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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlfunc - Perl builtin functions | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | The functions in this section can serve as terms in an expression. | |
8 | They fall into two major categories: list operators and named unary | |
9 | operators. These differ in their precedence relationship with a | |
10 | following comma. (See the precedence table in L<perlop>.) List | |
11 | operators take more than one argument, while unary operators can never | |
12 | take more than one argument. Thus, a comma terminates the argument of | |
13 | a unary operator, but merely separates the arguments of a list | |
14 | operator. A unary operator generally provides a scalar context to its | |
15 | argument, while a list operator may provide either scalar and list | |
16 | contexts for its arguments. If it does both, the scalar arguments will | |
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 | ||
57 | =over 5 | |
58 | ||
59 | =item * | |
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 | ||
73 | =over 8 | |
74 | ||
75 | =item -X FILEHANDLE | |
76 | ||
77 | =item -X EXPR | |
78 | ||
79 | =item -X | |
80 | ||
81 | A file test, where X is one of the letters listed below. This unary | |
82 | operator takes one argument, either a filename or a filehandle, and | |
83 | tests the associated file to see if something is true about it. If the | |
84 | argument is omitted, tests $_, except for C<-t>, which tests STDIN. | |
85 | Unless otherwise documented, it returns C<1> for TRUE and C<''> for FALSE, or | |
86 | the undefined value if the file doesn't exist. Despite the funny | |
87 | names, precedence is the same as any other named unary operator, and | |
88 | the argument may be parenthesized like any other unary operator. The | |
89 | operator may be any of: | |
90 | ||
91 | -r File is readable by effective uid/gid. | |
92 | -w File is writable by effective uid/gid. | |
93 | -x File is executable by effective uid/gid. | |
94 | -o File is owned by effective uid. | |
95 | ||
96 | -R File is readable by real uid/gid. | |
97 | -W File is writable by real uid/gid. | |
98 | -X File is executable by real uid/gid. | |
99 | -O File is owned by real uid. | |
100 | ||
101 | -e File exists. | |
102 | -z File has zero size. | |
103 | -s File has non-zero size (returns size). | |
104 | ||
105 | -f File is a plain file. | |
106 | -d File is a directory. | |
107 | -l File is a symbolic link. | |
108 | -p File is a named pipe (FIFO). | |
109 | -S File is a socket. | |
110 | -b File is a block special file. | |
111 | -c File is a character special file. | |
112 | -t Filehandle is opened to a tty. | |
113 | ||
114 | -u File has setuid bit set. | |
115 | -g File has setgid bit set. | |
116 | -k File has sticky bit set. | |
117 | ||
118 | -T File is a text file. | |
119 | -B File is a binary file (opposite of -T). | |
120 | ||
121 | -M Age of file in days when script started. | |
122 | -A Same for access time. | |
123 | -C Same for inode change time. | |
124 | ||
125 | The interpretation of the file permission operators C<-r>, C<-R>, C<-w>, | |
126 | C<-W>, C<-x> and C<-X> is based solely on the mode of the file and the | |
127 | uids and gids of the user. There may be other reasons you can't actually | |
128 | read, write or execute the file. Also note that, for the superuser, | |
129 | C<-r>, C<-R>, C<-w> and C<-W> always return 1, and C<-x> and C<-X> return | |
130 | 1 if any execute bit is set in the mode. Scripts run by the superuser may | |
131 | thus need to do a stat() in order to determine the actual mode of the | |
132 | file, or temporarily set the uid to something else. | |
133 | ||
134 | Example: | |
135 | ||
136 | while (<>) { | |
137 | chop; | |
138 | next unless -f $_; # ignore specials | |
139 | ... | |
140 | } | |
141 | ||
142 | Note that C<-s/a/b/> does not do a negated substitution. Saying | |
143 | C<-exp($foo)> still works as expected, however--only single letters | |
144 | following a minus are interpreted as file tests. | |
145 | ||
146 | The C<-T> and C<-B> switches work as follows. The first block or so of the | |
147 | file is examined for odd characters such as strange control codes or | |
148 | characters with the high bit set. If too many odd characters (>30%) | |
149 | are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file | |
150 | containing null in the first block is considered a binary file. If C<-T> | |
151 | or C<-B> is used on a filehandle, the current stdio buffer is examined | |
152 | rather than the first block. Both C<-T> and C<-B> return TRUE on a null | |
4633a7c4 LW |
153 | file, or a file at EOF when testing a filehandle. Because you have to |
154 | read a file to do the C<-T> test, on most occasions you want to use a C<-f> | |
155 | against the file first, as in C<next unless -f $file && -T $file>. | |
a0d0e21e LW |
156 | |
157 | If any of the file tests (or either the stat() or lstat() operators) are given the | |
158 | special filehandle consisting of a solitary underline, then the stat | |
159 | structure of the previous file test (or stat operator) is used, saving | |
160 | a system call. (This doesn't work with C<-t>, and you need to remember | |
161 | that lstat() and C<-l> will leave values in the stat structure for the | |
162 | symbolic link, not the real file.) Example: | |
163 | ||
164 | print "Can do.\n" if -r $a || -w _ || -x _; | |
165 | ||
166 | stat($filename); | |
167 | print "Readable\n" if -r _; | |
168 | print "Writable\n" if -w _; | |
169 | print "Executable\n" if -x _; | |
170 | print "Setuid\n" if -u _; | |
171 | print "Setgid\n" if -g _; | |
172 | print "Sticky\n" if -k _; | |
173 | print "Text\n" if -T _; | |
174 | print "Binary\n" if -B _; | |
175 | ||
176 | =item abs VALUE | |
177 | ||
178 | Returns the absolute value of its argument. | |
179 | ||
180 | =item accept NEWSOCKET,GENERICSOCKET | |
181 | ||
182 | Accepts an incoming socket connect, just as the accept(2) system call | |
183 | does. Returns the packed address if it succeeded, FALSE otherwise. | |
4633a7c4 | 184 | See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
185 | |
186 | =item alarm SECONDS | |
187 | ||
188 | Arranges to have a SIGALRM delivered to this process after the | |
189 | specified number of seconds have elapsed. (On some machines, | |
190 | unfortunately, the elapsed time may be up to one second less than you | |
191 | specified because of how seconds are counted.) Only one timer may be | |
192 | counting at once. Each call disables the previous timer, and an | |
193 | argument of 0 may be supplied to cancel the previous timer without | |
194 | starting a new one. The returned value is the amount of time remaining | |
195 | on the previous timer. | |
196 | ||
4633a7c4 | 197 | For delays of finer granularity than one second, you may use Perl's |
a0d0e21e | 198 | syscall() interface to access setitimer(2) if your system supports it, |
4633a7c4 LW |
199 | or else see L</select()> below. It is not advised to intermix alarm() |
200 | and sleep() calls. | |
a0d0e21e LW |
201 | |
202 | =item atan2 Y,X | |
203 | ||
204 | Returns the arctangent of Y/X in the range -PI to PI. | |
205 | ||
206 | =item bind SOCKET,NAME | |
207 | ||
208 | Binds a network address to a socket, just as the bind system call | |
209 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a | |
4633a7c4 LW |
210 | packed address of the appropriate type for the socket. See the examples in |
211 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e LW |
212 | |
213 | =item binmode FILEHANDLE | |
214 | ||
215 | Arranges for the file to be read or written in "binary" mode in | |
216 | operating systems that distinguish between binary and text files. | |
217 | Files that are not in binary mode have CR LF sequences translated to LF | |
218 | on input and LF translated to CR LF on output. Binmode has no effect | |
4633a7c4 LW |
219 | under Unix; in DOS, it may be imperative--otherwise your DOS C library |
220 | may mangle your file. If FILEHANDLE is an expression, | |
a0d0e21e LW |
221 | the value is taken as the name of the filehandle. |
222 | ||
4633a7c4 | 223 | =item bless REF,CLASSNAME |
a0d0e21e LW |
224 | |
225 | =item bless REF | |
226 | ||
227 | This function tells the referenced object (passed as REF) that it is now | |
4633a7c4 LW |
228 | an object in the CLASSNAME package--or the current package if no CLASSNAME |
229 | is specified, which is often the case. It returns the reference for | |
230 | convenience, since a bless() is often the last thing in a constructor. | |
231 | Always use the two-argument version if the function doing the blessing | |
232 | might be inherited by a derived class. See L<perlobj> for more about the | |
233 | blessing (and blessings) of objects. | |
a0d0e21e LW |
234 | |
235 | =item caller EXPR | |
236 | ||
237 | =item caller | |
238 | ||
239 | Returns the context of the current subroutine call. In a scalar context, | |
240 | returns TRUE if there is a caller, that is, if we're in a subroutine or | |
241 | eval() or require(), and FALSE otherwise. In a list context, returns | |
242 | ||
748a9306 | 243 | ($package, $filename, $line) = caller; |
a0d0e21e LW |
244 | |
245 | With EXPR, it returns some extra information that the debugger uses to | |
246 | print a stack trace. The value of EXPR indicates how many call frames | |
247 | to go back before the current one. | |
248 | ||
748a9306 LW |
249 | ($package, $filename, $line, |
250 | $subroutine, $hasargs, $wantargs) = caller($i); | |
251 | ||
252 | Furthermore, when called from within the DB package, caller returns more | |
4633a7c4 | 253 | detailed information: it sets the list variable @DB::args to be the |
748a9306 LW |
254 | arguments with which that subroutine was invoked. |
255 | ||
a0d0e21e LW |
256 | =item chdir EXPR |
257 | ||
258 | Changes the working directory to EXPR, if possible. If EXPR is | |
259 | omitted, changes to home directory. Returns TRUE upon success, FALSE | |
260 | otherwise. See example under die(). | |
261 | ||
262 | =item chmod LIST | |
263 | ||
264 | Changes the permissions of a list of files. The first element of the | |
4633a7c4 LW |
265 | list must be the numerical mode, which should probably be an octal |
266 | number. Returns the number of files successfully changed. | |
a0d0e21e LW |
267 | |
268 | $cnt = chmod 0755, 'foo', 'bar'; | |
269 | chmod 0755, @executables; | |
270 | ||
271 | =item chomp VARIABLE | |
272 | ||
273 | =item chomp LIST | |
274 | ||
275 | =item chomp | |
276 | ||
277 | This is a slightly safer version of chop (see below). It removes any | |
278 | line ending that corresponds to the current value of C<$/> (also known as | |
279 | $INPUT_RECORD_SEPARATOR in the C<English> module). It returns the number | |
280 | of characters removed. It's often used to remove the newline from the | |
281 | end of an input record when you're worried that the final record may be | |
282 | missing its newline. When in paragraph mode (C<$/ = "">), it removes all | |
283 | trailing newlines from the string. If VARIABLE is omitted, it chomps | |
284 | $_. Example: | |
285 | ||
286 | while (<>) { | |
287 | chomp; # avoid \n on last field | |
288 | @array = split(/:/); | |
289 | ... | |
290 | } | |
291 | ||
292 | You can actually chomp anything that's an lvalue, including an assignment: | |
293 | ||
294 | chomp($cwd = `pwd`); | |
295 | chomp($answer = <STDIN>); | |
296 | ||
297 | If you chomp a list, each element is chomped, and the total number of | |
298 | characters removed is returned. | |
299 | ||
300 | =item chop VARIABLE | |
301 | ||
302 | =item chop LIST | |
303 | ||
304 | =item chop | |
305 | ||
306 | Chops off the last character of a string and returns the character | |
307 | chopped. It's used primarily to remove the newline from the end of an | |
308 | input record, but is much more efficient than C<s/\n//> because it neither | |
309 | scans nor copies the string. If VARIABLE is omitted, chops $_. | |
310 | Example: | |
311 | ||
312 | while (<>) { | |
313 | chop; # avoid \n on last field | |
314 | @array = split(/:/); | |
315 | ... | |
316 | } | |
317 | ||
318 | You can actually chop anything that's an lvalue, including an assignment: | |
319 | ||
320 | chop($cwd = `pwd`); | |
321 | chop($answer = <STDIN>); | |
322 | ||
323 | If you chop a list, each element is chopped. Only the value of the | |
324 | last chop is returned. | |
325 | ||
748a9306 LW |
326 | Note that chop returns the last character. To return all but the last |
327 | character, use C<substr($string, 0, -1)>. | |
328 | ||
a0d0e21e LW |
329 | =item chown LIST |
330 | ||
331 | Changes the owner (and group) of a list of files. The first two | |
332 | elements of the list must be the I<NUMERICAL> uid and gid, in that order. | |
333 | Returns the number of files successfully changed. | |
334 | ||
335 | $cnt = chown $uid, $gid, 'foo', 'bar'; | |
336 | chown $uid, $gid, @filenames; | |
337 | ||
338 | Here's an example that looks up non-numeric uids in the passwd file: | |
339 | ||
340 | print "User: "; | |
341 | chop($user = <STDIN>); | |
342 | print "Files: " | |
343 | chop($pattern = <STDIN>); | |
344 | ||
345 | ($login,$pass,$uid,$gid) = getpwnam($user) | |
346 | or die "$user not in passwd file"; | |
347 | ||
348 | @ary = <${pattern}>; # expand filenames | |
349 | chown $uid, $gid, @ary; | |
350 | ||
4633a7c4 LW |
351 | On most systems, you are not allowed to change the ownership of the |
352 | file unless you're the superuser, although you should be able to change | |
353 | the group to any of your secondary groups. On insecure systems, these | |
354 | restrictions may be relaxed, but this is not a portable assumption. | |
355 | ||
a0d0e21e LW |
356 | =item chr NUMBER |
357 | ||
358 | Returns the character represented by that NUMBER in the character set. | |
359 | For example, C<chr(65)> is "A" in ASCII. | |
360 | ||
361 | =item chroot FILENAME | |
362 | ||
4633a7c4 LW |
363 | This function works as the system call by the same name: it makes the |
364 | named directory the new root directory for all further pathnames that | |
365 | begin with a "/" by your process and all of its children. (It doesn't | |
366 | change your current working directory is unaffected.) For security | |
367 | reasons, this call is restricted to the superuser. If FILENAME is | |
368 | omitted, does chroot to $_. | |
a0d0e21e LW |
369 | |
370 | =item close FILEHANDLE | |
371 | ||
372 | Closes the file or pipe associated with the file handle, returning TRUE | |
373 | only if stdio successfully flushes buffers and closes the system file | |
374 | descriptor. You don't have to close FILEHANDLE if you are immediately | |
4633a7c4 | 375 | going to do another open() on it, since open() will close it for you. (See |
a0d0e21e LW |
376 | open().) However, an explicit close on an input file resets the line |
377 | counter ($.), while the implicit close done by open() does not. Also, | |
378 | closing a pipe will wait for the process executing on the pipe to | |
379 | complete, in case you want to look at the output of the pipe | |
380 | afterwards. Closing a pipe explicitly also puts the status value of | |
381 | the command into C<$?>. Example: | |
382 | ||
383 | open(OUTPUT, '|sort >foo'); # pipe to sort | |
384 | ... # print stuff to output | |
385 | close OUTPUT; # wait for sort to finish | |
386 | open(INPUT, 'foo'); # get sort's results | |
387 | ||
388 | FILEHANDLE may be an expression whose value gives the real filehandle name. | |
389 | ||
390 | =item closedir DIRHANDLE | |
391 | ||
392 | Closes a directory opened by opendir(). | |
393 | ||
394 | =item connect SOCKET,NAME | |
395 | ||
396 | Attempts to connect to a remote socket, just as the connect system call | |
397 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a | |
4633a7c4 LW |
398 | packed address of the appropriate type for the socket. See the examples in |
399 | L<perlipc/"Sockets: Client/Server Communication">. | |
a0d0e21e LW |
400 | |
401 | =item cos EXPR | |
402 | ||
403 | Returns the cosine of EXPR (expressed in radians). If EXPR is omitted | |
404 | takes cosine of $_. | |
405 | ||
406 | =item crypt PLAINTEXT,SALT | |
407 | ||
4633a7c4 LW |
408 | Encrypts a string exactly like the crypt(3) function in the C library |
409 | (assuming that you actually have a version there that has not been | |
410 | extirpated as a potential munition). This can prove useful for checking | |
411 | the password file for lousy passwords, amongst other things. Only the | |
412 | guys wearing white hats should do this. | |
a0d0e21e LW |
413 | |
414 | Here's an example that makes sure that whoever runs this program knows | |
415 | their own password: | |
416 | ||
417 | $pwd = (getpwuid($<))[1]; | |
418 | $salt = substr($pwd, 0, 2); | |
419 | ||
420 | system "stty -echo"; | |
421 | print "Password: "; | |
422 | chop($word = <STDIN>); | |
423 | print "\n"; | |
424 | system "stty echo"; | |
425 | ||
426 | if (crypt($word, $salt) ne $pwd) { | |
427 | die "Sorry...\n"; | |
428 | } else { | |
429 | print "ok\n"; | |
430 | } | |
431 | ||
432 | Of course, typing in your own password to whoever asks you | |
748a9306 | 433 | for it is unwise. |
a0d0e21e LW |
434 | |
435 | =item dbmclose ASSOC_ARRAY | |
436 | ||
437 | [This function has been superseded by the untie() function.] | |
438 | ||
439 | Breaks the binding between a DBM file and an associative array. | |
440 | ||
441 | =item dbmopen ASSOC,DBNAME,MODE | |
442 | ||
443 | [This function has been superseded by the tie() function.] | |
444 | ||
4633a7c4 | 445 | This binds a dbm(3), ndbm(3), sdbm(3), gdbm(), or Berkeley DB file to an associative array. ASSOC is the |
a0d0e21e LW |
446 | name of the associative array. (Unlike normal open, the first argument |
447 | is I<NOT> a filehandle, even though it looks like one). DBNAME is the | |
4633a7c4 | 448 | name of the database (without the F<.dir> or F<.pag> extension if any). If the |
a0d0e21e LW |
449 | database does not exist, it is created with protection specified by |
450 | MODE (as modified by the umask()). If your system only supports the | |
451 | older DBM functions, you may perform only one dbmopen() in your program. | |
4633a7c4 LW |
452 | In order versions of Perl, |
453 | if your system had neither DBM nor ndbm, calling dbmopen() produced a | |
454 | fatal error; it now falls back to sdbm(3). | |
a0d0e21e LW |
455 | |
456 | If you don't have write access to the DBM file, you can only read | |
457 | associative array variables, not set them. If you want to test whether | |
458 | you can write, either use file tests or try setting a dummy array entry | |
459 | inside an eval(), which will trap the error. | |
460 | ||
461 | Note that functions such as keys() and values() may return huge array | |
462 | values when used on large DBM files. You may prefer to use the each() | |
463 | function to iterate over large DBM files. Example: | |
464 | ||
465 | # print out history file offsets | |
466 | dbmopen(%HIST,'/usr/lib/news/history',0666); | |
467 | while (($key,$val) = each %HIST) { | |
468 | print $key, ' = ', unpack('L',$val), "\n"; | |
469 | } | |
470 | dbmclose(%HIST); | |
471 | ||
4633a7c4 LW |
472 | See also L<DB_File> for many other interesting possibilities. |
473 | ||
a0d0e21e LW |
474 | =item defined EXPR |
475 | ||
476 | Returns a boolean value saying whether the lvalue EXPR has a real value | |
477 | or not. Many operations return the undefined value under exceptional | |
478 | conditions, such as end of file, uninitialized variable, system error | |
479 | and such. This function allows you to distinguish between an undefined | |
480 | null scalar and a defined null scalar with operations that might return | |
481 | a real null string, such as referencing elements of an array. You may | |
482 | also check to see if arrays or subroutines exist. Use of defined on | |
483 | predefined variables is not guaranteed to produce intuitive results. | |
484 | ||
485 | When used on a hash array element, it tells you whether the value | |
486 | is defined, not whether the key exists in the hash. Use exists() for that. | |
487 | ||
488 | Examples: | |
489 | ||
490 | print if defined $switch{'D'}; | |
491 | print "$val\n" while defined($val = pop(@ary)); | |
492 | die "Can't readlink $sym: $!" | |
493 | unless defined($value = readlink $sym); | |
494 | eval '@foo = ()' if defined(@foo); | |
495 | die "No XYZ package defined" unless defined %_XYZ; | |
496 | sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } | |
497 | ||
498 | See also undef(). | |
499 | ||
500 | =item delete EXPR | |
501 | ||
502 | Deletes the specified value from its hash array. Returns the deleted | |
503 | value, or the undefined value if nothing was deleted. Deleting from | |
504 | C<$ENV{}> modifies the environment. Deleting from an array tied to a DBM | |
505 | file deletes the entry from the DBM file. (But deleting from a tie()d | |
506 | hash doesn't necessarily return anything.) | |
507 | ||
508 | The following deletes all the values of an associative array: | |
509 | ||
510 | foreach $key (keys %ARRAY) { | |
511 | delete $ARRAY{$key}; | |
512 | } | |
513 | ||
514 | (But it would be faster to use the undef() command.) Note that the | |
515 | EXPR can be arbitrarily complicated as long as the final operation is | |
516 | a hash key lookup: | |
517 | ||
518 | delete $ref->[$x][$y]{$key}; | |
519 | ||
520 | =item die LIST | |
521 | ||
522 | Outside of an eval(), prints the value of LIST to C<STDERR> and exits with | |
4633a7c4 | 523 | the current value of $! (errno). If $! is 0, exits with the value of |
748a9306 LW |
524 | C<($? E<gt>E<gt> 8)> (backtick `command` status). If C<($? E<gt>E<gt> 8)> is 0, |
525 | exits with 255. Inside an eval(), the error message is stuffed into C<$@>, | |
4633a7c4 LW |
526 | and the eval() is terminated with the undefined value; this makes die() |
527 | the way to raise an exception. | |
a0d0e21e LW |
528 | |
529 | Equivalent examples: | |
530 | ||
531 | die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; | |
532 | chdir '/usr/spool/news' or die "Can't cd to spool: $!\n" | |
533 | ||
534 | If the value of EXPR does not end in a newline, the current script line | |
535 | number and input line number (if any) are also printed, and a newline | |
536 | is supplied. Hint: sometimes appending ", stopped" to your message | |
537 | will cause it to make better sense when the string "at foo line 123" is | |
538 | appended. Suppose you are running script "canasta". | |
539 | ||
540 | die "/etc/games is no good"; | |
541 | die "/etc/games is no good, stopped"; | |
542 | ||
543 | produce, respectively | |
544 | ||
545 | /etc/games is no good at canasta line 123. | |
546 | /etc/games is no good, stopped at canasta line 123. | |
547 | ||
548 | See also exit() and warn(). | |
549 | ||
550 | =item do BLOCK | |
551 | ||
552 | Not really a function. Returns the value of the last command in the | |
553 | sequence of commands indicated by BLOCK. When modified by a loop | |
554 | modifier, executes the BLOCK once before testing the loop condition. | |
555 | (On other statements the loop modifiers test the conditional first.) | |
556 | ||
557 | =item do SUBROUTINE(LIST) | |
558 | ||
559 | A deprecated form of subroutine call. See L<perlsub>. | |
560 | ||
561 | =item do EXPR | |
562 | ||
563 | Uses the value of EXPR as a filename and executes the contents of the | |
564 | file as a Perl script. Its primary use is to include subroutines | |
565 | from a Perl subroutine library. | |
566 | ||
567 | do 'stat.pl'; | |
568 | ||
569 | is just like | |
570 | ||
571 | eval `cat stat.pl`; | |
572 | ||
573 | except that it's more efficient, more concise, keeps track of the | |
574 | current filename for error messages, and searches all the B<-I> | |
575 | libraries if the file isn't in the current directory (see also the @INC | |
576 | array in L<perlvar/Predefined Names>). It's the same, however, in that it does | |
577 | reparse the file every time you call it, so you probably don't want to | |
578 | do this inside a loop. | |
579 | ||
580 | Note that inclusion of library modules is better done with the | |
4633a7c4 LW |
581 | use() and require() operators, which also do error checking |
582 | and raise an exception if there's a problem. | |
a0d0e21e LW |
583 | |
584 | =item dump LABEL | |
585 | ||
586 | This causes an immediate core dump. Primarily this is so that you can | |
587 | use the B<undump> program to turn your core dump into an executable binary | |
588 | after having initialized all your variables at the beginning of the | |
589 | program. When the new binary is executed it will begin by executing a | |
590 | C<goto LABEL> (with all the restrictions that C<goto> suffers). Think of | |
591 | it as a goto with an intervening core dump and reincarnation. If LABEL | |
592 | is omitted, restarts the program from the top. WARNING: any files | |
593 | opened at the time of the dump will NOT be open any more when the | |
594 | program is reincarnated, with possible resulting confusion on the part | |
595 | of Perl. See also B<-u> option in L<perlrun>. | |
596 | ||
597 | Example: | |
598 | ||
599 | #!/usr/bin/perl | |
600 | require 'getopt.pl'; | |
601 | require 'stat.pl'; | |
602 | %days = ( | |
603 | 'Sun' => 1, | |
604 | 'Mon' => 2, | |
605 | 'Tue' => 3, | |
606 | 'Wed' => 4, | |
607 | 'Thu' => 5, | |
608 | 'Fri' => 6, | |
609 | 'Sat' => 7, | |
610 | ); | |
611 | ||
612 | dump QUICKSTART if $ARGV[0] eq '-d'; | |
613 | ||
614 | QUICKSTART: | |
615 | Getopt('f'); | |
616 | ||
617 | =item each ASSOC_ARRAY | |
618 | ||
4633a7c4 | 619 | Returns a 2-element array consisting of the key and value for the next |
a0d0e21e LW |
620 | value of an associative array, so that you can iterate over it. |
621 | Entries are returned in an apparently random order. When the array is | |
622 | entirely read, a null array is returned (which when assigned produces a | |
623 | FALSE (0) value). The next call to each() after that will start | |
624 | iterating again. The iterator can be reset only by reading all the | |
625 | elements from the array. You should not add elements to an array while | |
626 | you're iterating over it. There is a single iterator for each | |
627 | associative array, shared by all each(), keys() and values() function | |
628 | calls in the program. The following prints out your environment like | |
629 | the printenv(1) program, only in a different order: | |
630 | ||
631 | while (($key,$value) = each %ENV) { | |
632 | print "$key=$value\n"; | |
633 | } | |
634 | ||
635 | See also keys() and values(). | |
636 | ||
637 | =item eof FILEHANDLE | |
638 | ||
4633a7c4 LW |
639 | =item eof () |
640 | ||
a0d0e21e LW |
641 | =item eof |
642 | ||
643 | Returns 1 if the next read on FILEHANDLE will return end of file, or if | |
644 | FILEHANDLE is not open. FILEHANDLE may be an expression whose value | |
645 | gives the real filehandle name. (Note that this function actually | |
646 | reads a character and then ungetc()s it, so it is not very useful in an | |
748a9306 LW |
647 | interactive context.) Do not read from a terminal file (or call |
648 | C<eof(FILEHANDLE)> on it) after end-of-file is reached. Filetypes such | |
649 | as terminals may lose the end-of-file condition if you do. | |
650 | ||
651 | An C<eof> without an argument uses the last file read as argument. | |
652 | Empty parentheses () may be used to indicate | |
4633a7c4 | 653 | the pseudofile formed of the files listed on the command line, i.e. |
a0d0e21e LW |
654 | C<eof()> is reasonable to use inside a while (<>) loop to detect the end |
655 | of only the last file. Use C<eof(ARGV)> or eof without the parentheses to | |
656 | test I<EACH> file in a while (<>) loop. Examples: | |
657 | ||
748a9306 LW |
658 | # reset line numbering on each input file |
659 | while (<>) { | |
660 | print "$.\t$_"; | |
661 | close(ARGV) if (eof); # Not eof(). | |
662 | } | |
663 | ||
a0d0e21e LW |
664 | # insert dashes just before last line of last file |
665 | while (<>) { | |
666 | if (eof()) { | |
667 | print "--------------\n"; | |
748a9306 LW |
668 | close(ARGV); # close or break; is needed if we |
669 | # are reading from the terminal | |
a0d0e21e LW |
670 | } |
671 | print; | |
672 | } | |
673 | ||
a0d0e21e | 674 | Practical hint: you almost never need to use C<eof> in Perl, because the |
4633a7c4 | 675 | input operators return undef when they run out of data. Testing C<eof> |
a0d0e21e LW |
676 | |
677 | =item eval EXPR | |
678 | ||
679 | =item eval BLOCK | |
680 | ||
681 | EXPR is parsed and executed as if it were a little Perl program. It | |
682 | is executed in the context of the current Perl program, so that any | |
683 | variable settings, subroutine or format definitions remain afterwards. | |
684 | The value returned is the value of the last expression evaluated, or a | |
685 | return statement may be used, just as with subroutines. | |
686 | ||
687 | If there is a syntax error or runtime error, or a die() statement is | |
688 | executed, an undefined value is returned by eval(), and C<$@> is set to the | |
689 | error message. If there was no error, C<$@> is guaranteed to be a null | |
690 | string. If EXPR is omitted, evaluates $_. The final semicolon, if | |
691 | any, may be omitted from the expression. | |
692 | ||
693 | Note that, since eval() traps otherwise-fatal errors, it is useful for | |
4633a7c4 | 694 | determining whether a particular feature (such as socket() or symlink()) |
a0d0e21e LW |
695 | is implemented. It is also Perl's exception trapping mechanism, where |
696 | the die operator is used to raise exceptions. | |
697 | ||
698 | If the code to be executed doesn't vary, you may use the eval-BLOCK | |
699 | form to trap run-time errors without incurring the penalty of | |
700 | recompiling each time. The error, if any, is still returned in C<$@>. | |
701 | Examples: | |
702 | ||
703 | # make divide-by-zero non-fatal | |
704 | eval { $answer = $a / $b; }; warn $@ if $@; | |
705 | ||
706 | # same thing, but less efficient | |
707 | eval '$answer = $a / $b'; warn $@ if $@; | |
708 | ||
709 | # a compile-time error | |
710 | eval { $answer = }; | |
711 | ||
712 | # a run-time error | |
713 | eval '$answer ='; # sets $@ | |
714 | ||
715 | With an eval(), you should be especially careful to remember what's | |
716 | being looked at when: | |
717 | ||
718 | eval $x; # CASE 1 | |
719 | eval "$x"; # CASE 2 | |
720 | ||
721 | eval '$x'; # CASE 3 | |
722 | eval { $x }; # CASE 4 | |
723 | ||
724 | eval "\$$x++" # CASE 5 | |
725 | $$x++; # CASE 6 | |
726 | ||
727 | Cases 1 and 2 above behave identically: they run the code contained in the | |
728 | variable $x. (Although case 2 has misleading double quotes making the | |
729 | reader wonder what else might be happening (nothing is).) Cases 3 and 4 | |
730 | likewise behave in the same way: they run the code <$x>, which does | |
731 | nothing at all. (Case 4 is preferred for purely visual reasons.) Case 5 | |
732 | is a place where normally you I<WOULD> like to use double quotes, except | |
748a9306 | 733 | in that particular situation, you can just use symbolic references |
a0d0e21e LW |
734 | instead, as in case 6. |
735 | ||
736 | =item exec LIST | |
737 | ||
738 | The exec() function executes a system command I<AND NEVER RETURNS>. Use | |
739 | the system() function if you want it to return. | |
740 | ||
741 | If there is more than one argument in LIST, or if LIST is an array with | |
742 | more than one value, calls execvp(3) with the arguments in LIST. If | |
743 | there is only one scalar argument, the argument is checked for shell | |
744 | metacharacters. If there are any, the entire argument is passed to | |
745 | C</bin/sh -c> for parsing. If there are none, the argument is split | |
746 | into words and passed directly to execvp(), which is more efficient. | |
747 | Note: exec() (and system(0) do not flush your output buffer, so you may | |
748 | need to set C<$|> to avoid lost output. Examples: | |
749 | ||
750 | exec '/bin/echo', 'Your arguments are: ', @ARGV; | |
751 | exec "sort $outfile | uniq"; | |
752 | ||
753 | If you don't really want to execute the first argument, but want to lie | |
754 | to the program you are executing about its own name, you can specify | |
755 | the program you actually want to run as an "indirect object" (without a | |
756 | comma) in front of the LIST. (This always forces interpretation of the | |
757 | LIST as a multi-valued list, even if there is only a single scalar in | |
758 | the list.) Example: | |
759 | ||
760 | $shell = '/bin/csh'; | |
761 | exec $shell '-sh'; # pretend it's a login shell | |
762 | ||
763 | or, more directly, | |
764 | ||
765 | exec {'/bin/csh'} '-sh'; # pretend it's a login shell | |
766 | ||
767 | =item exists EXPR | |
768 | ||
769 | Returns TRUE if the specified hash key exists in its hash array, even | |
770 | if the corresponding value is undefined. | |
771 | ||
772 | print "Exists\n" if exists $array{$key}; | |
773 | print "Defined\n" if defined $array{$key}; | |
774 | print "True\n" if $array{$key}; | |
775 | ||
776 | A hash element can only be TRUE if it's defined, and defined if | |
777 | it exists, but the reverse doesn't necessarily hold true. | |
778 | ||
779 | Note that the EXPR can be arbitrarily complicated as long as the final | |
780 | operation is a hash key lookup: | |
781 | ||
782 | if (exists $ref->[$x][$y]{$key}) { ... } | |
783 | ||
784 | =item exit EXPR | |
785 | ||
786 | Evaluates EXPR and exits immediately with that value. (Actually, it | |
787 | calls any defined C<END> routines first, but the C<END> routines may not | |
788 | abort the exit. Likewise any object destructors that need to be called | |
789 | are called before exit.) Example: | |
790 | ||
791 | $ans = <STDIN>; | |
792 | exit 0 if $ans =~ /^[Xx]/; | |
793 | ||
794 | See also die(). If EXPR is omitted, exits with 0 status. | |
795 | ||
796 | =item exp EXPR | |
797 | ||
798 | Returns I<e> (the natural logarithm base) to the power of EXPR. | |
799 | If EXPR is omitted, gives C<exp($_)>. | |
800 | ||
801 | =item fcntl FILEHANDLE,FUNCTION,SCALAR | |
802 | ||
803 | Implements the fcntl(2) function. You'll probably have to say | |
804 | ||
805 | use Fcntl; | |
806 | ||
807 | first to get the correct function definitions. Argument processing and | |
808 | value return works just like ioctl() below. Note that fcntl() will produce | |
809 | a fatal error if used on a machine that doesn't implement fcntl(2). | |
810 | For example: | |
811 | ||
812 | use Fcntl; | |
813 | fcntl($filehandle, F_GETLK, $packed_return_buffer); | |
814 | ||
815 | =item fileno FILEHANDLE | |
816 | ||
817 | Returns the file descriptor for a filehandle. This is useful for | |
818 | constructing bitmaps for select(). If FILEHANDLE is an expression, the | |
819 | value is taken as the name of the filehandle. | |
820 | ||
821 | =item flock FILEHANDLE,OPERATION | |
822 | ||
4633a7c4 LW |
823 | Calls flock(2) on FILEHANDLE. See L<flock(2)> for definition of |
824 | OPERATION. Returns TRUE for success, FALSE on failure. Will produce a | |
825 | fatal error if used on a machine that doesn't implement either flock(2) or | |
826 | fcntl(2). (fcntl(2) will be automatically used if flock(2) is missing.) | |
827 | ||
828 | Here's a mailbox appender for BSD systems. | |
a0d0e21e LW |
829 | |
830 | $LOCK_SH = 1; | |
831 | $LOCK_EX = 2; | |
832 | $LOCK_NB = 4; | |
833 | $LOCK_UN = 8; | |
834 | ||
835 | sub lock { | |
836 | flock(MBOX,$LOCK_EX); | |
837 | # and, in case someone appended | |
838 | # while we were waiting... | |
839 | seek(MBOX, 0, 2); | |
840 | } | |
841 | ||
842 | sub unlock { | |
843 | flock(MBOX,$LOCK_UN); | |
844 | } | |
845 | ||
846 | open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}") | |
847 | or die "Can't open mailbox: $!"; | |
848 | ||
849 | lock(); | |
850 | print MBOX $msg,"\n\n"; | |
851 | unlock(); | |
852 | ||
4633a7c4 LW |
853 | Note that many versions of flock() cannot lock things over the network. |
854 | You need to do locking with fcntl() for that. | |
a0d0e21e LW |
855 | |
856 | =item fork | |
857 | ||
858 | Does a fork(2) system call. Returns the child pid to the parent process | |
4633a7c4 | 859 | and 0 to the child process, or C<undef> if the fork is unsuccessful. |
a0d0e21e LW |
860 | Note: unflushed buffers remain unflushed in both processes, which means |
861 | you may need to set C<$|> ($AUTOFLUSH in English) or call the | |
862 | autoflush() FileHandle method to avoid duplicate output. | |
863 | ||
864 | If you fork() without ever waiting on your children, you will accumulate | |
865 | zombies: | |
866 | ||
4633a7c4 | 867 | $SIG{CHLD} = sub { wait }; |
a0d0e21e LW |
868 | |
869 | There's also the double-fork trick (error checking on | |
870 | fork() returns omitted); | |
871 | ||
872 | unless ($pid = fork) { | |
873 | unless (fork) { | |
874 | exec "what you really wanna do"; | |
875 | die "no exec"; | |
876 | # ... or ... | |
4633a7c4 | 877 | ## (some_perl_code_here) |
a0d0e21e LW |
878 | exit 0; |
879 | } | |
880 | exit 0; | |
881 | } | |
882 | waitpid($pid,0); | |
883 | ||
884 | ||
885 | =item formline PICTURE, LIST | |
886 | ||
4633a7c4 | 887 | This is an internal function used by C<format>s, though you may call it |
a0d0e21e LW |
888 | too. It formats (see L<perlform>) a list of values according to the |
889 | contents of PICTURE, placing the output into the format output | |
4633a7c4 LW |
890 | accumulator, C<$^A> (or $ACCUMULATOR in English). |
891 | Eventually, when a write() is done, the contents of | |
a0d0e21e LW |
892 | C<$^A> are written to some filehandle, but you could also read C<$^A> |
893 | yourself and then set C<$^A> back to "". Note that a format typically | |
894 | does one formline() per line of form, but the formline() function itself | |
748a9306 | 895 | doesn't care how many newlines are embedded in the PICTURE. This means |
4633a7c4 | 896 | that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line. |
748a9306 LW |
897 | You may therefore need to use multiple formlines to implement a single |
898 | record format, just like the format compiler. | |
899 | ||
900 | Be careful if you put double quotes around the picture, since an "C<@>" | |
901 | character may be taken to mean the beginning of an array name. | |
4633a7c4 | 902 | formline() always returns TRUE. See L<perlform> for other examples. |
a0d0e21e LW |
903 | |
904 | =item getc FILEHANDLE | |
905 | ||
906 | =item getc | |
907 | ||
908 | Returns the next character from the input file attached to FILEHANDLE, | |
909 | or a null string at end of file. If FILEHANDLE is omitted, reads from STDIN. | |
4633a7c4 LW |
910 | This is not particularly efficient. It cannot be used to get unbuffered |
911 | single-character | |
912 | ||
913 | if ($BSD_STYLE) { | |
914 | system "stty cbreak </dev/tty >/dev/tty 2>&1"; | |
915 | } | |
916 | else { | |
917 | system "stty", '-icanon', | |
918 | system "stty", 'eol', "\001"; | |
919 | } | |
920 | ||
921 | $key = getc(STDIN); | |
922 | ||
923 | if ($BSD_STYLE) { | |
924 | system "stty -cbreak </dev/tty >/dev/tty 2>&1"; | |
925 | } | |
926 | else { | |
927 | system "stty", 'icanon'; | |
928 | system "stty", 'eol', '^@'; # ascii null | |
929 | } | |
930 | print "\n"; | |
931 | ||
932 | Determination of whether to whether $BSD_STYLE should be set | |
933 | is left as an exercise to the reader. | |
a0d0e21e LW |
934 | |
935 | =item getlogin | |
936 | ||
937 | Returns the current login from F</etc/utmp>, if any. If null, use | |
4633a7c4 | 938 | getpwuid(). |
a0d0e21e LW |
939 | |
940 | $login = getlogin || (getpwuid($<))[0] || "Kilroy"; | |
941 | ||
4633a7c4 LW |
942 | Do not consider getlogin() for authorentication: it is not as |
943 | secure as getpwuid(). | |
944 | ||
a0d0e21e LW |
945 | =item getpeername SOCKET |
946 | ||
947 | Returns the packed sockaddr address of other end of the SOCKET connection. | |
948 | ||
4633a7c4 LW |
949 | use Socket; |
950 | $hersockaddr = getpeername(SOCK); | |
951 | ($port, $iaddr) = unpack_sockaddr_in($hersockaddr); | |
952 | $herhostname = gethostbyaddr($iaddr, AF_INET); | |
953 | $herstraddr = inet_ntoa($iaddr); | |
a0d0e21e LW |
954 | |
955 | =item getpgrp PID | |
956 | ||
957 | Returns the current process group for the specified PID, 0 for the | |
4633a7c4 | 958 | current process. Will raise an exception if used on a machine that |
a0d0e21e LW |
959 | doesn't implement getpgrp(2). If PID is omitted, returns process |
960 | group of current process. | |
961 | ||
962 | =item getppid | |
963 | ||
964 | Returns the process id of the parent process. | |
965 | ||
966 | =item getpriority WHICH,WHO | |
967 | ||
4633a7c4 LW |
968 | Returns the current priority for a process, a process group, or a user. |
969 | (See L<getpriority(2)>.) Will raise a fatal exception if used on a | |
a0d0e21e LW |
970 | machine that doesn't implement getpriority(2). |
971 | ||
972 | =item getpwnam NAME | |
973 | ||
974 | =item getgrnam NAME | |
975 | ||
976 | =item gethostbyname NAME | |
977 | ||
978 | =item getnetbyname NAME | |
979 | ||
980 | =item getprotobyname NAME | |
981 | ||
982 | =item getpwuid UID | |
983 | ||
984 | =item getgrgid GID | |
985 | ||
986 | =item getservbyname NAME,PROTO | |
987 | ||
988 | =item gethostbyaddr ADDR,ADDRTYPE | |
989 | ||
990 | =item getnetbyaddr ADDR,ADDRTYPE | |
991 | ||
992 | =item getprotobynumber NUMBER | |
993 | ||
994 | =item getservbyport PORT,PROTO | |
995 | ||
996 | =item getpwent | |
997 | ||
998 | =item getgrent | |
999 | ||
1000 | =item gethostent | |
1001 | ||
1002 | =item getnetent | |
1003 | ||
1004 | =item getprotoent | |
1005 | ||
1006 | =item getservent | |
1007 | ||
1008 | =item setpwent | |
1009 | ||
1010 | =item setgrent | |
1011 | ||
1012 | =item sethostent STAYOPEN | |
1013 | ||
1014 | =item setnetent STAYOPEN | |
1015 | ||
1016 | =item setprotoent STAYOPEN | |
1017 | ||
1018 | =item setservent STAYOPEN | |
1019 | ||
1020 | =item endpwent | |
1021 | ||
1022 | =item endgrent | |
1023 | ||
1024 | =item endhostent | |
1025 | ||
1026 | =item endnetent | |
1027 | ||
1028 | =item endprotoent | |
1029 | ||
1030 | =item endservent | |
1031 | ||
1032 | These routines perform the same functions as their counterparts in the | |
1033 | system library. Within a list context, the return values from the | |
1034 | various get routines are as follows: | |
1035 | ||
1036 | ($name,$passwd,$uid,$gid, | |
1037 | $quota,$comment,$gcos,$dir,$shell) = getpw* | |
1038 | ($name,$passwd,$gid,$members) = getgr* | |
1039 | ($name,$aliases,$addrtype,$length,@addrs) = gethost* | |
1040 | ($name,$aliases,$addrtype,$net) = getnet* | |
1041 | ($name,$aliases,$proto) = getproto* | |
1042 | ($name,$aliases,$port,$proto) = getserv* | |
1043 | ||
1044 | (If the entry doesn't exist you get a null list.) | |
1045 | ||
1046 | Within a scalar context, you get the name, unless the function was a | |
1047 | lookup by name, in which case you get the other thing, whatever it is. | |
1048 | (If the entry doesn't exist you get the undefined value.) For example: | |
1049 | ||
1050 | $uid = getpwnam | |
1051 | $name = getpwuid | |
1052 | $name = getpwent | |
1053 | $gid = getgrnam | |
1054 | $name = getgrgid | |
1055 | $name = getgrent | |
1056 | etc. | |
1057 | ||
1058 | The $members value returned by I<getgr*()> is a space separated list of | |
1059 | the login names of the members of the group. | |
1060 | ||
1061 | For the I<gethost*()> functions, if the C<h_errno> variable is supported in | |
1062 | C, it will be returned to you via C<$?> if the function call fails. The | |
1063 | @addrs value returned by a successful call is a list of the raw | |
1064 | addresses returned by the corresponding system library call. In the | |
1065 | Internet domain, each address is four bytes long and you can unpack it | |
1066 | by saying something like: | |
1067 | ||
1068 | ($a,$b,$c,$d) = unpack('C4',$addr[0]); | |
1069 | ||
1070 | =item getsockname SOCKET | |
1071 | ||
1072 | Returns the packed sockaddr address of this end of the SOCKET connection. | |
1073 | ||
4633a7c4 LW |
1074 | use Socket; |
1075 | $mysockaddr = getsockname(SOCK); | |
1076 | ($port, $myaddr) = unpack_sockaddr_in($mysockaddr); | |
a0d0e21e LW |
1077 | |
1078 | =item getsockopt SOCKET,LEVEL,OPTNAME | |
1079 | ||
1080 | Returns the socket option requested, or undefined if there is an error. | |
1081 | ||
1082 | =item glob EXPR | |
1083 | ||
1084 | Returns the value of EXPR with filename expansions such as a shell | |
1085 | would do. This is the internal function implementing the <*.*> | |
4633a7c4 | 1086 | operator, except it's easier to use. |
a0d0e21e LW |
1087 | |
1088 | =item gmtime EXPR | |
1089 | ||
1090 | Converts a time as returned by the time function to a 9-element array | |
4633a7c4 LW |
1091 | with the time localized for the standard Greenwich timezone. |
1092 | Typically used as follows: | |
a0d0e21e LW |
1093 | |
1094 | ||
1095 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = | |
1096 | gmtime(time); | |
1097 | ||
1098 | All array elements are numeric, and come straight out of a struct tm. | |
1099 | In particular this means that $mon has the range 0..11 and $wday has | |
1100 | the range 0..6. If EXPR is omitted, does C<gmtime(time())>. | |
1101 | ||
1102 | =item goto LABEL | |
1103 | ||
748a9306 LW |
1104 | =item goto EXPR |
1105 | ||
a0d0e21e LW |
1106 | =item goto &NAME |
1107 | ||
1108 | The goto-LABEL form finds the statement labeled with LABEL and resumes | |
1109 | execution there. It may not be used to go into any construct that | |
1110 | requires initialization, such as a subroutine or a foreach loop. It | |
1111 | also can't be used to go into a construct that is optimized away. It | |
1112 | can be used to go almost anywhere else within the dynamic scope, | |
1113 | including out of subroutines, but it's usually better to use some other | |
1114 | construct such as last or die. The author of Perl has never felt the | |
1115 | need to use this form of goto (in Perl, that is--C is another matter). | |
1116 | ||
748a9306 LW |
1117 | The goto-EXPR form expects a label name, whose scope will be resolved |
1118 | dynamically. This allows for computed gotos per FORTRAN, but isn't | |
1119 | necessarily recommended if you're optimizing for maintainability: | |
1120 | ||
1121 | goto ("FOO", "BAR", "GLARCH")[$i]; | |
1122 | ||
a0d0e21e LW |
1123 | The goto-&NAME form is highly magical, and substitutes a call to the |
1124 | named subroutine for the currently running subroutine. This is used by | |
1125 | AUTOLOAD subroutines that wish to load another subroutine and then | |
1126 | pretend that the other subroutine had been called in the first place | |
1127 | (except that any modifications to @_ in the current subroutine are | |
1128 | propagated to the other subroutine.) After the goto, not even caller() | |
1129 | will be able to tell that this routine was called first. | |
1130 | ||
1131 | =item grep BLOCK LIST | |
1132 | ||
1133 | =item grep EXPR,LIST | |
1134 | ||
1135 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting | |
1136 | $_ to each element) and returns the list value consisting of those | |
1137 | elements for which the expression evaluated to TRUE. In a scalar | |
1138 | context, returns the number of times the expression was TRUE. | |
1139 | ||
1140 | @foo = grep(!/^#/, @bar); # weed out comments | |
1141 | ||
1142 | or equivalently, | |
1143 | ||
1144 | @foo = grep {!/^#/} @bar; # weed out comments | |
1145 | ||
1146 | Note that, since $_ is a reference into the list value, it can be used | |
1147 | to modify the elements of the array. While this is useful and | |
1148 | supported, it can cause bizarre results if the LIST is not a named | |
1149 | array. | |
1150 | ||
1151 | =item hex EXPR | |
1152 | ||
4633a7c4 LW |
1153 | Interprets EXPR as a hex string and returns the corresponding decimal |
1154 | value. (To convert strings that might start with 0 or 0x see | |
1155 | oct().) If EXPR is omitted, uses $_. | |
a0d0e21e LW |
1156 | |
1157 | =item import | |
1158 | ||
1159 | There is no built-in import() function. It is merely an ordinary | |
4633a7c4 | 1160 | method (subroutine) defined (or inherited) by modules that wish to export |
a0d0e21e | 1161 | names to another module. The use() function calls the import() method |
4633a7c4 | 1162 | for the package used. See also L</use>, L<perlmod>, and L<Exporter>. |
a0d0e21e LW |
1163 | |
1164 | =item index STR,SUBSTR,POSITION | |
1165 | ||
1166 | =item index STR,SUBSTR | |
1167 | ||
4633a7c4 LW |
1168 | Returns the position of the first occurrence of SUBSTR in STR at or after |
1169 | POSITION. If POSITION is omitted, starts searching from the beginning of | |
1170 | the string. The return value is based at 0 (or whatever you've set the $[ | |
1171 | variable to--but don't do that). If the substring is not found, returns | |
a0d0e21e LW |
1172 | one less than the base, ordinarily -1. |
1173 | ||
1174 | =item int EXPR | |
1175 | ||
1176 | Returns the integer portion of EXPR. If EXPR is omitted, uses $_. | |
1177 | ||
1178 | =item ioctl FILEHANDLE,FUNCTION,SCALAR | |
1179 | ||
1180 | Implements the ioctl(2) function. You'll probably have to say | |
1181 | ||
4633a7c4 | 1182 | require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph |
a0d0e21e | 1183 | |
4633a7c4 | 1184 | first to get the correct function definitions. If F<ioctl.ph> doesn't |
a0d0e21e | 1185 | exist or doesn't have the correct definitions you'll have to roll your |
4633a7c4 LW |
1186 | own, based on your C header files such as F<E<lt>sys/ioctl.hE<gt>>. |
1187 | (There is a Perl script called B<h2ph> that comes with the Perl kit which | |
1188 | may help you in this, but it's non-trivial.) SCALAR will be read and/or | |
1189 | written depending on the FUNCTION--a pointer to the string value of SCALAR | |
1190 | will be passed as the third argument of the actual ioctl call. (If SCALAR | |
1191 | has no string value but does have a numeric value, that value will be | |
1192 | passed rather than a pointer to the string value. To guarantee this to be | |
1193 | TRUE, add a 0 to the scalar before using it.) The pack() and unpack() | |
1194 | functions are useful for manipulating the values of structures used by | |
1195 | ioctl(). The following example sets the erase character to DEL. | |
a0d0e21e LW |
1196 | |
1197 | require 'ioctl.ph'; | |
4633a7c4 LW |
1198 | $getp = &TIOCGETP; |
1199 | die "NO TIOCGETP" if $@ || !$getp; | |
a0d0e21e | 1200 | $sgttyb_t = "ccccs"; # 4 chars and a short |
4633a7c4 | 1201 | if (ioctl(STDIN,$getp,$sgttyb)) { |
a0d0e21e LW |
1202 | @ary = unpack($sgttyb_t,$sgttyb); |
1203 | $ary[2] = 127; | |
1204 | $sgttyb = pack($sgttyb_t,@ary); | |
4633a7c4 | 1205 | ioctl(STDIN,&TIOCSETP,$sgttyb) |
a0d0e21e LW |
1206 | || die "Can't ioctl: $!"; |
1207 | } | |
1208 | ||
1209 | The return value of ioctl (and fcntl) is as follows: | |
1210 | ||
1211 | if OS returns: then Perl returns: | |
1212 | -1 undefined value | |
1213 | 0 string "0 but true" | |
1214 | anything else that number | |
1215 | ||
1216 | Thus Perl returns TRUE on success and FALSE on failure, yet you can | |
1217 | still easily determine the actual value returned by the operating | |
1218 | system: | |
1219 | ||
1220 | ($retval = ioctl(...)) || ($retval = -1); | |
1221 | printf "System returned %d\n", $retval; | |
1222 | ||
1223 | =item join EXPR,LIST | |
1224 | ||
1225 | Joins the separate strings of LIST or ARRAY into a single string with | |
1226 | fields separated by the value of EXPR, and returns the string. | |
1227 | Example: | |
1228 | ||
1229 | $_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); | |
1230 | ||
1231 | See L<perlfunc/split>. | |
1232 | ||
1233 | =item keys ASSOC_ARRAY | |
1234 | ||
1235 | Returns a normal array consisting of all the keys of the named | |
1236 | associative array. (In a scalar context, returns the number of keys.) | |
1237 | The keys are returned in an apparently random order, but it is the same | |
1238 | order as either the values() or each() function produces (given that | |
1239 | the associative array has not been modified). Here is yet another way | |
1240 | to print your environment: | |
1241 | ||
1242 | @keys = keys %ENV; | |
1243 | @values = values %ENV; | |
1244 | while ($#keys >= 0) { | |
1245 | print pop(@keys), '=', pop(@values), "\n"; | |
1246 | } | |
1247 | ||
1248 | or how about sorted by key: | |
1249 | ||
1250 | foreach $key (sort(keys %ENV)) { | |
1251 | print $key, '=', $ENV{$key}, "\n"; | |
1252 | } | |
1253 | ||
4633a7c4 LW |
1254 | To sort an array by value, you'll need to use a C<sort{}> |
1255 | function. Here's a descending numeric sort by value: | |
1256 | ||
1257 | foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash)) { | |
1258 | printf "%4d %s\n", $hash{$key}, $key; | |
1259 | } | |
1260 | ||
a0d0e21e LW |
1261 | =item kill LIST |
1262 | ||
4633a7c4 LW |
1263 | Sends a signal to a list of processes. The first element of |
1264 | the list must be the signal to send. Returns the number of | |
1265 | processes successfully signaled. | |
a0d0e21e LW |
1266 | |
1267 | $cnt = kill 1, $child1, $child2; | |
1268 | kill 9, @goners; | |
1269 | ||
4633a7c4 LW |
1270 | Unlike in the shell, in Perl if the I<SIGNAL> is negative, it kills |
1271 | process groups instead of processes. (On System V, a negative I<PROCESS> | |
1272 | number will also kill process groups, but that's not portable.) That | |
1273 | means you usually want to use positive not negative signals. You may also | |
1274 | use a signal name in quotes. See the L<perlipc/"Signals"> man page for details. | |
a0d0e21e LW |
1275 | |
1276 | =item last LABEL | |
1277 | ||
1278 | =item last | |
1279 | ||
1280 | The C<last> command is like the C<break> statement in C (as used in | |
1281 | loops); it immediately exits the loop in question. If the LABEL is | |
1282 | omitted, the command refers to the innermost enclosing loop. The | |
1283 | C<continue> block, if any, is not executed: | |
1284 | ||
4633a7c4 LW |
1285 | LINE: while (<STDIN>) { |
1286 | last LINE if /^$/; # exit when done with header | |
a0d0e21e LW |
1287 | ... |
1288 | } | |
1289 | ||
1290 | =item lc EXPR | |
1291 | ||
1292 | Returns an lowercased version of EXPR. This is the internal function | |
4633a7c4 LW |
1293 | implementing the \L escape in double-quoted strings. |
1294 | Should respect any POSIX setlocale() settings. | |
a0d0e21e LW |
1295 | |
1296 | =item lcfirst EXPR | |
1297 | ||
1298 | Returns the value of EXPR with the first character lowercased. This is | |
1299 | the internal function implementing the \l escape in double-quoted strings. | |
4633a7c4 | 1300 | Should respect any POSIX setlocale() settings. |
a0d0e21e LW |
1301 | |
1302 | =item length EXPR | |
1303 | ||
1304 | Returns the length in characters of the value of EXPR. If EXPR is | |
1305 | omitted, returns length of $_. | |
1306 | ||
1307 | =item link OLDFILE,NEWFILE | |
1308 | ||
1309 | Creates a new filename linked to the old filename. Returns 1 for | |
1310 | success, 0 otherwise. | |
1311 | ||
1312 | =item listen SOCKET,QUEUESIZE | |
1313 | ||
1314 | Does the same thing that the listen system call does. Returns TRUE if | |
4633a7c4 | 1315 | it succeeded, FALSE otherwise. See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
1316 | |
1317 | =item local EXPR | |
1318 | ||
1319 | In general, you should be using "my" instead of "local", because it's | |
748a9306 LW |
1320 | faster and safer. Format variables often use "local" though, as |
1321 | do other variables whose current value must be visible to called | |
a0d0e21e LW |
1322 | subroutines. This is known as dynamic scoping. Lexical scoping is |
1323 | done with "my", which works more like C's auto declarations. | |
1324 | ||
1325 | A local modifies the listed variables to be local to the enclosing block, | |
1326 | subroutine, eval or "do". If more than one value is listed, the list | |
1327 | must be placed in parens. All the listed elements must be legal | |
1328 | lvalues. This operator works by saving the current values of those | |
1329 | variables in LIST on a hidden stack and restoring them upon exiting the | |
1330 | block, subroutine or eval. This means that called subroutines can also | |
1331 | reference the local variable, but not the global one. The LIST may be | |
1332 | assigned to if desired, which allows you to initialize your local | |
1333 | variables. (If no initializer is given for a particular variable, it | |
1334 | is created with an undefined value.) Commonly this is used to name the | |
1335 | parameters to a subroutine. Examples: | |
1336 | ||
1337 | sub RANGEVAL { | |
1338 | local($min, $max, $thunk) = @_; | |
1339 | local $result = ''; | |
1340 | local $i; | |
1341 | ||
1342 | # Presumably $thunk makes reference to $i | |
1343 | ||
1344 | for ($i = $min; $i < $max; $i++) { | |
1345 | $result .= eval $thunk; | |
1346 | } | |
1347 | ||
1348 | $result; | |
1349 | } | |
1350 | ||
1351 | ||
1352 | if ($sw eq '-v') { | |
1353 | # init local array with global array | |
1354 | local @ARGV = @ARGV; | |
1355 | unshift(@ARGV,'echo'); | |
1356 | system @ARGV; | |
1357 | } | |
1358 | # @ARGV restored | |
1359 | ||
1360 | ||
1361 | # temporarily add to digits associative array | |
1362 | if ($base12) { | |
1363 | # (NOTE: not claiming this is efficient!) | |
1364 | local(%digits) = (%digits,'t',10,'e',11); | |
1365 | parse_num(); | |
1366 | } | |
1367 | ||
1368 | Note that local() is a run-time command, and so gets executed every | |
748a9306 | 1369 | time through a loop. In Perl 4 it used more stack storage each |
a0d0e21e LW |
1370 | time until the loop was exited. Perl 5 reclaims the space each time |
1371 | through, but it's still more efficient to declare your variables | |
1372 | outside the loop. | |
1373 | ||
748a9306 | 1374 | A local is simply a modifier on an lvalue expression. |
a0d0e21e LW |
1375 | When you assign to a localized EXPR, the local doesn't change whether |
1376 | EXPR is viewed as a scalar or an array. So | |
1377 | ||
1378 | local($foo) = <STDIN>; | |
1379 | local @FOO = <STDIN>; | |
1380 | ||
1381 | both supply a list context to the righthand side, while | |
1382 | ||
1383 | local $foo = <STDIN>; | |
1384 | ||
1385 | supplies a scalar context. | |
1386 | ||
1387 | =item localtime EXPR | |
1388 | ||
1389 | Converts a time as returned by the time function to a 9-element array | |
1390 | with the time analyzed for the local timezone. Typically used as | |
1391 | follows: | |
1392 | ||
1393 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = | |
1394 | localtime(time); | |
1395 | ||
1396 | All array elements are numeric, and come straight out of a struct tm. | |
1397 | In particular this means that $mon has the range 0..11 and $wday has | |
1398 | the range 0..6. If EXPR is omitted, does localtime(time). | |
1399 | ||
1400 | In a scalar context, prints out the ctime(3) value: | |
1401 | ||
1402 | $now_string = localtime; # e.g. "Thu Oct 13 04:54:34 1994" | |
1403 | ||
1404 | See also L<perlmod/timelocal> and the strftime(3) function available | |
1405 | via the POSIX modulie. | |
1406 | ||
1407 | =item log EXPR | |
1408 | ||
1409 | Returns logarithm (base I<e>) of EXPR. If EXPR is omitted, returns log | |
1410 | of $_. | |
1411 | ||
1412 | =item lstat FILEHANDLE | |
1413 | ||
1414 | =item lstat EXPR | |
1415 | ||
1416 | Does the same thing as the stat() function, but stats a symbolic link | |
1417 | instead of the file the symbolic link points to. If symbolic links are | |
1418 | unimplemented on your system, a normal stat() is done. | |
1419 | ||
1420 | =item m// | |
1421 | ||
1422 | The match operator. See L<perlop>. | |
1423 | ||
1424 | =item map BLOCK LIST | |
1425 | ||
1426 | =item map EXPR,LIST | |
1427 | ||
1428 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each | |
1429 | element) and returns the list value composed of the results of each such | |
1430 | evaluation. Evaluates BLOCK or EXPR in a list context, so each element of LIST | |
1431 | may produce zero, one, or more elements in the returned value. | |
1432 | ||
1433 | @chars = map(chr, @nums); | |
1434 | ||
1435 | translates a list of numbers to the corresponding characters. And | |
1436 | ||
4633a7c4 | 1437 | %hash = map { getkey($_) => $_ } @array; |
a0d0e21e LW |
1438 | |
1439 | is just a funny way to write | |
1440 | ||
1441 | %hash = (); | |
1442 | foreach $_ (@array) { | |
4633a7c4 | 1443 | $hash{getkey($_)} = $_; |
a0d0e21e LW |
1444 | } |
1445 | ||
1446 | =item mkdir FILENAME,MODE | |
1447 | ||
1448 | Creates the directory specified by FILENAME, with permissions specified | |
1449 | by MODE (as modified by umask). If it succeeds it returns 1, otherwise | |
1450 | it returns 0 and sets $! (errno). | |
1451 | ||
1452 | =item msgctl ID,CMD,ARG | |
1453 | ||
4633a7c4 | 1454 | Calls the System V IPC function msgctl(2). If CMD is &IPC_STAT, then ARG |
a0d0e21e LW |
1455 | must be a variable which will hold the returned msqid_ds structure. |
1456 | Returns like ioctl: the undefined value for error, "0 but true" for | |
1457 | zero, or the actual return value otherwise. | |
1458 | ||
1459 | =item msgget KEY,FLAGS | |
1460 | ||
4633a7c4 | 1461 | Calls the System V IPC function msgget(2). Returns the message queue id, |
a0d0e21e LW |
1462 | or the undefined value if there is an error. |
1463 | ||
1464 | =item msgsnd ID,MSG,FLAGS | |
1465 | ||
1466 | Calls the System V IPC function msgsnd to send the message MSG to the | |
1467 | message queue ID. MSG must begin with the long integer message type, | |
1468 | which may be created with C<pack("L", $type)>. Returns TRUE if | |
1469 | successful, or FALSE if there is an error. | |
1470 | ||
1471 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS | |
1472 | ||
1473 | Calls the System V IPC function msgrcv to receive a message from | |
1474 | message queue ID into variable VAR with a maximum message size of | |
1475 | SIZE. Note that if a message is received, the message type will be the | |
1476 | first thing in VAR, and the maximum length of VAR is SIZE plus the size | |
1477 | of the message type. Returns TRUE if successful, or FALSE if there is | |
1478 | an error. | |
1479 | ||
1480 | =item my EXPR | |
1481 | ||
1482 | A "my" declares the listed variables to be local (lexically) to the | |
4633a7c4 | 1483 | enclosing block, subroutine, C<eval>, or C<do/require/use>'d file. If more than one value is |
a0d0e21e LW |
1484 | listed, the list must be placed in parens. All the listed elements |
1485 | must be legal lvalues. Only alphanumeric identifiers may be lexically | |
1486 | scoped--magical builtins like $/ must be localized with "local" | |
4633a7c4 LW |
1487 | instead. You also cannot use my() on a package variable. |
1488 | In particular, you're not allowed to say | |
a0d0e21e | 1489 | |
4633a7c4 LW |
1490 | my $_; # Illegal! |
1491 | my $pack::$var; # Illegal! | |
a0d0e21e LW |
1492 | |
1493 | Unlike the "local" declaration, variables declared with "my" | |
1494 | are totally hidden from the outside world, including any called | |
1495 | subroutines (even if it's the same subroutine--every call gets its own | |
4633a7c4 | 1496 | copy). |
a0d0e21e LW |
1497 | |
1498 | (An eval(), however, can see the lexical variables of the scope it is | |
1499 | being evaluated in so long as the names aren't hidden by declarations within | |
1500 | the eval() itself. See L<perlref>.) | |
1501 | ||
1502 | The EXPR may be assigned to if desired, which allows you to initialize | |
1503 | your variables. (If no initializer is given for a particular | |
1504 | variable, it is created with an undefined value.) Commonly this is | |
1505 | used to name the parameters to a subroutine. Examples: | |
1506 | ||
1507 | sub RANGEVAL { | |
1508 | my($min, $max, $thunk) = @_; | |
1509 | my $result = ''; | |
1510 | my $i; | |
1511 | ||
1512 | # Presumably $thunk makes reference to $i | |
1513 | ||
1514 | for ($i = $min; $i < $max; $i++) { | |
1515 | $result .= eval $thunk; | |
1516 | } | |
1517 | ||
1518 | $result; | |
1519 | } | |
1520 | ||
1521 | ||
1522 | if ($sw eq '-v') { | |
1523 | # init my array with global array | |
1524 | my @ARGV = @ARGV; | |
1525 | unshift(@ARGV,'echo'); | |
1526 | system @ARGV; | |
1527 | } | |
1528 | # Outer @ARGV again visible | |
1529 | ||
748a9306 LW |
1530 | The "my" is simply a modifier on something you might assign to. |
1531 | So when you do assign to the EXPR, the "my" doesn't change whether | |
a0d0e21e LW |
1532 | EXPR is viewed as a scalar or an array. So |
1533 | ||
748a9306 | 1534 | my ($foo) = <STDIN>; |
a0d0e21e LW |
1535 | my @FOO = <STDIN>; |
1536 | ||
1537 | both supply a list context to the righthand side, while | |
1538 | ||
1539 | my $foo = <STDIN>; | |
1540 | ||
748a9306 LW |
1541 | supplies a scalar context. But the following only declares one variable: |
1542 | ||
1543 | my $foo, $bar = 1; | |
1544 | ||
1545 | That has the same effect as | |
1546 | ||
1547 | my $foo; | |
1548 | $bar = 1; | |
1549 | ||
1550 | The declared variable is not introduced (is not visible) until after | |
1551 | the current statement. Thus, | |
1552 | ||
1553 | my $x = $x; | |
1554 | ||
1555 | can be used to initialize the new $x with the value of the old $x, and | |
1556 | the expression | |
1557 | ||
1558 | my $x = 123 and $x == 123 | |
1559 | ||
1560 | is false unless the old $x happened to have the value 123. | |
a0d0e21e LW |
1561 | |
1562 | Some users may wish to encourage the use of lexically scoped variables. | |
1563 | As an aid to catching implicit references to package variables, | |
1564 | if you say | |
1565 | ||
1566 | use strict 'vars'; | |
1567 | ||
1568 | then any variable reference from there to the end of the enclosing | |
1569 | block must either refer to a lexical variable, or must be fully | |
1570 | qualified with the package name. A compilation error results | |
1571 | otherwise. An inner block may countermand this with S<"no strict 'vars'">. | |
1572 | ||
4633a7c4 LW |
1573 | Variables declared with "my" are not part of any package and |
1574 | are therefore never fully qualified with the package name. | |
1575 | However, you may declare a "my" variable at the outer most | |
1576 | scope of a file to totally hide any such identifiers from the | |
1577 | outside world. This is similar to a C's static variables | |
1578 | at the file level. To do this with a subroutine requires the | |
1579 | use of a closure (anonymous function): | |
1580 | ||
1581 | my $secret_version = '1.001-beta'; | |
1582 | my $secret_sub = { print $secret_version }; | |
1583 | &$secret_sub(); | |
1584 | ||
1585 | This does not work with object methods, however; | |
1586 | all object methods have to be in the symbol table of some | |
1587 | package to be found. | |
1588 | ||
1589 | Just because the "my" variable is lexically scoped doesn't mean that | |
1590 | within a function it works like a C static. Here's a mechanism for giving | |
1591 | a function private variables with both lexical scoping and a static | |
1592 | lifetime. | |
1593 | ||
1594 | #!/usr/bin/perl -l | |
1595 | $var = "global"; | |
1596 | { my $count = 0; | |
1597 | my $var = "static"; | |
1598 | sub foo { | |
1599 | $count++; | |
1600 | print "$var (call # $count)"; | |
1601 | } | |
1602 | } | |
1603 | print $var; foo(); | |
1604 | print $var; foo(); | |
1605 | print $var; foo(); | |
1606 | ||
a0d0e21e LW |
1607 | =item next LABEL |
1608 | ||
1609 | =item next | |
1610 | ||
1611 | The C<next> command is like the C<continue> statement in C; it starts | |
1612 | the next iteration of the loop: | |
1613 | ||
4633a7c4 LW |
1614 | LINE: while (<STDIN>) { |
1615 | next LINE if /^#/; # discard comments | |
a0d0e21e LW |
1616 | ... |
1617 | } | |
1618 | ||
1619 | Note that if there were a C<continue> block on the above, it would get | |
1620 | executed even on discarded lines. If the LABEL is omitted, the command | |
1621 | refers to the innermost enclosing loop. | |
1622 | ||
1623 | =item no Module LIST | |
1624 | ||
1625 | See the "use" function, which "no" is the opposite of. | |
1626 | ||
1627 | =item oct EXPR | |
1628 | ||
4633a7c4 LW |
1629 | Interprets EXPR as an octal string and returns the corresponding |
1630 | decimal value. (If EXPR happens to start off with 0x, interprets it as | |
1631 | a hex string instead.) The following will handle decimal, octal, and | |
1632 | hex in the standard Perl or C notation: | |
a0d0e21e LW |
1633 | |
1634 | $val = oct($val) if $val =~ /^0/; | |
1635 | ||
1636 | If EXPR is omitted, uses $_. | |
1637 | ||
1638 | =item open FILEHANDLE,EXPR | |
1639 | ||
1640 | =item open FILEHANDLE | |
1641 | ||
1642 | Opens the file whose filename is given by EXPR, and associates it with | |
4633a7c4 LW |
1643 | FILEHANDLE. If FILEHANDLE is an expression, its value is used as the name |
1644 | of the real filehandle wanted. If EXPR is omitted, the scalar variable of | |
1645 | the same name as the FILEHANDLE contains the filename. If the filename | |
1646 | begins with "<" or nothing, the file is opened for input. If the filename | |
1647 | begins with ">", the file is opened for output. If the filename begins | |
1648 | with ">>", the file is opened for appending. (You can put a '+' in front | |
1649 | of the '>' or '<' to indicate that you want both read and write access to | |
1650 | the file.) If the filename begins with "|", the filename is interpreted | |
1651 | as a command to which output is to be piped, and if the filename ends with | |
1652 | a "|", the filename is interpreted See L<perlipc/"Using open() for IPC"> | |
1653 | for more examples of this. as command which pipes input to us. (You may | |
1654 | not have a command that pipes both in and out, but see See L<open2>, | |
1655 | L<open3>, and L<perlipc/"Bidirectional Communication"> for alternatives.) | |
1656 | Opening '-' opens STDIN and opening '>-' opens STDOUT. Open returns | |
1657 | non-zero upon success, the undefined value otherwise. If the open | |
1658 | involved a pipe, the return value happens to be the pid of the | |
1659 | subprocess. Examples: | |
a0d0e21e LW |
1660 | |
1661 | $ARTICLE = 100; | |
1662 | open ARTICLE or die "Can't find article $ARTICLE: $!\n"; | |
1663 | while (<ARTICLE>) {... | |
1664 | ||
1665 | open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved) | |
1666 | ||
4633a7c4 | 1667 | open(ARTICLE, "caesar <$article |"); # decrypt article |
a0d0e21e | 1668 | |
4633a7c4 | 1669 | open(EXTRACT, "|sort >/tmp/Tmp$$"); # $$ is our process id |
a0d0e21e LW |
1670 | |
1671 | # process argument list of files along with any includes | |
1672 | ||
1673 | foreach $file (@ARGV) { | |
1674 | process($file, 'fh00'); | |
1675 | } | |
1676 | ||
1677 | sub process { | |
1678 | local($filename, $input) = @_; | |
1679 | $input++; # this is a string increment | |
1680 | unless (open($input, $filename)) { | |
1681 | print STDERR "Can't open $filename: $!\n"; | |
1682 | return; | |
1683 | } | |
1684 | ||
1685 | while (<$input>) { # note use of indirection | |
1686 | if (/^#include "(.*)"/) { | |
1687 | process($1, $input); | |
1688 | next; | |
1689 | } | |
1690 | ... # whatever | |
1691 | } | |
1692 | } | |
1693 | ||
1694 | You may also, in the Bourne shell tradition, specify an EXPR beginning | |
1695 | with ">&", in which case the rest of the string is interpreted as the | |
1696 | name of a filehandle (or file descriptor, if numeric) which is to be | |
1697 | duped and opened. You may use & after >, >>, <, +>, +>> and +<. The | |
1698 | mode you specify should match the mode of the original filehandle. | |
1699 | Here is a script that saves, redirects, and restores STDOUT and | |
1700 | STDERR: | |
1701 | ||
1702 | #!/usr/bin/perl | |
1703 | open(SAVEOUT, ">&STDOUT"); | |
1704 | open(SAVEERR, ">&STDERR"); | |
1705 | ||
1706 | open(STDOUT, ">foo.out") || die "Can't redirect stdout"; | |
1707 | open(STDERR, ">&STDOUT") || die "Can't dup stdout"; | |
1708 | ||
1709 | select(STDERR); $| = 1; # make unbuffered | |
1710 | select(STDOUT); $| = 1; # make unbuffered | |
1711 | ||
1712 | print STDOUT "stdout 1\n"; # this works for | |
1713 | print STDERR "stderr 1\n"; # subprocesses too | |
1714 | ||
1715 | close(STDOUT); | |
1716 | close(STDERR); | |
1717 | ||
1718 | open(STDOUT, ">&SAVEOUT"); | |
1719 | open(STDERR, ">&SAVEERR"); | |
1720 | ||
1721 | print STDOUT "stdout 2\n"; | |
1722 | print STDERR "stderr 2\n"; | |
1723 | ||
1724 | ||
1725 | If you specify "<&=N", where N is a number, then Perl will do an | |
4633a7c4 LW |
1726 | equivalent of C's fdopen() of that file descriptor; this is more |
1727 | parsimonious of file descriptors. For example: | |
a0d0e21e LW |
1728 | |
1729 | open(FILEHANDLE, "<&=$fd") | |
1730 | ||
1731 | If you open a pipe on the command "-", i.e. either "|-" or "-|", then | |
1732 | there is an implicit fork done, and the return value of open is the pid | |
1733 | of the child within the parent process, and 0 within the child | |
1734 | process. (Use defined($pid) to determine whether the open was successful.) | |
1735 | The filehandle behaves normally for the parent, but i/o to that | |
1736 | filehandle is piped from/to the STDOUT/STDIN of the child process. | |
1737 | In the child process the filehandle isn't opened--i/o happens from/to | |
1738 | the new STDOUT or STDIN. Typically this is used like the normal | |
1739 | piped open when you want to exercise more control over just how the | |
1740 | pipe command gets executed, such as when you are running setuid, and | |
4633a7c4 LW |
1741 | don't want to have to scan shell commands for metacharacters. |
1742 | The following pairs are more or less equivalent: | |
a0d0e21e LW |
1743 | |
1744 | open(FOO, "|tr '[a-z]' '[A-Z]'"); | |
1745 | open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]'; | |
1746 | ||
1747 | open(FOO, "cat -n '$file'|"); | |
1748 | open(FOO, "-|") || exec 'cat', '-n', $file; | |
1749 | ||
4633a7c4 LW |
1750 | See L<perlipc/"Safe Pipe Opens"> for more examples of this. |
1751 | ||
a0d0e21e LW |
1752 | Explicitly closing any piped filehandle causes the parent process to |
1753 | wait for the child to finish, and returns the status value in $?. | |
1754 | Note: on any operation which may do a fork, unflushed buffers remain | |
1755 | unflushed in both processes, which means you may need to set $| to | |
1756 | avoid duplicate output. | |
1757 | ||
1758 | The filename that is passed to open will have leading and trailing | |
1759 | whitespace deleted. In order to open a file with arbitrary weird | |
1760 | characters in it, it's necessary to protect any leading and trailing | |
1761 | whitespace thusly: | |
1762 | ||
1763 | $file =~ s#^(\s)#./$1#; | |
1764 | open(FOO, "< $file\0"); | |
1765 | ||
1766 | =item opendir DIRHANDLE,EXPR | |
1767 | ||
1768 | Opens a directory named EXPR for processing by readdir(), telldir(), | |
1769 | seekdir(), rewinddir() and closedir(). Returns TRUE if successful. | |
1770 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. | |
1771 | ||
1772 | =item ord EXPR | |
1773 | ||
1774 | Returns the numeric ascii value of the first character of EXPR. If | |
1775 | EXPR is omitted, uses $_. | |
1776 | ||
1777 | =item pack TEMPLATE,LIST | |
1778 | ||
1779 | Takes an array or list of values and packs it into a binary structure, | |
1780 | returning the string containing the structure. The TEMPLATE is a | |
1781 | sequence of characters that give the order and type of values, as | |
1782 | follows: | |
1783 | ||
1784 | A An ascii string, will be space padded. | |
1785 | a An ascii string, will be null padded. | |
1786 | b A bit string (ascending bit order, like vec()). | |
1787 | B A bit string (descending bit order). | |
1788 | h A hex string (low nybble first). | |
1789 | H A hex string (high nybble first). | |
1790 | ||
1791 | c A signed char value. | |
1792 | C An unsigned char value. | |
1793 | s A signed short value. | |
1794 | S An unsigned short value. | |
1795 | i A signed integer value. | |
1796 | I An unsigned integer value. | |
1797 | l A signed long value. | |
1798 | L An unsigned long value. | |
1799 | ||
1800 | n A short in "network" order. | |
1801 | N A long in "network" order. | |
1802 | v A short in "VAX" (little-endian) order. | |
1803 | V A long in "VAX" (little-endian) order. | |
1804 | ||
1805 | f A single-precision float in the native format. | |
1806 | d A double-precision float in the native format. | |
1807 | ||
1808 | p A pointer to a null-terminated string. | |
1809 | P A pointer to a structure (fixed-length string). | |
1810 | ||
1811 | u A uuencoded string. | |
1812 | ||
1813 | x A null byte. | |
1814 | X Back up a byte. | |
1815 | @ Null fill to absolute position. | |
1816 | ||
1817 | Each letter may optionally be followed by a number which gives a repeat | |
1818 | count. With all types except "a", "A", "b", "B", "h" and "H", and "P" the | |
1819 | pack function will gobble up that many values from the LIST. A * for the | |
1820 | repeat count means to use however many items are left. The "a" and "A" | |
1821 | types gobble just one value, but pack it as a string of length count, | |
1822 | padding with nulls or spaces as necessary. (When unpacking, "A" strips | |
1823 | trailing spaces and nulls, but "a" does not.) Likewise, the "b" and "B" | |
1824 | fields pack a string that many bits long. The "h" and "H" fields pack a | |
1825 | string that many nybbles long. The "P" packs a pointer to a structure of | |
1826 | the size indicated by the length. Real numbers (floats and doubles) are | |
1827 | in the native machine format only; due to the multiplicity of floating | |
1828 | formats around, and the lack of a standard "network" representation, no | |
1829 | facility for interchange has been made. This means that packed floating | |
1830 | point data written on one machine may not be readable on another - even if | |
1831 | both use IEEE floating point arithmetic (as the endian-ness of the memory | |
1832 | representation is not part of the IEEE spec). Note that Perl uses doubles | |
1833 | internally for all numeric calculation, and converting from double into | |
1834 | float and thence back to double again will lose precision (i.e. | |
1835 | C<unpack("f", pack("f", $foo)>) will not in general equal $foo). | |
1836 | ||
1837 | Examples: | |
1838 | ||
1839 | $foo = pack("cccc",65,66,67,68); | |
1840 | # foo eq "ABCD" | |
1841 | $foo = pack("c4",65,66,67,68); | |
1842 | # same thing | |
1843 | ||
1844 | $foo = pack("ccxxcc",65,66,67,68); | |
1845 | # foo eq "AB\0\0CD" | |
1846 | ||
1847 | $foo = pack("s2",1,2); | |
1848 | # "\1\0\2\0" on little-endian | |
1849 | # "\0\1\0\2" on big-endian | |
1850 | ||
1851 | $foo = pack("a4","abcd","x","y","z"); | |
1852 | # "abcd" | |
1853 | ||
1854 | $foo = pack("aaaa","abcd","x","y","z"); | |
1855 | # "axyz" | |
1856 | ||
1857 | $foo = pack("a14","abcdefg"); | |
1858 | # "abcdefg\0\0\0\0\0\0\0" | |
1859 | ||
1860 | $foo = pack("i9pl", gmtime); | |
1861 | # a real struct tm (on my system anyway) | |
1862 | ||
1863 | sub bintodec { | |
1864 | unpack("N", pack("B32", substr("0" x 32 . shift, -32))); | |
1865 | } | |
1866 | ||
1867 | The same template may generally also be used in the unpack function. | |
1868 | ||
1869 | =item pipe READHANDLE,WRITEHANDLE | |
1870 | ||
1871 | Opens a pair of connected pipes like the corresponding system call. | |
1872 | Note that if you set up a loop of piped processes, deadlock can occur | |
1873 | unless you are very careful. In addition, note that Perl's pipes use | |
1874 | stdio buffering, so you may need to set $| to flush your WRITEHANDLE | |
1875 | after each command, depending on the application. | |
1876 | ||
4633a7c4 LW |
1877 | See L<open2>, L<open3>, and L<perlipc/"Bidirectional Communication"> |
1878 | for examples of such things. | |
1879 | ||
a0d0e21e LW |
1880 | =item pop ARRAY |
1881 | ||
1882 | Pops and returns the last value of the array, shortening the array by | |
1883 | 1. Has a similar effect to | |
1884 | ||
1885 | $tmp = $ARRAY[$#ARRAY--]; | |
1886 | ||
1887 | If there are no elements in the array, returns the undefined value. | |
1888 | ||
1889 | =item pos SCALAR | |
1890 | ||
4633a7c4 | 1891 | Returns the offset of where the last C<m//g> search left off for the variable |
a0d0e21e LW |
1892 | in question. May be modified to change that offset. |
1893 | ||
1894 | =item print FILEHANDLE LIST | |
1895 | ||
1896 | =item print LIST | |
1897 | ||
1898 | =item print | |
1899 | ||
1900 | Prints a string or a comma-separated list of strings. Returns non-zero | |
1901 | if successful. FILEHANDLE may be a scalar variable name, in which case | |
1902 | the variable contains the name of the filehandle, thus introducing one | |
1903 | level of indirection. (NOTE: If FILEHANDLE is a variable and the next | |
1904 | token is a term, it may be misinterpreted as an operator unless you | |
1905 | interpose a + or put parens around the arguments.) If FILEHANDLE is | |
1906 | omitted, prints by default to standard output (or to the last selected | |
1907 | output channel--see select()). If LIST is also omitted, prints $_ to | |
1908 | STDOUT. To set the default output channel to something other than | |
1909 | STDOUT use the select operation. Note that, because print takes a | |
1910 | LIST, anything in the LIST is evaluated in a list context, and any | |
1911 | subroutine that you call will have one or more of its expressions | |
1912 | evaluated in a list context. Also be careful not to follow the print | |
1913 | keyword with a left parenthesis unless you want the corresponding right | |
1914 | parenthesis to terminate the arguments to the print--interpose a + or | |
1915 | put parens around all the arguments. | |
1916 | ||
4633a7c4 LW |
1917 | Note that if you're storing FILEHANDLES in an array or other expression, |
1918 | you will have to use a block returning its value instead | |
1919 | ||
1920 | print { $files[$i] } "stuff\n"; | |
1921 | print { $OK ? STDOUT : STDERR } "stuff\n"; | |
1922 | ||
a0d0e21e LW |
1923 | =item printf FILEHANDLE LIST |
1924 | ||
1925 | =item printf LIST | |
1926 | ||
1927 | Equivalent to a "print FILEHANDLE sprintf(LIST)". The first argument | |
1928 | of the list will be interpreted as the printf format. | |
1929 | ||
1930 | =item push ARRAY,LIST | |
1931 | ||
1932 | Treats ARRAY as a stack, and pushes the values of LIST | |
1933 | onto the end of ARRAY. The length of ARRAY increases by the length of | |
1934 | LIST. Has the same effect as | |
1935 | ||
1936 | for $value (LIST) { | |
1937 | $ARRAY[++$#ARRAY] = $value; | |
1938 | } | |
1939 | ||
1940 | but is more efficient. Returns the new number of elements in the array. | |
1941 | ||
1942 | =item q/STRING/ | |
1943 | ||
1944 | =item qq/STRING/ | |
1945 | ||
1946 | =item qx/STRING/ | |
1947 | ||
1948 | =item qw/STRING/ | |
1949 | ||
1950 | Generalized quotes. See L<perlop>. | |
1951 | ||
1952 | =item quotemeta EXPR | |
1953 | ||
1954 | Returns the value of EXPR with with all regular expression | |
1955 | metacharacters backslashed. This is the internal function implementing | |
1956 | the \Q escape in double-quoted strings. | |
1957 | ||
1958 | =item rand EXPR | |
1959 | ||
1960 | =item rand | |
1961 | ||
1962 | Returns a random fractional number between 0 and the value of EXPR. | |
1963 | (EXPR should be positive.) If EXPR is omitted, returns a value between | |
1964 | 0 and 1. This function produces repeatable sequences unless srand() | |
1965 | is invoked. See also srand(). | |
1966 | ||
1967 | (Note: if your rand function consistently returns numbers that are too | |
1968 | large or too small, then your version of Perl was probably compiled | |
1969 | with the wrong number of RANDBITS. As a workaround, you can usually | |
1970 | multiply EXPR by the correct power of 2 to get the range you want. | |
1971 | This will make your script unportable, however. It's better to recompile | |
1972 | if you can.) | |
1973 | ||
1974 | =item read FILEHANDLE,SCALAR,LENGTH,OFFSET | |
1975 | ||
1976 | =item read FILEHANDLE,SCALAR,LENGTH | |
1977 | ||
1978 | Attempts to read LENGTH bytes of data into variable SCALAR from the | |
1979 | specified FILEHANDLE. Returns the number of bytes actually read, or | |
1980 | undef if there was an error. SCALAR will be grown or shrunk to the | |
1981 | length actually read. An OFFSET may be specified to place the read | |
1982 | data at some other place than the beginning of the string. This call | |
1983 | is actually implemented in terms of stdio's fread call. To get a true | |
1984 | read system call, see sysread(). | |
1985 | ||
1986 | =item readdir DIRHANDLE | |
1987 | ||
1988 | Returns the next directory entry for a directory opened by opendir(). | |
1989 | If used in a list context, returns all the rest of the entries in the | |
1990 | directory. If there are no more entries, returns an undefined value in | |
1991 | a scalar context or a null list in a list context. | |
1992 | ||
1993 | =item readlink EXPR | |
1994 | ||
1995 | Returns the value of a symbolic link, if symbolic links are | |
1996 | implemented. If not, gives a fatal error. If there is some system | |
1997 | error, returns the undefined value and sets $! (errno). If EXPR is | |
1998 | omitted, uses $_. | |
1999 | ||
2000 | =item recv SOCKET,SCALAR,LEN,FLAGS | |
2001 | ||
2002 | Receives a message on a socket. Attempts to receive LENGTH bytes of | |
2003 | data into variable SCALAR from the specified SOCKET filehandle. | |
2004 | Actually does a C recvfrom(), so that it can returns the address of the | |
2005 | sender. Returns the undefined value if there's an error. SCALAR will | |
2006 | be grown or shrunk to the length actually read. Takes the same flags | |
4633a7c4 LW |
2007 | as the system call of the same name. |
2008 | See L<perlipc/"UDP: Message Passing"> for examples. | |
a0d0e21e LW |
2009 | |
2010 | =item redo LABEL | |
2011 | ||
2012 | =item redo | |
2013 | ||
2014 | The C<redo> command restarts the loop block without evaluating the | |
2015 | conditional again. The C<continue> block, if any, is not executed. If | |
2016 | the LABEL is omitted, the command refers to the innermost enclosing | |
2017 | loop. This command is normally used by programs that want to lie to | |
2018 | themselves about what was just input: | |
2019 | ||
2020 | # a simpleminded Pascal comment stripper | |
2021 | # (warning: assumes no { or } in strings) | |
4633a7c4 | 2022 | LINE: while (<STDIN>) { |
a0d0e21e LW |
2023 | while (s|({.*}.*){.*}|$1 |) {} |
2024 | s|{.*}| |; | |
2025 | if (s|{.*| |) { | |
2026 | $front = $_; | |
2027 | while (<STDIN>) { | |
2028 | if (/}/) { # end of comment? | |
2029 | s|^|$front{|; | |
4633a7c4 | 2030 | redo LINE; |
a0d0e21e LW |
2031 | } |
2032 | } | |
2033 | } | |
2034 | print; | |
2035 | } | |
2036 | ||
2037 | =item ref EXPR | |
2038 | ||
2039 | Returns a TRUE value if EXPR is a reference, FALSE otherwise. The value | |
2040 | returned depends on the type of thing the reference is a reference to. | |
2041 | Builtin types include: | |
2042 | ||
2043 | REF | |
2044 | SCALAR | |
2045 | ARRAY | |
2046 | HASH | |
2047 | CODE | |
2048 | GLOB | |
2049 | ||
2050 | If the referenced object has been blessed into a package, then that package | |
2051 | name is returned instead. You can think of ref() as a typeof() operator. | |
2052 | ||
2053 | if (ref($r) eq "HASH") { | |
2054 | print "r is a reference to an associative array.\n"; | |
2055 | } | |
2056 | if (!ref ($r) { | |
2057 | print "r is not a reference at all.\n"; | |
2058 | } | |
2059 | ||
2060 | See also L<perlref>. | |
2061 | ||
2062 | =item rename OLDNAME,NEWNAME | |
2063 | ||
2064 | Changes the name of a file. Returns 1 for success, 0 otherwise. Will | |
2065 | not work across filesystem boundaries. | |
2066 | ||
2067 | =item require EXPR | |
2068 | ||
2069 | =item require | |
2070 | ||
2071 | Demands some semantics specified by EXPR, or by $_ if EXPR is not | |
2072 | supplied. If EXPR is numeric, demands that the current version of Perl | |
2073 | ($] or $PERL_VERSION) be equal or greater than EXPR. | |
2074 | ||
2075 | Otherwise, demands that a library file be included if it hasn't already | |
2076 | been included. The file is included via the do-FILE mechanism, which is | |
2077 | essentially just a variety of eval(). Has semantics similar to the following | |
2078 | subroutine: | |
2079 | ||
2080 | sub require { | |
2081 | local($filename) = @_; | |
2082 | return 1 if $INC{$filename}; | |
2083 | local($realfilename,$result); | |
2084 | ITER: { | |
2085 | foreach $prefix (@INC) { | |
2086 | $realfilename = "$prefix/$filename"; | |
2087 | if (-f $realfilename) { | |
2088 | $result = do $realfilename; | |
2089 | last ITER; | |
2090 | } | |
2091 | } | |
2092 | die "Can't find $filename in \@INC"; | |
2093 | } | |
2094 | die $@ if $@; | |
2095 | die "$filename did not return true value" unless $result; | |
2096 | $INC{$filename} = $realfilename; | |
2097 | $result; | |
2098 | } | |
2099 | ||
2100 | Note that the file will not be included twice under the same specified | |
2101 | name. The file must return TRUE as the last statement to indicate | |
2102 | successful execution of any initialization code, so it's customary to | |
2103 | end such a file with "1;" unless you're sure it'll return TRUE | |
2104 | otherwise. But it's better just to put the "C<1;>", in case you add more | |
2105 | statements. | |
2106 | ||
2107 | If EXPR is a bare word, the require assumes a "F<.pm>" extension for you, | |
2108 | to make it easy to load standard modules. This form of loading of | |
2109 | modules does not risk altering your namespace. | |
2110 | ||
748a9306 LW |
2111 | For a yet-more-powerful import facility, see the L</use()> and |
2112 | L<perlmod>. | |
a0d0e21e LW |
2113 | |
2114 | =item reset EXPR | |
2115 | ||
2116 | =item reset | |
2117 | ||
2118 | Generally used in a C<continue> block at the end of a loop to clear | |
2119 | variables and reset ?? searches so that they work again. The | |
2120 | expression is interpreted as a list of single characters (hyphens | |
2121 | allowed for ranges). All variables and arrays beginning with one of | |
2122 | those letters are reset to their pristine state. If the expression is | |
2123 | omitted, one-match searches (?pattern?) are reset to match again. Only | |
2124 | resets variables or searches in the current package. Always returns | |
2125 | 1. Examples: | |
2126 | ||
2127 | reset 'X'; # reset all X variables | |
2128 | reset 'a-z'; # reset lower case variables | |
2129 | reset; # just reset ?? searches | |
2130 | ||
2131 | Resetting "A-Z" is not recommended since you'll wipe out your | |
2132 | ARGV and ENV arrays. Only resets package variables--lexical variables | |
2133 | are unaffected, but they clean themselves up on scope exit anyway, | |
2134 | so anymore you probably want to use them instead. See L</my>. | |
2135 | ||
2136 | =item return LIST | |
2137 | ||
2138 | Returns from a subroutine or eval with the value specified. (Note that | |
4633a7c4 | 2139 | in the absence of a return a subroutine or eval() will automatically |
a0d0e21e LW |
2140 | return the value of the last expression evaluated.) |
2141 | ||
2142 | =item reverse LIST | |
2143 | ||
2144 | In a list context, returns a list value consisting of the elements | |
2145 | of LIST in the opposite order. In a scalar context, returns a string | |
2146 | value consisting of the bytes of the first element of LIST in the | |
4633a7c4 LW |
2147 | opposite order. |
2148 | ||
2149 | print reverse <>; # line tac | |
2150 | ||
2151 | undef $/; | |
2152 | print scalar reverse scalar <>; # byte tac | |
a0d0e21e LW |
2153 | |
2154 | =item rewinddir DIRHANDLE | |
2155 | ||
2156 | Sets the current position to the beginning of the directory for the | |
2157 | readdir() routine on DIRHANDLE. | |
2158 | ||
2159 | =item rindex STR,SUBSTR,POSITION | |
2160 | ||
2161 | =item rindex STR,SUBSTR | |
2162 | ||
2163 | Works just like index except that it returns the position of the LAST | |
2164 | occurrence of SUBSTR in STR. If POSITION is specified, returns the | |
2165 | last occurrence at or before that position. | |
2166 | ||
2167 | =item rmdir FILENAME | |
2168 | ||
2169 | Deletes the directory specified by FILENAME if it is empty. If it | |
2170 | succeeds it returns 1, otherwise it returns 0 and sets $! (errno). If | |
2171 | FILENAME is omitted, uses $_. | |
2172 | ||
2173 | =item s/// | |
2174 | ||
2175 | The substitution operator. See L<perlop>. | |
2176 | ||
2177 | =item scalar EXPR | |
2178 | ||
2179 | Forces EXPR to be interpreted in a scalar context and returns the value | |
2180 | of EXPR. | |
2181 | ||
2182 | =item seek FILEHANDLE,POSITION,WHENCE | |
2183 | ||
2184 | Randomly positions the file pointer for FILEHANDLE, just like the fseek() | |
2185 | call of stdio. FILEHANDLE may be an expression whose value gives the name | |
2186 | of the filehandle. The values for WHENCE are 0 to set the file pointer to | |
2187 | POSITION, 1 to set the it to current plus POSITION, and 2 to set it to EOF | |
2188 | plus offset. You may use the values SEEK_SET, SEEK_CUR, and SEEK_END for | |
4633a7c4 | 2189 | this from POSIX module. Returns 1 upon success, 0 otherwise. |
a0d0e21e LW |
2190 | |
2191 | =item seekdir DIRHANDLE,POS | |
2192 | ||
2193 | Sets the current position for the readdir() routine on DIRHANDLE. POS | |
2194 | must be a value returned by telldir(). Has the same caveats about | |
2195 | possible directory compaction as the corresponding system library | |
2196 | routine. | |
2197 | ||
2198 | =item select FILEHANDLE | |
2199 | ||
2200 | =item select | |
2201 | ||
2202 | Returns the currently selected filehandle. Sets the current default | |
2203 | filehandle for output, if FILEHANDLE is supplied. This has two | |
2204 | effects: first, a C<write> or a C<print> without a filehandle will | |
2205 | default to this FILEHANDLE. Second, references to variables related to | |
2206 | output will refer to this output channel. For example, if you have to | |
2207 | set the top of form format for more than one output channel, you might | |
2208 | do the following: | |
2209 | ||
2210 | select(REPORT1); | |
2211 | $^ = 'report1_top'; | |
2212 | select(REPORT2); | |
2213 | $^ = 'report2_top'; | |
2214 | ||
2215 | FILEHANDLE may be an expression whose value gives the name of the | |
2216 | actual filehandle. Thus: | |
2217 | ||
2218 | $oldfh = select(STDERR); $| = 1; select($oldfh); | |
2219 | ||
4633a7c4 LW |
2220 | Some programmers may prefer to think of filehandles as objects with |
2221 | methods, preferring to write the last example as: | |
a0d0e21e LW |
2222 | |
2223 | use FileHandle; | |
2224 | STDERR->autoflush(1); | |
2225 | ||
2226 | =item select RBITS,WBITS,EBITS,TIMEOUT | |
2227 | ||
4633a7c4 | 2228 | This calls the select(2) system call with the bitmasks specified, which |
a0d0e21e LW |
2229 | can be constructed using fileno() and vec(), along these lines: |
2230 | ||
2231 | $rin = $win = $ein = ''; | |
2232 | vec($rin,fileno(STDIN),1) = 1; | |
2233 | vec($win,fileno(STDOUT),1) = 1; | |
2234 | $ein = $rin | $win; | |
2235 | ||
2236 | If you want to select on many filehandles you might wish to write a | |
2237 | subroutine: | |
2238 | ||
2239 | sub fhbits { | |
2240 | local(@fhlist) = split(' ',$_[0]); | |
2241 | local($bits); | |
2242 | for (@fhlist) { | |
2243 | vec($bits,fileno($_),1) = 1; | |
2244 | } | |
2245 | $bits; | |
2246 | } | |
4633a7c4 | 2247 | $rin = fhbits('STDIN TTY SOCK'); |
a0d0e21e LW |
2248 | |
2249 | The usual idiom is: | |
2250 | ||
2251 | ($nfound,$timeleft) = | |
2252 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); | |
2253 | ||
2254 | or to block until something becomes ready: | |
2255 | ||
2256 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); | |
2257 | ||
2258 | Any of the bitmasks can also be undef. The timeout, if specified, is | |
2259 | in seconds, which may be fractional. Note: not all implementations are | |
2260 | capable of returning the $timeleft. If not, they always return | |
2261 | $timeleft equal to the supplied $timeout. | |
2262 | ||
4633a7c4 | 2263 | You can effect a 250-microsecond sleep this way: |
a0d0e21e LW |
2264 | |
2265 | select(undef, undef, undef, 0.25); | |
2266 | ||
2267 | ||
2268 | =item semctl ID,SEMNUM,CMD,ARG | |
2269 | ||
2270 | Calls the System V IPC function semctl. If CMD is &IPC_STAT or | |
2271 | &GETALL, then ARG must be a variable which will hold the returned | |
2272 | semid_ds structure or semaphore value array. Returns like ioctl: the | |
2273 | undefined value for error, "0 but true" for zero, or the actual return | |
2274 | value otherwise. | |
2275 | ||
2276 | =item semget KEY,NSEMS,FLAGS | |
2277 | ||
2278 | Calls the System V IPC function semget. Returns the semaphore id, or | |
2279 | the undefined value if there is an error. | |
2280 | ||
2281 | =item semop KEY,OPSTRING | |
2282 | ||
2283 | Calls the System V IPC function semop to perform semaphore operations | |
2284 | such as signaling and waiting. OPSTRING must be a packed array of | |
2285 | semop structures. Each semop structure can be generated with | |
2286 | C<pack("sss", $semnum, $semop, $semflag)>. The number of semaphore | |
2287 | operations is implied by the length of OPSTRING. Returns TRUE if | |
2288 | successful, or FALSE if there is an error. As an example, the | |
2289 | following code waits on semaphore $semnum of semaphore id $semid: | |
2290 | ||
2291 | $semop = pack("sss", $semnum, -1, 0); | |
2292 | die "Semaphore trouble: $!\n" unless semop($semid, $semop); | |
2293 | ||
2294 | To signal the semaphore, replace "-1" with "1". | |
2295 | ||
2296 | =item send SOCKET,MSG,FLAGS,TO | |
2297 | ||
2298 | =item send SOCKET,MSG,FLAGS | |
2299 | ||
2300 | Sends a message on a socket. Takes the same flags as the system call | |
2301 | of the same name. On unconnected sockets you must specify a | |
2302 | destination to send TO, in which case it does a C sendto(). Returns | |
2303 | the number of characters sent, or the undefined value if there is an | |
2304 | error. | |
4633a7c4 | 2305 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e LW |
2306 | |
2307 | =item setpgrp PID,PGRP | |
2308 | ||
2309 | Sets the current process group for the specified PID, 0 for the current | |
2310 | process. Will produce a fatal error if used on a machine that doesn't | |
2311 | implement setpgrp(2). | |
2312 | ||
2313 | =item setpriority WHICH,WHO,PRIORITY | |
2314 | ||
2315 | Sets the current priority for a process, a process group, or a user. | |
748a9306 | 2316 | (See setpriority(2).) Will produce a fatal error if used on a machine |
a0d0e21e LW |
2317 | that doesn't implement setpriority(2). |
2318 | ||
2319 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL | |
2320 | ||
2321 | Sets the socket option requested. Returns undefined if there is an | |
2322 | error. OPTVAL may be specified as undef if you don't want to pass an | |
2323 | argument. | |
2324 | ||
2325 | =item shift ARRAY | |
2326 | ||
2327 | =item shift | |
2328 | ||
2329 | Shifts the first value of the array off and returns it, shortening the | |
2330 | array by 1 and moving everything down. If there are no elements in the | |
2331 | array, returns the undefined value. If ARRAY is omitted, shifts the | |
2332 | @ARGV array in the main program, and the @_ array in subroutines. | |
2333 | (This is determined lexically.) See also unshift(), push(), and pop(). | |
2334 | Shift() and unshift() do the same thing to the left end of an array | |
2335 | that push() and pop() do to the right end. | |
2336 | ||
2337 | =item shmctl ID,CMD,ARG | |
2338 | ||
2339 | Calls the System V IPC function shmctl. If CMD is &IPC_STAT, then ARG | |
2340 | must be a variable which will hold the returned shmid_ds structure. | |
2341 | Returns like ioctl: the undefined value for error, "0 but true" for | |
2342 | zero, or the actual return value otherwise. | |
2343 | ||
2344 | =item shmget KEY,SIZE,FLAGS | |
2345 | ||
2346 | Calls the System V IPC function shmget. Returns the shared memory | |
2347 | segment id, or the undefined value if there is an error. | |
2348 | ||
2349 | =item shmread ID,VAR,POS,SIZE | |
2350 | ||
2351 | =item shmwrite ID,STRING,POS,SIZE | |
2352 | ||
2353 | Reads or writes the System V shared memory segment ID starting at | |
2354 | position POS for size SIZE by attaching to it, copying in/out, and | |
2355 | detaching from it. When reading, VAR must be a variable which will | |
2356 | hold the data read. When writing, if STRING is too long, only SIZE | |
2357 | bytes are used; if STRING is too short, nulls are written to fill out | |
2358 | SIZE bytes. Return TRUE if successful, or FALSE if there is an error. | |
2359 | ||
2360 | =item shutdown SOCKET,HOW | |
2361 | ||
2362 | Shuts down a socket connection in the manner indicated by HOW, which | |
2363 | has the same interpretation as in the system call of the same name. | |
2364 | ||
2365 | =item sin EXPR | |
2366 | ||
2367 | Returns the sine of EXPR (expressed in radians). If EXPR is omitted, | |
2368 | returns sine of $_. | |
2369 | ||
2370 | =item sleep EXPR | |
2371 | ||
2372 | =item sleep | |
2373 | ||
2374 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. | |
2375 | May be interrupted by sending the process a SIGALRM. Returns the | |
2376 | number of seconds actually slept. You probably cannot mix alarm() and | |
2377 | sleep() calls, since sleep() is often implemented using alarm(). | |
2378 | ||
2379 | On some older systems, it may sleep up to a full second less than what | |
2380 | you requested, depending on how it counts seconds. Most modern systems | |
2381 | always sleep the full amount. | |
2382 | ||
2383 | =item socket SOCKET,DOMAIN,TYPE,PROTOCOL | |
2384 | ||
2385 | Opens a socket of the specified kind and attaches it to filehandle | |
2386 | SOCKET. DOMAIN, TYPE and PROTOCOL are specified the same as for the | |
2387 | system call of the same name. You should "use Socket;" first to get | |
4633a7c4 | 2388 | the proper definitions imported. See the example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e LW |
2389 | |
2390 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL | |
2391 | ||
2392 | Creates an unnamed pair of sockets in the specified domain, of the | |
2393 | specified type. DOMAIN, TYPE and PROTOCOL are specified the same as | |
2394 | for the system call of the same name. If unimplemented, yields a fatal | |
2395 | error. Returns TRUE if successful. | |
2396 | ||
2397 | =item sort SUBNAME LIST | |
2398 | ||
2399 | =item sort BLOCK LIST | |
2400 | ||
2401 | =item sort LIST | |
2402 | ||
2403 | Sorts the LIST and returns the sorted list value. Nonexistent values | |
2404 | of arrays are stripped out. If SUBNAME or BLOCK is omitted, sorts | |
2405 | in standard string comparison order. If SUBNAME is specified, it | |
2406 | gives the name of a subroutine that returns an integer less than, equal | |
2407 | to, or greater than 0, depending on how the elements of the array are | |
2408 | to be ordered. (The <=> and cmp operators are extremely useful in such | |
2409 | routines.) SUBNAME may be a scalar variable name, in which case the | |
2410 | value provides the name of the subroutine to use. In place of a | |
2411 | SUBNAME, you can provide a BLOCK as an anonymous, in-line sort | |
2412 | subroutine. | |
2413 | ||
2414 | In the interests of efficiency the normal calling code for subroutines | |
2415 | is bypassed, with the following effects: the subroutine may not be a | |
2416 | recursive subroutine, and the two elements to be compared are passed | |
2417 | into the subroutine not via @_ but as $a and $b (see example below). | |
2418 | They are passed by reference, so don't modify $a and $b. | |
2419 | ||
2420 | Examples: | |
2421 | ||
2422 | # sort lexically | |
2423 | @articles = sort @files; | |
2424 | ||
2425 | # same thing, but with explicit sort routine | |
2426 | @articles = sort {$a cmp $b} @files; | |
2427 | ||
2428 | # same thing in reversed order | |
2429 | @articles = sort {$b cmp $a} @files; | |
2430 | ||
2431 | # sort numerically ascending | |
2432 | @articles = sort {$a <=> $b} @files; | |
2433 | ||
2434 | # sort numerically descending | |
2435 | @articles = sort {$b <=> $a} @files; | |
2436 | ||
2437 | # sort using explicit subroutine name | |
2438 | sub byage { | |
2439 | $age{$a} <=> $age{$b}; # presuming integers | |
2440 | } | |
2441 | @sortedclass = sort byage @class; | |
2442 | ||
2443 | sub backwards { $b cmp $a; } | |
2444 | @harry = ('dog','cat','x','Cain','Abel'); | |
2445 | @george = ('gone','chased','yz','Punished','Axed'); | |
2446 | print sort @harry; | |
2447 | # prints AbelCaincatdogx | |
2448 | print sort backwards @harry; | |
2449 | # prints xdogcatCainAbel | |
2450 | print sort @george, 'to', @harry; | |
2451 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz | |
2452 | ||
2453 | =item splice ARRAY,OFFSET,LENGTH,LIST | |
2454 | ||
2455 | =item splice ARRAY,OFFSET,LENGTH | |
2456 | ||
2457 | =item splice ARRAY,OFFSET | |
2458 | ||
2459 | Removes the elements designated by OFFSET and LENGTH from an array, and | |
2460 | replaces them with the elements of LIST, if any. Returns the elements | |
2461 | removed from the array. The array grows or shrinks as necessary. If | |
2462 | LENGTH is omitted, removes everything from OFFSET onward. The | |
2463 | following equivalencies hold (assuming $[ == 0): | |
2464 | ||
2465 | push(@a,$x,$y) splice(@a,$#a+1,0,$x,$y) | |
2466 | pop(@a) splice(@a,-1) | |
2467 | shift(@a) splice(@a,0,1) | |
2468 | unshift(@a,$x,$y) splice(@a,0,0,$x,$y) | |
2469 | $a[$x] = $y splice(@a,$x,1,$y); | |
2470 | ||
2471 | Example, assuming array lengths are passed before arrays: | |
2472 | ||
2473 | sub aeq { # compare two list values | |
2474 | local(@a) = splice(@_,0,shift); | |
2475 | local(@b) = splice(@_,0,shift); | |
2476 | return 0 unless @a == @b; # same len? | |
2477 | while (@a) { | |
2478 | return 0 if pop(@a) ne pop(@b); | |
2479 | } | |
2480 | return 1; | |
2481 | } | |
2482 | if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... } | |
2483 | ||
2484 | =item split /PATTERN/,EXPR,LIMIT | |
2485 | ||
2486 | =item split /PATTERN/,EXPR | |
2487 | ||
2488 | =item split /PATTERN/ | |
2489 | ||
2490 | =item split | |
2491 | ||
2492 | Splits a string into an array of strings, and returns it. | |
2493 | ||
2494 | If not in a list context, returns the number of fields found and splits into | |
2495 | the @_ array. (In a list context, you can force the split into @_ by | |
2496 | using C<??> as the pattern delimiters, but it still returns the array | |
2497 | value.) The use of implicit split to @_ is deprecated, however. | |
2498 | ||
2499 | If EXPR is omitted, splits the $_ string. If PATTERN is also omitted, | |
4633a7c4 LW |
2500 | splits on whitespace (after skipping any leading whitespace). Anything |
2501 | matching PATTERN is taken to be a delimiter separating the fields. (Note | |
2502 | that the delimiter may be longer than one character.) If LIMIT is | |
2503 | specified and is not negative, splits into no more than that many fields | |
2504 | (though it may split into fewer). If LIMIT is unspecified, trailing null | |
2505 | fields are stripped (which potential users of pop() would do well to | |
2506 | remember). If LIMIT is negative, it is treated as if an arbitrarily large | |
2507 | LIMIT had been specified. | |
a0d0e21e LW |
2508 | |
2509 | A pattern matching the null string (not to be confused with | |
748a9306 | 2510 | a null pattern C<//>, which is just one member of the set of patterns |
a0d0e21e LW |
2511 | matching a null string) will split the value of EXPR into separate |
2512 | characters at each point it matches that way. For example: | |
2513 | ||
2514 | print join(':', split(/ */, 'hi there')); | |
2515 | ||
2516 | produces the output 'h:i:t:h:e:r:e'. | |
2517 | ||
2518 | The LIMIT parameter can be used to partially split a line | |
2519 | ||
2520 | ($login, $passwd, $remainder) = split(/:/, $_, 3); | |
2521 | ||
2522 | When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT | |
2523 | one larger than the number of variables in the list, to avoid | |
2524 | unnecessary work. For the list above LIMIT would have been 4 by | |
2525 | default. In time critical applications it behooves you not to split | |
2526 | into more fields than you really need. | |
2527 | ||
2528 | If the PATTERN contains parentheses, additional array elements are | |
2529 | created from each matching substring in the delimiter. | |
2530 | ||
2531 | split(/([,-])/, "1-10,20"); | |
2532 | ||
2533 | produces the list value | |
2534 | ||
2535 | (1, '-', 10, ',', 20) | |
2536 | ||
4633a7c4 LW |
2537 | If you had the entire header of a normal Unix email message in $header, |
2538 | you could split it up into fields and their values this way: | |
2539 | ||
2540 | $header =~ s/\n\s+/ /g; # fix continuation lines | |
2541 | %hdrs = (UNIX_FROM => split /^(.*?):\s*/m, $header); | |
2542 | ||
a0d0e21e LW |
2543 | The pattern C</PATTERN/> may be replaced with an expression to specify |
2544 | patterns that vary at runtime. (To do runtime compilation only once, | |
748a9306 LW |
2545 | use C</$variable/o>.) |
2546 | ||
2547 | As a special case, specifying a PATTERN of space (C<' '>) will split on | |
2548 | white space just as split with no arguments does. Thus, split(' ') can | |
2549 | be used to emulate B<awk>'s default behavior, whereas C<split(/ /)> | |
2550 | will give you as many null initial fields as there are leading spaces. | |
2551 | A split on /\s+/ is like a split(' ') except that any leading | |
2552 | whitespace produces a null first field. A split with no arguments | |
2553 | really does a C<split(' ', $_)> internally. | |
a0d0e21e LW |
2554 | |
2555 | Example: | |
2556 | ||
2557 | open(passwd, '/etc/passwd'); | |
2558 | while (<passwd>) { | |
748a9306 LW |
2559 | ($login, $passwd, $uid, $gid, $gcos, |
2560 | $home, $shell) = split(/:/); | |
a0d0e21e LW |
2561 | ... |
2562 | } | |
2563 | ||
2564 | (Note that $shell above will still have a newline on it. See L</chop>, | |
2565 | L</chomp>, and L</join>.) | |
2566 | ||
2567 | =item sprintf FORMAT,LIST | |
2568 | ||
2569 | Returns a string formatted by the usual printf conventions of the C | |
2570 | language. (The * character for an indirectly specified length is not | |
2571 | supported, but you can get the same effect by interpolating a variable | |
4633a7c4 LW |
2572 | into the pattern.) Some C libraries' implementations of sprintf() can dump core |
2573 | when fed ludiocrous arguments. | |
a0d0e21e LW |
2574 | |
2575 | =item sqrt EXPR | |
2576 | ||
2577 | Return the square root of EXPR. If EXPR is omitted, returns square | |
2578 | root of $_. | |
2579 | ||
2580 | =item srand EXPR | |
2581 | ||
2582 | Sets the random number seed for the C<rand> operator. If EXPR is | |
2583 | omitted, does C<srand(time)>. Of course, you'd need something much more | |
2584 | random than that for cryptographic purposes, since it's easy to guess | |
2585 | the current time. Checksumming the compressed output of rapidly | |
2586 | changing operating system status programs is the usual method. | |
2587 | Examples are posted regularly to comp.security.unix. | |
2588 | ||
2589 | =item stat FILEHANDLE | |
2590 | ||
2591 | =item stat EXPR | |
2592 | ||
2593 | Returns a 13-element array giving the status info for a file, either the | |
2594 | file opened via FILEHANDLE, or named by EXPR. Returns a null list if | |
2595 | the stat fails. Typically used as follows: | |
2596 | ||
2597 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, | |
2598 | $atime,$mtime,$ctime,$blksize,$blocks) | |
2599 | = stat($filename); | |
2600 | ||
2601 | If stat is passed the special filehandle consisting of an underline, no | |
2602 | stat is done, but the current contents of the stat structure from the | |
2603 | last stat or filetest are returned. Example: | |
2604 | ||
2605 | if (-x $file && (($d) = stat(_)) && $d < 0) { | |
2606 | print "$file is executable NFS file\n"; | |
2607 | } | |
2608 | ||
2609 | (This only works on machines for which the device number is negative under NFS.) | |
2610 | ||
2611 | =item study SCALAR | |
2612 | ||
2613 | =item study | |
2614 | ||
2615 | Takes extra time to study SCALAR ($_ if unspecified) in anticipation of | |
2616 | doing many pattern matches on the string before it is next modified. | |
2617 | This may or may not save time, depending on the nature and number of | |
2618 | patterns you are searching on, and on the distribution of character | |
2619 | frequencies in the string to be searched--you probably want to compare | |
2620 | runtimes with and without it to see which runs faster. Those loops | |
2621 | which scan for many short constant strings (including the constant | |
2622 | parts of more complex patterns) will benefit most. You may have only | |
2623 | one study active at a time--if you study a different scalar the first | |
2624 | is "unstudied". (The way study works is this: a linked list of every | |
2625 | character in the string to be searched is made, so we know, for | |
2626 | example, where all the 'k' characters are. From each search string, | |
2627 | the rarest character is selected, based on some static frequency tables | |
2628 | constructed from some C programs and English text. Only those places | |
2629 | that contain this "rarest" character are examined.) | |
2630 | ||
2631 | For example, here is a loop which inserts index producing entries | |
2632 | before any line containing a certain pattern: | |
2633 | ||
2634 | while (<>) { | |
2635 | study; | |
2636 | print ".IX foo\n" if /\bfoo\b/; | |
2637 | print ".IX bar\n" if /\bbar\b/; | |
2638 | print ".IX blurfl\n" if /\bblurfl\b/; | |
2639 | ... | |
2640 | print; | |
2641 | } | |
2642 | ||
2643 | In searching for /\bfoo\b/, only those locations in $_ that contain "f" | |
2644 | will be looked at, because "f" is rarer than "o". In general, this is | |
2645 | a big win except in pathological cases. The only question is whether | |
2646 | it saves you more time than it took to build the linked list in the | |
2647 | first place. | |
2648 | ||
2649 | Note that if you have to look for strings that you don't know till | |
2650 | runtime, you can build an entire loop as a string and eval that to | |
2651 | avoid recompiling all your patterns all the time. Together with | |
2652 | undefining $/ to input entire files as one record, this can be very | |
2653 | fast, often faster than specialized programs like fgrep(1). The following | |
2654 | scans a list of files (@files) for a list of words (@words), and prints | |
2655 | out the names of those files that contain a match: | |
2656 | ||
2657 | $search = 'while (<>) { study;'; | |
2658 | foreach $word (@words) { | |
2659 | $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n"; | |
2660 | } | |
2661 | $search .= "}"; | |
2662 | @ARGV = @files; | |
2663 | undef $/; | |
2664 | eval $search; # this screams | |
2665 | $/ = "\n"; # put back to normal input delim | |
2666 | foreach $file (sort keys(%seen)) { | |
2667 | print $file, "\n"; | |
2668 | } | |
2669 | ||
2670 | =item substr EXPR,OFFSET,LEN | |
2671 | ||
2672 | =item substr EXPR,OFFSET | |
2673 | ||
2674 | Extracts a substring out of EXPR and returns it. First character is at | |
2675 | offset 0, or whatever you've set $[ to. If OFFSET is negative, starts | |
2676 | that far from the end of the string. If LEN is omitted, returns | |
748a9306 LW |
2677 | everything to the end of the string. If LEN is negative, leaves that |
2678 | many characters off the end of the string. | |
2679 | ||
2680 | You can use the substr() function | |
a0d0e21e LW |
2681 | as an lvalue, in which case EXPR must be an lvalue. If you assign |
2682 | something shorter than LEN, the string will shrink, and if you assign | |
2683 | something longer than LEN, the string will grow to accommodate it. To | |
2684 | keep the string the same length you may need to pad or chop your value | |
2685 | using sprintf(). | |
2686 | ||
2687 | =item symlink OLDFILE,NEWFILE | |
2688 | ||
2689 | Creates a new filename symbolically linked to the old filename. | |
2690 | Returns 1 for success, 0 otherwise. On systems that don't support | |
2691 | symbolic links, produces a fatal error at run time. To check for that, | |
2692 | use eval: | |
2693 | ||
2694 | $symlink_exists = (eval 'symlink("","");', $@ eq ''); | |
2695 | ||
2696 | =item syscall LIST | |
2697 | ||
2698 | Calls the system call specified as the first element of the list, | |
2699 | passing the remaining elements as arguments to the system call. If | |
2700 | unimplemented, produces a fatal error. The arguments are interpreted | |
2701 | as follows: if a given argument is numeric, the argument is passed as | |
2702 | an int. If not, the pointer to the string value is passed. You are | |
2703 | responsible to make sure a string is pre-extended long enough to | |
2704 | receive any result that might be written into a string. If your | |
2705 | integer arguments are not literals and have never been interpreted in a | |
2706 | numeric context, you may need to add 0 to them to force them to look | |
2707 | like numbers. | |
2708 | ||
2709 | require 'syscall.ph'; # may need to run h2ph | |
2710 | syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9); | |
2711 | ||
2712 | Note that Perl only supports passing of up to 14 arguments to your system call, | |
2713 | which in practice should usually suffice. | |
2714 | ||
2715 | =item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET | |
2716 | ||
2717 | =item sysread FILEHANDLE,SCALAR,LENGTH | |
2718 | ||
2719 | Attempts to read LENGTH bytes of data into variable SCALAR from the | |
2720 | specified FILEHANDLE, using the system call read(2). It bypasses | |
2721 | stdio, so mixing this with other kinds of reads may cause confusion. | |
2722 | Returns the number of bytes actually read, or undef if there was an | |
2723 | error. SCALAR will be grown or shrunk to the length actually read. An | |
2724 | OFFSET may be specified to place the read data at some other place than | |
2725 | the beginning of the string. | |
2726 | ||
2727 | =item system LIST | |
2728 | ||
2729 | Does exactly the same thing as "exec LIST" except that a fork is done | |
2730 | first, and the parent process waits for the child process to complete. | |
2731 | Note that argument processing varies depending on the number of | |
2732 | arguments. The return value is the exit status of the program as | |
2733 | returned by the wait() call. To get the actual exit value divide by | |
2734 | 256. See also L</exec>. | |
2735 | ||
2736 | =item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET | |
2737 | ||
2738 | =item syswrite FILEHANDLE,SCALAR,LENGTH | |
2739 | ||
2740 | Attempts to write LENGTH bytes of data from variable SCALAR to the | |
2741 | specified FILEHANDLE, using the system call write(2). It bypasses | |
2742 | stdio, so mixing this with prints may cause confusion. Returns the | |
2743 | number of bytes actually written, or undef if there was an error. An | |
2744 | OFFSET may be specified to place the read data at some other place than | |
2745 | the beginning of the string. | |
2746 | ||
2747 | =item tell FILEHANDLE | |
2748 | ||
2749 | =item tell | |
2750 | ||
2751 | Returns the current file position for FILEHANDLE. FILEHANDLE may be an | |
2752 | expression whose value gives the name of the actual filehandle. If | |
2753 | FILEHANDLE is omitted, assumes the file last read. | |
2754 | ||
2755 | =item telldir DIRHANDLE | |
2756 | ||
2757 | Returns the current position of the readdir() routines on DIRHANDLE. | |
2758 | Value may be given to seekdir() to access a particular location in a | |
2759 | directory. Has the same caveats about possible directory compaction as | |
2760 | the corresponding system library routine. | |
2761 | ||
4633a7c4 | 2762 | =item tie VARIABLE,CLASSNAME,LIST |
a0d0e21e | 2763 | |
4633a7c4 LW |
2764 | This function binds a variable to a package class that will provide the |
2765 | implementation for the variable. VARIABLE is the name of the variable | |
2766 | to be enchanted. CLASSNAME is the name of a class implementing objects | |
2767 | of correct type. Any additional arguments are passed to the "new" | |
2768 | method of the class (meaning TIESCALAR, TIEARRAY, or TIEHASH). | |
2769 | Typically these are arguments such as might be passed to the dbm_open() | |
2770 | function of C. The object returned by the "new" method +is also | |
2771 | returned by the tie() function, which would be useful if you +want to | |
2772 | access other methods in CLASSNAME. | |
a0d0e21e LW |
2773 | |
2774 | Note that functions such as keys() and values() may return huge array | |
748a9306 LW |
2775 | values when used on large objects, like DBM files. You may prefer to |
2776 | use the each() function to iterate over such. Example: | |
a0d0e21e LW |
2777 | |
2778 | # print out history file offsets | |
4633a7c4 | 2779 | use NDBM_File; |
a0d0e21e LW |
2780 | tie(%HIST, NDBM_File, '/usr/lib/news/history', 1, 0); |
2781 | while (($key,$val) = each %HIST) { | |
2782 | print $key, ' = ', unpack('L',$val), "\n"; | |
2783 | } | |
2784 | untie(%HIST); | |
2785 | ||
4633a7c4 | 2786 | A class implementing an associative array should have the following |
a0d0e21e LW |
2787 | methods: |
2788 | ||
4633a7c4 | 2789 | TIEHASH classname, LIST |
a0d0e21e LW |
2790 | DESTROY this |
2791 | FETCH this, key | |
2792 | STORE this, key, value | |
2793 | DELETE this, key | |
2794 | EXISTS this, key | |
2795 | FIRSTKEY this | |
2796 | NEXTKEY this, lastkey | |
2797 | ||
4633a7c4 | 2798 | A class implementing an ordinary array should have the following methods: |
a0d0e21e | 2799 | |
4633a7c4 | 2800 | TIEARRAY classname, LIST |
a0d0e21e LW |
2801 | DESTROY this |
2802 | FETCH this, key | |
2803 | STORE this, key, value | |
2804 | [others TBD] | |
2805 | ||
4633a7c4 | 2806 | A class implementing a scalar should have the following methods: |
a0d0e21e | 2807 | |
4633a7c4 | 2808 | TIESCALAR classname, LIST |
a0d0e21e LW |
2809 | DESTROY this |
2810 | FETCH this, | |
2811 | STORE this, value | |
2812 | ||
4633a7c4 LW |
2813 | Unlike dbmopen(), the tie() function will not use or require a module |
2814 | for you--you need to do that explicitly yourself. See L<DB_File> | |
2815 | or the F<Config> module for interesting tie() implementations. | |
2816 | ||
a0d0e21e LW |
2817 | =item time |
2818 | ||
2819 | Returns the number of non-leap seconds since 00:00:00 UTC, January 1, | |
2820 | 1970. Suitable for feeding to gmtime() and localtime(). | |
2821 | ||
2822 | =item times | |
2823 | ||
2824 | Returns a four-element array giving the user and system times, in | |
2825 | seconds, for this process and the children of this process. | |
2826 | ||
2827 | ($user,$system,$cuser,$csystem) = times; | |
2828 | ||
2829 | =item tr/// | |
2830 | ||
2831 | The translation operator. See L<perlop>. | |
2832 | ||
2833 | =item truncate FILEHANDLE,LENGTH | |
2834 | ||
2835 | =item truncate EXPR,LENGTH | |
2836 | ||
2837 | Truncates the file opened on FILEHANDLE, or named by EXPR, to the | |
2838 | specified length. Produces a fatal error if truncate isn't implemented | |
2839 | on your system. | |
2840 | ||
2841 | =item uc EXPR | |
2842 | ||
2843 | Returns an uppercased version of EXPR. This is the internal function | |
2844 | implementing the \U escape in double-quoted strings. | |
4633a7c4 | 2845 | Should respect any POSIX setlocale() settings. |
a0d0e21e LW |
2846 | |
2847 | =item ucfirst EXPR | |
2848 | ||
2849 | Returns the value of EXPR with the first character uppercased. This is | |
2850 | the internal function implementing the \u escape in double-quoted strings. | |
4633a7c4 | 2851 | Should respect any POSIX setlocale() settings. |
a0d0e21e LW |
2852 | |
2853 | =item umask EXPR | |
2854 | ||
2855 | =item umask | |
2856 | ||
2857 | Sets the umask for the process and returns the old one. If EXPR is | |
2858 | omitted, merely returns current umask. | |
2859 | ||
2860 | =item undef EXPR | |
2861 | ||
2862 | =item undef | |
2863 | ||
2864 | Undefines the value of EXPR, which must be an lvalue. Use only on a | |
2865 | scalar value, an entire array, or a subroutine name (using "&"). (Using undef() | |
2866 | will probably not do what you expect on most predefined variables or | |
2867 | DBM list values, so don't do that.) Always returns the undefined value. You can omit | |
2868 | the EXPR, in which case nothing is undefined, but you still get an | |
2869 | undefined value that you could, for instance, return from a | |
2870 | subroutine. Examples: | |
2871 | ||
2872 | undef $foo; | |
2873 | undef $bar{'blurfl'}; | |
2874 | undef @ary; | |
2875 | undef %assoc; | |
2876 | undef &mysub; | |
2877 | return (wantarray ? () : undef) if $they_blew_it; | |
2878 | ||
2879 | =item unlink LIST | |
2880 | ||
2881 | Deletes a list of files. Returns the number of files successfully | |
2882 | deleted. | |
2883 | ||
2884 | $cnt = unlink 'a', 'b', 'c'; | |
2885 | unlink @goners; | |
2886 | unlink <*.bak>; | |
2887 | ||
2888 | Note: unlink will not delete directories unless you are superuser and | |
2889 | the B<-U> flag is supplied to Perl. Even if these conditions are | |
2890 | met, be warned that unlinking a directory can inflict damage on your | |
2891 | filesystem. Use rmdir instead. | |
2892 | ||
2893 | =item unpack TEMPLATE,EXPR | |
2894 | ||
2895 | Unpack does the reverse of pack: it takes a string representing a | |
2896 | structure and expands it out into a list value, returning the array | |
2897 | value. (In a scalar context, it merely returns the first value | |
2898 | produced.) The TEMPLATE has the same format as in the pack function. | |
2899 | Here's a subroutine that does substring: | |
2900 | ||
2901 | sub substr { | |
2902 | local($what,$where,$howmuch) = @_; | |
2903 | unpack("x$where a$howmuch", $what); | |
2904 | } | |
2905 | ||
2906 | and then there's | |
2907 | ||
2908 | sub ordinal { unpack("c",$_[0]); } # same as ord() | |
2909 | ||
2910 | In addition, you may prefix a field with a %<number> to indicate that | |
2911 | you want a <number>-bit checksum of the items instead of the items | |
2912 | themselves. Default is a 16-bit checksum. For example, the following | |
2913 | computes the same number as the System V sum program: | |
2914 | ||
2915 | while (<>) { | |
2916 | $checksum += unpack("%16C*", $_); | |
2917 | } | |
2918 | $checksum %= 65536; | |
2919 | ||
2920 | The following efficiently counts the number of set bits in a bit vector: | |
2921 | ||
2922 | $setbits = unpack("%32b*", $selectmask); | |
2923 | ||
2924 | =item untie VARIABLE | |
2925 | ||
2926 | Breaks the binding between a variable and a package. (See tie().) | |
2927 | ||
2928 | =item unshift ARRAY,LIST | |
2929 | ||
2930 | Does the opposite of a C<shift>. Or the opposite of a C<push>, | |
2931 | depending on how you look at it. Prepends list to the front of the | |
2932 | array, and returns the new number of elements in the array. | |
2933 | ||
2934 | unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/; | |
2935 | ||
2936 | Note the LIST is prepended whole, not one element at a time, so the | |
2937 | prepended elements stay in the same order. Use reverse to do the | |
2938 | reverse. | |
2939 | ||
2940 | =item use Module LIST | |
2941 | ||
2942 | =item use Module | |
2943 | ||
2944 | Imports some semantics into the current package from the named module, | |
2945 | generally by aliasing certain subroutine or variable names into your | |
2946 | package. It is exactly equivalent to | |
2947 | ||
2948 | BEGIN { require Module; import Module LIST; } | |
2949 | ||
2950 | If you don't want your namespace altered, use require instead. | |
2951 | ||
2952 | The BEGIN forces the require and import to happen at compile time. The | |
2953 | require makes sure the module is loaded into memory if it hasn't been | |
2954 | yet. The import is not a builtin--it's just an ordinary static method | |
2955 | call into the "Module" package to tell the module to import the list of | |
2956 | features back into the current package. The module can implement its | |
2957 | import method any way it likes, though most modules just choose to | |
2958 | derive their import method via inheritance from the Exporter class that | |
2959 | is defined in the Exporter module. | |
2960 | ||
2961 | Because this is a wide-open interface, pragmas (compiler directives) | |
2962 | are also implemented this way. Currently implemented pragmas are: | |
2963 | ||
2964 | use integer; | |
4633a7c4 | 2965 | use diagnostics; |
a0d0e21e LW |
2966 | use sigtrap qw(SEGV BUS); |
2967 | use strict qw(subs vars refs); | |
2968 | use subs qw(afunc blurfl); | |
2969 | ||
2970 | These pseudomodules import semantics into the current block scope, unlike | |
2971 | ordinary modules, which import symbols into the current package (which are | |
2972 | effective through the end of the file). | |
2973 | ||
2974 | There's a corresponding "no" command that unimports meanings imported | |
2975 | by use. | |
2976 | ||
2977 | no integer; | |
2978 | no strict 'refs'; | |
2979 | ||
2980 | See L<perlmod> for a list of standard modules and pragmas. | |
2981 | ||
2982 | =item utime LIST | |
2983 | ||
2984 | Changes the access and modification times on each file of a list of | |
2985 | files. The first two elements of the list must be the NUMERICAL access | |
2986 | and modification times, in that order. Returns the number of files | |
2987 | successfully changed. The inode modification time of each file is set | |
2988 | to the current time. Example of a "touch" command: | |
2989 | ||
2990 | #!/usr/bin/perl | |
2991 | $now = time; | |
2992 | utime $now, $now, @ARGV; | |
2993 | ||
2994 | =item values ASSOC_ARRAY | |
2995 | ||
2996 | Returns a normal array consisting of all the values of the named | |
2997 | associative array. (In a scalar context, returns the number of | |
2998 | values.) The values are returned in an apparently random order, but it | |
2999 | is the same order as either the keys() or each() function would produce | |
3000 | on the same array. See also keys() and each(). | |
3001 | ||
3002 | =item vec EXPR,OFFSET,BITS | |
3003 | ||
3004 | Treats a string as a vector of unsigned integers, and returns the value | |
3005 | of the bitfield specified. May also be assigned to. BITS must be a | |
3006 | power of two from 1 to 32. | |
3007 | ||
3008 | Vectors created with vec() can also be manipulated with the logical | |
3009 | operators |, & and ^, which will assume a bit vector operation is | |
3010 | desired when both operands are strings. | |
3011 | ||
3012 | To transform a bit vector into a string or array of 0's and 1's, use these: | |
3013 | ||
3014 | $bits = unpack("b*", $vector); | |
3015 | @bits = split(//, unpack("b*", $vector)); | |
3016 | ||
3017 | If you know the exact length in bits, it can be used in place of the *. | |
3018 | ||
3019 | =item wait | |
3020 | ||
3021 | Waits for a child process to terminate and returns the pid of the | |
3022 | deceased process, or -1 if there are no child processes. The status is | |
3023 | returned in $?. | |
3024 | ||
3025 | =item waitpid PID,FLAGS | |
3026 | ||
3027 | Waits for a particular child process to terminate and returns the pid | |
3028 | of the deceased process, or -1 if there is no such child process. The | |
3029 | status is returned in $?. If you say | |
3030 | ||
3031 | use POSIX "wait_h"; | |
3032 | ... | |
3033 | waitpid(-1,&WNOHANG); | |
3034 | ||
3035 | then you can do a non-blocking wait for any process. Non-blocking wait | |
3036 | is only available on machines supporting either the waitpid(2) or | |
3037 | wait4(2) system calls. However, waiting for a particular pid with | |
3038 | FLAGS of 0 is implemented everywhere. (Perl emulates the system call | |
3039 | by remembering the status values of processes that have exited but have | |
3040 | not been harvested by the Perl script yet.) | |
3041 | ||
3042 | =item wantarray | |
3043 | ||
3044 | Returns TRUE if the context of the currently executing subroutine is | |
3045 | looking for a list value. Returns FALSE if the context is looking | |
3046 | for a scalar. | |
3047 | ||
3048 | return wantarray ? () : undef; | |
3049 | ||
3050 | =item warn LIST | |
3051 | ||
3052 | Produces a message on STDERR just like die(), but doesn't exit or | |
4633a7c4 | 3053 | on an exception. |
a0d0e21e LW |
3054 | |
3055 | =item write FILEHANDLE | |
3056 | ||
3057 | =item write EXPR | |
3058 | ||
3059 | =item write | |
3060 | ||
3061 | Writes a formatted record (possibly multi-line) to the specified file, | |
3062 | using the format associated with that file. By default the format for | |
3063 | a file is the one having the same name is the filehandle, but the | |
3064 | format for the current output channel (see the select() function) may be set | |
3065 | explicitly by assigning the name of the format to the $~ variable. | |
3066 | ||
3067 | Top of form processing is handled automatically: if there is | |
3068 | insufficient room on the current page for the formatted record, the | |
3069 | page is advanced by writing a form feed, a special top-of-page format | |
3070 | is used to format the new page header, and then the record is written. | |
3071 | By default the top-of-page format is the name of the filehandle with | |
3072 | "_TOP" appended, but it may be dynamically set to the format of your | |
3073 | choice by assigning the name to the $^ variable while the filehandle is | |
3074 | selected. The number of lines remaining on the current page is in | |
3075 | variable $-, which can be set to 0 to force a new page. | |
3076 | ||
3077 | If FILEHANDLE is unspecified, output goes to the current default output | |
3078 | channel, which starts out as STDOUT but may be changed by the | |
3079 | C<select> operator. If the FILEHANDLE is an EXPR, then the expression | |
3080 | is evaluated and the resulting string is used to look up the name of | |
3081 | the FILEHANDLE at run time. For more on formats, see L<perlform>. | |
3082 | ||
3083 | Note that write is I<NOT> the opposite of read. Unfortunately. | |
3084 | ||
3085 | =item y/// | |
3086 | ||
3087 | The translation operator. See L<perlop/tr///>. | |
3088 | ||
3089 | =back |