Commit | Line | Data |
a687059c |
1 | ''' Beginning of part 3 |
79a0689e |
2 | ''' $Header: perl.man.3,v 3.0.1.5 90/03/12 16:52:21 lwall Locked $ |
a687059c |
3 | ''' |
4 | ''' $Log: perl.man.3,v $ |
79a0689e |
5 | ''' Revision 3.0.1.5 90/03/12 16:52:21 lwall |
6 | ''' patch13: documented that print $filehandle &foo is ambiguous |
7 | ''' patch13: added splice operator: @oldelems = splice(@array,$offset,$len,LIST) |
8 | ''' |
ac58e20f |
9 | ''' Revision 3.0.1.4 90/02/28 18:00:09 lwall |
10 | ''' patch9: added pipe function |
11 | ''' patch9: documented how to handle arbitrary weird characters in filenames |
12 | ''' patch9: documented the unflushed buffers problem on piped opens |
13 | ''' patch9: documented how to force top of page |
14 | ''' |
663a0e37 |
15 | ''' Revision 3.0.1.3 89/12/21 20:10:12 lwall |
16 | ''' patch7: documented that s`pat`repl` does command substitution on replacement |
17 | ''' patch7: documented that $timeleft from select() is likely not implemented |
18 | ''' |
ffed7fef |
19 | ''' Revision 3.0.1.2 89/11/17 15:31:05 lwall |
20 | ''' patch5: fixed some manual typos and indent problems |
21 | ''' patch5: added warning about print making an array context |
22 | ''' |
ae986130 |
23 | ''' Revision 3.0.1.1 89/11/11 04:45:06 lwall |
24 | ''' patch2: made some line breaks depend on troff vs. nroff |
25 | ''' |
a687059c |
26 | ''' Revision 3.0 89/10/18 15:21:46 lwall |
27 | ''' 3.0 baseline |
28 | ''' |
29 | .Ip "next LABEL" 8 8 |
30 | .Ip "next" 8 |
31 | The |
32 | .I next |
33 | command is like the |
34 | .I continue |
35 | statement in C; it starts the next iteration of the loop: |
36 | .nf |
37 | |
38 | .ne 4 |
39 | line: while (<STDIN>) { |
40 | next line if /\|^#/; # discard comments |
41 | .\|.\|. |
42 | } |
43 | |
44 | .fi |
45 | Note that if there were a |
46 | .I continue |
47 | block on the above, it would get executed even on discarded lines. |
48 | If the LABEL is omitted, the command refers to the innermost enclosing loop. |
49 | .Ip "oct(EXPR)" 8 4 |
50 | .Ip "oct EXPR" 8 |
51 | Returns the decimal value of EXPR interpreted as an octal string. |
52 | (If EXPR happens to start off with 0x, interprets it as a hex string instead.) |
53 | The following will handle decimal, octal and hex in the standard notation: |
54 | .nf |
55 | |
56 | $val = oct($val) if $val =~ /^0/; |
57 | |
58 | .fi |
59 | If EXPR is omitted, uses $_. |
60 | .Ip "open(FILEHANDLE,EXPR)" 8 8 |
61 | .Ip "open(FILEHANDLE)" 8 |
62 | .Ip "open FILEHANDLE" 8 |
63 | Opens the file whose filename is given by EXPR, and associates it with |
64 | FILEHANDLE. |
65 | If FILEHANDLE is an expression, its value is used as the name of the |
66 | real filehandle wanted. |
67 | If EXPR is omitted, the scalar variable of the same name as the FILEHANDLE |
68 | contains the filename. |
69 | If the filename begins with \*(L"<\*(R" or nothing, the file is opened for |
70 | input. |
71 | If the filename begins with \*(L">\*(R", the file is opened for output. |
72 | If the filename begins with \*(L">>\*(R", the file is opened for appending. |
73 | (You can put a \'+\' in front of the \'>\' or \'<\' to indicate that you |
74 | want both read and write access to the file.) |
75 | If the filename begins with \*(L"|\*(R", the filename is interpreted |
76 | as a command to which output is to be piped, and if the filename ends |
77 | with a \*(L"|\*(R", the filename is interpreted as command which pipes |
78 | input to us. |
79 | (You may not have a command that pipes both in and out.) |
80 | Opening \'\-\' opens |
81 | .I STDIN |
82 | and opening \'>\-\' opens |
83 | .IR STDOUT . |
84 | Open returns non-zero upon success, the undefined value otherwise. |
85 | If the open involved a pipe, the return value happens to be the pid |
86 | of the subprocess. |
87 | Examples: |
88 | .nf |
89 | |
90 | .ne 3 |
91 | $article = 100; |
92 | open article || die "Can't find article $article: $!\en"; |
93 | while (<article>) {\|.\|.\|. |
94 | |
ae986130 |
95 | .ie t \{\ |
a687059c |
96 | open(LOG, \'>>/usr/spool/news/twitlog\'\|); # (log is reserved) |
ae986130 |
97 | 'br\} |
98 | .el \{\ |
99 | open(LOG, \'>>/usr/spool/news/twitlog\'\|); |
100 | # (log is reserved) |
101 | 'br\} |
a687059c |
102 | |
ae986130 |
103 | .ie t \{\ |
a687059c |
104 | open(article, "caesar <$article |"\|); # decrypt article |
ae986130 |
105 | 'br\} |
106 | .el \{\ |
107 | open(article, "caesar <$article |"\|); |
108 | # decrypt article |
109 | 'br\} |
a687059c |
110 | |
ae986130 |
111 | .ie t \{\ |
a687059c |
112 | open(extract, "|sort >/tmp/Tmp$$"\|); # $$ is our process# |
ae986130 |
113 | 'br\} |
114 | .el \{\ |
115 | open(extract, "|sort >/tmp/Tmp$$"\|); |
116 | # $$ is our process# |
117 | 'br\} |
a687059c |
118 | |
119 | .ne 7 |
120 | # process argument list of files along with any includes |
121 | |
122 | foreach $file (@ARGV) { |
123 | do process($file, \'fh00\'); # no pun intended |
124 | } |
125 | |
126 | sub process { |
127 | local($filename, $input) = @_; |
128 | $input++; # this is a string increment |
129 | unless (open($input, $filename)) { |
130 | print STDERR "Can't open $filename: $!\en"; |
131 | return; |
132 | } |
ae986130 |
133 | .ie t \{\ |
a687059c |
134 | while (<$input>) { # note the use of indirection |
ae986130 |
135 | 'br\} |
136 | .el \{\ |
137 | while (<$input>) { # note use of indirection |
138 | 'br\} |
a687059c |
139 | if (/^#include "(.*)"/) { |
140 | do process($1, $input); |
141 | next; |
142 | } |
143 | .\|.\|. # whatever |
144 | } |
145 | } |
146 | |
147 | .fi |
148 | You may also, in the Bourne shell tradition, specify an EXPR beginning |
149 | with \*(L">&\*(R", in which case the rest of the string |
150 | is interpreted as the name of a filehandle |
151 | (or file descriptor, if numeric) which is to be duped and opened. |
ae986130 |
152 | You may use & after >, >>, <, +>, +>> and +<. |
153 | The mode you specify should match the mode of the original filehandle. |
a687059c |
154 | Here is a script that saves, redirects, and restores |
155 | .I STDOUT |
156 | and |
ae986130 |
157 | .IR STDERR : |
a687059c |
158 | .nf |
159 | |
160 | .ne 21 |
161 | #!/usr/bin/perl |
162 | open(SAVEOUT, ">&STDOUT"); |
163 | open(SAVEERR, ">&STDERR"); |
164 | |
165 | open(STDOUT, ">foo.out") || die "Can't redirect stdout"; |
166 | open(STDERR, ">&STDOUT") || die "Can't dup stdout"; |
167 | |
168 | select(STDERR); $| = 1; # make unbuffered |
169 | select(STDOUT); $| = 1; # make unbuffered |
170 | |
171 | print STDOUT "stdout 1\en"; # this works for |
172 | print STDERR "stderr 1\en"; # subprocesses too |
173 | |
174 | close(STDOUT); |
175 | close(STDERR); |
176 | |
177 | open(STDOUT, ">&SAVEOUT"); |
178 | open(STDERR, ">&SAVEERR"); |
179 | |
180 | print STDOUT "stdout 2\en"; |
181 | print STDERR "stderr 2\en"; |
182 | |
183 | .fi |
184 | If you open a pipe on the command \*(L"\-\*(R", i.e. either \*(L"|\-\*(R" or \*(L"\-|\*(R", |
185 | then there is an implicit fork done, and the return value of open |
186 | is the pid of the child within the parent process, and 0 within the child |
187 | process. |
188 | (Use defined($pid) to determine if the open was successful.) |
189 | The filehandle behaves normally for the parent, but i/o to that |
190 | filehandle is piped from/to the |
191 | .IR STDOUT / STDIN |
192 | of the child process. |
193 | In the child process the filehandle isn't opened\*(--i/o happens from/to |
194 | the new |
195 | .I STDOUT |
196 | or |
197 | .IR STDIN . |
198 | Typically this is used like the normal piped open when you want to exercise |
199 | more control over just how the pipe command gets executed, such as when |
200 | you are running setuid, and don't want to have to scan shell commands |
201 | for metacharacters. |
202 | The following pairs are equivalent: |
203 | .nf |
204 | |
205 | .ne 5 |
206 | open(FOO, "|tr \'[a\-z]\' \'[A\-Z]\'"); |
207 | open(FOO, "|\-") || exec \'tr\', \'[a\-z]\', \'[A\-Z]\'; |
208 | |
209 | open(FOO, "cat \-n $file|"); |
210 | open(FOO, "\-|") || exec \'cat\', \'\-n\', $file; |
211 | |
212 | .fi |
213 | Explicitly closing any piped filehandle causes the parent process to wait for the |
214 | child to finish, and returns the status value in $?. |
ac58e20f |
215 | Note: on any operation which may do a fork, |
216 | unflushed buffers remain unflushed in both |
217 | processes, which means you may need to set $| to |
218 | avoid duplicate output. |
219 | .Sp |
220 | The filename that is passed to open will have leading and trailing |
221 | whitespace deleted. |
222 | In order to open a file with arbitrary weird characters in it, it's necessary |
223 | to protect any leading and trailing whitespace thusly: |
224 | .nf |
225 | |
226 | .ne 2 |
227 | $file =~ s#^(\es)#./$1#; |
228 | open(FOO, "< $file\e0"); |
229 | |
230 | .fi |
a687059c |
231 | .Ip "opendir(DIRHANDLE,EXPR)" 8 3 |
232 | Opens a directory named EXPR for processing by readdir(), telldir(), seekdir(), |
233 | rewinddir() and closedir(). |
234 | Returns true if successful. |
235 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
236 | .Ip "ord(EXPR)" 8 4 |
237 | .Ip "ord EXPR" 8 |
238 | Returns the ascii value of the first character of EXPR. |
239 | If EXPR is omitted, uses $_. |
240 | .Ip "pack(TEMPLATE,LIST)" 8 4 |
241 | Takes an array or list of values and packs it into a binary structure, |
242 | returning the string containing the structure. |
243 | The TEMPLATE is a sequence of characters that give the order and type |
244 | of values, as follows: |
245 | .nf |
246 | |
247 | A An ascii string, will be space padded. |
248 | a An ascii string, will be null padded. |
249 | c A native char value. |
250 | C An unsigned char value. |
251 | s A signed short value. |
252 | S An unsigned short value. |
253 | i A signed integer value. |
254 | I An unsigned integer value. |
255 | l A signed long value. |
256 | L An unsigned long value. |
257 | n A short in \*(L"network\*(R" order. |
258 | N A long in \*(L"network\*(R" order. |
259 | p A pointer to a string. |
260 | x A null byte. |
261 | |
262 | .fi |
263 | Each letter may optionally be followed by a number which gives a repeat |
264 | count. |
265 | With all types except "a" and "A" the pack function will gobble up that many values |
266 | from the LIST. |
267 | The "a" and "A" types gobble just one value, but pack it as a string that long, |
268 | padding with nulls or spaces as necessary. |
269 | (When unpacking, "A" strips trailing spaces and nulls, but "a" does not.) |
270 | Examples: |
271 | .nf |
272 | |
273 | $foo = pack("cccc",65,66,67,68); |
274 | # foo eq "ABCD" |
275 | $foo = pack("c4",65,66,67,68); |
276 | # same thing |
277 | |
278 | $foo = pack("ccxxcc",65,66,67,68); |
279 | # foo eq "AB\e0\e0CD" |
280 | |
281 | $foo = pack("s2",1,2); |
282 | # "\e1\e0\e2\e0" on little-endian |
283 | # "\e0\e1\e0\e2" on big-endian |
284 | |
285 | $foo = pack("a4","abcd","x","y","z"); |
286 | # "abcd" |
287 | |
288 | $foo = pack("aaaa","abcd","x","y","z"); |
289 | # "axyz" |
290 | |
291 | $foo = pack("a14","abcdefg"); |
292 | # "abcdefg\e0\e0\e0\e0\e0\e0\e0" |
293 | |
ae986130 |
294 | $foo = pack("i9pl", gmtime); |
a687059c |
295 | # a real struct tm (on my system anyway) |
296 | |
297 | .fi |
298 | The same template may generally also be used in the unpack function. |
ac58e20f |
299 | .Ip "pipe(READHANDLE,WRITEHANDLE)" 8 3 |
300 | Opens a pair of connected pipes like the corresponding system call. |
301 | Note that if you set up a loop of piped processes, deadlock can occur |
302 | unless you are very careful. |
303 | In addition, note that perl's pipes use stdio buffering, so you may need |
304 | to set $| to flush your WRITEHANDLE after each command, depending on |
305 | the application. |
306 | [Requires version 3.0 patchlevel 9.] |
a687059c |
307 | .Ip "pop(ARRAY)" 8 |
308 | .Ip "pop ARRAY" 8 6 |
309 | Pops and returns the last value of the array, shortening the array by 1. |
310 | Has the same effect as |
311 | .nf |
312 | |
313 | $tmp = $ARRAY[$#ARRAY\-\|\-]; |
314 | |
315 | .fi |
316 | If there are no elements in the array, returns the undefined value. |
317 | .Ip "print(FILEHANDLE LIST)" 8 10 |
318 | .Ip "print(LIST)" 8 |
319 | .Ip "print FILEHANDLE LIST" 8 |
320 | .Ip "print LIST" 8 |
321 | .Ip "print" 8 |
322 | Prints a string or a comma-separated list of strings. |
323 | Returns non-zero if successful. |
324 | FILEHANDLE may be a scalar variable name, in which case the variable contains |
325 | the name of the filehandle, thus introducing one level of indirection. |
79a0689e |
326 | (NOTE: If FILEHANDLE is a variable and the next token is a term, it may be |
327 | misinterpreted as an operator unless you interpose a + or put parens around |
328 | the arguments.) |
a687059c |
329 | If FILEHANDLE is omitted, prints by default to standard output (or to the |
330 | last selected output channel\*(--see select()). |
331 | If LIST is also omitted, prints $_ to |
332 | .IR STDOUT . |
333 | To set the default output channel to something other than |
334 | .I STDOUT |
335 | use the select operation. |
ffed7fef |
336 | Note that, because print takes a LIST, anything in the LIST is evaluated |
337 | in an array context, and any subroutine that you call will have one or more |
338 | of its expressions evaluated in an array context. |
79a0689e |
339 | Also be careful not to follow the print keyword with a left parenthesis |
340 | unless you want the corresponding right parenthesis to terminate the |
341 | arguments to the print--interpose a + or put parens around all the arguments. |
a687059c |
342 | .Ip "printf(FILEHANDLE LIST)" 8 10 |
343 | .Ip "printf(LIST)" 8 |
344 | .Ip "printf FILEHANDLE LIST" 8 |
345 | .Ip "printf LIST" 8 |
346 | Equivalent to a \*(L"print FILEHANDLE sprintf(LIST)\*(R". |
347 | .Ip "push(ARRAY,LIST)" 8 7 |
348 | Treats ARRAY (@ is optional) as a stack, and pushes the values of LIST |
349 | onto the end of ARRAY. |
350 | The length of ARRAY increases by the length of LIST. |
351 | Has the same effect as |
352 | .nf |
353 | |
354 | for $value (LIST) { |
355 | $ARRAY[++$#ARRAY] = $value; |
356 | } |
357 | |
358 | .fi |
359 | but is more efficient. |
360 | .Ip "q/STRING/" 8 5 |
361 | .Ip "qq/STRING/" 8 |
362 | These are not really functions, but simply syntactic sugar to let you |
363 | avoid putting too many backslashes into quoted strings. |
364 | The q operator is a generalized single quote, and the qq operator a |
365 | generalized double quote. |
366 | Any delimiter can be used in place of /, including newline. |
367 | If the delimiter is an opening bracket or parenthesis, the final delimiter |
368 | will be the corresponding closing bracket or parenthesis. |
369 | (Embedded occurrences of the closing bracket need to be backslashed as usual.) |
370 | Examples: |
371 | .nf |
372 | |
373 | .ne 5 |
374 | $foo = q!I said, "You said, \'She said it.\'"!; |
375 | $bar = q(\'This is it.\'); |
376 | $_ .= qq |
377 | *** The previous line contains the naughty word "$&".\en |
378 | if /(ibm|apple|awk)/; # :-) |
379 | |
380 | .fi |
381 | .Ip "rand(EXPR)" 8 8 |
382 | .Ip "rand EXPR" 8 |
383 | .Ip "rand" 8 |
384 | Returns a random fractional number between 0 and the value of EXPR. |
385 | (EXPR should be positive.) |
386 | If EXPR is omitted, returns a value between 0 and 1. |
387 | See also srand(). |
388 | .Ip "read(FILEHANDLE,SCALAR,LENGTH)" 8 5 |
389 | Attempts to read LENGTH bytes of data into variable SCALAR from the specified |
390 | FILEHANDLE. |
391 | Returns the number of bytes actually read. |
392 | SCALAR will be grown or shrunk to the length actually read. |
393 | .Ip "readdir(DIRHANDLE)" 8 3 |
ae986130 |
394 | .Ip "readdir DIRHANDLE" 8 |
a687059c |
395 | Returns the next directory entry for a directory opened by opendir(). |
396 | If used in an array context, returns all the rest of the entries in the |
397 | directory. |
398 | If there are no more entries, returns an undefined value in a scalar context |
399 | or a null list in an array context. |
400 | .Ip "readlink(EXPR)" 8 6 |
401 | .Ip "readlink EXPR" 8 |
402 | Returns the value of a symbolic link, if symbolic links are implemented. |
403 | If not, gives a fatal error. |
404 | If there is some system error, returns the undefined value and sets $! (errno). |
405 | If EXPR is omitted, uses $_. |
406 | .Ip "recv(SOCKET,SCALAR,LEN,FLAGS)" 8 4 |
407 | Receives a message on a socket. |
408 | Attempts to receive LENGTH bytes of data into variable SCALAR from the specified |
409 | SOCKET filehandle. |
410 | Returns the address of the sender, or the undefined value if there's an error. |
411 | SCALAR will be grown or shrunk to the length actually read. |
412 | Takes the same flags as the system call of the same name. |
413 | .Ip "redo LABEL" 8 8 |
414 | .Ip "redo" 8 |
415 | The |
416 | .I redo |
417 | command restarts the loop block without evaluating the conditional again. |
418 | The |
419 | .I continue |
420 | block, if any, is not executed. |
421 | If the LABEL is omitted, the command refers to the innermost enclosing loop. |
422 | This command is normally used by programs that want to lie to themselves |
423 | about what was just input: |
424 | .nf |
425 | |
426 | .ne 16 |
427 | # a simpleminded Pascal comment stripper |
428 | # (warning: assumes no { or } in strings) |
429 | line: while (<STDIN>) { |
430 | while (s|\|({.*}.*\|){.*}|$1 \||) {} |
431 | s|{.*}| \||; |
432 | if (s|{.*| \||) { |
433 | $front = $_; |
434 | while (<STDIN>) { |
435 | if (\|/\|}/\|) { # end of comment? |
436 | s|^|$front{|; |
437 | redo line; |
438 | } |
439 | } |
440 | } |
441 | print; |
442 | } |
443 | |
444 | .fi |
445 | .Ip "rename(OLDNAME,NEWNAME)" 8 2 |
446 | Changes the name of a file. |
447 | Returns 1 for success, 0 otherwise. |
448 | Will not work across filesystem boundaries. |
449 | .Ip "reset(EXPR)" 8 6 |
450 | .Ip "reset EXPR" 8 |
451 | .Ip "reset" 8 |
452 | Generally used in a |
453 | .I continue |
454 | block at the end of a loop to clear variables and reset ?? searches |
455 | so that they work again. |
456 | The expression is interpreted as a list of single characters (hyphens allowed |
457 | for ranges). |
458 | All variables and arrays beginning with one of those letters are reset to |
459 | their pristine state. |
460 | If the expression is omitted, one-match searches (?pattern?) are reset to |
461 | match again. |
462 | Only resets variables or searches in the current package. |
463 | Always returns 1. |
464 | Examples: |
465 | .nf |
466 | |
467 | .ne 3 |
468 | reset \'X\'; \h'|2i'# reset all X variables |
469 | reset \'a\-z\';\h'|2i'# reset lower case variables |
470 | reset; \h'|2i'# just reset ?? searches |
471 | |
472 | .fi |
473 | Note: resetting \*(L"A\-Z\*(R" is not recommended since you'll wipe out your ARGV and ENV |
474 | arrays. |
475 | .Sp |
476 | The use of reset on dbm associative arrays does not change the dbm file. |
477 | (It does, however, flush any entries cached by perl, which may be useful if |
478 | you are sharing the dbm file. |
479 | Then again, maybe not.) |
480 | .Ip "return LIST" 8 3 |
481 | Returns from a subroutine with the value specified. |
482 | (Note that a subroutine can automatically return |
483 | the value of the last expression evaluated. |
484 | That's the preferred method\*(--use of an explicit |
485 | .I return |
486 | is a bit slower.) |
487 | .Ip "reverse(LIST)" 8 4 |
488 | .Ip "reverse LIST" 8 |
489 | Returns an array value consisting of the elements of LIST in the opposite order. |
490 | .Ip "rewinddir(DIRHANDLE)" 8 5 |
491 | .Ip "rewinddir DIRHANDLE" 8 |
492 | Sets the current position to the beginning of the directory for the readdir() routine on DIRHANDLE. |
493 | .Ip "rindex(STR,SUBSTR)" 8 4 |
494 | Works just like index except that it |
495 | returns the position of the LAST occurrence of SUBSTR in STR. |
496 | .Ip "rmdir(FILENAME)" 8 4 |
497 | .Ip "rmdir FILENAME" 8 |
498 | Deletes the directory specified by FILENAME if it is empty. |
499 | If it succeeds it returns 1, otherwise it returns 0 and sets $! (errno). |
500 | If FILENAME is omitted, uses $_. |
501 | .Ip "s/PATTERN/REPLACEMENT/gieo" 8 3 |
502 | Searches a string for a pattern, and if found, replaces that pattern with the |
503 | replacement text and returns the number of substitutions made. |
504 | Otherwise it returns false (0). |
505 | The \*(L"g\*(R" is optional, and if present, indicates that all occurrences |
506 | of the pattern are to be replaced. |
507 | The \*(L"i\*(R" is also optional, and if present, indicates that matching |
508 | is to be done in a case-insensitive manner. |
509 | The \*(L"e\*(R" is likewise optional, and if present, indicates that |
510 | the replacement string is to be evaluated as an expression rather than just |
511 | as a double-quoted string. |
512 | Any delimiter may replace the slashes; if single quotes are used, no |
513 | interpretation is done on the replacement string (the e modifier overrides |
663a0e37 |
514 | this, however); if backquotes are used, the replacement string is a command |
515 | to execute whose output will be used as the actual replacement text. |
a687059c |
516 | If no string is specified via the =~ or !~ operator, |
517 | the $_ string is searched and modified. |
518 | (The string specified with =~ must be a scalar variable, an array element, |
519 | or an assignment to one of those, i.e. an lvalue.) |
520 | If the pattern contains a $ that looks like a variable rather than an |
521 | end-of-string test, the variable will be interpolated into the pattern at |
522 | run-time. |
523 | If you only want the pattern compiled once the first time the variable is |
524 | interpolated, add an \*(L"o\*(R" at the end. |
525 | See also the section on regular expressions. |
526 | Examples: |
527 | .nf |
528 | |
529 | s/\|\e\|bgreen\e\|b/mauve/g; # don't change wintergreen |
530 | |
531 | $path \|=~ \|s|\|/usr/bin|\|/usr/local/bin|; |
532 | |
533 | s/Login: $foo/Login: $bar/; # run-time pattern |
534 | |
535 | ($foo = $bar) =~ s/bar/foo/; |
536 | |
537 | $_ = \'abc123xyz\'; |
538 | s/\ed+/$&*2/e; # yields \*(L'abc246xyz\*(R' |
539 | s/\ed+/sprintf("%5d",$&)/e; # yields \*(L'abc 246xyz\*(R' |
540 | s/\ew/$& x 2/eg; # yields \*(L'aabbcc 224466xxyyzz\*(R' |
541 | |
542 | s/\|([^ \|]*\|) *\|([^ \|]*\|)\|/\|$2 $1/; # reverse 1st two fields |
543 | |
544 | .fi |
545 | (Note the use of $ instead of \|\e\| in the last example. See section |
546 | on regular expressions.) |
547 | .Ip "seek(FILEHANDLE,POSITION,WHENCE)" 8 3 |
548 | Randomly positions the file pointer for FILEHANDLE, just like the fseek() |
549 | call of stdio. |
550 | FILEHANDLE may be an expression whose value gives the name of the filehandle. |
551 | Returns 1 upon success, 0 otherwise. |
552 | .Ip "seekdir(DIRHANDLE,POS)" 8 3 |
553 | Sets the current position for the readdir() routine on DIRHANDLE. |
554 | POS must be a value returned by seekdir(). |
555 | Has the same caveats about possible directory compaction as the corresponding |
556 | system library routine. |
557 | .Ip "select(FILEHANDLE)" 8 3 |
558 | .Ip "select" 8 3 |
559 | Returns the currently selected filehandle. |
560 | Sets the current default filehandle for output, if FILEHANDLE is supplied. |
561 | This has two effects: first, a |
562 | .I write |
563 | or a |
564 | .I print |
565 | without a filehandle will default to this FILEHANDLE. |
566 | Second, references to variables related to output will refer to this output |
567 | channel. |
568 | For example, if you have to set the top of form format for more than |
569 | one output channel, you might do the following: |
570 | .nf |
571 | |
572 | .ne 4 |
573 | select(REPORT1); |
574 | $^ = \'report1_top\'; |
575 | select(REPORT2); |
576 | $^ = \'report2_top\'; |
577 | |
578 | .fi |
579 | FILEHANDLE may be an expression whose value gives the name of the actual filehandle. |
580 | Thus: |
581 | .nf |
582 | |
583 | $oldfh = select(STDERR); $| = 1; select($oldfh); |
584 | |
585 | .fi |
586 | .Ip "select(RBITS,WBITS,EBITS,TIMEOUT)" 8 3 |
587 | This calls the select system call with the bitmasks specified, which can |
588 | be constructed using fileno() and vec(), along these lines: |
589 | .nf |
590 | |
591 | $rin = $win = $ein = ''; |
592 | vec($rin,fileno(STDIN),1) = 1; |
593 | vec($win,fileno(STDOUT),1) = 1; |
594 | $ein = $rin | $win; |
595 | |
596 | .fi |
597 | If you want to select on many filehandles you might wish to write a subroutine: |
598 | .nf |
599 | |
600 | sub fhbits { |
601 | local(@fhlist) = split(' ',$_[0]); |
602 | local($bits); |
603 | for (@fhlist) { |
604 | vec($bits,fileno($_),1) = 1; |
605 | } |
606 | $bits; |
607 | } |
608 | $rin = &fhbits('STDIN TTY SOCK'); |
609 | |
610 | .fi |
611 | The usual idiom is: |
612 | .nf |
613 | |
614 | ($nfound,$timeleft) = |
615 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); |
616 | |
617 | or to block until something becomes ready: |
618 | |
ae986130 |
619 | .ie t \{\ |
a687059c |
620 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); |
ae986130 |
621 | 'br\} |
622 | .el \{\ |
623 | $nfound = select($rout=$rin, $wout=$win, |
624 | $eout=$ein, undef); |
625 | 'br\} |
a687059c |
626 | |
627 | .fi |
628 | Any of the bitmasks can also be undef. |
629 | The timeout, if specified, is in seconds, which may be fractional. |
663a0e37 |
630 | NOTE: not all implementations are capable of returning the $timeleft. |
631 | If not, they always return $timeleft equal to the supplied $timeout. |
a687059c |
632 | .Ip "setpgrp(PID,PGRP)" 8 4 |
633 | Sets the current process group for the specified PID, 0 for the current |
634 | process. |
635 | Will produce a fatal error if used on a machine that doesn't implement |
636 | setpgrp(2). |
637 | .Ip "send(SOCKET,MSG,FLAGS,TO)" 8 4 |
638 | .Ip "send(SOCKET,MSG,FLAGS)" 8 |
639 | Sends a message on a socket. |
640 | Takes the same flags as the system call of the same name. |
641 | On unconnected sockets you must specify a destination to send TO. |
642 | Returns the number of characters sent, or the undefined value if |
643 | there is an error. |
644 | .Ip "setpriority(WHICH,WHO,PRIORITY)" 8 4 |
645 | Sets the current priority for a process, a process group, or a user. |
646 | (See setpriority(2).) |
647 | Will produce a fatal error if used on a machine that doesn't implement |
648 | setpriority(2). |
649 | .Ip "setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)" 8 3 |
650 | Sets the socket option requested. |
651 | Returns undefined if there is an error. |
652 | OPTVAL may be specified as undef if you don't want to pass an argument. |
653 | .Ip "shift(ARRAY)" 8 6 |
654 | .Ip "shift ARRAY" 8 |
655 | .Ip "shift" 8 |
656 | Shifts the first value of the array off and returns it, |
657 | shortening the array by 1 and moving everything down. |
658 | If there are no elements in the array, returns the undefined value. |
659 | If ARRAY is omitted, shifts the @ARGV array in the main program, and the @_ |
660 | array in subroutines. |
661 | See also unshift(), push() and pop(). |
662 | Shift() and unshift() do the same thing to the left end of an array that push() |
663 | and pop() do to the right end. |
664 | .Ip "shutdown(SOCKET,HOW)" 8 3 |
665 | Shuts down a socket connection in the manner indicated by HOW, which has |
666 | the same interpretation as in the system call of the same name. |
667 | .Ip "sin(EXPR)" 8 4 |
668 | .Ip "sin EXPR" 8 |
669 | Returns the sine of EXPR (expressed in radians). |
670 | If EXPR is omitted, returns sine of $_. |
671 | .Ip "sleep(EXPR)" 8 6 |
672 | .Ip "sleep EXPR" 8 |
673 | .Ip "sleep" 8 |
674 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. |
675 | May be interrupted by sending the process a SIGALARM. |
676 | Returns the number of seconds actually slept. |
677 | .Ip "socket(SOCKET,DOMAIN,TYPE,PROTOCOL)" 8 3 |
678 | Opens a socket of the specified kind and attaches it to filehandle SOCKET. |
679 | DOMAIN, TYPE and PROTOCOL are specified the same as for the system call |
680 | of the same name. |
681 | You may need to run makelib on sys/socket.h to get the proper values handy |
682 | in a perl library file. |
683 | Return true if successful. |
684 | See the example in the section on Interprocess Communication. |
685 | .Ip "socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)" 8 3 |
686 | Creates an unnamed pair of sockets in the specified domain, of the specified |
687 | type. |
688 | DOMAIN, TYPE and PROTOCOL are specified the same as for the system call |
689 | of the same name. |
690 | If unimplemented, yields a fatal error. |
691 | Return true if successful. |
692 | .Ip "sort(SUBROUTINE LIST)" 8 9 |
693 | .Ip "sort(LIST)" 8 |
694 | .Ip "sort SUBROUTINE LIST" 8 |
695 | .Ip "sort LIST" 8 |
696 | Sorts the LIST and returns the sorted array value. |
697 | Nonexistent values of arrays are stripped out. |
698 | If SUBROUTINE is omitted, sorts in standard string comparison order. |
699 | If SUBROUTINE is specified, gives the name of a subroutine that returns |
700 | an integer less than, equal to, or greater than 0, |
701 | depending on how the elements of the array are to be ordered. |
702 | In the interests of efficiency the normal calling code for subroutines |
703 | is bypassed, with the following effects: the subroutine may not be a recursive |
704 | subroutine, and the two elements to be compared are passed into the subroutine |
705 | not via @_ but as $a and $b (see example below). |
706 | They are passed by reference so don't modify $a and $b. |
707 | SUBROUTINE may be a scalar variable name, in which case the value provides |
708 | the name of the subroutine to use. |
709 | Examples: |
710 | .nf |
711 | |
712 | .ne 4 |
713 | sub byage { |
714 | $age{$a} - $age{$b}; # presuming integers |
715 | } |
716 | @sortedclass = sort byage @class; |
717 | |
718 | .ne 9 |
719 | sub reverse { $a lt $b ? 1 : $a gt $b ? \-1 : 0; } |
720 | @harry = (\'dog\',\'cat\',\'x\',\'Cain\',\'Abel\'); |
721 | @george = (\'gone\',\'chased\',\'yz\',\'Punished\',\'Axed\'); |
722 | print sort @harry; |
723 | # prints AbelCaincatdogx |
724 | print sort reverse @harry; |
725 | # prints xdogcatCainAbel |
726 | print sort @george, \'to\', @harry; |
727 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz |
728 | |
729 | .fi |
79a0689e |
730 | .Ip "splice(ARRAY,OFFSET,LENGTH,LIST)" 8 8 |
731 | .Ip "splice(ARRAY,OFFSET,LENGTH)" 8 |
732 | .Ip "splice(ARRAY,OFFSET)" 8 |
733 | Removes the elements designated by OFFSET and LENGTH from an array, and |
734 | replaces them with the elements of LIST, if any. |
735 | Returns the elements removed from the array. |
736 | The array grows or shrinks as necessary. |
737 | If LENGTH is omitted, removes everything from OFFSET onward. |
738 | The following equivalencies hold (assuming $[ == 0): |
739 | .nf |
740 | |
741 | push(@a,$x,$y)\h'|3.5i'splice(@a,$#x+1,0,$x,$y) |
742 | pop(@a)\h'|3.5i'splice(@a,-1) |
743 | shift(@a)\h'|3.5i'splice(@a,0,1) |
744 | unshift(@a,$x,$y)\h'|3.5i'splice(@a,0,0,$x,$y) |
745 | $a[$x] = $y\h'|3.5i'splice(@a,$x,1,$y); |
746 | |
747 | Example, assuming array lengths are passed before arrays: |
748 | |
749 | sub aeq { # compare two array values |
750 | local(@a) = splice(@_,0,shift); |
751 | local(@b) = splice(@_,0,shift); |
752 | return 0 unless @a == @b; # same len? |
753 | while (@a) { |
754 | return 0 if pop(@a) ne pop(@b); |
755 | } |
756 | return 1; |
757 | } |
758 | if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... } |
759 | |
760 | .fi |
a687059c |
761 | .Ip "split(/PATTERN/,EXPR,LIMIT)" 8 8 |
762 | .Ip "split(/PATTERN/,EXPR)" 8 8 |
763 | .Ip "split(/PATTERN/)" 8 |
764 | .Ip "split" 8 |
765 | Splits a string into an array of strings, and returns it. |
766 | (If not in an array context, returns the number of fields found and splits |
ac58e20f |
767 | into the @_ array. |
768 | (In an array context, you can force the split into @_ |
769 | by using ?? as the pattern delimiters, but it still returns the array value.)) |
a687059c |
770 | If EXPR is omitted, splits the $_ string. |
771 | If PATTERN is also omitted, splits on whitespace (/[\ \et\en]+/). |
772 | Anything matching PATTERN is taken to be a delimiter separating the fields. |
773 | (Note that the delimiter may be longer than one character.) |
774 | If LIMIT is specified, splits into no more than that many fields (though it |
775 | may split into fewer). |
776 | If LIMIT is unspecified, trailing null fields are stripped (which |
777 | potential users of pop() would do well to remember). |
778 | A pattern matching the null string (not to be confused with a null pattern, |
779 | which is one member of the set of patterns matching a null string) |
780 | will split the value of EXPR into separate characters at each point it |
781 | matches that way. |
782 | For example: |
783 | .nf |
784 | |
785 | print join(\':\', split(/ */, \'hi there\')); |
786 | |
787 | .fi |
788 | produces the output \*(L'h:i:t:h:e:r:e\*(R'. |
ffed7fef |
789 | .Sp |
663a0e37 |
790 | The LIMIT parameter can be used to partially split a line |
a687059c |
791 | .nf |
792 | |
793 | ($login, $passwd, $remainder) = split(\|/\|:\|/\|, $_, 3); |
794 | |
795 | .fi |
663a0e37 |
796 | (When assigning to a list, if LIMIT is omitted, perl supplies a LIMIT one |
a687059c |
797 | larger than the number of variables in the list, to avoid unnecessary work. |
663a0e37 |
798 | For the list above LIMIT would have been 4 by default. |
a687059c |
799 | In time critical applications it behooves you not to split into |
800 | more fields than you really need.) |
801 | .Sp |
802 | If the PATTERN contains parentheses, additional array elements are created |
803 | from each matching substring in the delimiter. |
804 | .Sp |
805 | split(/([,-])/,"1-10,20"); |
806 | .Sp |
807 | produces the array value |
808 | .Sp |
809 | (1,'-',10,',',20) |
810 | .Sp |
811 | The pattern /PATTERN/ may be replaced with an expression to specify patterns |
812 | that vary at runtime. |
813 | (To do runtime compilation only once, use /$variable/o.) |
814 | As a special case, specifying a space (\'\ \') will split on white space |
815 | just as split with no arguments does, but leading white space does NOT |
816 | produce a null first field. |
817 | Thus, split(\'\ \') can be used to emulate |
818 | .IR awk 's |
819 | default behavior, whereas |
820 | split(/\ /) will give you as many null initial fields as there are |
821 | leading spaces. |
822 | .Sp |
823 | Example: |
824 | .nf |
825 | |
826 | .ne 5 |
827 | open(passwd, \'/etc/passwd\'); |
828 | while (<passwd>) { |
829 | .ie t \{\ |
830 | ($login, $passwd, $uid, $gid, $gcos, $home, $shell) = split(\|/\|:\|/\|); |
831 | 'br\} |
832 | .el \{\ |
833 | ($login, $passwd, $uid, $gid, $gcos, $home, $shell) |
834 | = split(\|/\|:\|/\|); |
835 | 'br\} |
836 | .\|.\|. |
837 | } |
838 | |
839 | .fi |
840 | (Note that $shell above will still have a newline on it. See chop().) |
841 | See also |
842 | .IR join . |
843 | .Ip "sprintf(FORMAT,LIST)" 8 4 |
844 | Returns a string formatted by the usual printf conventions. |
845 | The * character is not supported. |
846 | .Ip "sqrt(EXPR)" 8 4 |
847 | .Ip "sqrt EXPR" 8 |
848 | Return the square root of EXPR. |
849 | If EXPR is omitted, returns square root of $_. |
850 | .Ip "srand(EXPR)" 8 4 |
851 | .Ip "srand EXPR" 8 |
852 | Sets the random number seed for the |
853 | .I rand |
854 | operator. |
855 | If EXPR is omitted, does srand(time). |
ae986130 |
856 | .Ip "stat(FILEHANDLE)" 8 8 |
a687059c |
857 | .Ip "stat FILEHANDLE" 8 |
858 | .Ip "stat(EXPR)" 8 |
ae986130 |
859 | .Ip "stat SCALARVARIABLE" 8 |
a687059c |
860 | Returns a 13-element array giving the statistics for a file, either the file |
861 | opened via FILEHANDLE, or named by EXPR. |
862 | Typically used as follows: |
863 | .nf |
864 | |
865 | .ne 3 |
866 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, |
867 | $atime,$mtime,$ctime,$blksize,$blocks) |
868 | = stat($filename); |
869 | |
870 | .fi |
871 | If stat is passed the special filehandle consisting of an underline, |
872 | no stat is done, but the current contents of the stat structure from |
873 | the last stat or filetest are returned. |
874 | Example: |
875 | .nf |
876 | |
877 | .ne 3 |
878 | if (-x $file && (($d) = stat(_)) && $d < 0) { |
879 | print "$file is executable NFS file\en"; |
880 | } |
881 | |
882 | .fi |
883 | .Ip "study(SCALAR)" 8 6 |
884 | .Ip "study SCALAR" 8 |
885 | .Ip "study" |
886 | Takes extra time to study SCALAR ($_ if unspecified) in anticipation of |
887 | doing many pattern matches on the string before it is next modified. |
888 | This may or may not save time, depending on the nature and number of patterns |
889 | you are searching on, and on the distribution of character frequencies in |
890 | the string to be searched\*(--you probably want to compare runtimes with and |
891 | without it to see which runs faster. |
892 | Those loops which scan for many short constant strings (including the constant |
893 | parts of more complex patterns) will benefit most. |
894 | You may have only one study active at a time\*(--if you study a different |
895 | scalar the first is \*(L"unstudied\*(R". |
896 | (The way study works is this: a linked list of every character in the string |
897 | to be searched is made, so we know, for example, where all the \*(L'k\*(R' characters |
898 | are. |
899 | From each search string, the rarest character is selected, based on some |
900 | static frequency tables constructed from some C programs and English text. |
901 | Only those places that contain this \*(L"rarest\*(R" character are examined.) |
902 | .Sp |
903 | For example, here is a loop which inserts index producing entries before any line |
904 | containing a certain pattern: |
905 | .nf |
906 | |
907 | .ne 8 |
908 | while (<>) { |
909 | study; |
910 | print ".IX foo\en" if /\ebfoo\eb/; |
911 | print ".IX bar\en" if /\ebbar\eb/; |
912 | print ".IX blurfl\en" if /\ebblurfl\eb/; |
913 | .\|.\|. |
914 | print; |
915 | } |
916 | |
917 | .fi |
918 | In searching for /\ebfoo\eb/, only those locations in $_ that contain \*(L'f\*(R' |
919 | will be looked at, because \*(L'f\*(R' is rarer than \*(L'o\*(R'. |
920 | In general, this is a big win except in pathological cases. |
921 | The only question is whether it saves you more time than it took to build |
922 | the linked list in the first place. |
923 | .Sp |
924 | Note that if you have to look for strings that you don't know till runtime, |
925 | you can build an entire loop as a string and eval that to avoid recompiling |
926 | all your patterns all the time. |
927 | Together with setting $/ to input entire files as one record, this can |
928 | be very fast, often faster than specialized programs like fgrep. |
929 | The following scans a list of files (@files) |
930 | for a list of words (@words), and prints out the names of those files that |
931 | contain a match: |
932 | .nf |
933 | |
934 | .ne 12 |
935 | $search = \'while (<>) { study;\'; |
936 | foreach $word (@words) { |
937 | $search .= "++\e$seen{\e$ARGV} if /\eb$word\eb/;\en"; |
938 | } |
939 | $search .= "}"; |
940 | @ARGV = @files; |
941 | $/ = "\e177"; # something that doesn't occur |
942 | eval $search; # this screams |
943 | $/ = "\en"; # put back to normal input delim |
944 | foreach $file (sort keys(%seen)) { |
945 | print $file, "\en"; |
946 | } |
947 | |
948 | .fi |
949 | .Ip "substr(EXPR,OFFSET,LEN)" 8 2 |
950 | Extracts a substring out of EXPR and returns it. |
951 | First character is at offset 0, or whatever you've set $[ to. |
952 | If OFFSET is negative, starts that far from the end of the string. |
953 | You can use the substr() function as an lvalue, in which case EXPR must |
954 | be an lvalue. |
955 | If you assign something shorter than LEN, the string will shrink, and |
ae986130 |
956 | if you assign something longer than LEN, the string will grow to accommodate it. |
a687059c |
957 | To keep the string the same length you may need to pad or chop your value using |
958 | sprintf(). |
959 | .Ip "syscall(LIST)" 8 6 |
960 | .Ip "syscall LIST" 8 |
961 | Calls the system call specified as the first element of the list, passing |
962 | the remaining elements as arguments to the system call. |
963 | If unimplemented, produces a fatal error. |
964 | The arguments are interpreted as follows: if a given argument is numeric, |
965 | the argument is passed as an int. |
966 | If not, the pointer to the string value is passed. |
967 | You are responsible to make sure a string is pre-extended long enough |
968 | to receive any result that might be written into a string. |
969 | If your integer arguments are not literals and have never been interpreted |
970 | in a numeric context, you may need to add 0 to them to force them to look |
971 | like numbers. |
972 | .nf |
973 | |
974 | do 'syscall.h'; # may need to run makelib |
975 | syscall(&SYS_write, fileno(STDOUT), "hi there\en", 9); |
976 | |
977 | .fi |
978 | .Ip "system(LIST)" 8 6 |
979 | .Ip "system LIST" 8 |
980 | Does exactly the same thing as \*(L"exec LIST\*(R" except that a fork |
981 | is done first, and the parent process waits for the child process to complete. |
982 | Note that argument processing varies depending on the number of arguments. |
983 | The return value is the exit status of the program as returned by the wait() |
984 | call. |
985 | To get the actual exit value divide by 256. |
986 | See also |
987 | .IR exec . |
988 | .Ip "symlink(OLDFILE,NEWFILE)" 8 2 |
989 | Creates a new filename symbolically linked to the old filename. |
990 | Returns 1 for success, 0 otherwise. |
991 | On systems that don't support symbolic links, produces a fatal error at |
992 | run time. |
993 | To check for that, use eval: |
994 | .nf |
995 | |
996 | $symlink_exists = (eval \'symlink("","");\', $@ eq \'\'); |
997 | |
998 | .fi |
999 | .Ip "tell(FILEHANDLE)" 8 6 |
1000 | .Ip "tell FILEHANDLE" 8 6 |
1001 | .Ip "tell" 8 |
1002 | Returns the current file position for FILEHANDLE. |
1003 | FILEHANDLE may be an expression whose value gives the name of the actual |
1004 | filehandle. |
1005 | If FILEHANDLE is omitted, assumes the file last read. |
1006 | .Ip "telldir(DIRHANDLE)" 8 5 |
1007 | .Ip "telldir DIRHANDLE" 8 |
1008 | Returns the current position of the readdir() routines on DIRHANDLE. |
1009 | Value may be given to seekdir() to access a particular location in |
1010 | a directory. |
1011 | Has the same caveats about possible directory compaction as the corresponding |
1012 | system library routine. |
1013 | .Ip "time" 8 4 |
1014 | Returns the number of non-leap seconds since January 1, 1970, UTC. |
1015 | Suitable for feeding to gmtime() and localtime(). |
1016 | .Ip "times" 8 4 |
1017 | Returns a four-element array giving the user and system times, in seconds, for this |
1018 | process and the children of this process. |
1019 | .Sp |
1020 | ($user,$system,$cuser,$csystem) = times; |
1021 | .Sp |
1022 | .Ip "tr/SEARCHLIST/REPLACEMENTLIST/" 8 5 |
1023 | .Ip "y/SEARCHLIST/REPLACEMENTLIST/" 8 |
1024 | Translates all occurrences of the characters found in the search list with |
1025 | the corresponding character in the replacement list. |
1026 | It returns the number of characters replaced. |
1027 | If no string is specified via the =~ or !~ operator, |
1028 | the $_ string is translated. |
1029 | (The string specified with =~ must be a scalar variable, an array element, |
1030 | or an assignment to one of those, i.e. an lvalue.) |
1031 | For |
1032 | .I sed |
1033 | devotees, |
1034 | .I y |
1035 | is provided as a synonym for |
1036 | .IR tr . |
1037 | Examples: |
1038 | .nf |
1039 | |
1040 | $ARGV[1] \|=~ \|y/A\-Z/a\-z/; \h'|3i'# canonicalize to lower case |
1041 | |
1042 | $cnt = tr/*/*/; \h'|3i'# count the stars in $_ |
1043 | |
1044 | ($HOST = $host) =~ tr/a\-z/A\-Z/; |
1045 | |
1046 | y/\e001\-@[\-_{\-\e177/ /; \h'|3i'# change non-alphas to space |
1047 | |
1048 | .fi |
1049 | .Ip "umask(EXPR)" 8 4 |
1050 | .Ip "umask EXPR" 8 |
ae986130 |
1051 | .Ip "umask" 8 |
a687059c |
1052 | Sets the umask for the process and returns the old one. |
1053 | If EXPR is omitted, merely returns current umask. |
1054 | .Ip "undef(EXPR)" 8 6 |
1055 | .Ip "undef EXPR" 8 |
1056 | .Ip "undef" 8 |
1057 | Undefines the value of EXPR, which must be an lvalue. |
1058 | Use only on a scalar value, an entire array, or a subroutine name (using &). |
1059 | (Undef will probably not do what you expect on most predefined variables or |
1060 | dbm array values.) |
1061 | Always returns the undefined value. |
1062 | You can omit the EXPR, in which case nothing is undefined, but you still |
1063 | get an undefined value that you could, for instance, return from a subroutine. |
1064 | Examples: |
1065 | .nf |
1066 | |
1067 | .ne 6 |
1068 | undef $foo; |
1069 | undef $bar{'blurfl'}; |
1070 | undef @ary; |
1071 | undef %assoc; |
1072 | undef &mysub; |
1073 | return (wantarray ? () : undef) if $they_blew_it; |
1074 | |
1075 | .fi |
1076 | .Ip "unlink(LIST)" 8 4 |
1077 | .Ip "unlink LIST" 8 |
1078 | Deletes a list of files. |
1079 | Returns the number of files successfully deleted. |
1080 | .nf |
1081 | |
1082 | .ne 2 |
1083 | $cnt = unlink \'a\', \'b\', \'c\'; |
1084 | unlink @goners; |
1085 | unlink <*.bak>; |
1086 | |
1087 | .fi |
1088 | Note: unlink will not delete directories unless you are superuser and the |
1089 | .B \-U |
1090 | flag is supplied to |
1091 | .IR perl . |
1092 | Even if these conditions are met, be warned that unlinking a directory |
1093 | can inflict damage on your filesystem. |
1094 | Use rmdir instead. |
1095 | .Ip "unpack(TEMPLATE,EXPR)" 8 4 |
1096 | Unpack does the reverse of pack: it takes a string representing |
1097 | a structure and expands it out into an array value, returning the array |
1098 | value. |
1099 | The TEMPLATE has the same format as in the pack function. |
1100 | Here's a subroutine that does substring: |
1101 | .nf |
1102 | |
1103 | .ne 4 |
1104 | sub substr { |
1105 | local($what,$where,$howmuch) = @_; |
1106 | unpack("x$where a$howmuch", $what); |
1107 | } |
1108 | |
1109 | .ne 3 |
1110 | and then there's |
1111 | |
1112 | sub ord { unpack("c",$_[0]); } |
1113 | |
1114 | .fi |
1115 | .Ip "unshift(ARRAY,LIST)" 8 4 |
1116 | Does the opposite of a |
1117 | .IR shift . |
1118 | Or the opposite of a |
1119 | .IR push , |
1120 | depending on how you look at it. |
1121 | Prepends list to the front of the array, and returns the number of elements |
1122 | in the new array. |
1123 | .nf |
1124 | |
1125 | unshift(ARGV, \'\-e\') unless $ARGV[0] =~ /^\-/; |
1126 | |
1127 | .fi |
1128 | .Ip "utime(LIST)" 8 2 |
1129 | .Ip "utime LIST" 8 2 |
1130 | Changes the access and modification times on each file of a list of files. |
1131 | The first two elements of the list must be the NUMERICAL access and |
1132 | modification times, in that order. |
1133 | Returns the number of files successfully changed. |
1134 | The inode modification time of each file is set to the current time. |
1135 | Example of a \*(L"touch\*(R" command: |
1136 | .nf |
1137 | |
1138 | .ne 3 |
1139 | #!/usr/bin/perl |
1140 | $now = time; |
1141 | utime $now, $now, @ARGV; |
1142 | |
1143 | .fi |
1144 | .Ip "values(ASSOC_ARRAY)" 8 6 |
1145 | .Ip "values ASSOC_ARRAY" 8 |
1146 | Returns a normal array consisting of all the values of the named associative |
1147 | array. |
1148 | The values are returned in an apparently random order, but it is the same order |
1149 | as either the keys() or each() function would produce on the same array. |
1150 | See also keys() and each(). |
1151 | .Ip "vec(EXPR,OFFSET,BITS)" 8 2 |
1152 | Treats a string as a vector of unsigned integers, and returns the value |
1153 | of the bitfield specified. |
1154 | May also be assigned to. |
1155 | BITS must be a power of two from 1 to 32. |
1156 | .Sp |
1157 | Vectors created with vec() can also be manipulated with the logical operators |
1158 | |, & and ^, |
1159 | which will assume a bit vector operation is desired when both operands are |
1160 | strings. |
1161 | This interpretation is not enabled unless there is at least one vec() in |
1162 | your program, to protect older programs. |
1163 | .Ip "wait" 8 6 |
1164 | Waits for a child process to terminate and returns the pid of the deceased |
ae986130 |
1165 | process, or -1 if there are no child processes. |
a687059c |
1166 | The status is returned in $?. |
ae986130 |
1167 | If you expected a child and didn't find it, you probably had a call to |
1168 | system, a close on a pipe, or backticks between the fork and the wait. |
1169 | These constructs also do a wait and may have harvested your child process. |
a687059c |
1170 | .Ip "wantarray" 8 4 |
1171 | Returns true if the context of the currently executing subroutine |
1172 | is looking for an array value. |
1173 | Returns false if the context is looking for a scalar. |
1174 | .nf |
1175 | |
1176 | return wantarray ? () : undef; |
1177 | |
1178 | .fi |
1179 | .Ip "warn(LIST)" 8 4 |
1180 | .Ip "warn LIST" 8 |
1181 | Produces a message on STDERR just like \*(L"die\*(R", but doesn't exit. |
1182 | .Ip "write(FILEHANDLE)" 8 6 |
1183 | .Ip "write(EXPR)" 8 |
ae986130 |
1184 | .Ip "write" 8 |
a687059c |
1185 | Writes a formatted record (possibly multi-line) to the specified file, |
1186 | using the format associated with that file. |
1187 | By default the format for a file is the one having the same name is the |
1188 | filehandle, but the format for the current output channel (see |
1189 | .IR select ) |
1190 | may be set explicitly |
1191 | by assigning the name of the format to the $~ variable. |
1192 | .Sp |
1193 | Top of form processing is handled automatically: |
1194 | if there is insufficient room on the current page for the formatted |
ac58e20f |
1195 | record, the page is advanced by writing a form feed, |
1196 | a special top-of-page format is used |
a687059c |
1197 | to format the new page header, and then the record is written. |
1198 | By default the top-of-page format is \*(L"top\*(R", but it |
1199 | may be set to the |
1200 | format of your choice by assigning the name to the $^ variable. |
ac58e20f |
1201 | The number of lines remaining on the current page is in variable $-, which |
1202 | can be set to 0 to force a new page. |
a687059c |
1203 | .Sp |
1204 | If FILEHANDLE is unspecified, output goes to the current default output channel, |
1205 | which starts out as |
1206 | .I STDOUT |
1207 | but may be changed by the |
1208 | .I select |
1209 | operator. |
1210 | If the FILEHANDLE is an EXPR, then the expression is evaluated and the |
1211 | resulting string is used to look up the name of the FILEHANDLE at run time. |
1212 | For more on formats, see the section on formats later on. |
1213 | .Sp |
1214 | Note that write is NOT the opposite of read. |