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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlvar - Perl predefined variables | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | =head2 Predefined Names | |
8 | ||
9 | The following names have special meaning to Perl. Most of the | |
10 | punctuational names have reasonable mnemonics, or analogues in one of | |
11 | the shells. Nevertheless, if you wish to use the long variable names, | |
12 | you just need to say | |
13 | ||
14 | use English; | |
15 | ||
16 | at the top of your program. This will alias all the short names to the | |
17 | long names in the current package. Some of them even have medium names, | |
18 | generally borrowed from B<awk>. | |
19 | ||
20 | To go a step further, those variables that depend on the currently | |
21 | selected filehandle may instead be set by calling an object method on | |
22 | the FileHandle object. (Summary lines below for this contain the word | |
23 | HANDLE.) First you must say | |
24 | ||
25 | use FileHandle; | |
26 | ||
27 | after which you may use either | |
28 | ||
29 | method HANDLE EXPR | |
30 | ||
31 | or | |
32 | ||
33 | HANDLE->method(EXPR) | |
34 | ||
35 | Each of the methods returns the old value of the FileHandle attribute. | |
36 | The methods each take an optional EXPR, which if supplied specifies the | |
37 | new value for the FileHandle attribute in question. If not supplied, | |
38 | most of the methods do nothing to the current value, except for | |
39 | autoflush(), which will assume a 1 for you, just to be different. | |
40 | ||
748a9306 LW |
41 | A few of these variables are considered "read-only". This means that if |
42 | you try to assign to this variable, either directly or indirectly through | |
43 | a reference, you'll raise a run-time exception. | |
a0d0e21e LW |
44 | |
45 | =over 8 | |
46 | ||
47 | =item $ARG | |
48 | ||
49 | =item $_ | |
50 | ||
51 | The default input and pattern-searching space. The following pairs are | |
52 | equivalent: | |
53 | ||
54 | while (<>) {...} # only equivalent in while! | |
55 | while ($_ = <>) {...} | |
56 | ||
57 | /^Subject:/ | |
58 | $_ =~ /^Subject:/ | |
59 | ||
60 | tr/a-z/A-Z/ | |
61 | $_ =~ tr/a-z/A-Z/ | |
62 | ||
63 | chop | |
64 | chop($_) | |
65 | ||
66 | (Mnemonic: underline is understood in certain operations.) | |
67 | ||
68 | =item $<I<digit>> | |
69 | ||
70 | Contains the subpattern from the corresponding set of parentheses in | |
71 | the last pattern matched, not counting patterns matched in nested | |
72 | blocks that have been exited already. (Mnemonic: like \digit.) | |
73 | These variables are all read-only. | |
74 | ||
75 | =item $MATCH | |
76 | ||
77 | =item $& | |
78 | ||
79 | The string matched by the last successful pattern match (not counting | |
80 | any matches hidden within a BLOCK or eval() enclosed by the current | |
81 | BLOCK). (Mnemonic: like & in some editors.) This variable is read-only. | |
82 | ||
83 | =item $PREMATCH | |
84 | ||
85 | =item $` | |
86 | ||
87 | The string preceding whatever was matched by the last successful | |
88 | pattern match (not counting any matches hidden within a BLOCK or eval | |
89 | enclosed by the current BLOCK). (Mnemonic: ` often precedes a quoted | |
90 | string.) This variable is read-only. | |
91 | ||
92 | =item $POSTMATCH | |
93 | ||
94 | =item $' | |
95 | ||
96 | The string following whatever was matched by the last successful | |
97 | pattern match (not counting any matches hidden within a BLOCK or eval() | |
98 | enclosed by the current BLOCK). (Mnemonic: ' often follows a quoted | |
99 | string.) Example: | |
100 | ||
101 | $_ = 'abcdefghi'; | |
102 | /def/; | |
103 | print "$`:$&:$'\n"; # prints abc:def:ghi | |
104 | ||
105 | This variable is read-only. | |
106 | ||
107 | =item $LAST_PAREN_MATCH | |
108 | ||
109 | =item $+ | |
110 | ||
111 | The last bracket matched by the last search pattern. This is useful if | |
112 | you don't know which of a set of alternative patterns matched. For | |
113 | example: | |
114 | ||
115 | /Version: (.*)|Revision: (.*)/ && ($rev = $+); | |
116 | ||
117 | (Mnemonic: be positive and forward looking.) | |
118 | This variable is read-only. | |
119 | ||
120 | =item $MULTILINE_MATCHING | |
121 | ||
122 | =item $* | |
123 | ||
124 | Set to 1 to do multiline matching within a string, 0 to tell Perl | |
125 | that it can assume that strings contain a single line, for the purpose | |
126 | of optimizing pattern matches. Pattern matches on strings containing | |
127 | multiple newlines can produce confusing results when "C<$*>" is 0. Default | |
128 | is 0. (Mnemonic: * matches multiple things.) Note that this variable | |
129 | only influences the interpretation of "C<^>" and "C<$>". A literal newline can | |
130 | be searched for even when C<$* == 0>. | |
131 | ||
132 | Use of "C<$*>" is deprecated in Perl 5. | |
133 | ||
134 | =item input_line_number HANDLE EXPR | |
135 | ||
136 | =item $INPUT_LINE_NUMBER | |
137 | ||
138 | =item $NR | |
139 | ||
140 | =item $. | |
141 | ||
142 | The current input line number of the last filehandle that was read. | |
143 | This variable should be considered read-only. | |
144 | Remember that only an explicit close on the filehandle | |
145 | resets the line number. Since "C<E<lt>E<gt>>" never does an explicit close, line | |
146 | numbers increase across ARGV files (but see examples under eof()). | |
147 | (Mnemonic: many programs use "." to mean the current line number.) | |
148 | ||
149 | =item input_record_separator HANDLE EXPR | |
150 | ||
151 | =item $INPUT_RECORD_SEPARATOR | |
152 | ||
153 | =item $RS | |
154 | ||
155 | =item $/ | |
156 | ||
157 | The input record separator, newline by default. Works like B<awk>'s RS | |
158 | variable, including treating blank lines as delimiters if set to the | |
159 | null string. You may set it to a multicharacter string to match a | |
160 | multi-character delimiter. Note that setting it to C<"\n\n"> means | |
161 | something slightly different than setting it to C<"">, if the file | |
162 | contains consecutive blank lines. Setting it to C<""> will treat two or | |
163 | more consecutive blank lines as a single blank line. Setting it to | |
164 | C<"\n\n"> will blindly assume that the next input character belongs to the | |
165 | next paragraph, even if it's a newline. (Mnemonic: / is used to | |
166 | delimit line boundaries when quoting poetry.) | |
167 | ||
168 | undef $/; | |
169 | $_ = <FH>; # whole file now here | |
170 | s/\n[ \t]+/ /g; | |
171 | ||
172 | =item autoflush HANDLE EXPR | |
173 | ||
174 | =item $OUTPUT_AUTOFLUSH | |
175 | ||
176 | =item $| | |
177 | ||
178 | If set to nonzero, forces a flush after every write or print on the | |
179 | currently selected output channel. Default is 0. Note that STDOUT | |
180 | will typically be line buffered if output is to the terminal and block | |
181 | buffered otherwise. Setting this variable is useful primarily when you | |
182 | are outputting to a pipe, such as when you are running a Perl script | |
183 | under rsh and want to see the output as it's happening. (Mnemonic: | |
184 | when you want your pipes to be piping hot.) | |
185 | ||
186 | =item output_field_separator HANDLE EXPR | |
187 | ||
188 | =item $OUTPUT_FIELD_SEPARATOR | |
189 | ||
190 | =item $OFS | |
191 | ||
192 | =item $, | |
193 | ||
194 | The output field separator for the print operator. Ordinarily the | |
195 | print operator simply prints out the comma separated fields you | |
196 | specify. In order to get behavior more like B<awk>, set this variable | |
197 | as you would set B<awk>'s OFS variable to specify what is printed | |
198 | between fields. (Mnemonic: what is printed when there is a , in your | |
199 | print statement.) | |
200 | ||
201 | =item output_record_separator HANDLE EXPR | |
202 | ||
203 | =item $OUTPUT_RECORD_SEPARATOR | |
204 | ||
205 | =item $ORS | |
206 | ||
207 | =item $\ | |
208 | ||
209 | The output record separator for the print operator. Ordinarily the | |
210 | print operator simply prints out the comma separated fields you | |
211 | specify, with no trailing newline or record separator assumed. In | |
212 | order to get behavior more like B<awk>, set this variable as you would | |
213 | set B<awk>'s ORS variable to specify what is printed at the end of the | |
214 | print. (Mnemonic: you set "C<$\>" instead of adding \n at the end of the | |
215 | print. Also, it's just like /, but it's what you get "back" from | |
216 | Perl.) | |
217 | ||
218 | =item $LIST_SEPARATOR | |
219 | ||
220 | =item $" | |
221 | ||
222 | This is like "C<$,>" except that it applies to array values interpolated | |
223 | into a double-quoted string (or similar interpreted string). Default | |
224 | is a space. (Mnemonic: obvious, I think.) | |
225 | ||
226 | =item $SUBSCRIPT_SEPARATOR | |
227 | ||
228 | =item $SUBSEP | |
229 | ||
230 | =item $; | |
231 | ||
232 | The subscript separator for multi-dimensional array emulation. If you | |
233 | refer to a hash element as | |
234 | ||
235 | $foo{$a,$b,$c} | |
236 | ||
237 | it really means | |
238 | ||
239 | $foo{join($;, $a, $b, $c)} | |
240 | ||
241 | But don't put | |
242 | ||
243 | @foo{$a,$b,$c} # a slice--note the @ | |
244 | ||
245 | which means | |
246 | ||
247 | ($foo{$a},$foo{$b},$foo{$c}) | |
248 | ||
249 | Default is "\034", the same as SUBSEP in B<awk>. Note that if your | |
250 | keys contain binary data there might not be any safe value for "C<$;>". | |
251 | (Mnemonic: comma (the syntactic subscript separator) is a | |
252 | semi-semicolon. Yeah, I know, it's pretty lame, but "C<$,>" is already | |
253 | taken for something more important.) | |
254 | ||
255 | Consider using "real" multi-dimensional arrays in Perl 5. | |
256 | ||
257 | =item $OFMT | |
258 | ||
259 | =item $# | |
260 | ||
261 | The output format for printed numbers. This variable is a half-hearted | |
262 | attempt to emulate B<awk>'s OFMT variable. There are times, however, | |
263 | when B<awk> and Perl have differing notions of what is in fact | |
264 | numeric. Also, the initial value is %.20g rather than %.6g, so you | |
265 | need to set "C<$#>" explicitly to get B<awk>'s value. (Mnemonic: # is the | |
266 | number sign.) | |
267 | ||
268 | Use of "C<$#>" is deprecated in Perl 5. | |
269 | ||
270 | =item format_page_number HANDLE EXPR | |
271 | ||
272 | =item $FORMAT_PAGE_NUMBER | |
273 | ||
274 | =item $% | |
275 | ||
276 | The current page number of the currently selected output channel. | |
277 | (Mnemonic: % is page number in B<nroff>.) | |
278 | ||
279 | =item format_lines_per_page HANDLE EXPR | |
280 | ||
281 | =item $FORMAT_LINES_PER_PAGE | |
282 | ||
283 | =item $= | |
284 | ||
285 | The current page length (printable lines) of the currently selected | |
286 | output channel. Default is 60. (Mnemonic: = has horizontal lines.) | |
287 | ||
288 | =item format_lines_left HANDLE EXPR | |
289 | ||
290 | =item $FORMAT_LINES_LEFT | |
291 | ||
292 | =item $- | |
293 | ||
294 | The number of lines left on the page of the currently selected output | |
295 | channel. (Mnemonic: lines_on_page - lines_printed.) | |
296 | ||
297 | =item format_name HANDLE EXPR | |
298 | ||
299 | =item $FORMAT_NAME | |
300 | ||
301 | =item $~ | |
302 | ||
303 | The name of the current report format for the currently selected output | |
304 | channel. Default is name of the filehandle. (Mnemonic: brother to | |
305 | "C<$^>".) | |
306 | ||
307 | =item format_top_name HANDLE EXPR | |
308 | ||
309 | =item $FORMAT_TOP_NAME | |
310 | ||
311 | =item $^ | |
312 | ||
313 | The name of the current top-of-page format for the currently selected | |
314 | output channel. Default is name of the filehandle with _TOP | |
315 | appended. (Mnemonic: points to top of page.) | |
316 | ||
317 | =item format_line_break_characters HANDLE EXPR | |
318 | ||
319 | =item $FORMAT_LINE_BREAK_CHARACTERS | |
320 | ||
321 | =item $: | |
322 | ||
323 | The current set of characters after which a string may be broken to | |
324 | fill continuation fields (starting with ^) in a format. Default is | |
325 | S<" \n-">, to break on whitespace or hyphens. (Mnemonic: a "colon" in | |
326 | poetry is a part of a line.) | |
327 | ||
328 | =item format_formfeed HANDLE EXPR | |
329 | ||
330 | =item $FORMAT_FORMFEED | |
331 | ||
332 | =item $^L | |
333 | ||
334 | What formats output to perform a formfeed. Default is \f. | |
335 | ||
336 | =item $ACCUMULATOR | |
337 | ||
338 | =item $^A | |
339 | ||
340 | The current value of the write() accumulator for format() lines. A format | |
341 | contains formline() commands that put their result into C<$^A>. After | |
342 | calling its format, write() prints out the contents of C<$^A> and empties. | |
343 | So you never actually see the contents of C<$^A> unless you call | |
344 | formline() yourself and then look at it. See L<perlform> and | |
345 | L<perlfunc/formline()>. | |
346 | ||
347 | =item $CHILD_ERROR | |
348 | ||
349 | =item $? | |
350 | ||
351 | The status returned by the last pipe close, backtick (C<``>) command, | |
352 | or system() operator. Note that this is the status word returned by | |
353 | the wait() system call, so the exit value of the subprocess is actually | |
354 | (C<$? E<gt>E<gt> 8>). Thus on many systems, C<$? & 255> gives which signal, | |
355 | if any, the process died from, and whether there was a core dump. | |
356 | (Mnemonic: similar to B<sh> and B<ksh>.) | |
357 | ||
358 | =item $OS_ERROR | |
359 | ||
360 | =item $ERRNO | |
361 | ||
362 | =item $! | |
363 | ||
364 | If used in a numeric context, yields the current value of errno, with | |
365 | all the usual caveats. (This means that you shouldn't depend on the | |
366 | value of "C<$!>" to be anything in particular unless you've gotten a | |
367 | specific error return indicating a system error.) If used in a string | |
368 | context, yields the corresponding system error string. You can assign | |
369 | to "C<$!>" in order to set I<errno> if, for instance, you want "C<$!>" to return the | |
370 | string for error I<n>, or you want to set the exit value for the die() | |
371 | operator. (Mnemonic: What just went bang?) | |
372 | ||
373 | =item $EVAL_ERROR | |
374 | ||
375 | =item $@ | |
376 | ||
377 | The Perl syntax error message from the last eval() command. If null, the | |
378 | last eval() parsed and executed correctly (although the operations you | |
379 | invoked may have failed in the normal fashion). (Mnemonic: Where was | |
380 | the syntax error "at"?) | |
381 | ||
748a9306 LW |
382 | Note that warning messages are not collected in this variable. You can, |
383 | however, set up a routine to process warnings by setting $SIG{__WARN__} below. | |
384 | ||
a0d0e21e LW |
385 | =item $PROCESS_ID |
386 | ||
387 | =item $PID | |
388 | ||
389 | =item $$ | |
390 | ||
391 | The process number of the Perl running this script. (Mnemonic: same | |
392 | as shells.) | |
393 | ||
394 | =item $REAL_USER_ID | |
395 | ||
396 | =item $UID | |
397 | ||
398 | =item $< | |
399 | ||
400 | The real uid of this process. (Mnemonic: it's the uid you came I<FROM>, | |
401 | if you're running setuid.) | |
402 | ||
403 | =item $EFFECTIVE_USER_ID | |
404 | ||
405 | =item $EUID | |
406 | ||
407 | =item $> | |
408 | ||
409 | The effective uid of this process. Example: | |
410 | ||
411 | $< = $>; # set real to effective uid | |
412 | ($<,$>) = ($>,$<); # swap real and effective uid | |
413 | ||
414 | (Mnemonic: it's the uid you went I<TO>, if you're running setuid.) Note: | |
415 | "C<$E<lt>>" and "C<$E<gt>>" can only be swapped on machines supporting setreuid(). | |
416 | ||
417 | =item $REAL_GROUP_ID | |
418 | ||
419 | =item $GID | |
420 | ||
421 | =item $( | |
422 | ||
423 | The real gid of this process. If you are on a machine that supports | |
424 | membership in multiple groups simultaneously, gives a space separated | |
425 | list of groups you are in. The first number is the one returned by | |
426 | getgid(), and the subsequent ones by getgroups(), one of which may be | |
427 | the same as the first number. (Mnemonic: parentheses are used to I<GROUP> | |
428 | things. The real gid is the group you I<LEFT>, if you're running setgid.) | |
429 | ||
430 | =item $EFFECTIVE_GROUP_ID | |
431 | ||
432 | =item $EGID | |
433 | ||
434 | =item $) | |
435 | ||
436 | The effective gid of this process. If you are on a machine that | |
437 | supports membership in multiple groups simultaneously, gives a space | |
438 | separated list of groups you are in. The first number is the one | |
439 | returned by getegid(), and the subsequent ones by getgroups(), one of | |
440 | which may be the same as the first number. (Mnemonic: parentheses are | |
441 | used to I<GROUP> things. The effective gid is the group that's I<RIGHT> for | |
442 | you, if you're running setgid.) | |
443 | ||
444 | Note: "C<$E<lt>>", "C<$E<gt>>", "C<$(>" and "C<$)>" can only be set on machines | |
445 | that support the corresponding I<set[re][ug]id()> routine. "C<$(>" and "C<$)>" | |
446 | can only be swapped on machines supporting setregid(). | |
447 | ||
448 | =item $PROGRAM_NAME | |
449 | ||
450 | =item $0 | |
451 | ||
452 | Contains the name of the file containing the Perl script being | |
453 | executed. Assigning to "C<$0>" modifies the argument area that the ps(1) | |
454 | program sees. This is more useful as a way of indicating the | |
455 | current program state than it is for hiding the program you're running. | |
456 | (Mnemonic: same as B<sh> and B<ksh>.) | |
457 | ||
458 | =item $[ | |
459 | ||
460 | The index of the first element in an array, and of the first character | |
461 | in a substring. Default is 0, but you could set it to 1 to make | |
462 | Perl behave more like B<awk> (or Fortran) when subscripting and when | |
463 | evaluating the index() and substr() functions. (Mnemonic: [ begins | |
464 | subscripts.) | |
465 | ||
466 | As of Perl 5, assignment to "C<$[>" is treated as a compiler directive, | |
467 | and cannot influence the behavior of any other file. Its use is | |
468 | discouraged. | |
469 | ||
470 | =item $PERL_VERSION | |
471 | ||
472 | =item $] | |
473 | ||
474 | The string printed out when you say C<perl -v>. It can be used to | |
475 | determine at the beginning of a script whether the perl interpreter | |
476 | executing the script is in the right range of versions. If used in a | |
477 | numeric context, returns the version + patchlevel / 1000. Example: | |
478 | ||
479 | # see if getc is available | |
480 | ($version,$patchlevel) = | |
481 | $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/; | |
482 | print STDERR "(No filename completion available.)\n" | |
483 | if $version * 1000 + $patchlevel < 2016; | |
484 | ||
485 | or, used numerically, | |
486 | ||
487 | warn "No checksumming!\n" if $] < 3.019; | |
488 | ||
489 | (Mnemonic: Is this version of perl in the right bracket?) | |
490 | ||
491 | =item $DEBUGGING | |
492 | ||
493 | =item $^D | |
494 | ||
495 | The current value of the debugging flags. (Mnemonic: value of B<-D> | |
496 | switch.) | |
497 | ||
498 | =item $SYSTEM_FD_MAX | |
499 | ||
500 | =item $^F | |
501 | ||
502 | The maximum system file descriptor, ordinarily 2. System file | |
503 | descriptors are passed to exec()ed processes, while higher file | |
504 | descriptors are not. Also, during an open(), system file descriptors are | |
505 | preserved even if the open() fails. (Ordinary file descriptors are | |
506 | closed before the open() is attempted.) Note that the close-on-exec | |
507 | status of a file descriptor will be decided according to the value of | |
508 | C<$^F> at the time of the open, not the time of the exec. | |
509 | ||
510 | =item $INPLACE_EDIT | |
511 | ||
512 | =item $^I | |
513 | ||
514 | The current value of the inplace-edit extension. Use C<undef> to disable | |
515 | inplace editing. (Mnemonic: value of B<-i> switch.) | |
516 | ||
517 | =item $PERLDB | |
518 | ||
519 | =item $^P | |
520 | ||
521 | The internal flag that the debugger clears so that it doesn't debug | |
522 | itself. You could conceivable disable debugging yourself by clearing | |
523 | it. | |
524 | ||
525 | =item $BASETIME | |
526 | ||
527 | =item $^T | |
528 | ||
529 | The time at which the script began running, in seconds since the | |
530 | epoch (beginning of 1970). The values returned by the B<-M>, B<-A> | |
531 | and B<-C> filetests are | |
532 | based on this value. | |
533 | ||
534 | =item $WARNING | |
535 | ||
536 | =item $^W | |
537 | ||
538 | The current value of the warning switch, either TRUE or FALSE. (Mnemonic: related to the | |
539 | B<-w> switch.) | |
540 | ||
541 | =item $EXECUTABLE_NAME | |
542 | ||
543 | =item $^X | |
544 | ||
545 | The name that the Perl binary itself was executed as, from C's C<argv[0]>. | |
546 | ||
547 | =item $ARGV | |
548 | ||
549 | contains the name of the current file when reading from <>. | |
550 | ||
551 | =item @ARGV | |
552 | ||
553 | The array @ARGV contains the command line arguments intended for the | |
554 | script. Note that C<$#ARGV> is the generally number of arguments minus | |
555 | one, since C<$ARGV[0]> is the first argument, I<NOT> the command name. See | |
556 | "C<$0>" for the command name. | |
557 | ||
558 | =item @INC | |
559 | ||
560 | The array @INC contains the list of places to look for Perl scripts to | |
561 | be evaluated by the C<do EXPR>, C<require>, or C<use> constructs. It | |
562 | initially consists of the arguments to any B<-I> command line switches, | |
563 | followed by the default Perl library, probably "/usr/local/lib/perl", | |
564 | followed by ".", to represent the current directory. | |
565 | ||
566 | =item %INC | |
567 | ||
568 | The hash %INC contains entries for each filename that has | |
569 | been included via C<do> or C<require>. The key is the filename you | |
570 | specified, and the value is the location of the file actually found. | |
571 | The C<require> command uses this array to determine whether a given file | |
572 | has already been included. | |
573 | ||
574 | =item $ENV{expr} | |
575 | ||
576 | The hash %ENV contains your current environment. Setting a | |
577 | value in C<ENV> changes the environment for child processes. | |
578 | ||
579 | =item $SIG{expr} | |
580 | ||
581 | The hash %SIG is used to set signal handlers for various | |
582 | signals. Example: | |
583 | ||
584 | sub handler { # 1st argument is signal name | |
585 | local($sig) = @_; | |
586 | print "Caught a SIG$sig--shutting down\n"; | |
587 | close(LOG); | |
588 | exit(0); | |
589 | } | |
590 | ||
591 | $SIG{'INT'} = 'handler'; | |
592 | $SIG{'QUIT'} = 'handler'; | |
593 | ... | |
594 | $SIG{'INT'} = 'DEFAULT'; # restore default action | |
595 | $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT | |
596 | ||
597 | The %SIG array only contains values for the signals actually set within | |
598 | the Perl script. Here are some other examples: | |
599 | ||
600 | $SIG{PIPE} = Plumber; # SCARY!! | |
601 | $SIG{"PIPE"} = "Plumber"; # just fine, assumes main::Plumber | |
602 | $SIG{"PIPE"} = \&Plumber; # just fine; assume current Plumber | |
603 | $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return?? | |
604 | ||
605 | The one marked scary is problematic because it's a bareword, which means | |
606 | sometimes it's a string representing the function, and sometimes it's | |
607 | going to call the subroutine call right then and there! Best to be sure | |
748a9306 LW |
608 | and quote it or take a reference to it. *Plumber works too. See L<perlsubs>. |
609 | ||
610 | Certain internal hooks can be also set using the %SIG hash. The | |
611 | routine indicated by $SIG{__WARN__} is called when a warning message is | |
612 | about to be printed. The warning message is passed as the first | |
613 | argument. The presence of a __WARN__ hook causes the ordinary printing | |
614 | of warnings to STDERR to be suppressed. You can use this to save warnings | |
615 | in a variable, or turn warnings into fatal errors, like this: | |
616 | ||
617 | local $SIG{__WARN__} = sub { die $_[0] }; | |
618 | eval $proggie; | |
619 | ||
620 | The routine indicated by $SIG{__DIE__} is called when a fatal exception | |
621 | is about to be thrown. The error message is passed as the first | |
622 | argument. When a __DIE__ hook routine returns, the exception | |
623 | processing continues as it would have in the absence of the hook, | |
624 | unless the hook routine itself exits via a goto, a loop exit, or a die. | |
a0d0e21e LW |
625 | |
626 | =back | |
627 |