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a687059c |
1 | ''' Beginning of part 3 |
2 | ''' $Header: perl.man.3,v 3.0 89/10/18 15:21:46 lwall Locked $ |
3 | ''' |
4 | ''' $Log: perl.man.3,v $ |
5 | ''' Revision 3.0 89/10/18 15:21:46 lwall |
6 | ''' 3.0 baseline |
7 | ''' |
8 | .Ip "next LABEL" 8 8 |
9 | .Ip "next" 8 |
10 | The |
11 | .I next |
12 | command is like the |
13 | .I continue |
14 | statement in C; it starts the next iteration of the loop: |
15 | .nf |
16 | |
17 | .ne 4 |
18 | line: while (<STDIN>) { |
19 | next line if /\|^#/; # discard comments |
20 | .\|.\|. |
21 | } |
22 | |
23 | .fi |
24 | Note that if there were a |
25 | .I continue |
26 | block on the above, it would get executed even on discarded lines. |
27 | If the LABEL is omitted, the command refers to the innermost enclosing loop. |
28 | .Ip "oct(EXPR)" 8 4 |
29 | .Ip "oct EXPR" 8 |
30 | Returns the decimal value of EXPR interpreted as an octal string. |
31 | (If EXPR happens to start off with 0x, interprets it as a hex string instead.) |
32 | The following will handle decimal, octal and hex in the standard notation: |
33 | .nf |
34 | |
35 | $val = oct($val) if $val =~ /^0/; |
36 | |
37 | .fi |
38 | If EXPR is omitted, uses $_. |
39 | .Ip "open(FILEHANDLE,EXPR)" 8 8 |
40 | .Ip "open(FILEHANDLE)" 8 |
41 | .Ip "open FILEHANDLE" 8 |
42 | Opens the file whose filename is given by EXPR, and associates it with |
43 | FILEHANDLE. |
44 | If FILEHANDLE is an expression, its value is used as the name of the |
45 | real filehandle wanted. |
46 | If EXPR is omitted, the scalar variable of the same name as the FILEHANDLE |
47 | contains the filename. |
48 | If the filename begins with \*(L"<\*(R" or nothing, the file is opened for |
49 | input. |
50 | If the filename begins with \*(L">\*(R", the file is opened for output. |
51 | If the filename begins with \*(L">>\*(R", the file is opened for appending. |
52 | (You can put a \'+\' in front of the \'>\' or \'<\' to indicate that you |
53 | want both read and write access to the file.) |
54 | If the filename begins with \*(L"|\*(R", the filename is interpreted |
55 | as a command to which output is to be piped, and if the filename ends |
56 | with a \*(L"|\*(R", the filename is interpreted as command which pipes |
57 | input to us. |
58 | (You may not have a command that pipes both in and out.) |
59 | Opening \'\-\' opens |
60 | .I STDIN |
61 | and opening \'>\-\' opens |
62 | .IR STDOUT . |
63 | Open returns non-zero upon success, the undefined value otherwise. |
64 | If the open involved a pipe, the return value happens to be the pid |
65 | of the subprocess. |
66 | Examples: |
67 | .nf |
68 | |
69 | .ne 3 |
70 | $article = 100; |
71 | open article || die "Can't find article $article: $!\en"; |
72 | while (<article>) {\|.\|.\|. |
73 | |
74 | open(LOG, \'>>/usr/spool/news/twitlog\'\|); # (log is reserved) |
75 | |
76 | open(article, "caesar <$article |"\|); # decrypt article |
77 | |
78 | open(extract, "|sort >/tmp/Tmp$$"\|); # $$ is our process# |
79 | |
80 | .ne 7 |
81 | # process argument list of files along with any includes |
82 | |
83 | foreach $file (@ARGV) { |
84 | do process($file, \'fh00\'); # no pun intended |
85 | } |
86 | |
87 | sub process { |
88 | local($filename, $input) = @_; |
89 | $input++; # this is a string increment |
90 | unless (open($input, $filename)) { |
91 | print STDERR "Can't open $filename: $!\en"; |
92 | return; |
93 | } |
94 | while (<$input>) { # note the use of indirection |
95 | if (/^#include "(.*)"/) { |
96 | do process($1, $input); |
97 | next; |
98 | } |
99 | .\|.\|. # whatever |
100 | } |
101 | } |
102 | |
103 | .fi |
104 | You may also, in the Bourne shell tradition, specify an EXPR beginning |
105 | with \*(L">&\*(R", in which case the rest of the string |
106 | is interpreted as the name of a filehandle |
107 | (or file descriptor, if numeric) which is to be duped and opened. |
108 | Here is a script that saves, redirects, and restores |
109 | .I STDOUT |
110 | and |
111 | .IR STDIN : |
112 | .nf |
113 | |
114 | .ne 21 |
115 | #!/usr/bin/perl |
116 | open(SAVEOUT, ">&STDOUT"); |
117 | open(SAVEERR, ">&STDERR"); |
118 | |
119 | open(STDOUT, ">foo.out") || die "Can't redirect stdout"; |
120 | open(STDERR, ">&STDOUT") || die "Can't dup stdout"; |
121 | |
122 | select(STDERR); $| = 1; # make unbuffered |
123 | select(STDOUT); $| = 1; # make unbuffered |
124 | |
125 | print STDOUT "stdout 1\en"; # this works for |
126 | print STDERR "stderr 1\en"; # subprocesses too |
127 | |
128 | close(STDOUT); |
129 | close(STDERR); |
130 | |
131 | open(STDOUT, ">&SAVEOUT"); |
132 | open(STDERR, ">&SAVEERR"); |
133 | |
134 | print STDOUT "stdout 2\en"; |
135 | print STDERR "stderr 2\en"; |
136 | |
137 | .fi |
138 | If you open a pipe on the command \*(L"\-\*(R", i.e. either \*(L"|\-\*(R" or \*(L"\-|\*(R", |
139 | then there is an implicit fork done, and the return value of open |
140 | is the pid of the child within the parent process, and 0 within the child |
141 | process. |
142 | (Use defined($pid) to determine if the open was successful.) |
143 | The filehandle behaves normally for the parent, but i/o to that |
144 | filehandle is piped from/to the |
145 | .IR STDOUT / STDIN |
146 | of the child process. |
147 | In the child process the filehandle isn't opened\*(--i/o happens from/to |
148 | the new |
149 | .I STDOUT |
150 | or |
151 | .IR STDIN . |
152 | Typically this is used like the normal piped open when you want to exercise |
153 | more control over just how the pipe command gets executed, such as when |
154 | you are running setuid, and don't want to have to scan shell commands |
155 | for metacharacters. |
156 | The following pairs are equivalent: |
157 | .nf |
158 | |
159 | .ne 5 |
160 | open(FOO, "|tr \'[a\-z]\' \'[A\-Z]\'"); |
161 | open(FOO, "|\-") || exec \'tr\', \'[a\-z]\', \'[A\-Z]\'; |
162 | |
163 | open(FOO, "cat \-n $file|"); |
164 | open(FOO, "\-|") || exec \'cat\', \'\-n\', $file; |
165 | |
166 | .fi |
167 | Explicitly closing any piped filehandle causes the parent process to wait for the |
168 | child to finish, and returns the status value in $?. |
169 | .Ip "opendir(DIRHANDLE,EXPR)" 8 3 |
170 | Opens a directory named EXPR for processing by readdir(), telldir(), seekdir(), |
171 | rewinddir() and closedir(). |
172 | Returns true if successful. |
173 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
174 | .Ip "ord(EXPR)" 8 4 |
175 | .Ip "ord EXPR" 8 |
176 | Returns the ascii value of the first character of EXPR. |
177 | If EXPR is omitted, uses $_. |
178 | .Ip "pack(TEMPLATE,LIST)" 8 4 |
179 | Takes an array or list of values and packs it into a binary structure, |
180 | returning the string containing the structure. |
181 | The TEMPLATE is a sequence of characters that give the order and type |
182 | of values, as follows: |
183 | .nf |
184 | |
185 | A An ascii string, will be space padded. |
186 | a An ascii string, will be null padded. |
187 | c A native char value. |
188 | C An unsigned char value. |
189 | s A signed short value. |
190 | S An unsigned short value. |
191 | i A signed integer value. |
192 | I An unsigned integer value. |
193 | l A signed long value. |
194 | L An unsigned long value. |
195 | n A short in \*(L"network\*(R" order. |
196 | N A long in \*(L"network\*(R" order. |
197 | p A pointer to a string. |
198 | x A null byte. |
199 | |
200 | .fi |
201 | Each letter may optionally be followed by a number which gives a repeat |
202 | count. |
203 | With all types except "a" and "A" the pack function will gobble up that many values |
204 | from the LIST. |
205 | The "a" and "A" types gobble just one value, but pack it as a string that long, |
206 | padding with nulls or spaces as necessary. |
207 | (When unpacking, "A" strips trailing spaces and nulls, but "a" does not.) |
208 | Examples: |
209 | .nf |
210 | |
211 | $foo = pack("cccc",65,66,67,68); |
212 | # foo eq "ABCD" |
213 | $foo = pack("c4",65,66,67,68); |
214 | # same thing |
215 | |
216 | $foo = pack("ccxxcc",65,66,67,68); |
217 | # foo eq "AB\e0\e0CD" |
218 | |
219 | $foo = pack("s2",1,2); |
220 | # "\e1\e0\e2\e0" on little-endian |
221 | # "\e0\e1\e0\e2" on big-endian |
222 | |
223 | $foo = pack("a4","abcd","x","y","z"); |
224 | # "abcd" |
225 | |
226 | $foo = pack("aaaa","abcd","x","y","z"); |
227 | # "axyz" |
228 | |
229 | $foo = pack("a14","abcdefg"); |
230 | # "abcdefg\e0\e0\e0\e0\e0\e0\e0" |
231 | |
232 | $foo = pack("i9pl", gmtime()); |
233 | # a real struct tm (on my system anyway) |
234 | |
235 | .fi |
236 | The same template may generally also be used in the unpack function. |
237 | .Ip "pop(ARRAY)" 8 |
238 | .Ip "pop ARRAY" 8 6 |
239 | Pops and returns the last value of the array, shortening the array by 1. |
240 | Has the same effect as |
241 | .nf |
242 | |
243 | $tmp = $ARRAY[$#ARRAY\-\|\-]; |
244 | |
245 | .fi |
246 | If there are no elements in the array, returns the undefined value. |
247 | .Ip "print(FILEHANDLE LIST)" 8 10 |
248 | .Ip "print(LIST)" 8 |
249 | .Ip "print FILEHANDLE LIST" 8 |
250 | .Ip "print LIST" 8 |
251 | .Ip "print" 8 |
252 | Prints a string or a comma-separated list of strings. |
253 | Returns non-zero if successful. |
254 | FILEHANDLE may be a scalar variable name, in which case the variable contains |
255 | the name of the filehandle, thus introducing one level of indirection. |
256 | If FILEHANDLE is omitted, prints by default to standard output (or to the |
257 | last selected output channel\*(--see select()). |
258 | If LIST is also omitted, prints $_ to |
259 | .IR STDOUT . |
260 | To set the default output channel to something other than |
261 | .I STDOUT |
262 | use the select operation. |
263 | .Ip "printf(FILEHANDLE LIST)" 8 10 |
264 | .Ip "printf(LIST)" 8 |
265 | .Ip "printf FILEHANDLE LIST" 8 |
266 | .Ip "printf LIST" 8 |
267 | Equivalent to a \*(L"print FILEHANDLE sprintf(LIST)\*(R". |
268 | .Ip "push(ARRAY,LIST)" 8 7 |
269 | Treats ARRAY (@ is optional) as a stack, and pushes the values of LIST |
270 | onto the end of ARRAY. |
271 | The length of ARRAY increases by the length of LIST. |
272 | Has the same effect as |
273 | .nf |
274 | |
275 | for $value (LIST) { |
276 | $ARRAY[++$#ARRAY] = $value; |
277 | } |
278 | |
279 | .fi |
280 | but is more efficient. |
281 | .Ip "q/STRING/" 8 5 |
282 | .Ip "qq/STRING/" 8 |
283 | These are not really functions, but simply syntactic sugar to let you |
284 | avoid putting too many backslashes into quoted strings. |
285 | The q operator is a generalized single quote, and the qq operator a |
286 | generalized double quote. |
287 | Any delimiter can be used in place of /, including newline. |
288 | If the delimiter is an opening bracket or parenthesis, the final delimiter |
289 | will be the corresponding closing bracket or parenthesis. |
290 | (Embedded occurrences of the closing bracket need to be backslashed as usual.) |
291 | Examples: |
292 | .nf |
293 | |
294 | .ne 5 |
295 | $foo = q!I said, "You said, \'She said it.\'"!; |
296 | $bar = q(\'This is it.\'); |
297 | $_ .= qq |
298 | *** The previous line contains the naughty word "$&".\en |
299 | if /(ibm|apple|awk)/; # :-) |
300 | |
301 | .fi |
302 | .Ip "rand(EXPR)" 8 8 |
303 | .Ip "rand EXPR" 8 |
304 | .Ip "rand" 8 |
305 | Returns a random fractional number between 0 and the value of EXPR. |
306 | (EXPR should be positive.) |
307 | If EXPR is omitted, returns a value between 0 and 1. |
308 | See also srand(). |
309 | .Ip "read(FILEHANDLE,SCALAR,LENGTH)" 8 5 |
310 | Attempts to read LENGTH bytes of data into variable SCALAR from the specified |
311 | FILEHANDLE. |
312 | Returns the number of bytes actually read. |
313 | SCALAR will be grown or shrunk to the length actually read. |
314 | .Ip "readdir(DIRHANDLE)" 8 3 |
315 | Returns the next directory entry for a directory opened by opendir(). |
316 | If used in an array context, returns all the rest of the entries in the |
317 | directory. |
318 | If there are no more entries, returns an undefined value in a scalar context |
319 | or a null list in an array context. |
320 | .Ip "readlink(EXPR)" 8 6 |
321 | .Ip "readlink EXPR" 8 |
322 | Returns the value of a symbolic link, if symbolic links are implemented. |
323 | If not, gives a fatal error. |
324 | If there is some system error, returns the undefined value and sets $! (errno). |
325 | If EXPR is omitted, uses $_. |
326 | .Ip "recv(SOCKET,SCALAR,LEN,FLAGS)" 8 4 |
327 | Receives a message on a socket. |
328 | Attempts to receive LENGTH bytes of data into variable SCALAR from the specified |
329 | SOCKET filehandle. |
330 | Returns the address of the sender, or the undefined value if there's an error. |
331 | SCALAR will be grown or shrunk to the length actually read. |
332 | Takes the same flags as the system call of the same name. |
333 | .Ip "redo LABEL" 8 8 |
334 | .Ip "redo" 8 |
335 | The |
336 | .I redo |
337 | command restarts the loop block without evaluating the conditional again. |
338 | The |
339 | .I continue |
340 | block, if any, is not executed. |
341 | If the LABEL is omitted, the command refers to the innermost enclosing loop. |
342 | This command is normally used by programs that want to lie to themselves |
343 | about what was just input: |
344 | .nf |
345 | |
346 | .ne 16 |
347 | # a simpleminded Pascal comment stripper |
348 | # (warning: assumes no { or } in strings) |
349 | line: while (<STDIN>) { |
350 | while (s|\|({.*}.*\|){.*}|$1 \||) {} |
351 | s|{.*}| \||; |
352 | if (s|{.*| \||) { |
353 | $front = $_; |
354 | while (<STDIN>) { |
355 | if (\|/\|}/\|) { # end of comment? |
356 | s|^|$front{|; |
357 | redo line; |
358 | } |
359 | } |
360 | } |
361 | print; |
362 | } |
363 | |
364 | .fi |
365 | .Ip "rename(OLDNAME,NEWNAME)" 8 2 |
366 | Changes the name of a file. |
367 | Returns 1 for success, 0 otherwise. |
368 | Will not work across filesystem boundaries. |
369 | .Ip "reset(EXPR)" 8 6 |
370 | .Ip "reset EXPR" 8 |
371 | .Ip "reset" 8 |
372 | Generally used in a |
373 | .I continue |
374 | block at the end of a loop to clear variables and reset ?? searches |
375 | so that they work again. |
376 | The expression is interpreted as a list of single characters (hyphens allowed |
377 | for ranges). |
378 | All variables and arrays beginning with one of those letters are reset to |
379 | their pristine state. |
380 | If the expression is omitted, one-match searches (?pattern?) are reset to |
381 | match again. |
382 | Only resets variables or searches in the current package. |
383 | Always returns 1. |
384 | Examples: |
385 | .nf |
386 | |
387 | .ne 3 |
388 | reset \'X\'; \h'|2i'# reset all X variables |
389 | reset \'a\-z\';\h'|2i'# reset lower case variables |
390 | reset; \h'|2i'# just reset ?? searches |
391 | |
392 | .fi |
393 | Note: resetting \*(L"A\-Z\*(R" is not recommended since you'll wipe out your ARGV and ENV |
394 | arrays. |
395 | .Sp |
396 | The use of reset on dbm associative arrays does not change the dbm file. |
397 | (It does, however, flush any entries cached by perl, which may be useful if |
398 | you are sharing the dbm file. |
399 | Then again, maybe not.) |
400 | .Ip "return LIST" 8 3 |
401 | Returns from a subroutine with the value specified. |
402 | (Note that a subroutine can automatically return |
403 | the value of the last expression evaluated. |
404 | That's the preferred method\*(--use of an explicit |
405 | .I return |
406 | is a bit slower.) |
407 | .Ip "reverse(LIST)" 8 4 |
408 | .Ip "reverse LIST" 8 |
409 | Returns an array value consisting of the elements of LIST in the opposite order. |
410 | .Ip "rewinddir(DIRHANDLE)" 8 5 |
411 | .Ip "rewinddir DIRHANDLE" 8 |
412 | Sets the current position to the beginning of the directory for the readdir() routine on DIRHANDLE. |
413 | .Ip "rindex(STR,SUBSTR)" 8 4 |
414 | Works just like index except that it |
415 | returns the position of the LAST occurrence of SUBSTR in STR. |
416 | .Ip "rmdir(FILENAME)" 8 4 |
417 | .Ip "rmdir FILENAME" 8 |
418 | Deletes the directory specified by FILENAME if it is empty. |
419 | If it succeeds it returns 1, otherwise it returns 0 and sets $! (errno). |
420 | If FILENAME is omitted, uses $_. |
421 | .Ip "s/PATTERN/REPLACEMENT/gieo" 8 3 |
422 | Searches a string for a pattern, and if found, replaces that pattern with the |
423 | replacement text and returns the number of substitutions made. |
424 | Otherwise it returns false (0). |
425 | The \*(L"g\*(R" is optional, and if present, indicates that all occurrences |
426 | of the pattern are to be replaced. |
427 | The \*(L"i\*(R" is also optional, and if present, indicates that matching |
428 | is to be done in a case-insensitive manner. |
429 | The \*(L"e\*(R" is likewise optional, and if present, indicates that |
430 | the replacement string is to be evaluated as an expression rather than just |
431 | as a double-quoted string. |
432 | Any delimiter may replace the slashes; if single quotes are used, no |
433 | interpretation is done on the replacement string (the e modifier overrides |
434 | this, however). |
435 | If no string is specified via the =~ or !~ operator, |
436 | the $_ string is searched and modified. |
437 | (The string specified with =~ must be a scalar variable, an array element, |
438 | or an assignment to one of those, i.e. an lvalue.) |
439 | If the pattern contains a $ that looks like a variable rather than an |
440 | end-of-string test, the variable will be interpolated into the pattern at |
441 | run-time. |
442 | If you only want the pattern compiled once the first time the variable is |
443 | interpolated, add an \*(L"o\*(R" at the end. |
444 | See also the section on regular expressions. |
445 | Examples: |
446 | .nf |
447 | |
448 | s/\|\e\|bgreen\e\|b/mauve/g; # don't change wintergreen |
449 | |
450 | $path \|=~ \|s|\|/usr/bin|\|/usr/local/bin|; |
451 | |
452 | s/Login: $foo/Login: $bar/; # run-time pattern |
453 | |
454 | ($foo = $bar) =~ s/bar/foo/; |
455 | |
456 | $_ = \'abc123xyz\'; |
457 | s/\ed+/$&*2/e; # yields \*(L'abc246xyz\*(R' |
458 | s/\ed+/sprintf("%5d",$&)/e; # yields \*(L'abc 246xyz\*(R' |
459 | s/\ew/$& x 2/eg; # yields \*(L'aabbcc 224466xxyyzz\*(R' |
460 | |
461 | s/\|([^ \|]*\|) *\|([^ \|]*\|)\|/\|$2 $1/; # reverse 1st two fields |
462 | |
463 | .fi |
464 | (Note the use of $ instead of \|\e\| in the last example. See section |
465 | on regular expressions.) |
466 | .Ip "seek(FILEHANDLE,POSITION,WHENCE)" 8 3 |
467 | Randomly positions the file pointer for FILEHANDLE, just like the fseek() |
468 | call of stdio. |
469 | FILEHANDLE may be an expression whose value gives the name of the filehandle. |
470 | Returns 1 upon success, 0 otherwise. |
471 | .Ip "seekdir(DIRHANDLE,POS)" 8 3 |
472 | Sets the current position for the readdir() routine on DIRHANDLE. |
473 | POS must be a value returned by seekdir(). |
474 | Has the same caveats about possible directory compaction as the corresponding |
475 | system library routine. |
476 | .Ip "select(FILEHANDLE)" 8 3 |
477 | .Ip "select" 8 3 |
478 | Returns the currently selected filehandle. |
479 | Sets the current default filehandle for output, if FILEHANDLE is supplied. |
480 | This has two effects: first, a |
481 | .I write |
482 | or a |
483 | .I print |
484 | without a filehandle will default to this FILEHANDLE. |
485 | Second, references to variables related to output will refer to this output |
486 | channel. |
487 | For example, if you have to set the top of form format for more than |
488 | one output channel, you might do the following: |
489 | .nf |
490 | |
491 | .ne 4 |
492 | select(REPORT1); |
493 | $^ = \'report1_top\'; |
494 | select(REPORT2); |
495 | $^ = \'report2_top\'; |
496 | |
497 | .fi |
498 | FILEHANDLE may be an expression whose value gives the name of the actual filehandle. |
499 | Thus: |
500 | .nf |
501 | |
502 | $oldfh = select(STDERR); $| = 1; select($oldfh); |
503 | |
504 | .fi |
505 | .Ip "select(RBITS,WBITS,EBITS,TIMEOUT)" 8 3 |
506 | This calls the select system call with the bitmasks specified, which can |
507 | be constructed using fileno() and vec(), along these lines: |
508 | .nf |
509 | |
510 | $rin = $win = $ein = ''; |
511 | vec($rin,fileno(STDIN),1) = 1; |
512 | vec($win,fileno(STDOUT),1) = 1; |
513 | $ein = $rin | $win; |
514 | |
515 | .fi |
516 | If you want to select on many filehandles you might wish to write a subroutine: |
517 | .nf |
518 | |
519 | sub fhbits { |
520 | local(@fhlist) = split(' ',$_[0]); |
521 | local($bits); |
522 | for (@fhlist) { |
523 | vec($bits,fileno($_),1) = 1; |
524 | } |
525 | $bits; |
526 | } |
527 | $rin = &fhbits('STDIN TTY SOCK'); |
528 | |
529 | .fi |
530 | The usual idiom is: |
531 | .nf |
532 | |
533 | ($nfound,$timeleft) = |
534 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); |
535 | |
536 | or to block until something becomes ready: |
537 | |
538 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); |
539 | |
540 | .fi |
541 | Any of the bitmasks can also be undef. |
542 | The timeout, if specified, is in seconds, which may be fractional. |
543 | .Ip "setpgrp(PID,PGRP)" 8 4 |
544 | Sets the current process group for the specified PID, 0 for the current |
545 | process. |
546 | Will produce a fatal error if used on a machine that doesn't implement |
547 | setpgrp(2). |
548 | .Ip "send(SOCKET,MSG,FLAGS,TO)" 8 4 |
549 | .Ip "send(SOCKET,MSG,FLAGS)" 8 |
550 | Sends a message on a socket. |
551 | Takes the same flags as the system call of the same name. |
552 | On unconnected sockets you must specify a destination to send TO. |
553 | Returns the number of characters sent, or the undefined value if |
554 | there is an error. |
555 | .Ip "setpriority(WHICH,WHO,PRIORITY)" 8 4 |
556 | Sets the current priority for a process, a process group, or a user. |
557 | (See setpriority(2).) |
558 | Will produce a fatal error if used on a machine that doesn't implement |
559 | setpriority(2). |
560 | .Ip "setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)" 8 3 |
561 | Sets the socket option requested. |
562 | Returns undefined if there is an error. |
563 | OPTVAL may be specified as undef if you don't want to pass an argument. |
564 | .Ip "shift(ARRAY)" 8 6 |
565 | .Ip "shift ARRAY" 8 |
566 | .Ip "shift" 8 |
567 | Shifts the first value of the array off and returns it, |
568 | shortening the array by 1 and moving everything down. |
569 | If there are no elements in the array, returns the undefined value. |
570 | If ARRAY is omitted, shifts the @ARGV array in the main program, and the @_ |
571 | array in subroutines. |
572 | See also unshift(), push() and pop(). |
573 | Shift() and unshift() do the same thing to the left end of an array that push() |
574 | and pop() do to the right end. |
575 | .Ip "shutdown(SOCKET,HOW)" 8 3 |
576 | Shuts down a socket connection in the manner indicated by HOW, which has |
577 | the same interpretation as in the system call of the same name. |
578 | .Ip "sin(EXPR)" 8 4 |
579 | .Ip "sin EXPR" 8 |
580 | Returns the sine of EXPR (expressed in radians). |
581 | If EXPR is omitted, returns sine of $_. |
582 | .Ip "sleep(EXPR)" 8 6 |
583 | .Ip "sleep EXPR" 8 |
584 | .Ip "sleep" 8 |
585 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. |
586 | May be interrupted by sending the process a SIGALARM. |
587 | Returns the number of seconds actually slept. |
588 | .Ip "socket(SOCKET,DOMAIN,TYPE,PROTOCOL)" 8 3 |
589 | Opens a socket of the specified kind and attaches it to filehandle SOCKET. |
590 | DOMAIN, TYPE and PROTOCOL are specified the same as for the system call |
591 | of the same name. |
592 | You may need to run makelib on sys/socket.h to get the proper values handy |
593 | in a perl library file. |
594 | Return true if successful. |
595 | See the example in the section on Interprocess Communication. |
596 | .Ip "socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)" 8 3 |
597 | Creates an unnamed pair of sockets in the specified domain, of the specified |
598 | type. |
599 | DOMAIN, TYPE and PROTOCOL are specified the same as for the system call |
600 | of the same name. |
601 | If unimplemented, yields a fatal error. |
602 | Return true if successful. |
603 | .Ip "sort(SUBROUTINE LIST)" 8 9 |
604 | .Ip "sort(LIST)" 8 |
605 | .Ip "sort SUBROUTINE LIST" 8 |
606 | .Ip "sort LIST" 8 |
607 | Sorts the LIST and returns the sorted array value. |
608 | Nonexistent values of arrays are stripped out. |
609 | If SUBROUTINE is omitted, sorts in standard string comparison order. |
610 | If SUBROUTINE is specified, gives the name of a subroutine that returns |
611 | an integer less than, equal to, or greater than 0, |
612 | depending on how the elements of the array are to be ordered. |
613 | In the interests of efficiency the normal calling code for subroutines |
614 | is bypassed, with the following effects: the subroutine may not be a recursive |
615 | subroutine, and the two elements to be compared are passed into the subroutine |
616 | not via @_ but as $a and $b (see example below). |
617 | They are passed by reference so don't modify $a and $b. |
618 | SUBROUTINE may be a scalar variable name, in which case the value provides |
619 | the name of the subroutine to use. |
620 | Examples: |
621 | .nf |
622 | |
623 | .ne 4 |
624 | sub byage { |
625 | $age{$a} - $age{$b}; # presuming integers |
626 | } |
627 | @sortedclass = sort byage @class; |
628 | |
629 | .ne 9 |
630 | sub reverse { $a lt $b ? 1 : $a gt $b ? \-1 : 0; } |
631 | @harry = (\'dog\',\'cat\',\'x\',\'Cain\',\'Abel\'); |
632 | @george = (\'gone\',\'chased\',\'yz\',\'Punished\',\'Axed\'); |
633 | print sort @harry; |
634 | # prints AbelCaincatdogx |
635 | print sort reverse @harry; |
636 | # prints xdogcatCainAbel |
637 | print sort @george, \'to\', @harry; |
638 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz |
639 | |
640 | .fi |
641 | .Ip "split(/PATTERN/,EXPR,LIMIT)" 8 8 |
642 | .Ip "split(/PATTERN/,EXPR)" 8 8 |
643 | .Ip "split(/PATTERN/)" 8 |
644 | .Ip "split" 8 |
645 | Splits a string into an array of strings, and returns it. |
646 | (If not in an array context, returns the number of fields found and splits |
647 | into the @_ array.) |
648 | If EXPR is omitted, splits the $_ string. |
649 | If PATTERN is also omitted, splits on whitespace (/[\ \et\en]+/). |
650 | Anything matching PATTERN is taken to be a delimiter separating the fields. |
651 | (Note that the delimiter may be longer than one character.) |
652 | If LIMIT is specified, splits into no more than that many fields (though it |
653 | may split into fewer). |
654 | If LIMIT is unspecified, trailing null fields are stripped (which |
655 | potential users of pop() would do well to remember). |
656 | A pattern matching the null string (not to be confused with a null pattern, |
657 | which is one member of the set of patterns matching a null string) |
658 | will split the value of EXPR into separate characters at each point it |
659 | matches that way. |
660 | For example: |
661 | .nf |
662 | |
663 | print join(\':\', split(/ */, \'hi there\')); |
664 | |
665 | .fi |
666 | produces the output \*(L'h:i:t:h:e:r:e\*(R'. |
667 | .P |
668 | The NUM parameter can be used to partially split a line |
669 | .nf |
670 | |
671 | ($login, $passwd, $remainder) = split(\|/\|:\|/\|, $_, 3); |
672 | |
673 | .fi |
674 | (When assigning to a list, if NUM is omitted, perl supplies a NUM one |
675 | larger than the number of variables in the list, to avoid unnecessary work. |
676 | For the list above NUM would have been 4 by default. |
677 | In time critical applications it behooves you not to split into |
678 | more fields than you really need.) |
679 | .Sp |
680 | If the PATTERN contains parentheses, additional array elements are created |
681 | from each matching substring in the delimiter. |
682 | .Sp |
683 | split(/([,-])/,"1-10,20"); |
684 | .Sp |
685 | produces the array value |
686 | .Sp |
687 | (1,'-',10,',',20) |
688 | .Sp |
689 | The pattern /PATTERN/ may be replaced with an expression to specify patterns |
690 | that vary at runtime. |
691 | (To do runtime compilation only once, use /$variable/o.) |
692 | As a special case, specifying a space (\'\ \') will split on white space |
693 | just as split with no arguments does, but leading white space does NOT |
694 | produce a null first field. |
695 | Thus, split(\'\ \') can be used to emulate |
696 | .IR awk 's |
697 | default behavior, whereas |
698 | split(/\ /) will give you as many null initial fields as there are |
699 | leading spaces. |
700 | .Sp |
701 | Example: |
702 | .nf |
703 | |
704 | .ne 5 |
705 | open(passwd, \'/etc/passwd\'); |
706 | while (<passwd>) { |
707 | .ie t \{\ |
708 | ($login, $passwd, $uid, $gid, $gcos, $home, $shell) = split(\|/\|:\|/\|); |
709 | 'br\} |
710 | .el \{\ |
711 | ($login, $passwd, $uid, $gid, $gcos, $home, $shell) |
712 | = split(\|/\|:\|/\|); |
713 | 'br\} |
714 | .\|.\|. |
715 | } |
716 | |
717 | .fi |
718 | (Note that $shell above will still have a newline on it. See chop().) |
719 | See also |
720 | .IR join . |
721 | .Ip "sprintf(FORMAT,LIST)" 8 4 |
722 | Returns a string formatted by the usual printf conventions. |
723 | The * character is not supported. |
724 | .Ip "sqrt(EXPR)" 8 4 |
725 | .Ip "sqrt EXPR" 8 |
726 | Return the square root of EXPR. |
727 | If EXPR is omitted, returns square root of $_. |
728 | .Ip "srand(EXPR)" 8 4 |
729 | .Ip "srand EXPR" 8 |
730 | Sets the random number seed for the |
731 | .I rand |
732 | operator. |
733 | If EXPR is omitted, does srand(time). |
734 | .Ip "stat(FILEHANDLE)" 8 6 |
735 | .Ip "stat FILEHANDLE" 8 |
736 | .Ip "stat(EXPR)" 8 |
737 | Returns a 13-element array giving the statistics for a file, either the file |
738 | opened via FILEHANDLE, or named by EXPR. |
739 | Typically used as follows: |
740 | .nf |
741 | |
742 | .ne 3 |
743 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, |
744 | $atime,$mtime,$ctime,$blksize,$blocks) |
745 | = stat($filename); |
746 | |
747 | .fi |
748 | If stat is passed the special filehandle consisting of an underline, |
749 | no stat is done, but the current contents of the stat structure from |
750 | the last stat or filetest are returned. |
751 | Example: |
752 | .nf |
753 | |
754 | .ne 3 |
755 | if (-x $file && (($d) = stat(_)) && $d < 0) { |
756 | print "$file is executable NFS file\en"; |
757 | } |
758 | |
759 | .fi |
760 | .Ip "study(SCALAR)" 8 6 |
761 | .Ip "study SCALAR" 8 |
762 | .Ip "study" |
763 | Takes extra time to study SCALAR ($_ if unspecified) in anticipation of |
764 | doing many pattern matches on the string before it is next modified. |
765 | This may or may not save time, depending on the nature and number of patterns |
766 | you are searching on, and on the distribution of character frequencies in |
767 | the string to be searched\*(--you probably want to compare runtimes with and |
768 | without it to see which runs faster. |
769 | Those loops which scan for many short constant strings (including the constant |
770 | parts of more complex patterns) will benefit most. |
771 | You may have only one study active at a time\*(--if you study a different |
772 | scalar the first is \*(L"unstudied\*(R". |
773 | (The way study works is this: a linked list of every character in the string |
774 | to be searched is made, so we know, for example, where all the \*(L'k\*(R' characters |
775 | are. |
776 | From each search string, the rarest character is selected, based on some |
777 | static frequency tables constructed from some C programs and English text. |
778 | Only those places that contain this \*(L"rarest\*(R" character are examined.) |
779 | .Sp |
780 | For example, here is a loop which inserts index producing entries before any line |
781 | containing a certain pattern: |
782 | .nf |
783 | |
784 | .ne 8 |
785 | while (<>) { |
786 | study; |
787 | print ".IX foo\en" if /\ebfoo\eb/; |
788 | print ".IX bar\en" if /\ebbar\eb/; |
789 | print ".IX blurfl\en" if /\ebblurfl\eb/; |
790 | .\|.\|. |
791 | print; |
792 | } |
793 | |
794 | .fi |
795 | In searching for /\ebfoo\eb/, only those locations in $_ that contain \*(L'f\*(R' |
796 | will be looked at, because \*(L'f\*(R' is rarer than \*(L'o\*(R'. |
797 | In general, this is a big win except in pathological cases. |
798 | The only question is whether it saves you more time than it took to build |
799 | the linked list in the first place. |
800 | .Sp |
801 | Note that if you have to look for strings that you don't know till runtime, |
802 | you can build an entire loop as a string and eval that to avoid recompiling |
803 | all your patterns all the time. |
804 | Together with setting $/ to input entire files as one record, this can |
805 | be very fast, often faster than specialized programs like fgrep. |
806 | The following scans a list of files (@files) |
807 | for a list of words (@words), and prints out the names of those files that |
808 | contain a match: |
809 | .nf |
810 | |
811 | .ne 12 |
812 | $search = \'while (<>) { study;\'; |
813 | foreach $word (@words) { |
814 | $search .= "++\e$seen{\e$ARGV} if /\eb$word\eb/;\en"; |
815 | } |
816 | $search .= "}"; |
817 | @ARGV = @files; |
818 | $/ = "\e177"; # something that doesn't occur |
819 | eval $search; # this screams |
820 | $/ = "\en"; # put back to normal input delim |
821 | foreach $file (sort keys(%seen)) { |
822 | print $file, "\en"; |
823 | } |
824 | |
825 | .fi |
826 | .Ip "substr(EXPR,OFFSET,LEN)" 8 2 |
827 | Extracts a substring out of EXPR and returns it. |
828 | First character is at offset 0, or whatever you've set $[ to. |
829 | If OFFSET is negative, starts that far from the end of the string. |
830 | You can use the substr() function as an lvalue, in which case EXPR must |
831 | be an lvalue. |
832 | If you assign something shorter than LEN, the string will shrink, and |
833 | if you assign something longer than LEN, the string will grow to accomodate it. |
834 | To keep the string the same length you may need to pad or chop your value using |
835 | sprintf(). |
836 | .Ip "syscall(LIST)" 8 6 |
837 | .Ip "syscall LIST" 8 |
838 | Calls the system call specified as the first element of the list, passing |
839 | the remaining elements as arguments to the system call. |
840 | If unimplemented, produces a fatal error. |
841 | The arguments are interpreted as follows: if a given argument is numeric, |
842 | the argument is passed as an int. |
843 | If not, the pointer to the string value is passed. |
844 | You are responsible to make sure a string is pre-extended long enough |
845 | to receive any result that might be written into a string. |
846 | If your integer arguments are not literals and have never been interpreted |
847 | in a numeric context, you may need to add 0 to them to force them to look |
848 | like numbers. |
849 | .nf |
850 | |
851 | do 'syscall.h'; # may need to run makelib |
852 | syscall(&SYS_write, fileno(STDOUT), "hi there\en", 9); |
853 | |
854 | .fi |
855 | .Ip "system(LIST)" 8 6 |
856 | .Ip "system LIST" 8 |
857 | Does exactly the same thing as \*(L"exec LIST\*(R" except that a fork |
858 | is done first, and the parent process waits for the child process to complete. |
859 | Note that argument processing varies depending on the number of arguments. |
860 | The return value is the exit status of the program as returned by the wait() |
861 | call. |
862 | To get the actual exit value divide by 256. |
863 | See also |
864 | .IR exec . |
865 | .Ip "symlink(OLDFILE,NEWFILE)" 8 2 |
866 | Creates a new filename symbolically linked to the old filename. |
867 | Returns 1 for success, 0 otherwise. |
868 | On systems that don't support symbolic links, produces a fatal error at |
869 | run time. |
870 | To check for that, use eval: |
871 | .nf |
872 | |
873 | $symlink_exists = (eval \'symlink("","");\', $@ eq \'\'); |
874 | |
875 | .fi |
876 | .Ip "tell(FILEHANDLE)" 8 6 |
877 | .Ip "tell FILEHANDLE" 8 6 |
878 | .Ip "tell" 8 |
879 | Returns the current file position for FILEHANDLE. |
880 | FILEHANDLE may be an expression whose value gives the name of the actual |
881 | filehandle. |
882 | If FILEHANDLE is omitted, assumes the file last read. |
883 | .Ip "telldir(DIRHANDLE)" 8 5 |
884 | .Ip "telldir DIRHANDLE" 8 |
885 | Returns the current position of the readdir() routines on DIRHANDLE. |
886 | Value may be given to seekdir() to access a particular location in |
887 | a directory. |
888 | Has the same caveats about possible directory compaction as the corresponding |
889 | system library routine. |
890 | .Ip "time" 8 4 |
891 | Returns the number of non-leap seconds since January 1, 1970, UTC. |
892 | Suitable for feeding to gmtime() and localtime(). |
893 | .Ip "times" 8 4 |
894 | Returns a four-element array giving the user and system times, in seconds, for this |
895 | process and the children of this process. |
896 | .Sp |
897 | ($user,$system,$cuser,$csystem) = times; |
898 | .Sp |
899 | .Ip "tr/SEARCHLIST/REPLACEMENTLIST/" 8 5 |
900 | .Ip "y/SEARCHLIST/REPLACEMENTLIST/" 8 |
901 | Translates all occurrences of the characters found in the search list with |
902 | the corresponding character in the replacement list. |
903 | It returns the number of characters replaced. |
904 | If no string is specified via the =~ or !~ operator, |
905 | the $_ string is translated. |
906 | (The string specified with =~ must be a scalar variable, an array element, |
907 | or an assignment to one of those, i.e. an lvalue.) |
908 | For |
909 | .I sed |
910 | devotees, |
911 | .I y |
912 | is provided as a synonym for |
913 | .IR tr . |
914 | Examples: |
915 | .nf |
916 | |
917 | $ARGV[1] \|=~ \|y/A\-Z/a\-z/; \h'|3i'# canonicalize to lower case |
918 | |
919 | $cnt = tr/*/*/; \h'|3i'# count the stars in $_ |
920 | |
921 | ($HOST = $host) =~ tr/a\-z/A\-Z/; |
922 | |
923 | y/\e001\-@[\-_{\-\e177/ /; \h'|3i'# change non-alphas to space |
924 | |
925 | .fi |
926 | .Ip "umask(EXPR)" 8 4 |
927 | .Ip "umask EXPR" 8 |
928 | Sets the umask for the process and returns the old one. |
929 | If EXPR is omitted, merely returns current umask. |
930 | .Ip "undef(EXPR)" 8 6 |
931 | .Ip "undef EXPR" 8 |
932 | .Ip "undef" 8 |
933 | Undefines the value of EXPR, which must be an lvalue. |
934 | Use only on a scalar value, an entire array, or a subroutine name (using &). |
935 | (Undef will probably not do what you expect on most predefined variables or |
936 | dbm array values.) |
937 | Always returns the undefined value. |
938 | You can omit the EXPR, in which case nothing is undefined, but you still |
939 | get an undefined value that you could, for instance, return from a subroutine. |
940 | Examples: |
941 | .nf |
942 | |
943 | .ne 6 |
944 | undef $foo; |
945 | undef $bar{'blurfl'}; |
946 | undef @ary; |
947 | undef %assoc; |
948 | undef &mysub; |
949 | return (wantarray ? () : undef) if $they_blew_it; |
950 | |
951 | .fi |
952 | .Ip "unlink(LIST)" 8 4 |
953 | .Ip "unlink LIST" 8 |
954 | Deletes a list of files. |
955 | Returns the number of files successfully deleted. |
956 | .nf |
957 | |
958 | .ne 2 |
959 | $cnt = unlink \'a\', \'b\', \'c\'; |
960 | unlink @goners; |
961 | unlink <*.bak>; |
962 | |
963 | .fi |
964 | Note: unlink will not delete directories unless you are superuser and the |
965 | .B \-U |
966 | flag is supplied to |
967 | .IR perl . |
968 | Even if these conditions are met, be warned that unlinking a directory |
969 | can inflict damage on your filesystem. |
970 | Use rmdir instead. |
971 | .Ip "unpack(TEMPLATE,EXPR)" 8 4 |
972 | Unpack does the reverse of pack: it takes a string representing |
973 | a structure and expands it out into an array value, returning the array |
974 | value. |
975 | The TEMPLATE has the same format as in the pack function. |
976 | Here's a subroutine that does substring: |
977 | .nf |
978 | |
979 | .ne 4 |
980 | sub substr { |
981 | local($what,$where,$howmuch) = @_; |
982 | unpack("x$where a$howmuch", $what); |
983 | } |
984 | |
985 | .ne 3 |
986 | and then there's |
987 | |
988 | sub ord { unpack("c",$_[0]); } |
989 | |
990 | .fi |
991 | .Ip "unshift(ARRAY,LIST)" 8 4 |
992 | Does the opposite of a |
993 | .IR shift . |
994 | Or the opposite of a |
995 | .IR push , |
996 | depending on how you look at it. |
997 | Prepends list to the front of the array, and returns the number of elements |
998 | in the new array. |
999 | .nf |
1000 | |
1001 | unshift(ARGV, \'\-e\') unless $ARGV[0] =~ /^\-/; |
1002 | |
1003 | .fi |
1004 | .Ip "utime(LIST)" 8 2 |
1005 | .Ip "utime LIST" 8 2 |
1006 | Changes the access and modification times on each file of a list of files. |
1007 | The first two elements of the list must be the NUMERICAL access and |
1008 | modification times, in that order. |
1009 | Returns the number of files successfully changed. |
1010 | The inode modification time of each file is set to the current time. |
1011 | Example of a \*(L"touch\*(R" command: |
1012 | .nf |
1013 | |
1014 | .ne 3 |
1015 | #!/usr/bin/perl |
1016 | $now = time; |
1017 | utime $now, $now, @ARGV; |
1018 | |
1019 | .fi |
1020 | .Ip "values(ASSOC_ARRAY)" 8 6 |
1021 | .Ip "values ASSOC_ARRAY" 8 |
1022 | Returns a normal array consisting of all the values of the named associative |
1023 | array. |
1024 | The values are returned in an apparently random order, but it is the same order |
1025 | as either the keys() or each() function would produce on the same array. |
1026 | See also keys() and each(). |
1027 | .Ip "vec(EXPR,OFFSET,BITS)" 8 2 |
1028 | Treats a string as a vector of unsigned integers, and returns the value |
1029 | of the bitfield specified. |
1030 | May also be assigned to. |
1031 | BITS must be a power of two from 1 to 32. |
1032 | .Sp |
1033 | Vectors created with vec() can also be manipulated with the logical operators |
1034 | |, & and ^, |
1035 | which will assume a bit vector operation is desired when both operands are |
1036 | strings. |
1037 | This interpretation is not enabled unless there is at least one vec() in |
1038 | your program, to protect older programs. |
1039 | .Ip "wait" 8 6 |
1040 | Waits for a child process to terminate and returns the pid of the deceased |
1041 | process. |
1042 | The status is returned in $?. |
1043 | .Ip "wantarray" 8 4 |
1044 | Returns true if the context of the currently executing subroutine |
1045 | is looking for an array value. |
1046 | Returns false if the context is looking for a scalar. |
1047 | .nf |
1048 | |
1049 | return wantarray ? () : undef; |
1050 | |
1051 | .fi |
1052 | .Ip "warn(LIST)" 8 4 |
1053 | .Ip "warn LIST" 8 |
1054 | Produces a message on STDERR just like \*(L"die\*(R", but doesn't exit. |
1055 | .Ip "write(FILEHANDLE)" 8 6 |
1056 | .Ip "write(EXPR)" 8 |
1057 | .Ip "write(\|)" 8 |
1058 | Writes a formatted record (possibly multi-line) to the specified file, |
1059 | using the format associated with that file. |
1060 | By default the format for a file is the one having the same name is the |
1061 | filehandle, but the format for the current output channel (see |
1062 | .IR select ) |
1063 | may be set explicitly |
1064 | by assigning the name of the format to the $~ variable. |
1065 | .Sp |
1066 | Top of form processing is handled automatically: |
1067 | if there is insufficient room on the current page for the formatted |
1068 | record, the page is advanced, a special top-of-page format is used |
1069 | to format the new page header, and then the record is written. |
1070 | By default the top-of-page format is \*(L"top\*(R", but it |
1071 | may be set to the |
1072 | format of your choice by assigning the name to the $^ variable. |
1073 | .Sp |
1074 | If FILEHANDLE is unspecified, output goes to the current default output channel, |
1075 | which starts out as |
1076 | .I STDOUT |
1077 | but may be changed by the |
1078 | .I select |
1079 | operator. |
1080 | If the FILEHANDLE is an EXPR, then the expression is evaluated and the |
1081 | resulting string is used to look up the name of the FILEHANDLE at run time. |
1082 | For more on formats, see the section on formats later on. |
1083 | .Sp |
1084 | Note that write is NOT the opposite of read. |