322 | filehandle for output, if FILEHANDLE is supplied. This has two |
2323 | effects: first, a C<write> or a C<print> without a filehandle will |
2324 | default to this FILEHANDLE. Second, references to variables related to |
2325 | output will refer to this output channel. For example, if you have to |
2326 | set the top of form format for more than one output channel, you might |
2327 | do the following: |
2328 | |
2329 | select(REPORT1); |
2330 | $^ = 'report1_top'; |
2331 | select(REPORT2); |
2332 | $^ = 'report2_top'; |
2333 | |
2334 | FILEHANDLE may be an expression whose value gives the name of the |
2335 | actual filehandle. Thus: |
2336 | |
2337 | $oldfh = select(STDERR); $| = 1; select($oldfh); |
2338 | |
4633a7c4 |
2339 | Some programmers may prefer to think of filehandles as objects with |
2340 | methods, preferring to write the last example as: |
a0d0e21e |
2341 | |
2342 | use FileHandle; |
2343 | STDERR->autoflush(1); |
2344 | |
2345 | =item select RBITS,WBITS,EBITS,TIMEOUT |
2346 | |
4633a7c4 |
2347 | This calls the select(2) system call with the bitmasks specified, which |
a0d0e21e |
2348 | can be constructed using fileno() and vec(), along these lines: |
2349 | |
2350 | $rin = $win = $ein = ''; |
2351 | vec($rin,fileno(STDIN),1) = 1; |
2352 | vec($win,fileno(STDOUT),1) = 1; |
2353 | $ein = $rin | $win; |
2354 | |
2355 | If you want to select on many filehandles you might wish to write a |
2356 | subroutine: |
2357 | |
2358 | sub fhbits { |
2359 | local(@fhlist) = split(' ',$_[0]); |
2360 | local($bits); |
2361 | for (@fhlist) { |
2362 | vec($bits,fileno($_),1) = 1; |
2363 | } |
2364 | $bits; |
2365 | } |
4633a7c4 |
2366 | $rin = fhbits('STDIN TTY SOCK'); |
a0d0e21e |
2367 | |
2368 | The usual idiom is: |
2369 | |
2370 | ($nfound,$timeleft) = |
2371 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); |
2372 | |
c07a80fd |
2373 | or to block until something becomes ready just do this |
a0d0e21e |
2374 | |
2375 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); |
2376 | |
c07a80fd |
2377 | Most systems do not both to return anything useful in $timeleft, so |
2378 | calling select() in a scalar context just returns $nfound. |
2379 | |
a0d0e21e |
2380 | Any of the bitmasks can also be undef. The timeout, if specified, is |
2381 | in seconds, which may be fractional. Note: not all implementations are |
2382 | capable of returning the $timeleft. If not, they always return |
2383 | $timeleft equal to the supplied $timeout. |
2384 | |
4633a7c4 |
2385 | You can effect a 250-microsecond sleep this way: |
a0d0e21e |
2386 | |
2387 | select(undef, undef, undef, 0.25); |
2388 | |
cb1a09d0 |
2389 | B<WARNING>: Do not attempt to mix buffered I/O (like read() or <FH>) |
2390 | with select(). You have to use sysread() instead. |
a0d0e21e |
2391 | |
2392 | =item semctl ID,SEMNUM,CMD,ARG |
2393 | |
2394 | Calls the System V IPC function semctl. If CMD is &IPC_STAT or |
2395 | &GETALL, then ARG must be a variable which will hold the returned |
2396 | semid_ds structure or semaphore value array. Returns like ioctl: the |
2397 | undefined value for error, "0 but true" for zero, or the actual return |
2398 | value otherwise. |
2399 | |
2400 | =item semget KEY,NSEMS,FLAGS |
2401 | |
2402 | Calls the System V IPC function semget. Returns the semaphore id, or |
2403 | the undefined value if there is an error. |
2404 | |
2405 | =item semop KEY,OPSTRING |
2406 | |
2407 | Calls the System V IPC function semop to perform semaphore operations |
2408 | such as signaling and waiting. OPSTRING must be a packed array of |
2409 | semop structures. Each semop structure can be generated with |
2410 | C<pack("sss", $semnum, $semop, $semflag)>. The number of semaphore |
2411 | operations is implied by the length of OPSTRING. Returns TRUE if |
2412 | successful, or FALSE if there is an error. As an example, the |
2413 | following code waits on semaphore $semnum of semaphore id $semid: |
2414 | |
2415 | $semop = pack("sss", $semnum, -1, 0); |
2416 | die "Semaphore trouble: $!\n" unless semop($semid, $semop); |
2417 | |
2418 | To signal the semaphore, replace "-1" with "1". |
2419 | |
2420 | =item send SOCKET,MSG,FLAGS,TO |
2421 | |
2422 | =item send SOCKET,MSG,FLAGS |
2423 | |
2424 | Sends a message on a socket. Takes the same flags as the system call |
2425 | of the same name. On unconnected sockets you must specify a |
2426 | destination to send TO, in which case it does a C sendto(). Returns |
2427 | the number of characters sent, or the undefined value if there is an |
2428 | error. |
4633a7c4 |
2429 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e |
2430 | |
2431 | =item setpgrp PID,PGRP |
2432 | |
2433 | Sets the current process group for the specified PID, 0 for the current |
2434 | process. Will produce a fatal error if used on a machine that doesn't |
2435 | implement setpgrp(2). |
2436 | |
2437 | =item setpriority WHICH,WHO,PRIORITY |
2438 | |
2439 | Sets the current priority for a process, a process group, or a user. |
748a9306 |
2440 | (See setpriority(2).) Will produce a fatal error if used on a machine |
a0d0e21e |
2441 | that doesn't implement setpriority(2). |
2442 | |
2443 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL |
2444 | |
2445 | Sets the socket option requested. Returns undefined if there is an |
2446 | error. OPTVAL may be specified as undef if you don't want to pass an |
2447 | argument. |
2448 | |
2449 | =item shift ARRAY |
2450 | |
2451 | =item shift |
2452 | |
2453 | Shifts the first value of the array off and returns it, shortening the |
2454 | array by 1 and moving everything down. If there are no elements in the |
2455 | array, returns the undefined value. If ARRAY is omitted, shifts the |
2456 | @ARGV array in the main program, and the @_ array in subroutines. |
2457 | (This is determined lexically.) See also unshift(), push(), and pop(). |
2458 | Shift() and unshift() do the same thing to the left end of an array |
2459 | that push() and pop() do to the right end. |
2460 | |
2461 | =item shmctl ID,CMD,ARG |
2462 | |
2463 | Calls the System V IPC function shmctl. If CMD is &IPC_STAT, then ARG |
2464 | must be a variable which will hold the returned shmid_ds structure. |
2465 | Returns like ioctl: the undefined value for error, "0 but true" for |
2466 | zero, or the actual return value otherwise. |
2467 | |
2468 | =item shmget KEY,SIZE,FLAGS |
2469 | |
2470 | Calls the System V IPC function shmget. Returns the shared memory |
2471 | segment id, or the undefined value if there is an error. |
2472 | |
2473 | =item shmread ID,VAR,POS,SIZE |
2474 | |
2475 | =item shmwrite ID,STRING,POS,SIZE |
2476 | |
2477 | Reads or writes the System V shared memory segment ID starting at |
2478 | position POS for size SIZE by attaching to it, copying in/out, and |
2479 | detaching from it. When reading, VAR must be a variable which will |
2480 | hold the data read. When writing, if STRING is too long, only SIZE |
2481 | bytes are used; if STRING is too short, nulls are written to fill out |
2482 | SIZE bytes. Return TRUE if successful, or FALSE if there is an error. |
2483 | |
2484 | =item shutdown SOCKET,HOW |
2485 | |
2486 | Shuts down a socket connection in the manner indicated by HOW, which |
2487 | has the same interpretation as in the system call of the same name. |
2488 | |
2489 | =item sin EXPR |
2490 | |
2491 | Returns the sine of EXPR (expressed in radians). If EXPR is omitted, |
2492 | returns sine of $_. |
2493 | |
2494 | =item sleep EXPR |
2495 | |
2496 | =item sleep |
2497 | |
2498 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. |
2499 | May be interrupted by sending the process a SIGALRM. Returns the |
2500 | number of seconds actually slept. You probably cannot mix alarm() and |
2501 | sleep() calls, since sleep() is often implemented using alarm(). |
2502 | |
2503 | On some older systems, it may sleep up to a full second less than what |
2504 | you requested, depending on how it counts seconds. Most modern systems |
2505 | always sleep the full amount. |
2506 | |
cb1a09d0 |
2507 | For delays of finer granularity than one second, you may use Perl's |
2508 | syscall() interface to access setitimer(2) if your system supports it, |
2509 | or else see L</select()> below. |
2510 | |
a0d0e21e |
2511 | =item socket SOCKET,DOMAIN,TYPE,PROTOCOL |
2512 | |
2513 | Opens a socket of the specified kind and attaches it to filehandle |
2514 | SOCKET. DOMAIN, TYPE and PROTOCOL are specified the same as for the |
2515 | system call of the same name. You should "use Socket;" first to get |
4633a7c4 |
2516 | the proper definitions imported. See the example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e |
2517 | |
2518 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL |
2519 | |
2520 | Creates an unnamed pair of sockets in the specified domain, of the |
2521 | specified type. DOMAIN, TYPE and PROTOCOL are specified the same as |
2522 | for the system call of the same name. If unimplemented, yields a fatal |
2523 | error. Returns TRUE if successful. |
2524 | |
2525 | =item sort SUBNAME LIST |
2526 | |
2527 | =item sort BLOCK LIST |
2528 | |
2529 | =item sort LIST |
2530 | |
2531 | Sorts the LIST and returns the sorted list value. Nonexistent values |
2532 | of arrays are stripped out. If SUBNAME or BLOCK is omitted, sorts |
2533 | in standard string comparison order. If SUBNAME is specified, it |
2534 | gives the name of a subroutine that returns an integer less than, equal |
2535 | to, or greater than 0, depending on how the elements of the array are |
2536 | to be ordered. (The <=> and cmp operators are extremely useful in such |
2537 | routines.) SUBNAME may be a scalar variable name, in which case the |
2538 | value provides the name of the subroutine to use. In place of a |
2539 | SUBNAME, you can provide a BLOCK as an anonymous, in-line sort |
2540 | subroutine. |
2541 | |
cb1a09d0 |
2542 | In the interests of efficiency the normal calling code for subroutines is |
2543 | bypassed, with the following effects: the subroutine may not be a |
2544 | recursive subroutine, and the two elements to be compared are passed into |
2545 | the subroutine not via @_ but as the package global variables $a and |
2546 | $b (see example below). They are passed by reference, so don't |
2547 | modify $a and $b. And don't try to declare them as lexicals either. |
a0d0e21e |
2548 | |
2549 | Examples: |
2550 | |
2551 | # sort lexically |
2552 | @articles = sort @files; |
2553 | |
2554 | # same thing, but with explicit sort routine |
2555 | @articles = sort {$a cmp $b} @files; |
2556 | |
cb1a09d0 |
2557 | # now case-insensitively |
2558 | @articles = sort { uc($a) cmp uc($b)} @files; |
2559 | |
a0d0e21e |
2560 | # same thing in reversed order |
2561 | @articles = sort {$b cmp $a} @files; |
2562 | |
2563 | # sort numerically ascending |
2564 | @articles = sort {$a <=> $b} @files; |
2565 | |
2566 | # sort numerically descending |
2567 | @articles = sort {$b <=> $a} @files; |
2568 | |
2569 | # sort using explicit subroutine name |
2570 | sub byage { |
2571 | $age{$a} <=> $age{$b}; # presuming integers |
2572 | } |
2573 | @sortedclass = sort byage @class; |
2574 | |
c07a80fd |
2575 | # this sorts the %age associative arrays by value |
2576 | # instead of key using an inline function |
2577 | @eldest = sort { $age{$b} <=> $age{$a} } keys %age; |
2578 | |
a0d0e21e |
2579 | sub backwards { $b cmp $a; } |
2580 | @harry = ('dog','cat','x','Cain','Abel'); |
2581 | @george = ('gone','chased','yz','Punished','Axed'); |
2582 | print sort @harry; |
2583 | # prints AbelCaincatdogx |
2584 | print sort backwards @harry; |
2585 | # prints xdogcatCainAbel |
2586 | print sort @george, 'to', @harry; |
2587 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz |
2588 | |
cb1a09d0 |
2589 | # inefficiently sort by descending numeric compare using |
2590 | # the first integer after the first = sign, or the |
2591 | # whole record case-insensitively otherwise |
2592 | |
2593 | @new = sort { |
2594 | ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0] |
2595 | || |
2596 | uc($a) cmp uc($b) |
2597 | } @old; |
2598 | |
2599 | # same thing, but much more efficiently; |
2600 | # we'll build auxiliary indices instead |
2601 | # for speed |
2602 | @nums = @caps = (); |
2603 | for (@old) { |
2604 | push @nums, /=(\d+)/; |
2605 | push @caps, uc($_); |
2606 | } |
2607 | |
2608 | @new = @old[ sort { |
2609 | $nums[$b] <=> $nums[$a] |
2610 | || |
2611 | $caps[$a] cmp $caps[$b] |
2612 | } 0..$#old |
2613 | ]; |
2614 | |
2615 | # same thing using a Schwartzian Transform (no temps) |
2616 | @new = map { $_->[0] } |
2617 | sort { $b->[1] <=> $a->[1] |
2618 | || |
2619 | $a->[2] cmp $b->[2] |
2620 | } map { [$_, /=(\d+)/, uc($_)] } @old; |
2621 | |
2622 | If you're and using strict, you I<MUST NOT> declare $a |
2623 | and $b as lexicals. They are package globals. That means |
2624 | if you're in the C<main> package, it's |
2625 | |
2626 | @articles = sort {$main::b <=> $main::a} @files; |
2627 | |
2628 | or just |
2629 | |
2630 | @articles = sort {$::b <=> $::a} @files; |
2631 | |
2632 | but if you're in the C<FooPack> package, it's |
2633 | |
2634 | @articles = sort {$FooPack::b <=> $FooPack::a} @files; |
2635 | |
a0d0e21e |
2636 | =item splice ARRAY,OFFSET,LENGTH,LIST |
2637 | |
2638 | =item splice ARRAY,OFFSET,LENGTH |
2639 | |
2640 | =item splice ARRAY,OFFSET |
2641 | |
2642 | Removes the elements designated by OFFSET and LENGTH from an array, and |
2643 | replaces them with the elements of LIST, if any. Returns the elements |
2644 | removed from the array. The array grows or shrinks as necessary. If |
2645 | LENGTH is omitted, removes everything from OFFSET onward. The |
2646 | following equivalencies hold (assuming $[ == 0): |
2647 | |
2648 | push(@a,$x,$y) splice(@a,$#a+1,0,$x,$y) |
2649 | pop(@a) splice(@a,-1) |
2650 | shift(@a) splice(@a,0,1) |
2651 | unshift(@a,$x,$y) splice(@a,0,0,$x,$y) |
2652 | $a[$x] = $y splice(@a,$x,1,$y); |
2653 | |
2654 | Example, assuming array lengths are passed before arrays: |
2655 | |
2656 | sub aeq { # compare two list values |
2657 | local(@a) = splice(@_,0,shift); |
2658 | local(@b) = splice(@_,0,shift); |
2659 | return 0 unless @a == @b; # same len? |
2660 | while (@a) { |
2661 | return 0 if pop(@a) ne pop(@b); |
2662 | } |
2663 | return 1; |
2664 | } |
2665 | if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... } |
2666 | |
2667 | =item split /PATTERN/,EXPR,LIMIT |
2668 | |
2669 | =item split /PATTERN/,EXPR |
2670 | |
2671 | =item split /PATTERN/ |
2672 | |
2673 | =item split |
2674 | |
2675 | Splits a string into an array of strings, and returns it. |
2676 | |
2677 | If not in a list context, returns the number of fields found and splits into |
2678 | the @_ array. (In a list context, you can force the split into @_ by |
2679 | using C<??> as the pattern delimiters, but it still returns the array |
2680 | value.) The use of implicit split to @_ is deprecated, however. |
2681 | |
2682 | If EXPR is omitted, splits the $_ string. If PATTERN is also omitted, |
4633a7c4 |
2683 | splits on whitespace (after skipping any leading whitespace). Anything |
2684 | matching PATTERN is taken to be a delimiter separating the fields. (Note |
2685 | that the delimiter may be longer than one character.) If LIMIT is |
2686 | specified and is not negative, splits into no more than that many fields |
2687 | (though it may split into fewer). If LIMIT is unspecified, trailing null |
2688 | fields are stripped (which potential users of pop() would do well to |
2689 | remember). If LIMIT is negative, it is treated as if an arbitrarily large |
2690 | LIMIT had been specified. |
a0d0e21e |
2691 | |
2692 | A pattern matching the null string (not to be confused with |
748a9306 |
2693 | a null pattern C<//>, which is just one member of the set of patterns |
a0d0e21e |
2694 | matching a null string) will split the value of EXPR into separate |
2695 | characters at each point it matches that way. For example: |
2696 | |
2697 | print join(':', split(/ */, 'hi there')); |
2698 | |
2699 | produces the output 'h:i:t:h:e:r:e'. |
2700 | |
2701 | The LIMIT parameter can be used to partially split a line |
2702 | |
2703 | ($login, $passwd, $remainder) = split(/:/, $_, 3); |
2704 | |
2705 | When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT |
2706 | one larger than the number of variables in the list, to avoid |
2707 | unnecessary work. For the list above LIMIT would have been 4 by |
2708 | default. In time critical applications it behooves you not to split |
2709 | into more fields than you really need. |
2710 | |
2711 | If the PATTERN contains parentheses, additional array elements are |
2712 | created from each matching substring in the delimiter. |
2713 | |
2714 | split(/([,-])/, "1-10,20"); |
2715 | |
2716 | produces the list value |
2717 | |
2718 | (1, '-', 10, ',', 20) |
2719 | |
4633a7c4 |
2720 | If you had the entire header of a normal Unix email message in $header, |
2721 | you could split it up into fields and their values this way: |
2722 | |
2723 | $header =~ s/\n\s+/ /g; # fix continuation lines |
2724 | %hdrs = (UNIX_FROM => split /^(.*?):\s*/m, $header); |
2725 | |
a0d0e21e |
2726 | The pattern C</PATTERN/> may be replaced with an expression to specify |
2727 | patterns that vary at runtime. (To do runtime compilation only once, |
748a9306 |
2728 | use C</$variable/o>.) |
2729 | |
2730 | As a special case, specifying a PATTERN of space (C<' '>) will split on |
2731 | white space just as split with no arguments does. Thus, split(' ') can |
2732 | be used to emulate B<awk>'s default behavior, whereas C<split(/ /)> |
2733 | will give you as many null initial fields as there are leading spaces. |
2734 | A split on /\s+/ is like a split(' ') except that any leading |
2735 | whitespace produces a null first field. A split with no arguments |
2736 | really does a C<split(' ', $_)> internally. |
a0d0e21e |
2737 | |
2738 | Example: |
2739 | |
2740 | open(passwd, '/etc/passwd'); |
2741 | while (<passwd>) { |
748a9306 |
2742 | ($login, $passwd, $uid, $gid, $gcos, |
2743 | $home, $shell) = split(/:/); |
a0d0e21e |
2744 | ... |
2745 | } |
2746 | |
2747 | (Note that $shell above will still have a newline on it. See L</chop>, |
2748 | L</chomp>, and L</join>.) |
2749 | |
2750 | =item sprintf FORMAT,LIST |
2751 | |
2752 | Returns a string formatted by the usual printf conventions of the C |
cb1a09d0 |
2753 | language. See L<sprintf(3)> or L<printf(3)> on your system for details. |
2754 | (The * character for an indirectly specified length is not |
a0d0e21e |
2755 | supported, but you can get the same effect by interpolating a variable |
cb1a09d0 |
2756 | into the pattern.) Some C libraries' implementations of sprintf() can |
2757 | dump core when fed ludicrous arguments. |
a0d0e21e |
2758 | |
2759 | =item sqrt EXPR |
2760 | |
2761 | Return the square root of EXPR. If EXPR is omitted, returns square |
2762 | root of $_. |
2763 | |
2764 | =item srand EXPR |
2765 | |
cb1a09d0 |
2766 | Sets the random number seed for the C<rand> operator. If EXPR is omitted, |
2767 | does C<srand(time)>. Many folks use an explicit C<srand(time ^ $$)> |
2768 | instead. Of course, you'd need something much more random than that for |
2769 | cryptographic purposes, since it's easy to guess the current time. |
2770 | Checksumming the compressed output of rapidly changing operating system |
2771 | status programs is the usual method. Examples are posted regularly to |
2772 | the comp.security.unix newsgroup. |
a0d0e21e |
2773 | |
2774 | =item stat FILEHANDLE |
2775 | |
2776 | =item stat EXPR |
2777 | |
2778 | Returns a 13-element array giving the status info for a file, either the |
2779 | file opened via FILEHANDLE, or named by EXPR. Returns a null list if |
2780 | the stat fails. Typically used as follows: |
2781 | |
2782 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, |
2783 | $atime,$mtime,$ctime,$blksize,$blocks) |
2784 | = stat($filename); |
2785 | |
c07a80fd |
2786 | Not all fields are supported on all filesystem types. Here are the |
2787 | meaning of the fields: |
2788 | |
2789 | dev device number of filesystem |
2790 | ino inode number |
2791 | mode file mode (type and permissions) |
2792 | nlink number of (hard) links to the file |
2793 | uid numeric user ID of file's owner |
2794 | gid numer group ID of file's owner |
2795 | rdev the device identifier (special files only) |
2796 | size total size of file, in bytes |
2797 | atime last access time since the epoch |
2798 | mtime last modify time since the epoch |
2799 | ctime inode change time (NOT creation type!) since the epoch |
2800 | blksize preferred blocksize for file system I/O |
2801 | blocks actual number of blocks allocated |
2802 | |
2803 | (The epoch was at 00:00 January 1, 1970 GMT.) |
2804 | |
a0d0e21e |
2805 | If stat is passed the special filehandle consisting of an underline, no |
2806 | stat is done, but the current contents of the stat structure from the |
2807 | last stat or filetest are returned. Example: |
2808 | |
2809 | if (-x $file && (($d) = stat(_)) && $d < 0) { |
2810 | print "$file is executable NFS file\n"; |
2811 | } |
2812 | |
2813 | (This only works on machines for which the device number is negative under NFS.) |
2814 | |
2815 | =item study SCALAR |
2816 | |
2817 | =item study |
2818 | |
2819 | Takes extra time to study SCALAR ($_ if unspecified) in anticipation of |
2820 | doing many pattern matches on the string before it is next modified. |
2821 | This may or may not save time, depending on the nature and number of |
2822 | patterns you are searching on, and on the distribution of character |
2823 | frequencies in the string to be searched--you probably want to compare |
2824 | runtimes with and without it to see which runs faster. Those loops |
2825 | which scan for many short constant strings (including the constant |
2826 | parts of more complex patterns) will benefit most. You may have only |
2827 | one study active at a time--if you study a different scalar the first |
2828 | is "unstudied". (The way study works is this: a linked list of every |
2829 | character in the string to be searched is made, so we know, for |
2830 | example, where all the 'k' characters are. From each search string, |
2831 | the rarest character is selected, based on some static frequency tables |
2832 | constructed from some C programs and English text. Only those places |
2833 | that contain this "rarest" character are examined.) |
2834 | |
2835 | For example, here is a loop which inserts index producing entries |
2836 | before any line containing a certain pattern: |
2837 | |
2838 | while (<>) { |
2839 | study; |
2840 | print ".IX foo\n" if /\bfoo\b/; |
2841 | print ".IX bar\n" if /\bbar\b/; |
2842 | print ".IX blurfl\n" if /\bblurfl\b/; |
2843 | ... |
2844 | print; |
2845 | } |
2846 | |
2847 | In searching for /\bfoo\b/, only those locations in $_ that contain "f" |
2848 | will be looked at, because "f" is rarer than "o". In general, this is |
2849 | a big win except in pathological cases. The only question is whether |
2850 | it saves you more time than it took to build the linked list in the |
2851 | first place. |
2852 | |
2853 | Note that if you have to look for strings that you don't know till |
2854 | runtime, you can build an entire loop as a string and eval that to |
2855 | avoid recompiling all your patterns all the time. Together with |
2856 | undefining $/ to input entire files as one record, this can be very |
2857 | fast, often faster than specialized programs like fgrep(1). The following |
2858 | scans a list of files (@files) for a list of words (@words), and prints |
2859 | out the names of those files that contain a match: |
2860 | |
2861 | $search = 'while (<>) { study;'; |
2862 | foreach $word (@words) { |
2863 | $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n"; |
2864 | } |
2865 | $search .= "}"; |
2866 | @ARGV = @files; |
2867 | undef $/; |
2868 | eval $search; # this screams |
2869 | $/ = "\n"; # put back to normal input delim |
2870 | foreach $file (sort keys(%seen)) { |
2871 | print $file, "\n"; |
2872 | } |
2873 | |
cb1a09d0 |
2874 | =item sub BLOCK |
2875 | |
2876 | =item sub NAME |
2877 | |
2878 | =item sub NAME BLOCK |
2879 | |
2880 | This is subroutine definition, not a real function I<per se>. With just a |
2881 | NAME (and possibly prototypes), it's just a forward declaration. Without |
2882 | a NAME, it's an anonymous function declaration, and does actually return a |
2883 | value: the CODE ref of the closure you just created. See L<perlsub> and |
2884 | L<perlref> for details. |
2885 | |
a0d0e21e |
2886 | =item substr EXPR,OFFSET,LEN |
2887 | |
2888 | =item substr EXPR,OFFSET |
2889 | |
2890 | Extracts a substring out of EXPR and returns it. First character is at |
2891 | offset 0, or whatever you've set $[ to. If OFFSET is negative, starts |
2892 | that far from the end of the string. If LEN is omitted, returns |
748a9306 |
2893 | everything to the end of the string. If LEN is negative, leaves that |
2894 | many characters off the end of the string. |
2895 | |
2896 | You can use the substr() function |
a0d0e21e |
2897 | as an lvalue, in which case EXPR must be an lvalue. If you assign |
2898 | something shorter than LEN, the string will shrink, and if you assign |
2899 | something longer than LEN, the string will grow to accommodate it. To |
2900 | keep the string the same length you may need to pad or chop your value |
2901 | using sprintf(). |
2902 | |
2903 | =item symlink OLDFILE,NEWFILE |
2904 | |
2905 | Creates a new filename symbolically linked to the old filename. |
2906 | Returns 1 for success, 0 otherwise. On systems that don't support |
2907 | symbolic links, produces a fatal error at run time. To check for that, |
2908 | use eval: |
2909 | |
2910 | $symlink_exists = (eval 'symlink("","");', $@ eq ''); |
2911 | |
2912 | =item syscall LIST |
2913 | |
2914 | Calls the system call specified as the first element of the list, |
2915 | passing the remaining elements as arguments to the system call. If |
2916 | unimplemented, produces a fatal error. The arguments are interpreted |
2917 | as follows: if a given argument is numeric, the argument is passed as |
2918 | an int. If not, the pointer to the string value is passed. You are |
2919 | responsible to make sure a string is pre-extended long enough to |
2920 | receive any result that might be written into a string. If your |
2921 | integer arguments are not literals and have never been interpreted in a |
2922 | numeric context, you may need to add 0 to them to force them to look |
2923 | like numbers. |
2924 | |
2925 | require 'syscall.ph'; # may need to run h2ph |
2926 | syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9); |
2927 | |
2928 | Note that Perl only supports passing of up to 14 arguments to your system call, |
2929 | which in practice should usually suffice. |
2930 | |
c07a80fd |
2931 | =item sysopen FILEHANDLE,FILENAME,MODE |
2932 | |
2933 | =item sysopen FILEHANDLE,FILENAME,MODE,PERMS |
2934 | |
2935 | Opens the file whose filename is given by FILENAME, and associates it |
2936 | with FILEHANDLE. If FILEHANDLE is an expression, its value is used as |
2937 | the name of the real filehandle wanted. This function calls the |
2938 | underlying operating system's C<open> function with the parameters |
2939 | FILENAME, MODE, PERMS. |
2940 | |
2941 | The possible values and flag bits of the MODE parameter are |
2942 | system-dependent; they are available via the standard module C<Fcntl>. |
2943 | However, for historical reasons, some values are universal: zero means |
2944 | read-only, one means write-only, and two means read/write. |
2945 | |
2946 | If the file named by FILENAME does not exist and the C<open> call |
2947 | creates it (typically because MODE includes the O_CREAT flag), then |
2948 | the value of PERMS specifies the permissions of the newly created |
2949 | file. If PERMS is omitted, the default value is 0666, which allows |
2950 | read and write for all. This default is reasonable: see C<umask>. |
2951 | |
a0d0e21e |
2952 | =item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET |
2953 | |
2954 | =item sysread FILEHANDLE,SCALAR,LENGTH |
2955 | |
2956 | Attempts to read LENGTH bytes of data into variable SCALAR from the |
2957 | specified FILEHANDLE, using the system call read(2). It bypasses |
2958 | stdio, so mixing this with other kinds of reads may cause confusion. |
2959 | Returns the number of bytes actually read, or undef if there was an |
2960 | error. SCALAR will be grown or shrunk to the length actually read. An |
2961 | OFFSET may be specified to place the read data at some other place than |
2962 | the beginning of the string. |
2963 | |
2964 | =item system LIST |
2965 | |
2966 | Does exactly the same thing as "exec LIST" except that a fork is done |
2967 | first, and the parent process waits for the child process to complete. |
2968 | Note that argument processing varies depending on the number of |
2969 | arguments. The return value is the exit status of the program as |
2970 | returned by the wait() call. To get the actual exit value divide by |
cb1a09d0 |
2971 | 256. See also L</exec>. This is I<NOT> what you want to use to capture |
2972 | the output from a command, for that you should merely use backticks, as |
2973 | described in L<perlop/"`STRING`">. |
a0d0e21e |
2974 | |
2975 | =item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET |
2976 | |
2977 | =item syswrite FILEHANDLE,SCALAR,LENGTH |
2978 | |
2979 | Attempts to write LENGTH bytes of data from variable SCALAR to the |
2980 | specified FILEHANDLE, using the system call write(2). It bypasses |
2981 | stdio, so mixing this with prints may cause confusion. Returns the |
2982 | number of bytes actually written, or undef if there was an error. An |
22dc801b |
2983 | OFFSET may be specified to get the write data from some other place than |
a0d0e21e |
2984 | the beginning of the string. |
2985 | |
2986 | =item tell FILEHANDLE |
2987 | |
2988 | =item tell |
2989 | |
2990 | Returns the current file position for FILEHANDLE. FILEHANDLE may be an |
2991 | expression whose value gives the name of the actual filehandle. If |
2992 | FILEHANDLE is omitted, assumes the file last read. |
2993 | |
2994 | =item telldir DIRHANDLE |
2995 | |
2996 | Returns the current position of the readdir() routines on DIRHANDLE. |
2997 | Value may be given to seekdir() to access a particular location in a |
2998 | directory. Has the same caveats about possible directory compaction as |
2999 | the corresponding system library routine. |
3000 | |
4633a7c4 |
3001 | =item tie VARIABLE,CLASSNAME,LIST |
a0d0e21e |
3002 | |
4633a7c4 |
3003 | This function binds a variable to a package class that will provide the |
3004 | implementation for the variable. VARIABLE is the name of the variable |
3005 | to be enchanted. CLASSNAME is the name of a class implementing objects |
3006 | of correct type. Any additional arguments are passed to the "new" |
3007 | method of the class (meaning TIESCALAR, TIEARRAY, or TIEHASH). |
3008 | Typically these are arguments such as might be passed to the dbm_open() |
cb1a09d0 |
3009 | function of C. The object returned by the "new" method is also |
3010 | returned by the tie() function, which would be useful if you want to |
4633a7c4 |
3011 | access other methods in CLASSNAME. |
a0d0e21e |
3012 | |
3013 | Note that functions such as keys() and values() may return huge array |
748a9306 |
3014 | values when used on large objects, like DBM files. You may prefer to |
3015 | use the each() function to iterate over such. Example: |
a0d0e21e |
3016 | |
3017 | # print out history file offsets |
4633a7c4 |
3018 | use NDBM_File; |
a0d0e21e |
3019 | tie(%HIST, NDBM_File, '/usr/lib/news/history', 1, 0); |
3020 | while (($key,$val) = each %HIST) { |
3021 | print $key, ' = ', unpack('L',$val), "\n"; |
3022 | } |
3023 | untie(%HIST); |
3024 | |
4633a7c4 |
3025 | A class implementing an associative array should have the following |
a0d0e21e |
3026 | methods: |
3027 | |
4633a7c4 |
3028 | TIEHASH classname, LIST |
a0d0e21e |
3029 | DESTROY this |
3030 | FETCH this, key |
3031 | STORE this, key, value |
3032 | DELETE this, key |
3033 | EXISTS this, key |
3034 | FIRSTKEY this |
3035 | NEXTKEY this, lastkey |
3036 | |
4633a7c4 |
3037 | A class implementing an ordinary array should have the following methods: |
a0d0e21e |
3038 | |
4633a7c4 |
3039 | TIEARRAY classname, LIST |
a0d0e21e |
3040 | DESTROY this |
3041 | FETCH this, key |
3042 | STORE this, key, value |
3043 | [others TBD] |
3044 | |
4633a7c4 |
3045 | A class implementing a scalar should have the following methods: |
a0d0e21e |
3046 | |
4633a7c4 |
3047 | TIESCALAR classname, LIST |
a0d0e21e |
3048 | DESTROY this |
3049 | FETCH this, |
3050 | STORE this, value |
3051 | |
4633a7c4 |
3052 | Unlike dbmopen(), the tie() function will not use or require a module |
3053 | for you--you need to do that explicitly yourself. See L<DB_File> |
3054 | or the F<Config> module for interesting tie() implementations. |
3055 | |
f3cbc334 |
3056 | =item tied VARIABLE |
3057 | |
3058 | Returns a reference to the object underlying VARIABLE (the same value |
3059 | that was originally returned by the tie() call which bound the variable |
3060 | to a package.) Returns the undefined value if VARIABLE isn't tied to a |
3061 | package. |
3062 | |
a0d0e21e |
3063 | =item time |
3064 | |
3065 | Returns the number of non-leap seconds since 00:00:00 UTC, January 1, |
3066 | 1970. Suitable for feeding to gmtime() and localtime(). |
3067 | |
3068 | =item times |
3069 | |
3070 | Returns a four-element array giving the user and system times, in |
3071 | seconds, for this process and the children of this process. |
3072 | |
3073 | ($user,$system,$cuser,$csystem) = times; |
3074 | |
3075 | =item tr/// |
3076 | |
3077 | The translation operator. See L<perlop>. |
3078 | |
3079 | =item truncate FILEHANDLE,LENGTH |
3080 | |
3081 | =item truncate EXPR,LENGTH |
3082 | |
3083 | Truncates the file opened on FILEHANDLE, or named by EXPR, to the |
3084 | specified length. Produces a fatal error if truncate isn't implemented |
3085 | on your system. |
3086 | |
3087 | =item uc EXPR |
3088 | |
3089 | Returns an uppercased version of EXPR. This is the internal function |
3090 | implementing the \U escape in double-quoted strings. |
4633a7c4 |
3091 | Should respect any POSIX setlocale() settings. |
a0d0e21e |
3092 | |
3093 | =item ucfirst EXPR |
3094 | |
3095 | Returns the value of EXPR with the first character uppercased. This is |
3096 | the internal function implementing the \u escape in double-quoted strings. |
4633a7c4 |
3097 | Should respect any POSIX setlocale() settings. |
a0d0e21e |
3098 | |
3099 | =item umask EXPR |
3100 | |
3101 | =item umask |
3102 | |
3103 | Sets the umask for the process and returns the old one. If EXPR is |
3104 | omitted, merely returns current umask. |
3105 | |
3106 | =item undef EXPR |
3107 | |
3108 | =item undef |
3109 | |
3110 | Undefines the value of EXPR, which must be an lvalue. Use only on a |
3111 | scalar value, an entire array, or a subroutine name (using "&"). (Using undef() |
3112 | will probably not do what you expect on most predefined variables or |
3113 | DBM list values, so don't do that.) Always returns the undefined value. You can omit |
3114 | the EXPR, in which case nothing is undefined, but you still get an |
3115 | undefined value that you could, for instance, return from a |
3116 | subroutine. Examples: |
3117 | |
3118 | undef $foo; |
3119 | undef $bar{'blurfl'}; |
3120 | undef @ary; |
3121 | undef %assoc; |
3122 | undef &mysub; |
3123 | return (wantarray ? () : undef) if $they_blew_it; |
3124 | |
3125 | =item unlink LIST |
3126 | |
3127 | Deletes a list of files. Returns the number of files successfully |
3128 | deleted. |
3129 | |
3130 | $cnt = unlink 'a', 'b', 'c'; |
3131 | unlink @goners; |
3132 | unlink <*.bak>; |
3133 | |
3134 | Note: unlink will not delete directories unless you are superuser and |
3135 | the B<-U> flag is supplied to Perl. Even if these conditions are |
3136 | met, be warned that unlinking a directory can inflict damage on your |
3137 | filesystem. Use rmdir instead. |
3138 | |
3139 | =item unpack TEMPLATE,EXPR |
3140 | |
3141 | Unpack does the reverse of pack: it takes a string representing a |
3142 | structure and expands it out into a list value, returning the array |
3143 | value. (In a scalar context, it merely returns the first value |
3144 | produced.) The TEMPLATE has the same format as in the pack function. |
3145 | Here's a subroutine that does substring: |
3146 | |
3147 | sub substr { |
3148 | local($what,$where,$howmuch) = @_; |
3149 | unpack("x$where a$howmuch", $what); |
3150 | } |
3151 | |
3152 | and then there's |
3153 | |
3154 | sub ordinal { unpack("c",$_[0]); } # same as ord() |
3155 | |
3156 | In addition, you may prefix a field with a %<number> to indicate that |
3157 | you want a <number>-bit checksum of the items instead of the items |
3158 | themselves. Default is a 16-bit checksum. For example, the following |
3159 | computes the same number as the System V sum program: |
3160 | |
3161 | while (<>) { |
3162 | $checksum += unpack("%16C*", $_); |
3163 | } |
3164 | $checksum %= 65536; |
3165 | |
3166 | The following efficiently counts the number of set bits in a bit vector: |
3167 | |
3168 | $setbits = unpack("%32b*", $selectmask); |
3169 | |
3170 | =item untie VARIABLE |
3171 | |
3172 | Breaks the binding between a variable and a package. (See tie().) |
3173 | |
3174 | =item unshift ARRAY,LIST |
3175 | |
3176 | Does the opposite of a C<shift>. Or the opposite of a C<push>, |
3177 | depending on how you look at it. Prepends list to the front of the |
3178 | array, and returns the new number of elements in the array. |
3179 | |
3180 | unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/; |
3181 | |
3182 | Note the LIST is prepended whole, not one element at a time, so the |
3183 | prepended elements stay in the same order. Use reverse to do the |
3184 | reverse. |
3185 | |
3186 | =item use Module LIST |
3187 | |
3188 | =item use Module |
3189 | |
3190 | Imports some semantics into the current package from the named module, |
3191 | generally by aliasing certain subroutine or variable names into your |
3192 | package. It is exactly equivalent to |
3193 | |
3194 | BEGIN { require Module; import Module LIST; } |
3195 | |
a0d0e21e |
3196 | The BEGIN forces the require and import to happen at compile time. The |
3197 | require makes sure the module is loaded into memory if it hasn't been |
3198 | yet. The import is not a builtin--it's just an ordinary static method |
3199 | call into the "Module" package to tell the module to import the list of |
3200 | features back into the current package. The module can implement its |
3201 | import method any way it likes, though most modules just choose to |
3202 | derive their import method via inheritance from the Exporter class that |
cb1a09d0 |
3203 | is defined in the Exporter module. See L<Exporter>. |
3204 | |
3205 | If you don't want your namespace altered, explicitly supply an empty list: |
3206 | |
3207 | use Module (); |
3208 | |
3209 | That is exactly equivalent to |
3210 | |
3211 | BEGIN { require Module; } |
a0d0e21e |
3212 | |
3213 | Because this is a wide-open interface, pragmas (compiler directives) |
3214 | are also implemented this way. Currently implemented pragmas are: |
3215 | |
3216 | use integer; |
4633a7c4 |
3217 | use diagnostics; |
a0d0e21e |
3218 | use sigtrap qw(SEGV BUS); |
3219 | use strict qw(subs vars refs); |
3220 | use subs qw(afunc blurfl); |
3221 | |
3222 | These pseudomodules import semantics into the current block scope, unlike |
3223 | ordinary modules, which import symbols into the current package (which are |
3224 | effective through the end of the file). |
3225 | |
3226 | There's a corresponding "no" command that unimports meanings imported |
3227 | by use. |
3228 | |
3229 | no integer; |
3230 | no strict 'refs'; |
3231 | |
3232 | See L<perlmod> for a list of standard modules and pragmas. |
3233 | |
3234 | =item utime LIST |
3235 | |
3236 | Changes the access and modification times on each file of a list of |
3237 | files. The first two elements of the list must be the NUMERICAL access |
3238 | and modification times, in that order. Returns the number of files |
3239 | successfully changed. The inode modification time of each file is set |
3240 | to the current time. Example of a "touch" command: |
3241 | |
3242 | #!/usr/bin/perl |
3243 | $now = time; |
3244 | utime $now, $now, @ARGV; |
3245 | |
3246 | =item values ASSOC_ARRAY |
3247 | |
3248 | Returns a normal array consisting of all the values of the named |
3249 | associative array. (In a scalar context, returns the number of |
3250 | values.) The values are returned in an apparently random order, but it |
3251 | is the same order as either the keys() or each() function would produce |
c07a80fd |
3252 | on the same array. See also keys(), each(), and sort(). |
a0d0e21e |
3253 | |
3254 | =item vec EXPR,OFFSET,BITS |
3255 | |
22dc801b |
3256 | Treats the string in EXPR as a vector of unsigned integers, and |
3257 | returns the value of the bitfield specified by OFFSET. BITS specifies |
3258 | the number of bits that are reserved for each entry in the bit |
3259 | vector. This must be a power of two from 1 to 32. vec() may also be |
3260 | assigned to, in which case parens are needed to give the expression |
3261 | the correct precedence as in |
3262 | |
3263 | vec($image, $max_x * $x + $y, 8) = 3; |
a0d0e21e |
3264 | |
3265 | Vectors created with vec() can also be manipulated with the logical |
3266 | operators |, & and ^, which will assume a bit vector operation is |
3267 | desired when both operands are strings. |
3268 | |
3269 | To transform a bit vector into a string or array of 0's and 1's, use these: |
3270 | |
3271 | $bits = unpack("b*", $vector); |
3272 | @bits = split(//, unpack("b*", $vector)); |
3273 | |
3274 | If you know the exact length in bits, it can be used in place of the *. |
3275 | |
3276 | =item wait |
3277 | |
3278 | Waits for a child process to terminate and returns the pid of the |
3279 | deceased process, or -1 if there are no child processes. The status is |
3280 | returned in $?. |
3281 | |
3282 | =item waitpid PID,FLAGS |
3283 | |
3284 | Waits for a particular child process to terminate and returns the pid |
3285 | of the deceased process, or -1 if there is no such child process. The |
3286 | status is returned in $?. If you say |
3287 | |
3288 | use POSIX "wait_h"; |
3289 | ... |
3290 | waitpid(-1,&WNOHANG); |
3291 | |
3292 | then you can do a non-blocking wait for any process. Non-blocking wait |
3293 | is only available on machines supporting either the waitpid(2) or |
3294 | wait4(2) system calls. However, waiting for a particular pid with |
3295 | FLAGS of 0 is implemented everywhere. (Perl emulates the system call |
3296 | by remembering the status values of processes that have exited but have |
3297 | not been harvested by the Perl script yet.) |
3298 | |
3299 | =item wantarray |
3300 | |
3301 | Returns TRUE if the context of the currently executing subroutine is |
3302 | looking for a list value. Returns FALSE if the context is looking |
3303 | for a scalar. |
3304 | |
3305 | return wantarray ? () : undef; |
3306 | |
3307 | =item warn LIST |
3308 | |
3309 | Produces a message on STDERR just like die(), but doesn't exit or |
4633a7c4 |
3310 | on an exception. |
a0d0e21e |
3311 | |
3312 | =item write FILEHANDLE |
3313 | |
3314 | =item write EXPR |
3315 | |
3316 | =item write |
3317 | |
3318 | Writes a formatted record (possibly multi-line) to the specified file, |
3319 | using the format associated with that file. By default the format for |
3320 | a file is the one having the same name is the filehandle, but the |
3321 | format for the current output channel (see the select() function) may be set |
3322 | explicitly by assigning the name of the format to the $~ variable. |
3323 | |
3324 | Top of form processing is handled automatically: if there is |
3325 | insufficient room on the current page for the formatted record, the |
3326 | page is advanced by writing a form feed, a special top-of-page format |
3327 | is used to format the new page header, and then the record is written. |
3328 | By default the top-of-page format is the name of the filehandle with |
3329 | "_TOP" appended, but it may be dynamically set to the format of your |
3330 | choice by assigning the name to the $^ variable while the filehandle is |
3331 | selected. The number of lines remaining on the current page is in |
3332 | variable $-, which can be set to 0 to force a new page. |
3333 | |
3334 | If FILEHANDLE is unspecified, output goes to the current default output |
3335 | channel, which starts out as STDOUT but may be changed by the |
3336 | C<select> operator. If the FILEHANDLE is an EXPR, then the expression |
3337 | is evaluated and the resulting string is used to look up the name of |
3338 | the FILEHANDLE at run time. For more on formats, see L<perlform>. |
3339 | |
3340 | Note that write is I<NOT> the opposite of read. Unfortunately. |
3341 | |
3342 | =item y/// |
3343 | |
37798a01 |
3344 | The translation operator. See L<perlop>. |
a0d0e21e |
3345 | |
3346 | =back |