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