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128 | .rm #[ #] #H #V #F C | |
129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "PERLVAR 1" | |
132 | .TH PERLVAR 1 "2006-01-07" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | perlvar \- Perl predefined variables | |
135 | .SH "DESCRIPTION" | |
136 | .IX Header "DESCRIPTION" | |
137 | .Sh "Predefined Names" | |
138 | .IX Subsection "Predefined Names" | |
139 | The following names have special meaning to Perl. Most | |
140 | punctuation names have reasonable mnemonics, or analogs in the | |
141 | shells. Nevertheless, if you wish to use long variable names, | |
142 | you need only say | |
143 | .PP | |
144 | .Vb 1 | |
145 | \& use English; | |
146 | .Ve | |
147 | .PP | |
148 | at the top of your program. This aliases all the short names to the long | |
149 | names in the current package. Some even have medium names, generally | |
150 | borrowed from \fBawk\fR. In general, it's best to use the | |
151 | .PP | |
152 | .Vb 1 | |
153 | \& use English '-no_match_vars'; | |
154 | .Ve | |
155 | .PP | |
156 | invocation if you don't need \f(CW$PREMATCH\fR, \f(CW$MATCH\fR, or \f(CW$POSTMATCH\fR, as it avoids | |
157 | a certain performance hit with the use of regular expressions. See | |
158 | English. | |
159 | .PP | |
160 | Variables that depend on the currently selected filehandle may be set by | |
161 | calling an appropriate object method on the IO::Handle object, although | |
162 | this is less efficient than using the regular built-in variables. (Summary | |
163 | lines below for this contain the word \s-1HANDLE\s0.) First you must say | |
164 | .PP | |
165 | .Vb 1 | |
166 | \& use IO::Handle; | |
167 | .Ve | |
168 | .PP | |
169 | after which you may use either | |
170 | .PP | |
171 | .Vb 1 | |
172 | \& method HANDLE EXPR | |
173 | .Ve | |
174 | .PP | |
175 | or more safely, | |
176 | .PP | |
177 | .Vb 1 | |
178 | \& HANDLE->method(EXPR) | |
179 | .Ve | |
180 | .PP | |
181 | Each method returns the old value of the IO::Handle attribute. | |
182 | The methods each take an optional \s-1EXPR\s0, which, if supplied, specifies the | |
183 | new value for the IO::Handle attribute in question. If not supplied, | |
184 | most methods do nothing to the current value\*(--except for | |
185 | \&\fIautoflush()\fR, which will assume a 1 for you, just to be different. | |
186 | .PP | |
187 | Because loading in the IO::Handle class is an expensive operation, you should | |
188 | learn how to use the regular built-in variables. | |
189 | .PP | |
190 | A few of these variables are considered \*(L"read\-only\*(R". This means that if | |
191 | you try to assign to this variable, either directly or indirectly through | |
192 | a reference, you'll raise a run-time exception. | |
193 | .PP | |
194 | You should be very careful when modifying the default values of most | |
195 | special variables described in this document. In most cases you want | |
196 | to localize these variables before changing them, since if you don't, | |
197 | the change may affect other modules which rely on the default values | |
198 | of the special variables that you have changed. This is one of the | |
199 | correct ways to read the whole file at once: | |
200 | .PP | |
201 | .Vb 4 | |
202 | \& open my $fh, "foo" or die $!; | |
203 | \& local $/; # enable localized slurp mode | |
204 | \& my $content = <$fh>; | |
205 | \& close $fh; | |
206 | .Ve | |
207 | .PP | |
208 | But the following code is quite bad: | |
209 | .PP | |
210 | .Vb 4 | |
211 | \& open my $fh, "foo" or die $!; | |
212 | \& undef $/; # enable slurp mode | |
213 | \& my $content = <$fh>; | |
214 | \& close $fh; | |
215 | .Ve | |
216 | .PP | |
217 | since some other module, may want to read data from some file in the | |
218 | default \*(L"line mode\*(R", so if the code we have just presented has been | |
219 | executed, the global value of \f(CW$/\fR is now changed for any other code | |
220 | running inside the same Perl interpreter. | |
221 | .PP | |
222 | Usually when a variable is localized you want to make sure that this | |
223 | change affects the shortest scope possible. So unless you are already | |
224 | inside some short \f(CW\*(C`{}\*(C'\fR block, you should create one yourself. For | |
225 | example: | |
226 | .PP | |
227 | .Vb 7 | |
228 | \& my $content = ''; | |
229 | \& open my $fh, "foo" or die $!; | |
230 | \& { | |
231 | \& local $/; | |
232 | \& $content = <$fh>; | |
233 | \& } | |
234 | \& close $fh; | |
235 | .Ve | |
236 | .PP | |
237 | Here is an example of how your own code can go broken: | |
238 | .PP | |
239 | .Vb 8 | |
240 | \& for (1..5){ | |
241 | \& nasty_break(); | |
242 | \& print "$_ "; | |
243 | \& } | |
244 | \& sub nasty_break { | |
245 | \& $_ = 5; | |
246 | \& # do something with $_ | |
247 | \& } | |
248 | .Ve | |
249 | .PP | |
250 | You probably expect this code to print: | |
251 | .PP | |
252 | .Vb 1 | |
253 | \& 1 2 3 4 5 | |
254 | .Ve | |
255 | .PP | |
256 | but instead you get: | |
257 | .PP | |
258 | .Vb 1 | |
259 | \& 5 5 5 5 5 | |
260 | .Ve | |
261 | .PP | |
262 | Why? Because \fInasty_break()\fR modifies \f(CW$_\fR without localizing it | |
263 | first. The fix is to add \fIlocal()\fR: | |
264 | .PP | |
265 | .Vb 1 | |
266 | \& local $_ = 5; | |
267 | .Ve | |
268 | .PP | |
269 | It's easy to notice the problem in such a short example, but in more | |
270 | complicated code you are looking for trouble if you don't localize | |
271 | changes to the special variables. | |
272 | .PP | |
273 | The following list is ordered by scalar variables first, then the | |
274 | arrays, then the hashes. | |
275 | .IP "$ARG" 8 | |
276 | .IX Item "$ARG" | |
277 | .PD 0 | |
278 | .IP "$_" 8 | |
279 | .IX Item "$_" | |
280 | .PD | |
281 | The default input and pattern-searching space. The following pairs are | |
282 | equivalent: | |
283 | .Sp | |
284 | .Vb 2 | |
285 | \& while (<>) {...} # equivalent only in while! | |
286 | \& while (defined($_ = <>)) {...} | |
287 | .Ve | |
288 | .Sp | |
289 | .Vb 2 | |
290 | \& /^Subject:/ | |
291 | \& $_ =~ /^Subject:/ | |
292 | .Ve | |
293 | .Sp | |
294 | .Vb 2 | |
295 | \& tr/a-z/A-Z/ | |
296 | \& $_ =~ tr/a-z/A-Z/ | |
297 | .Ve | |
298 | .Sp | |
299 | .Vb 2 | |
300 | \& chomp | |
301 | \& chomp($_) | |
302 | .Ve | |
303 | .Sp | |
304 | Here are the places where Perl will assume \f(CW$_\fR even if you | |
305 | don't use it: | |
306 | .RS 8 | |
307 | .IP "*" 3 | |
308 | Various unary functions, including functions like \fIord()\fR and \fIint()\fR, as well | |
309 | as the all file tests (\f(CW\*(C`\-f\*(C'\fR, \f(CW\*(C`\-d\*(C'\fR) except for \f(CW\*(C`\-t\*(C'\fR, which defaults to | |
310 | \&\s-1STDIN\s0. | |
311 | .IP "*" 3 | |
312 | Various list functions like \fIprint()\fR and \fIunlink()\fR. | |
313 | .IP "*" 3 | |
314 | The pattern matching operations \f(CW\*(C`m//\*(C'\fR, \f(CW\*(C`s///\*(C'\fR, and \f(CW\*(C`tr///\*(C'\fR when used | |
315 | without an \f(CW\*(C`=~\*(C'\fR operator. | |
316 | .IP "*" 3 | |
317 | The default iterator variable in a \f(CW\*(C`foreach\*(C'\fR loop if no other | |
318 | variable is supplied. | |
319 | .IP "*" 3 | |
320 | The implicit iterator variable in the \fIgrep()\fR and \fImap()\fR functions. | |
321 | .IP "*" 3 | |
322 | The default place to put an input record when a \f(CW\*(C`<FH>\*(C'\fR | |
323 | operation's result is tested by itself as the sole criterion of a \f(CW\*(C`while\*(C'\fR | |
324 | test. Outside a \f(CW\*(C`while\*(C'\fR test, this will not happen. | |
325 | .RE | |
326 | .RS 8 | |
327 | .Sp | |
328 | (Mnemonic: underline is understood in certain operations.) | |
329 | .RE | |
330 | .IP "$a" 8 | |
331 | .IX Item "$a" | |
332 | .PD 0 | |
333 | .IP "$b" 8 | |
334 | .IX Item "$b" | |
335 | .PD | |
336 | Special package variables when using \fIsort()\fR, see \*(L"sort\*(R" in perlfunc. | |
337 | Because of this specialness \f(CW$a\fR and \f(CW$b\fR don't need to be declared | |
338 | (using use vars, or \fIour()\fR) even when using the \f(CW\*(C`strict 'vars'\*(C'\fR pragma. | |
339 | Don't lexicalize them with \f(CW\*(C`my $a\*(C'\fR or \f(CW\*(C`my $b\*(C'\fR if you want to be | |
340 | able to use them in the \fIsort()\fR comparison block or function. | |
341 | .IP "$<\fIdigits\fR>" 8 | |
342 | .IX Item "$<digits>" | |
343 | Contains the subpattern from the corresponding set of capturing | |
344 | parentheses from the last pattern match, not counting patterns | |
345 | matched in nested blocks that have been exited already. (Mnemonic: | |
346 | like \edigits.) These variables are all read-only and dynamically | |
347 | scoped to the current \s-1BLOCK\s0. | |
348 | .IP "$MATCH" 8 | |
349 | .IX Item "$MATCH" | |
350 | .PD 0 | |
351 | .IP "$&" 8 | |
352 | .PD | |
353 | The string matched by the last successful pattern match (not counting | |
354 | any matches hidden within a \s-1BLOCK\s0 or \fIeval()\fR enclosed by the current | |
355 | \&\s-1BLOCK\s0). (Mnemonic: like & in some editors.) This variable is read-only | |
356 | and dynamically scoped to the current \s-1BLOCK\s0. | |
357 | .Sp | |
358 | The use of this variable anywhere in a program imposes a considerable | |
359 | performance penalty on all regular expression matches. See \*(L"\s-1BUGS\s0\*(R". | |
360 | .IP "$PREMATCH" 8 | |
361 | .IX Item "$PREMATCH" | |
362 | .PD 0 | |
363 | .IP "$`" 8 | |
364 | .PD | |
365 | The string preceding whatever was matched by the last successful | |
366 | pattern match (not counting any matches hidden within a \s-1BLOCK\s0 or eval | |
367 | enclosed by the current \s-1BLOCK\s0). (Mnemonic: \f(CW\*(C``\*(C'\fR often precedes a quoted | |
368 | string.) This variable is read\-only. | |
369 | .Sp | |
370 | The use of this variable anywhere in a program imposes a considerable | |
371 | performance penalty on all regular expression matches. See \*(L"\s-1BUGS\s0\*(R". | |
372 | .IP "$POSTMATCH" 8 | |
373 | .IX Item "$POSTMATCH" | |
374 | .PD 0 | |
375 | .IP "$'" 8 | |
376 | .PD | |
377 | The string following whatever was matched by the last successful | |
378 | pattern match (not counting any matches hidden within a \s-1BLOCK\s0 or \fIeval()\fR | |
379 | enclosed by the current \s-1BLOCK\s0). (Mnemonic: \f(CW\*(C`'\*(C'\fR often follows a quoted | |
380 | string.) Example: | |
381 | .Sp | |
382 | .Vb 3 | |
383 | \& local $_ = 'abcdefghi'; | |
384 | \& /def/; | |
385 | \& print "$`:$&:$'\en"; # prints abc:def:ghi | |
386 | .Ve | |
387 | .Sp | |
388 | This variable is read-only and dynamically scoped to the current \s-1BLOCK\s0. | |
389 | .Sp | |
390 | The use of this variable anywhere in a program imposes a considerable | |
391 | performance penalty on all regular expression matches. See \*(L"\s-1BUGS\s0\*(R". | |
392 | .IP "$LAST_PAREN_MATCH" 8 | |
393 | .IX Item "$LAST_PAREN_MATCH" | |
394 | .PD 0 | |
395 | .IP "$+" 8 | |
396 | .PD | |
397 | The text matched by the last bracket of the last successful search pattern. | |
398 | This is useful if you don't know which one of a set of alternative patterns | |
399 | matched. For example: | |
400 | .Sp | |
401 | .Vb 1 | |
402 | \& /Version: (.*)|Revision: (.*)/ && ($rev = $+); | |
403 | .Ve | |
404 | .Sp | |
405 | (Mnemonic: be positive and forward looking.) | |
406 | This variable is read-only and dynamically scoped to the current \s-1BLOCK\s0. | |
407 | .IP "$^N" 8 | |
408 | .IX Item "$^N" | |
409 | The text matched by the used group most-recently closed (i.e. the group | |
410 | with the rightmost closing parenthesis) of the last successful search | |
411 | pattern. (Mnemonic: the (possibly) Nested parenthesis that most | |
412 | recently closed.) | |
413 | .Sp | |
414 | This is primarily used inside \f(CW\*(C`(?{...})\*(C'\fR blocks for examining text | |
415 | recently matched. For example, to effectively capture text to a variable | |
416 | (in addition to \f(CW$1\fR, \f(CW$2\fR, etc.), replace \f(CW\*(C`(...)\*(C'\fR with | |
417 | .Sp | |
418 | .Vb 1 | |
419 | \& (?:(...)(?{ $var = $^N })) | |
420 | .Ve | |
421 | .Sp | |
422 | By setting and then using \f(CW$var\fR in this way relieves you from having to | |
423 | worry about exactly which numbered set of parentheses they are. | |
424 | .Sp | |
425 | This variable is dynamically scoped to the current \s-1BLOCK\s0. | |
426 | .IP "@LAST_MATCH_END" 8 | |
427 | .IX Item "@LAST_MATCH_END" | |
428 | .PD 0 | |
429 | .IP "@+" 8 | |
430 | .PD | |
431 | This array holds the offsets of the ends of the last successful | |
432 | submatches in the currently active dynamic scope. \f(CW$+[0]\fR is | |
433 | the offset into the string of the end of the entire match. This | |
434 | is the same value as what the \f(CW\*(C`pos\*(C'\fR function returns when called | |
435 | on the variable that was matched against. The \fIn\fRth element | |
436 | of this array holds the offset of the \fIn\fRth submatch, so | |
437 | \&\f(CW$+[1]\fR is the offset past where \f(CW$1\fR ends, \f(CW$+[2]\fR the offset | |
438 | past where \f(CW$2\fR ends, and so on. You can use \f(CW$#+\fR to determine | |
439 | how many subgroups were in the last successful match. See the | |
440 | examples given for the \f(CW\*(C`@\-\*(C'\fR variable. | |
441 | .IP "$*" 8 | |
442 | Set to a non-zero integer value to do multi-line matching within a | |
443 | string, 0 (or undefined) to tell Perl that it can assume that strings | |
444 | contain a single line, for the purpose of optimizing pattern matches. | |
445 | Pattern matches on strings containing multiple newlines can produce | |
446 | confusing results when \f(CW$*\fR is 0 or undefined. Default is undefined. | |
447 | (Mnemonic: * matches multiple things.) This variable influences the | |
448 | interpretation of only \f(CW\*(C`^\*(C'\fR and \f(CW\*(C`$\*(C'\fR. A literal newline can be searched | |
449 | for even when \f(CW\*(C`$* == 0\*(C'\fR. | |
450 | .Sp | |
451 | Use of \f(CW$*\fR is deprecated in modern Perl, supplanted by | |
452 | the \f(CW\*(C`/s\*(C'\fR and \f(CW\*(C`/m\*(C'\fR modifiers on pattern matching. | |
453 | .Sp | |
454 | Assigning a non-numerical value to \f(CW$*\fR triggers a warning (and makes | |
455 | \&\f(CW$*\fR act if \f(CW\*(C`$* == 0\*(C'\fR), while assigning a numerical value to \f(CW$*\fR | |
456 | makes that an implicit \f(CW\*(C`int\*(C'\fR is applied on the value. | |
457 | .IP "\s-1HANDLE\-\s0>input_line_number(\s-1EXPR\s0)" 8 | |
458 | .IX Item "HANDLE->input_line_number(EXPR)" | |
459 | .PD 0 | |
460 | .IP "$INPUT_LINE_NUMBER" 8 | |
461 | .IX Item "$INPUT_LINE_NUMBER" | |
462 | .IP "$NR" 8 | |
463 | .IX Item "$NR" | |
464 | .IP "$." 8 | |
465 | .PD | |
466 | Current line number for the last filehandle accessed. | |
467 | .Sp | |
468 | Each filehandle in Perl counts the number of lines that have been read | |
469 | from it. (Depending on the value of \f(CW$/\fR, Perl's idea of what | |
470 | constitutes a line may not match yours.) When a line is read from a | |
471 | filehandle (via \fIreadline()\fR or \f(CW\*(C`<>\*(C'\fR), or when \fItell()\fR or \fIseek()\fR is | |
472 | called on it, \f(CW$.\fR becomes an alias to the line counter for that | |
473 | filehandle. | |
474 | .Sp | |
475 | You can adjust the counter by assigning to \f(CW$.\fR, but this will not | |
476 | actually move the seek pointer. \fILocalizing \f(CI$.\fI will not localize | |
477 | the filehandle's line count\fR. Instead, it will localize perl's notion | |
478 | of which filehandle \f(CW$.\fR is currently aliased to. | |
479 | .Sp | |
480 | \&\f(CW$.\fR is reset when the filehandle is closed, but \fBnot\fR when an open | |
481 | filehandle is reopened without an intervening \fIclose()\fR. For more | |
482 | details, see "I/O Operators" in perlop. Because \f(CW\*(C`<>\*(C'\fR never does | |
483 | an explicit close, line numbers increase across \s-1ARGV\s0 files (but see | |
484 | examples in \*(L"eof\*(R" in perlfunc). | |
485 | .Sp | |
486 | You can also use \f(CW\*(C`HANDLE\->input_line_number(EXPR)\*(C'\fR to access the | |
487 | line counter for a given filehandle without having to worry about | |
488 | which handle you last accessed. | |
489 | .Sp | |
490 | (Mnemonic: many programs use \*(L".\*(R" to mean the current line number.) | |
491 | .IP "IO::Handle\->input_record_separator(\s-1EXPR\s0)" 8 | |
492 | .IX Item "IO::Handle->input_record_separator(EXPR)" | |
493 | .PD 0 | |
494 | .IP "$INPUT_RECORD_SEPARATOR" 8 | |
495 | .IX Item "$INPUT_RECORD_SEPARATOR" | |
496 | .IP "$RS" 8 | |
497 | .IX Item "$RS" | |
498 | .IP "$/" 8 | |
499 | .PD | |
500 | The input record separator, newline by default. This | |
501 | influences Perl's idea of what a \*(L"line\*(R" is. Works like \fBawk\fR's \s-1RS\s0 | |
502 | variable, including treating empty lines as a terminator if set to | |
503 | the null string. (An empty line cannot contain any spaces | |
504 | or tabs.) You may set it to a multi-character string to match a | |
505 | multi-character terminator, or to \f(CW\*(C`undef\*(C'\fR to read through the end | |
506 | of file. Setting it to \f(CW"\en\en"\fR means something slightly | |
507 | different than setting to \f(CW""\fR, if the file contains consecutive | |
508 | empty lines. Setting to \f(CW""\fR will treat two or more consecutive | |
509 | empty lines as a single empty line. Setting to \f(CW"\en\en"\fR will | |
510 | blindly assume that the next input character belongs to the next | |
511 | paragraph, even if it's a newline. (Mnemonic: / delimits | |
512 | line boundaries when quoting poetry.) | |
513 | .Sp | |
514 | .Vb 3 | |
515 | \& local $/; # enable "slurp" mode | |
516 | \& local $_ = <FH>; # whole file now here | |
517 | \& s/\en[ \et]+/ /g; | |
518 | .Ve | |
519 | .Sp | |
520 | Remember: the value of \f(CW$/\fR is a string, not a regex. \fBawk\fR has to be | |
521 | better for something. :\-) | |
522 | .Sp | |
523 | Setting \f(CW$/\fR to a reference to an integer, scalar containing an integer, or | |
524 | scalar that's convertible to an integer will attempt to read records | |
525 | instead of lines, with the maximum record size being the referenced | |
526 | integer. So this: | |
527 | .Sp | |
528 | .Vb 3 | |
529 | \& local $/ = \e32768; # or \e"32768", or \e$var_containing_32768 | |
530 | \& open my $fh, $myfile or die $!; | |
531 | \& local $_ = <$fh>; | |
532 | .Ve | |
533 | .Sp | |
534 | will read a record of no more than 32768 bytes from \s-1FILE\s0. If you're | |
535 | not reading from a record-oriented file (or your \s-1OS\s0 doesn't have | |
536 | record-oriented files), then you'll likely get a full chunk of data | |
537 | with every read. If a record is larger than the record size you've | |
538 | set, you'll get the record back in pieces. | |
539 | .Sp | |
540 | On \s-1VMS\s0, record reads are done with the equivalent of \f(CW\*(C`sysread\*(C'\fR, | |
541 | so it's best not to mix record and non-record reads on the same | |
542 | file. (This is unlikely to be a problem, because any file you'd | |
543 | want to read in record mode is probably unusable in line mode.) | |
544 | Non-VMS systems do normal I/O, so it's safe to mix record and | |
545 | non-record reads of a file. | |
546 | .Sp | |
547 | See also \*(L"Newlines\*(R" in perlport. Also see \f(CW$.\fR. | |
548 | .IP "\s-1HANDLE\-\s0>autoflush(\s-1EXPR\s0)" 8 | |
549 | .IX Item "HANDLE->autoflush(EXPR)" | |
550 | .PD 0 | |
551 | .IP "$OUTPUT_AUTOFLUSH" 8 | |
552 | .IX Item "$OUTPUT_AUTOFLUSH" | |
553 | .IP "$|" 8 | |
554 | .PD | |
555 | If set to nonzero, forces a flush right away and after every write | |
556 | or print on the currently selected output channel. Default is 0 | |
557 | (regardless of whether the channel is really buffered by the | |
558 | system or not; \f(CW$|\fR tells you only whether you've asked Perl | |
559 | explicitly to flush after each write). \s-1STDOUT\s0 will | |
560 | typically be line buffered if output is to the terminal and block | |
561 | buffered otherwise. Setting this variable is useful primarily when | |
562 | you are outputting to a pipe or socket, such as when you are running | |
563 | a Perl program under \fBrsh\fR and want to see the output as it's | |
564 | happening. This has no effect on input buffering. See \*(L"getc\*(R" in perlfunc | |
565 | for that. (Mnemonic: when you want your pipes to be piping hot.) | |
566 | .IP "IO::Handle\->output_field_separator \s-1EXPR\s0" 8 | |
567 | .IX Item "IO::Handle->output_field_separator EXPR" | |
568 | .PD 0 | |
569 | .IP "$OUTPUT_FIELD_SEPARATOR" 8 | |
570 | .IX Item "$OUTPUT_FIELD_SEPARATOR" | |
571 | .IP "$OFS" 8 | |
572 | .IX Item "$OFS" | |
573 | .IP "$," 8 | |
574 | .PD | |
575 | The output field separator for the print operator. If defined, this | |
576 | value is printed between each of print's arguments. Default is \f(CW\*(C`undef\*(C'\fR. | |
577 | (Mnemonic: what is printed when there is a \*(L",\*(R" in your print statement.) | |
578 | .IP "IO::Handle\->output_record_separator \s-1EXPR\s0" 8 | |
579 | .IX Item "IO::Handle->output_record_separator EXPR" | |
580 | .PD 0 | |
581 | .IP "$OUTPUT_RECORD_SEPARATOR" 8 | |
582 | .IX Item "$OUTPUT_RECORD_SEPARATOR" | |
583 | .IP "$ORS" 8 | |
584 | .IX Item "$ORS" | |
585 | .IP "$\e" 8 | |
586 | .IX Item "$" | |
587 | .PD | |
588 | The output record separator for the print operator. If defined, this | |
589 | value is printed after the last of print's arguments. Default is \f(CW\*(C`undef\*(C'\fR. | |
590 | (Mnemonic: you set \f(CW\*(C`$\e\*(C'\fR instead of adding \*(L"\en\*(R" at the end of the print. | |
591 | Also, it's just like \f(CW$/\fR, but it's what you get \*(L"back\*(R" from Perl.) | |
592 | .IP "$LIST_SEPARATOR" 8 | |
593 | .IX Item "$LIST_SEPARATOR" | |
594 | .PD 0 | |
595 | .IP "$""" 8 | |
596 | .PD | |
597 | This is like \f(CW$,\fR except that it applies to array and slice values | |
598 | interpolated into a double-quoted string (or similar interpreted | |
599 | string). Default is a space. (Mnemonic: obvious, I think.) | |
600 | .IP "$SUBSCRIPT_SEPARATOR" 8 | |
601 | .IX Item "$SUBSCRIPT_SEPARATOR" | |
602 | .PD 0 | |
603 | .IP "$SUBSEP" 8 | |
604 | .IX Item "$SUBSEP" | |
605 | .IP "$;" 8 | |
606 | .PD | |
607 | The subscript separator for multidimensional array emulation. If you | |
608 | refer to a hash element as | |
609 | .Sp | |
610 | .Vb 1 | |
611 | \& $foo{$a,$b,$c} | |
612 | .Ve | |
613 | .Sp | |
614 | it really means | |
615 | .Sp | |
616 | .Vb 1 | |
617 | \& $foo{join($;, $a, $b, $c)} | |
618 | .Ve | |
619 | .Sp | |
620 | But don't put | |
621 | .Sp | |
622 | .Vb 1 | |
623 | \& @foo{$a,$b,$c} # a slice--note the @ | |
624 | .Ve | |
625 | .Sp | |
626 | which means | |
627 | .Sp | |
628 | .Vb 1 | |
629 | \& ($foo{$a},$foo{$b},$foo{$c}) | |
630 | .Ve | |
631 | .Sp | |
632 | Default is \*(L"\e034\*(R", the same as \s-1SUBSEP\s0 in \fBawk\fR. If your | |
633 | keys contain binary data there might not be any safe value for \f(CW$;\fR. | |
634 | (Mnemonic: comma (the syntactic subscript separator) is a | |
635 | semi\-semicolon. Yeah, I know, it's pretty lame, but \f(CW$,\fR is already | |
636 | taken for something more important.) | |
637 | .Sp | |
638 | Consider using \*(L"real\*(R" multidimensional arrays as described | |
639 | in perllol. | |
640 | .IP "$#" 8 | |
641 | The output format for printed numbers. This variable is a half-hearted | |
642 | attempt to emulate \fBawk\fR's \s-1OFMT\s0 variable. There are times, however, | |
643 | when \fBawk\fR and Perl have differing notions of what counts as | |
644 | numeric. The initial value is "%.\fIn\fRg", where \fIn\fR is the value | |
645 | of the macro \s-1DBL_DIG\s0 from your system's \fIfloat.h\fR. This is different from | |
646 | \&\fBawk\fR's default \s-1OFMT\s0 setting of \*(L"%.6g\*(R", so you need to set \f(CW$#\fR | |
647 | explicitly to get \fBawk\fR's value. (Mnemonic: # is the number sign.) | |
648 | .Sp | |
649 | Use of \f(CW$#\fR is deprecated. | |
650 | .IP "\s-1HANDLE\-\s0>format_page_number(\s-1EXPR\s0)" 8 | |
651 | .IX Item "HANDLE->format_page_number(EXPR)" | |
652 | .PD 0 | |
653 | .IP "$FORMAT_PAGE_NUMBER" 8 | |
654 | .IX Item "$FORMAT_PAGE_NUMBER" | |
655 | .IP "$%" 8 | |
656 | .PD | |
657 | The current page number of the currently selected output channel. | |
658 | Used with formats. | |
659 | (Mnemonic: % is page number in \fBnroff\fR.) | |
660 | .IP "\s-1HANDLE\-\s0>format_lines_per_page(\s-1EXPR\s0)" 8 | |
661 | .IX Item "HANDLE->format_lines_per_page(EXPR)" | |
662 | .PD 0 | |
663 | .IP "$FORMAT_LINES_PER_PAGE" 8 | |
664 | .IX Item "$FORMAT_LINES_PER_PAGE" | |
665 | .IP "$=" 8 | |
666 | .PD | |
667 | The current page length (printable lines) of the currently selected | |
668 | output channel. Default is 60. | |
669 | Used with formats. | |
670 | (Mnemonic: = has horizontal lines.) | |
671 | .IP "\s-1HANDLE\-\s0>format_lines_left(\s-1EXPR\s0)" 8 | |
672 | .IX Item "HANDLE->format_lines_left(EXPR)" | |
673 | .PD 0 | |
674 | .IP "$FORMAT_LINES_LEFT" 8 | |
675 | .IX Item "$FORMAT_LINES_LEFT" | |
676 | .IP "$\-" 8 | |
677 | .PD | |
678 | The number of lines left on the page of the currently selected output | |
679 | channel. | |
680 | Used with formats. | |
681 | (Mnemonic: lines_on_page \- lines_printed.) | |
682 | .IP "@LAST_MATCH_START" 8 | |
683 | .IX Item "@LAST_MATCH_START" | |
684 | .PD 0 | |
685 | .IP "@\-" 8 | |
686 | .PD | |
687 | $\-[0] is the offset of the start of the last successful match. | |
688 | \&\f(CW\*(C`$\-[\*(C'\fR\fIn\fR\f(CW\*(C`]\*(C'\fR is the offset of the start of the substring matched by | |
689 | \&\fIn\fR\-th subpattern, or undef if the subpattern did not match. | |
690 | .Sp | |
691 | Thus after a match against \f(CW$_\fR, $& coincides with \f(CW\*(C`substr $_, $\-[0], | |
692 | $+[0] \- $\-[0]\*(C'\fR. Similarly, $\fIn\fR coincides with \f(CW\*(C`substr $_, $\-[n], | |
693 | $+[n] \- $\-[n]\*(C'\fR if \f(CW\*(C`$\-[n]\*(C'\fR is defined, and $+ coincides with | |
694 | \&\f(CW\*(C`substr $_, $\-[$#\-], $+[$#\-] \- $\-[$#\-]\*(C'\fR. One can use \f(CW\*(C`$#\-\*(C'\fR to find the last | |
695 | matched subgroup in the last successful match. Contrast with | |
696 | \&\f(CW$#+\fR, the number of subgroups in the regular expression. Compare | |
697 | with \f(CW\*(C`@+\*(C'\fR. | |
698 | .Sp | |
699 | This array holds the offsets of the beginnings of the last | |
700 | successful submatches in the currently active dynamic scope. | |
701 | \&\f(CW\*(C`$\-[0]\*(C'\fR is the offset into the string of the beginning of the | |
702 | entire match. The \fIn\fRth element of this array holds the offset | |
703 | of the \fIn\fRth submatch, so \f(CW\*(C`$\-[1]\*(C'\fR is the offset where \f(CW$1\fR | |
704 | begins, \f(CW\*(C`$\-[2]\*(C'\fR the offset where \f(CW$2\fR begins, and so on. | |
705 | .Sp | |
706 | After a match against some variable \f(CW$var:\fR | |
707 | .RS 8 | |
708 | .ie n .IP "$`\fR is the same as \f(CW""substr($var, 0, $\-[0])""" 5 | |
709 | .el .IP "\f(CW$`\fR is the same as \f(CWsubstr($var, 0, $\-[0])\fR" 5 | |
710 | .IX Item "$` is the same as substr($var, 0, $-[0])" | |
711 | .PD 0 | |
712 | .ie n .IP "$&\fR is the same as \f(CW""substr($var, $\-[0], $+[0] \- $\-[0])""" 5 | |
713 | .el .IP "\f(CW$&\fR is the same as \f(CWsubstr($var, $\-[0], $+[0] \- $\-[0])\fR" 5 | |
714 | .IX Item "$& is the same as substr($var, $-[0], $+[0] - $-[0])" | |
715 | .ie n .IP "$'\fR is the same as \f(CW""substr($var, $+[0])""" 5 | |
716 | .el .IP "\f(CW$'\fR is the same as \f(CWsubstr($var, $+[0])\fR" 5 | |
717 | .IX Item "$' is the same as substr($var, $+[0])" | |
718 | .ie n .IP "$1\fR is the same as \f(CW""substr($var, $\-[1], $+[1] \- $\-[1])""" 5 | |
719 | .el .IP "\f(CW$1\fR is the same as \f(CWsubstr($var, $\-[1], $+[1] \- $\-[1])\fR" 5 | |
720 | .IX Item "$1 is the same as substr($var, $-[1], $+[1] - $-[1])" | |
721 | .ie n .IP "$2\fR is the same as \f(CW""substr($var, $\-[2], $+[2] \- $\-[2])""" 5 | |
722 | .el .IP "\f(CW$2\fR is the same as \f(CWsubstr($var, $\-[2], $+[2] \- $\-[2])\fR" 5 | |
723 | .IX Item "$2 is the same as substr($var, $-[2], $+[2] - $-[2])" | |
724 | .ie n .IP "$3\fR is the same as \f(CW""substr($var, $\-[3], $+[3] \- $\-[3])""" 5 | |
725 | .el .IP "\f(CW$3\fR is the same as \f(CWsubstr($var, $\-[3], $+[3] \- $\-[3])\fR" 5 | |
726 | .IX Item "$3 is the same as substr($var, $-[3], $+[3] - $-[3])" | |
727 | .RE | |
728 | .RS 8 | |
729 | .RE | |
730 | .IP "\s-1HANDLE\-\s0>format_name(\s-1EXPR\s0)" 8 | |
731 | .IX Item "HANDLE->format_name(EXPR)" | |
732 | .IP "$FORMAT_NAME" 8 | |
733 | .IX Item "$FORMAT_NAME" | |
734 | .IP "$~" 8 | |
735 | .PD | |
736 | The name of the current report format for the currently selected output | |
737 | channel. Default is the name of the filehandle. (Mnemonic: brother to | |
738 | \&\f(CW$^\fR.) | |
739 | .IP "\s-1HANDLE\-\s0>format_top_name(\s-1EXPR\s0)" 8 | |
740 | .IX Item "HANDLE->format_top_name(EXPR)" | |
741 | .PD 0 | |
742 | .IP "$FORMAT_TOP_NAME" 8 | |
743 | .IX Item "$FORMAT_TOP_NAME" | |
744 | .IP "$^" 8 | |
745 | .PD | |
746 | The name of the current top-of-page format for the currently selected | |
747 | output channel. Default is the name of the filehandle with _TOP | |
748 | appended. (Mnemonic: points to top of page.) | |
749 | .IP "IO::Handle\->format_line_break_characters \s-1EXPR\s0" 8 | |
750 | .IX Item "IO::Handle->format_line_break_characters EXPR" | |
751 | .PD 0 | |
752 | .IP "$FORMAT_LINE_BREAK_CHARACTERS" 8 | |
753 | .IX Item "$FORMAT_LINE_BREAK_CHARACTERS" | |
754 | .IP "$:" 8 | |
755 | .PD | |
756 | The current set of characters after which a string may be broken to | |
757 | fill continuation fields (starting with ^) in a format. Default is | |
758 | \&\*(L"\ \en\-\*(R", to break on whitespace or hyphens. (Mnemonic: a \*(L"colon\*(R" in | |
759 | poetry is a part of a line.) | |
760 | .IP "IO::Handle\->format_formfeed \s-1EXPR\s0" 8 | |
761 | .IX Item "IO::Handle->format_formfeed EXPR" | |
762 | .PD 0 | |
763 | .IP "$FORMAT_FORMFEED" 8 | |
764 | .IX Item "$FORMAT_FORMFEED" | |
765 | .IP "$^L" 8 | |
766 | .IX Item "$^L" | |
767 | .PD | |
768 | What formats output as a form feed. Default is \ef. | |
769 | .IP "$ACCUMULATOR" 8 | |
770 | .IX Item "$ACCUMULATOR" | |
771 | .PD 0 | |
772 | .IP "$^A" 8 | |
773 | .IX Item "$^A" | |
774 | .PD | |
775 | The current value of the \fIwrite()\fR accumulator for \fIformat()\fR lines. A format | |
776 | contains \fIformline()\fR calls that put their result into \f(CW$^A\fR. After | |
777 | calling its format, \fIwrite()\fR prints out the contents of \f(CW$^A\fR and empties. | |
778 | So you never really see the contents of \f(CW$^A\fR unless you call | |
779 | \&\fIformline()\fR yourself and then look at it. See perlform and | |
780 | \&\*(L"\fIformline()\fR\*(R" in perlfunc. | |
781 | .IP "$CHILD_ERROR" 8 | |
782 | .IX Item "$CHILD_ERROR" | |
783 | .PD 0 | |
784 | .IP "$?" 8 | |
785 | .PD | |
786 | The status returned by the last pipe close, backtick (\f(CW``\fR) command, | |
787 | successful call to \fIwait()\fR or \fIwaitpid()\fR, or from the \fIsystem()\fR | |
788 | operator. This is just the 16\-bit status word returned by the | |
789 | \&\fIwait()\fR system call (or else is made up to look like it). Thus, the | |
790 | exit value of the subprocess is really (\f(CW\*(C`$? >> 8\*(C'\fR), and | |
791 | \&\f(CW\*(C`$? & 127\*(C'\fR gives which signal, if any, the process died from, and | |
792 | \&\f(CW\*(C`$? & 128\*(C'\fR reports whether there was a core dump. (Mnemonic: | |
793 | similar to \fBsh\fR and \fBksh\fR.) | |
794 | .Sp | |
795 | Additionally, if the \f(CW\*(C`h_errno\*(C'\fR variable is supported in C, its value | |
796 | is returned via $? if any \f(CW\*(C`gethost*()\*(C'\fR function fails. | |
797 | .Sp | |
798 | If you have installed a signal handler for \f(CW\*(C`SIGCHLD\*(C'\fR, the | |
799 | value of \f(CW$?\fR will usually be wrong outside that handler. | |
800 | .Sp | |
801 | Inside an \f(CW\*(C`END\*(C'\fR subroutine \f(CW$?\fR contains the value that is going to be | |
802 | given to \f(CW\*(C`exit()\*(C'\fR. You can modify \f(CW$?\fR in an \f(CW\*(C`END\*(C'\fR subroutine to | |
803 | change the exit status of your program. For example: | |
804 | .Sp | |
805 | .Vb 3 | |
806 | \& END { | |
807 | \& $? = 1 if $? == 255; # die would make it 255 | |
808 | \& } | |
809 | .Ve | |
810 | .Sp | |
811 | Under \s-1VMS\s0, the pragma \f(CW\*(C`use vmsish 'status'\*(C'\fR makes \f(CW$?\fR reflect the | |
812 | actual \s-1VMS\s0 exit status, instead of the default emulation of \s-1POSIX\s0 | |
813 | status; see \*(L"$?\*(R" in perlvms for details. | |
814 | .Sp | |
815 | Also see \*(L"Error Indicators\*(R". | |
816 | .IP "${^ENCODING}" 8 | |
817 | .IX Item "${^ENCODING}" | |
818 | The \fIobject reference\fR to the Encode object that is used to convert | |
819 | the source code to Unicode. Thanks to this variable your perl script | |
820 | does not have to be written in \s-1UTF\-8\s0. Default is \fIundef\fR. The direct | |
821 | manipulation of this variable is highly discouraged. See encoding | |
822 | for more details. | |
823 | .IP "$OS_ERROR" 8 | |
824 | .IX Item "$OS_ERROR" | |
825 | .PD 0 | |
826 | .IP "$ERRNO" 8 | |
827 | .IX Item "$ERRNO" | |
828 | .IP "$!" 8 | |
829 | .PD | |
830 | If used numerically, yields the current value of the C \f(CW\*(C`errno\*(C'\fR | |
831 | variable, or in other words, if a system or library call fails, it | |
832 | sets this variable. This means that the value of \f(CW$!\fR is meaningful | |
833 | only \fIimmediately\fR after a \fBfailure\fR: | |
834 | .Sp | |
835 | .Vb 10 | |
836 | \& if (open(FH, $filename)) { | |
837 | \& # Here $! is meaningless. | |
838 | \& ... | |
839 | \& } else { | |
840 | \& # ONLY here is $! meaningful. | |
841 | \& ... | |
842 | \& # Already here $! might be meaningless. | |
843 | \& } | |
844 | \& # Since here we might have either success or failure, | |
845 | \& # here $! is meaningless. | |
846 | .Ve | |
847 | .Sp | |
848 | In the above \fImeaningless\fR stands for anything: zero, non\-zero, | |
849 | \&\f(CW\*(C`undef\*(C'\fR. A successful system or library call does \fBnot\fR set | |
850 | the variable to zero. | |
851 | .Sp | |
852 | If used as a string, yields the corresponding system error string. | |
853 | You can assign a number to \f(CW$!\fR to set \fIerrno\fR if, for instance, | |
854 | you want \f(CW"$!"\fR to return the string for error \fIn\fR, or you want | |
855 | to set the exit value for the \fIdie()\fR operator. (Mnemonic: What just | |
856 | went bang?) | |
857 | .Sp | |
858 | Also see \*(L"Error Indicators\*(R". | |
859 | .IP "%!" 8 | |
860 | Each element of \f(CW\*(C`%!\*(C'\fR has a true value only if \f(CW$!\fR is set to that | |
861 | value. For example, \f(CW$!{ENOENT}\fR is true if and only if the current | |
862 | value of \f(CW$!\fR is \f(CW\*(C`ENOENT\*(C'\fR; that is, if the most recent error was | |
863 | \&\*(L"No such file or directory\*(R" (or its moral equivalent: not all operating | |
864 | systems give that exact error, and certainly not all languages). | |
865 | To check if a particular key is meaningful on your system, use | |
866 | \&\f(CW\*(C`exists $!{the_key}\*(C'\fR; for a list of legal keys, use \f(CW\*(C`keys %!\*(C'\fR. | |
867 | See Errno for more information, and also see above for the | |
868 | validity of \f(CW$!\fR. | |
869 | .IP "$EXTENDED_OS_ERROR" 8 | |
870 | .IX Item "$EXTENDED_OS_ERROR" | |
871 | .PD 0 | |
872 | .IP "$^E" 8 | |
873 | .IX Item "$^E" | |
874 | .PD | |
875 | Error information specific to the current operating system. At | |
876 | the moment, this differs from \f(CW$!\fR under only \s-1VMS\s0, \s-1OS/2\s0, and Win32 | |
877 | (and for MacPerl). On all other platforms, \f(CW$^E\fR is always just | |
878 | the same as \f(CW$!\fR. | |
879 | .Sp | |
880 | Under \s-1VMS\s0, \f(CW$^E\fR provides the \s-1VMS\s0 status value from the last | |
881 | system error. This is more specific information about the last | |
882 | system error than that provided by \f(CW$!\fR. This is particularly | |
883 | important when \f(CW$!\fR is set to \fB\s-1EVMSERR\s0\fR. | |
884 | .Sp | |
885 | Under \s-1OS/2\s0, \f(CW$^E\fR is set to the error code of the last call to | |
886 | \&\s-1OS/2\s0 \s-1API\s0 either via \s-1CRT\s0, or directly from perl. | |
887 | .Sp | |
888 | Under Win32, \f(CW$^E\fR always returns the last error information | |
889 | reported by the Win32 call \f(CW\*(C`GetLastError()\*(C'\fR which describes | |
890 | the last error from within the Win32 \s-1API\s0. Most Win32\-specific | |
891 | code will report errors via \f(CW$^E\fR. \s-1ANSI\s0 C and Unix-like calls | |
892 | set \f(CW\*(C`errno\*(C'\fR and so most portable Perl code will report errors | |
893 | via \f(CW$!\fR. | |
894 | .Sp | |
895 | Caveats mentioned in the description of \f(CW$!\fR generally apply to | |
896 | \&\f(CW$^E\fR, also. (Mnemonic: Extra error explanation.) | |
897 | .Sp | |
898 | Also see \*(L"Error Indicators\*(R". | |
899 | .IP "$EVAL_ERROR" 8 | |
900 | .IX Item "$EVAL_ERROR" | |
901 | .PD 0 | |
902 | .IP "$@" 8 | |
903 | .PD | |
904 | The Perl syntax error message from the last \fIeval()\fR operator. | |
905 | If $@ is the null string, the last \fIeval()\fR parsed and executed | |
906 | correctly (although the operations you invoked may have failed in the | |
907 | normal fashion). (Mnemonic: Where was the syntax error \*(L"at\*(R"?) | |
908 | .Sp | |
909 | Warning messages are not collected in this variable. You can, | |
910 | however, set up a routine to process warnings by setting \f(CW$SIG{_\|_WARN_\|_}\fR | |
911 | as described below. | |
912 | .Sp | |
913 | Also see \*(L"Error Indicators\*(R". | |
914 | .IP "$PROCESS_ID" 8 | |
915 | .IX Item "$PROCESS_ID" | |
916 | .PD 0 | |
917 | .IP "$PID" 8 | |
918 | .IX Item "$PID" | |
919 | .IP "$$" 8 | |
920 | .PD | |
921 | The process number of the Perl running this script. You should | |
922 | consider this variable read\-only, although it will be altered | |
923 | across \fIfork()\fR calls. (Mnemonic: same as shells.) | |
924 | .Sp | |
925 | Note for Linux users: on Linux, the C functions \f(CW\*(C`getpid()\*(C'\fR and | |
926 | \&\f(CW\*(C`getppid()\*(C'\fR return different values from different threads. In order to | |
927 | be portable, this behavior is not reflected by \f(CW$$\fR, whose value remains | |
928 | consistent across threads. If you want to call the underlying \f(CW\*(C`getpid()\*(C'\fR, | |
929 | you may use the \s-1CPAN\s0 module \f(CW\*(C`Linux::Pid\*(C'\fR. | |
930 | .IP "$REAL_USER_ID" 8 | |
931 | .IX Item "$REAL_USER_ID" | |
932 | .PD 0 | |
933 | .IP "$UID" 8 | |
934 | .IX Item "$UID" | |
935 | .IP "$<" 8 | |
936 | .PD | |
937 | The real uid of this process. (Mnemonic: it's the uid you came \fIfrom\fR, | |
938 | if you're running setuid.) You can change both the real uid and | |
939 | the effective uid at the same time by using \fIPOSIX::setuid()\fR. Since | |
940 | changes to $< require a system call, check $! after a change attempt to | |
941 | detect any possible errors. | |
942 | .IP "$EFFECTIVE_USER_ID" 8 | |
943 | .IX Item "$EFFECTIVE_USER_ID" | |
944 | .PD 0 | |
945 | .IP "$EUID" 8 | |
946 | .IX Item "$EUID" | |
947 | .IP "$>" 8 | |
948 | .PD | |
949 | The effective uid of this process. Example: | |
950 | .Sp | |
951 | .Vb 2 | |
952 | \& $< = $>; # set real to effective uid | |
953 | \& ($<,$>) = ($>,$<); # swap real and effective uid | |
954 | .Ve | |
955 | .Sp | |
956 | You can change both the effective uid and the real uid at the same | |
957 | time by using \fIPOSIX::setuid()\fR. Changes to $> require a check to $! | |
958 | to detect any possible errors after an attempted change. | |
959 | .Sp | |
960 | (Mnemonic: it's the uid you went \fIto\fR, if you're running setuid.) | |
961 | \&\f(CW$<\fR and \f(CW$>\fR can be swapped only on machines | |
962 | supporting \fIsetreuid()\fR. | |
963 | .IP "$REAL_GROUP_ID" 8 | |
964 | .IX Item "$REAL_GROUP_ID" | |
965 | .PD 0 | |
966 | .IP "$GID" 8 | |
967 | .IX Item "$GID" | |
968 | .IP "$(" 8 | |
969 | .PD | |
970 | The real gid of this process. If you are on a machine that supports | |
971 | membership in multiple groups simultaneously, gives a space separated | |
972 | list of groups you are in. The first number is the one returned by | |
973 | \&\fIgetgid()\fR, and the subsequent ones by \fIgetgroups()\fR, one of which may be | |
974 | the same as the first number. | |
975 | .Sp | |
976 | However, a value assigned to \f(CW$(\fR must be a single number used to | |
977 | set the real gid. So the value given by \f(CW$(\fR should \fInot\fR be assigned | |
978 | back to \f(CW$(\fR without being forced numeric, such as by adding zero. | |
979 | .Sp | |
980 | You can change both the real gid and the effective gid at the same | |
981 | time by using \fIPOSIX::setgid()\fR. Changes to $( require a check to $! | |
982 | to detect any possible errors after an attempted change. | |
983 | .Sp | |
984 | (Mnemonic: parentheses are used to \fIgroup\fR things. The real gid is the | |
985 | group you \fIleft\fR, if you're running setgid.) | |
986 | .IP "$EFFECTIVE_GROUP_ID" 8 | |
987 | .IX Item "$EFFECTIVE_GROUP_ID" | |
988 | .PD 0 | |
989 | .IP "$EGID" 8 | |
990 | .IX Item "$EGID" | |
991 | .IP "$)" 8 | |
992 | .PD | |
993 | The effective gid of this process. If you are on a machine that | |
994 | supports membership in multiple groups simultaneously, gives a space | |
995 | separated list of groups you are in. The first number is the one | |
996 | returned by \fIgetegid()\fR, and the subsequent ones by \fIgetgroups()\fR, one of | |
997 | which may be the same as the first number. | |
998 | .Sp | |
999 | Similarly, a value assigned to \f(CW$)\fR must also be a space-separated | |
1000 | list of numbers. The first number sets the effective gid, and | |
1001 | the rest (if any) are passed to \fIsetgroups()\fR. To get the effect of an | |
1002 | empty list for \fIsetgroups()\fR, just repeat the new effective gid; that is, | |
1003 | to force an effective gid of 5 and an effectively empty \fIsetgroups()\fR | |
1004 | list, say \f(CW\*(C` $) = "5 5" \*(C'\fR. | |
1005 | .Sp | |
1006 | You can change both the effective gid and the real gid at the same | |
1007 | time by using \fIPOSIX::setgid()\fR (use only a single numeric argument). | |
1008 | Changes to $) require a check to $! to detect any possible errors | |
1009 | after an attempted change. | |
1010 | .Sp | |
1011 | (Mnemonic: parentheses are used to \fIgroup\fR things. The effective gid | |
1012 | is the group that's \fIright\fR for you, if you're running setgid.) | |
1013 | .Sp | |
1014 | \&\f(CW$<\fR, \f(CW$>\fR, \f(CW$(\fR and \f(CW$)\fR can be set only on | |
1015 | machines that support the corresponding \fIset[re][ug]\fIid()\fI\fR routine. \f(CW$(\fR | |
1016 | and \f(CW$)\fR can be swapped only on machines supporting \fIsetregid()\fR. | |
1017 | .IP "$PROGRAM_NAME" 8 | |
1018 | .IX Item "$PROGRAM_NAME" | |
1019 | .PD 0 | |
1020 | .IP "$0" 8 | |
1021 | .IX Item "$0" | |
1022 | .PD | |
1023 | Contains the name of the program being executed. | |
1024 | .Sp | |
1025 | On some (read: not all) operating systems assigning to \f(CW$0\fR modifies | |
1026 | the argument area that the \f(CW\*(C`ps\*(C'\fR program sees. On some platforms you | |
1027 | may have to use special \f(CW\*(C`ps\*(C'\fR options or a different \f(CW\*(C`ps\*(C'\fR to see the | |
1028 | changes. Modifying the \f(CW$0\fR is more useful as a way of indicating the | |
1029 | current program state than it is for hiding the program you're | |
1030 | running. (Mnemonic: same as \fBsh\fR and \fBksh\fR.) | |
1031 | .Sp | |
1032 | Note that there are platform specific limitations on the maximum | |
1033 | length of \f(CW$0\fR. In the most extreme case it may be limited to the | |
1034 | space occupied by the original \f(CW$0\fR. | |
1035 | .Sp | |
1036 | In some platforms there may be arbitrary amount of padding, for | |
1037 | example space characters, after the modified name as shown by \f(CW\*(C`ps\*(C'\fR. | |
1038 | In some platforms this padding may extend all the way to the original | |
1039 | length of the argument area, no matter what you do (this is the case | |
1040 | for example with Linux 2.2). | |
1041 | .Sp | |
1042 | Note for \s-1BSD\s0 users: setting \f(CW$0\fR does not completely remove \*(L"perl\*(R" | |
1043 | from the \fIps\fR\|(1) output. For example, setting \f(CW$0\fR to \f(CW"foobar"\fR may | |
1044 | result in \f(CW"perl: foobar (perl)"\fR (whether both the \f(CW"perl: "\fR prefix | |
1045 | and the \*(L" (perl)\*(R" suffix are shown depends on your exact \s-1BSD\s0 variant | |
1046 | and version). This is an operating system feature, Perl cannot help it. | |
1047 | .Sp | |
1048 | In multithreaded scripts Perl coordinates the threads so that any | |
1049 | thread may modify its copy of the \f(CW$0\fR and the change becomes visible | |
1050 | to \fIps\fR\|(1) (assuming the operating system plays along). Note that | |
1051 | the view of \f(CW$0\fR the other threads have will not change since they | |
1052 | have their own copies of it. | |
1053 | .IP "$[" 8 | |
1054 | The index of the first element in an array, and of the first character | |
1055 | in a substring. Default is 0, but you could theoretically set it | |
1056 | to 1 to make Perl behave more like \fBawk\fR (or Fortran) when | |
1057 | subscripting and when evaluating the \fIindex()\fR and \fIsubstr()\fR functions. | |
1058 | (Mnemonic: [ begins subscripts.) | |
1059 | .Sp | |
1060 | As of release 5 of Perl, assignment to \f(CW$[\fR is treated as a compiler | |
1061 | directive, and cannot influence the behavior of any other file. | |
1062 | (That's why you can only assign compile-time constants to it.) | |
1063 | Its use is highly discouraged. | |
1064 | .Sp | |
1065 | Note that, unlike other compile-time directives (such as strict), | |
1066 | assignment to \f(CW$[\fR can be seen from outer lexical scopes in the same file. | |
1067 | However, you can use \fIlocal()\fR on it to strictly bind its value to a | |
1068 | lexical block. | |
1069 | .IP "$]" 8 | |
1070 | The version + patchlevel / 1000 of the Perl interpreter. This variable | |
1071 | can be used to determine whether the Perl interpreter executing a | |
1072 | script is in the right range of versions. (Mnemonic: Is this version | |
1073 | of perl in the right bracket?) Example: | |
1074 | .Sp | |
1075 | .Vb 1 | |
1076 | \& warn "No checksumming!\en" if $] < 3.019; | |
1077 | .Ve | |
1078 | .Sp | |
1079 | See also the documentation of \f(CW\*(C`use VERSION\*(C'\fR and \f(CW\*(C`require VERSION\*(C'\fR | |
1080 | for a convenient way to fail if the running Perl interpreter is too old. | |
1081 | .Sp | |
1082 | When testing the variable, to steer clear of floating point | |
1083 | inaccuracies you might want to prefer the inequality tests \f(CW\*(C`<\*(C'\fR | |
1084 | and \f(CW\*(C`>\*(C'\fR to the tests containing equivalence: \f(CW\*(C`<=\*(C'\fR, \f(CW\*(C`==\*(C'\fR, | |
1085 | and \f(CW\*(C`>=\*(C'\fR. | |
1086 | .Sp | |
1087 | The floating point representation can sometimes lead to inaccurate | |
1088 | numeric comparisons. See \f(CW$^V\fR for a more modern representation of | |
1089 | the Perl version that allows accurate string comparisons. | |
1090 | .IP "$COMPILING" 8 | |
1091 | .IX Item "$COMPILING" | |
1092 | .PD 0 | |
1093 | .IP "$^C" 8 | |
1094 | .IX Item "$^C" | |
1095 | .PD | |
1096 | The current value of the flag associated with the \fB\-c\fR switch. | |
1097 | Mainly of use with \fB\-MO=...\fR to allow code to alter its behavior | |
1098 | when being compiled, such as for example to \s-1AUTOLOAD\s0 at compile | |
1099 | time rather than normal, deferred loading. See perlcc. Setting | |
1100 | \&\f(CW\*(C`$^C = 1\*(C'\fR is similar to calling \f(CW\*(C`B::minus_c\*(C'\fR. | |
1101 | .IP "$DEBUGGING" 8 | |
1102 | .IX Item "$DEBUGGING" | |
1103 | .PD 0 | |
1104 | .IP "$^D" 8 | |
1105 | .IX Item "$^D" | |
1106 | .PD | |
1107 | The current value of the debugging flags. (Mnemonic: value of \fB\-D\fR | |
1108 | switch.) May be read or set. Like its command-line equivalent, you can use | |
1109 | numeric or symbolic values, eg \f(CW\*(C`$^D = 10\*(C'\fR or \f(CW\*(C`$^D = "st"\*(C'\fR. | |
1110 | .IP "$SYSTEM_FD_MAX" 8 | |
1111 | .IX Item "$SYSTEM_FD_MAX" | |
1112 | .PD 0 | |
1113 | .IP "$^F" 8 | |
1114 | .IX Item "$^F" | |
1115 | .PD | |
1116 | The maximum system file descriptor, ordinarily 2. System file | |
1117 | descriptors are passed to \fIexec()\fRed processes, while higher file | |
1118 | descriptors are not. Also, during an \fIopen()\fR, system file descriptors are | |
1119 | preserved even if the \fIopen()\fR fails. (Ordinary file descriptors are | |
1120 | closed before the \fIopen()\fR is attempted.) The close-on-exec | |
1121 | status of a file descriptor will be decided according to the value of | |
1122 | \&\f(CW$^F\fR when the corresponding file, pipe, or socket was opened, not the | |
1123 | time of the \fIexec()\fR. | |
1124 | .IP "$^H" 8 | |
1125 | .IX Item "$^H" | |
1126 | \&\s-1WARNING:\s0 This variable is strictly for internal use only. Its availability, | |
1127 | behavior, and contents are subject to change without notice. | |
1128 | .Sp | |
1129 | This variable contains compile-time hints for the Perl interpreter. At the | |
1130 | end of compilation of a \s-1BLOCK\s0 the value of this variable is restored to the | |
1131 | value when the interpreter started to compile the \s-1BLOCK\s0. | |
1132 | .Sp | |
1133 | When perl begins to parse any block construct that provides a lexical scope | |
1134 | (e.g., eval body, required file, subroutine body, loop body, or conditional | |
1135 | block), the existing value of $^H is saved, but its value is left unchanged. | |
1136 | When the compilation of the block is completed, it regains the saved value. | |
1137 | Between the points where its value is saved and restored, code that | |
1138 | executes within \s-1BEGIN\s0 blocks is free to change the value of $^H. | |
1139 | .Sp | |
1140 | This behavior provides the semantic of lexical scoping, and is used in, | |
1141 | for instance, the \f(CW\*(C`use strict\*(C'\fR pragma. | |
1142 | .Sp | |
1143 | The contents should be an integer; different bits of it are used for | |
1144 | different pragmatic flags. Here's an example: | |
1145 | .Sp | |
1146 | .Vb 1 | |
1147 | \& sub add_100 { $^H |= 0x100 } | |
1148 | .Ve | |
1149 | .Sp | |
1150 | .Vb 4 | |
1151 | \& sub foo { | |
1152 | \& BEGIN { add_100() } | |
1153 | \& bar->baz($boon); | |
1154 | \& } | |
1155 | .Ve | |
1156 | .Sp | |
1157 | Consider what happens during execution of the \s-1BEGIN\s0 block. At this point | |
1158 | the \s-1BEGIN\s0 block has already been compiled, but the body of \fIfoo()\fR is still | |
1159 | being compiled. The new value of $^H will therefore be visible only while | |
1160 | the body of \fIfoo()\fR is being compiled. | |
1161 | .Sp | |
1162 | Substitution of the above \s-1BEGIN\s0 block with: | |
1163 | .Sp | |
1164 | .Vb 1 | |
1165 | \& BEGIN { require strict; strict->import('vars') } | |
1166 | .Ve | |
1167 | .Sp | |
1168 | demonstrates how \f(CW\*(C`use strict 'vars'\*(C'\fR is implemented. Here's a conditional | |
1169 | version of the same lexical pragma: | |
1170 | .Sp | |
1171 | .Vb 1 | |
1172 | \& BEGIN { require strict; strict->import('vars') if $condition } | |
1173 | .Ve | |
1174 | .IP "%^H" 8 | |
1175 | .IX Item "%^H" | |
1176 | \&\s-1WARNING:\s0 This variable is strictly for internal use only. Its availability, | |
1177 | behavior, and contents are subject to change without notice. | |
1178 | .Sp | |
1179 | The %^H hash provides the same scoping semantic as $^H. This makes it | |
1180 | useful for implementation of lexically scoped pragmas. | |
1181 | .IP "$INPLACE_EDIT" 8 | |
1182 | .IX Item "$INPLACE_EDIT" | |
1183 | .PD 0 | |
1184 | .IP "$^I" 8 | |
1185 | .IX Item "$^I" | |
1186 | .PD | |
1187 | The current value of the inplace-edit extension. Use \f(CW\*(C`undef\*(C'\fR to disable | |
1188 | inplace editing. (Mnemonic: value of \fB\-i\fR switch.) | |
1189 | .IP "$^M" 8 | |
1190 | .IX Item "$^M" | |
1191 | By default, running out of memory is an untrappable, fatal error. | |
1192 | However, if suitably built, Perl can use the contents of \f(CW$^M\fR | |
1193 | as an emergency memory pool after \fIdie()\fRing. Suppose that your Perl | |
1194 | were compiled with \f(CW\*(C`\-DPERL_EMERGENCY_SBRK\*(C'\fR and used Perl's malloc. | |
1195 | Then | |
1196 | .Sp | |
1197 | .Vb 1 | |
1198 | \& $^M = 'a' x (1 << 16); | |
1199 | .Ve | |
1200 | .Sp | |
1201 | would allocate a 64K buffer for use in an emergency. See the | |
1202 | \&\fI\s-1INSTALL\s0\fR file in the Perl distribution for information on how to | |
1203 | add custom C compilation flags when compiling perl. To discourage casual | |
1204 | use of this advanced feature, there is no English long name for | |
1205 | this variable. | |
1206 | .IP "$OSNAME" 8 | |
1207 | .IX Item "$OSNAME" | |
1208 | .PD 0 | |
1209 | .IP "$^O" 8 | |
1210 | .IX Item "$^O" | |
1211 | .PD | |
1212 | The name of the operating system under which this copy of Perl was | |
1213 | built, as determined during the configuration process. The value | |
1214 | is identical to \f(CW$Config{'osname'}\fR. See also Config and the | |
1215 | \&\fB\-V\fR command-line switch documented in perlrun. | |
1216 | .Sp | |
1217 | In Windows platforms, $^O is not very helpful: since it is always | |
1218 | \&\f(CW\*(C`MSWin32\*(C'\fR, it doesn't tell the difference between | |
1219 | 95/98/ME/NT/2000/XP/CE/.NET. Use \fIWin32::GetOSName()\fR or | |
1220 | \&\fIWin32::GetOSVersion()\fR (see Win32 and perlport) to distinguish | |
1221 | between the variants. | |
1222 | .IP "${^OPEN}" 8 | |
1223 | .IX Item "${^OPEN}" | |
1224 | An internal variable used by PerlIO. A string in two parts, separated | |
1225 | by a \f(CW\*(C`\e0\*(C'\fR byte, the first part describes the input layers, the second | |
1226 | part describes the output layers. | |
1227 | .IP "$PERLDB" 8 | |
1228 | .IX Item "$PERLDB" | |
1229 | .PD 0 | |
1230 | .IP "$^P" 8 | |
1231 | .IX Item "$^P" | |
1232 | .PD | |
1233 | The internal variable for debugging support. The meanings of the | |
1234 | various bits are subject to change, but currently indicate: | |
1235 | .RS 8 | |
1236 | .IP "0x01" 6 | |
1237 | .IX Item "0x01" | |
1238 | Debug subroutine enter/exit. | |
1239 | .IP "0x02" 6 | |
1240 | .IX Item "0x02" | |
1241 | Line-by-line debugging. | |
1242 | .IP "0x04" 6 | |
1243 | .IX Item "0x04" | |
1244 | Switch off optimizations. | |
1245 | .IP "0x08" 6 | |
1246 | .IX Item "0x08" | |
1247 | Preserve more data for future interactive inspections. | |
1248 | .IP "0x10" 6 | |
1249 | .IX Item "0x10" | |
1250 | Keep info about source lines on which a subroutine is defined. | |
1251 | .IP "0x20" 6 | |
1252 | .IX Item "0x20" | |
1253 | Start with single-step on. | |
1254 | .IP "0x40" 6 | |
1255 | .IX Item "0x40" | |
1256 | Use subroutine address instead of name when reporting. | |
1257 | .IP "0x80" 6 | |
1258 | .IX Item "0x80" | |
1259 | Report \f(CW\*(C`goto &subroutine\*(C'\fR as well. | |
1260 | .IP "0x100" 6 | |
1261 | .IX Item "0x100" | |
1262 | Provide informative \*(L"file\*(R" names for evals based on the place they were compiled. | |
1263 | .IP "0x200" 6 | |
1264 | .IX Item "0x200" | |
1265 | Provide informative names to anonymous subroutines based on the place they | |
1266 | were compiled. | |
1267 | .IP "0x400" 6 | |
1268 | .IX Item "0x400" | |
1269 | Debug assertion subroutines enter/exit. | |
1270 | .RE | |
1271 | .RS 8 | |
1272 | .Sp | |
1273 | Some bits may be relevant at compile-time only, some at | |
1274 | run-time only. This is a new mechanism and the details may change. | |
1275 | .RE | |
1276 | .IP "$LAST_REGEXP_CODE_RESULT" 8 | |
1277 | .IX Item "$LAST_REGEXP_CODE_RESULT" | |
1278 | .PD 0 | |
1279 | .IP "$^R" 8 | |
1280 | .IX Item "$^R" | |
1281 | .PD | |
1282 | The result of evaluation of the last successful \f(CW\*(C`(?{ code })\*(C'\fR | |
1283 | regular expression assertion (see perlre). May be written to. | |
1284 | .IP "$EXCEPTIONS_BEING_CAUGHT" 8 | |
1285 | .IX Item "$EXCEPTIONS_BEING_CAUGHT" | |
1286 | .PD 0 | |
1287 | .IP "$^S" 8 | |
1288 | .IX Item "$^S" | |
1289 | .PD | |
1290 | Current state of the interpreter. | |
1291 | .Sp | |
1292 | .Vb 5 | |
1293 | \& $^S State | |
1294 | \& --------- ------------------- | |
1295 | \& undef Parsing module/eval | |
1296 | \& true (1) Executing an eval | |
1297 | \& false (0) Otherwise | |
1298 | .Ve | |
1299 | .Sp | |
1300 | The first state may happen in \f(CW$SIG\fR{_\|_DIE_\|_} and \f(CW$SIG\fR{_\|_WARN_\|_} handlers. | |
1301 | .IP "$BASETIME" 8 | |
1302 | .IX Item "$BASETIME" | |
1303 | .PD 0 | |
1304 | .IP "$^T" 8 | |
1305 | .IX Item "$^T" | |
1306 | .PD | |
1307 | The time at which the program began running, in seconds since the | |
1308 | epoch (beginning of 1970). The values returned by the \fB\-M\fR, \fB\-A\fR, | |
1309 | and \fB\-C\fR filetests are based on this value. | |
1310 | .IP "${^TAINT}" 8 | |
1311 | .IX Item "${^TAINT}" | |
1312 | Reflects if taint mode is on or off. 1 for on (the program was run with | |
1313 | \&\fB\-T\fR), 0 for off, \-1 when only taint warnings are enabled (i.e. with | |
1314 | \&\fB\-t\fR or \fB\-TU\fR). | |
1315 | .IP "${^UNICODE}" 8 | |
1316 | .IX Item "${^UNICODE}" | |
1317 | Reflects certain Unicode settings of Perl. See perlrun | |
1318 | documentation for the \f(CW\*(C`\-C\*(C'\fR switch for more information about | |
1319 | the possible values. This variable is set during Perl startup | |
1320 | and is thereafter read\-only. | |
1321 | .IP "${^UTF8LOCALE}" 8 | |
1322 | .IX Item "${^UTF8LOCALE}" | |
1323 | This variable indicates whether an \s-1UTF\-8\s0 locale was detected by perl at | |
1324 | startup. This information is used by perl when it's in | |
1325 | adjust\-utf8ness\-to\-locale mode (as when run with the \f(CW\*(C`\-CL\*(C'\fR command-line | |
1326 | switch); see perlrun for more info on this. | |
1327 | .IP "$PERL_VERSION" 8 | |
1328 | .IX Item "$PERL_VERSION" | |
1329 | .PD 0 | |
1330 | .IP "$^V" 8 | |
1331 | .IX Item "$^V" | |
1332 | .PD | |
1333 | The revision, version, and subversion of the Perl interpreter, represented | |
1334 | as a string composed of characters with those ordinals. Thus in Perl v5.6.0 | |
1335 | it equals \f(CW\*(C`chr(5) . chr(6) . chr(0)\*(C'\fR and will return true for | |
1336 | \&\f(CW\*(C`$^V eq v5.6.0\*(C'\fR. Note that the characters in this string value can | |
1337 | potentially be in Unicode range. | |
1338 | .Sp | |
1339 | This can be used to determine whether the Perl interpreter executing a | |
1340 | script is in the right range of versions. (Mnemonic: use ^V for Version | |
1341 | Control.) Example: | |
1342 | .Sp | |
1343 | .Vb 1 | |
1344 | \& warn "No \e"our\e" declarations!\en" if $^V and $^V lt v5.6.0; | |
1345 | .Ve | |
1346 | .Sp | |
1347 | To convert \f(CW$^V\fR into its string representation use \fIsprintf()\fR's | |
1348 | \&\f(CW"%vd"\fR conversion: | |
1349 | .Sp | |
1350 | .Vb 1 | |
1351 | \& printf "version is v%vd\en", $^V; # Perl's version | |
1352 | .Ve | |
1353 | .Sp | |
1354 | See the documentation of \f(CW\*(C`use VERSION\*(C'\fR and \f(CW\*(C`require VERSION\*(C'\fR | |
1355 | for a convenient way to fail if the running Perl interpreter is too old. | |
1356 | .Sp | |
1357 | See also \f(CW$]\fR for an older representation of the Perl version. | |
1358 | .IP "$WARNING" 8 | |
1359 | .IX Item "$WARNING" | |
1360 | .PD 0 | |
1361 | .IP "$^W" 8 | |
1362 | .IX Item "$^W" | |
1363 | .PD | |
1364 | The current value of the warning switch, initially true if \fB\-w\fR | |
1365 | was used, false otherwise, but directly modifiable. (Mnemonic: | |
1366 | related to the \fB\-w\fR switch.) See also warnings. | |
1367 | .IP "${^WARNING_BITS}" 8 | |
1368 | .IX Item "${^WARNING_BITS}" | |
1369 | The current set of warning checks enabled by the \f(CW\*(C`use warnings\*(C'\fR pragma. | |
1370 | See the documentation of \f(CW\*(C`warnings\*(C'\fR for more details. | |
1371 | .IP "$EXECUTABLE_NAME" 8 | |
1372 | .IX Item "$EXECUTABLE_NAME" | |
1373 | .PD 0 | |
1374 | .IP "$^X" 8 | |
1375 | .IX Item "$^X" | |
1376 | .PD | |
1377 | The name used to execute the current copy of Perl, from C's | |
1378 | \&\f(CW\*(C`argv[0]\*(C'\fR or (where supported) \fI/proc/self/exe\fR. | |
1379 | .Sp | |
1380 | Depending on the host operating system, the value of $^X may be | |
1381 | a relative or absolute pathname of the perl program file, or may | |
1382 | be the string used to invoke perl but not the pathname of the | |
1383 | perl program file. Also, most operating systems permit invoking | |
1384 | programs that are not in the \s-1PATH\s0 environment variable, so there | |
1385 | is no guarantee that the value of $^X is in \s-1PATH\s0. For \s-1VMS\s0, the | |
1386 | value may or may not include a version number. | |
1387 | .Sp | |
1388 | You usually can use the value of $^X to re-invoke an independent | |
1389 | copy of the same perl that is currently running, e.g., | |
1390 | .Sp | |
1391 | .Vb 1 | |
1392 | \& @first_run = `$^X -le "print int rand 100 for 1..100"`; | |
1393 | .Ve | |
1394 | .Sp | |
1395 | But recall that not all operating systems support forking or | |
1396 | capturing of the output of commands, so this complex statement | |
1397 | may not be portable. | |
1398 | .Sp | |
1399 | It is not safe to use the value of $^X as a path name of a file, | |
1400 | as some operating systems that have a mandatory suffix on | |
1401 | executable files do not require use of the suffix when invoking | |
1402 | a command. To convert the value of $^X to a path name, use the | |
1403 | following statements: | |
1404 | .Sp | |
1405 | .Vb 6 | |
1406 | \& # Build up a set of file names (not command names). | |
1407 | \& use Config; | |
1408 | \& $this_perl = $^X; | |
1409 | \& if ($^O ne 'VMS') | |
1410 | \& {$this_perl .= $Config{_exe} | |
1411 | \& unless $this_perl =~ m/$Config{_exe}$/i;} | |
1412 | .Ve | |
1413 | .Sp | |
1414 | Because many operating systems permit anyone with read access to | |
1415 | the Perl program file to make a copy of it, patch the copy, and | |
1416 | then execute the copy, the security-conscious Perl programmer | |
1417 | should take care to invoke the installed copy of perl, not the | |
1418 | copy referenced by $^X. The following statements accomplish | |
1419 | this goal, and produce a pathname that can be invoked as a | |
1420 | command or referenced as a file. | |
1421 | .Sp | |
1422 | .Vb 5 | |
1423 | \& use Config; | |
1424 | \& $secure_perl_path = $Config{perlpath}; | |
1425 | \& if ($^O ne 'VMS') | |
1426 | \& {$secure_perl_path .= $Config{_exe} | |
1427 | \& unless $secure_perl_path =~ m/$Config{_exe}$/i;} | |
1428 | .Ve | |
1429 | .IP "\s-1ARGV\s0" 8 | |
1430 | .IX Item "ARGV" | |
1431 | The special filehandle that iterates over command-line filenames in | |
1432 | \&\f(CW@ARGV\fR. Usually written as the null filehandle in the angle operator | |
1433 | \&\f(CW\*(C`<>\*(C'\fR. Note that currently \f(CW\*(C`ARGV\*(C'\fR only has its magical effect | |
1434 | within the \f(CW\*(C`<>\*(C'\fR operator; elsewhere it is just a plain filehandle | |
1435 | corresponding to the last file opened by \f(CW\*(C`<>\*(C'\fR. In particular, | |
1436 | passing \f(CW\*(C`\e*ARGV\*(C'\fR as a parameter to a function that expects a filehandle | |
1437 | may not cause your function to automatically read the contents of all the | |
1438 | files in \f(CW@ARGV\fR. | |
1439 | .IP "$ARGV" 8 | |
1440 | .IX Item "$ARGV" | |
1441 | contains the name of the current file when reading from <>. | |
1442 | .IP "@ARGV" 8 | |
1443 | .IX Item "@ARGV" | |
1444 | The array \f(CW@ARGV\fR contains the command-line arguments intended for | |
1445 | the script. \f(CW$#ARGV\fR is generally the number of arguments minus | |
1446 | one, because \f(CW$ARGV[0]\fR is the first argument, \fInot\fR the program's | |
1447 | command name itself. See \f(CW$0\fR for the command name. | |
1448 | .IP "\s-1ARGVOUT\s0" 8 | |
1449 | .IX Item "ARGVOUT" | |
1450 | The special filehandle that points to the currently open output file | |
1451 | when doing edit-in-place processing with \fB\-i\fR. Useful when you have | |
1452 | to do a lot of inserting and don't want to keep modifying \f(CW$_\fR. See | |
1453 | perlrun for the \fB\-i\fR switch. | |
1454 | .IP "@F" 8 | |
1455 | .IX Item "@F" | |
1456 | The array \f(CW@F\fR contains the fields of each line read in when autosplit | |
1457 | mode is turned on. See perlrun for the \fB\-a\fR switch. This array | |
1458 | is package\-specific, and must be declared or given a full package name | |
1459 | if not in package main when running under \f(CW\*(C`strict 'vars'\*(C'\fR. | |
1460 | .IP "@INC" 8 | |
1461 | .IX Item "@INC" | |
1462 | The array \f(CW@INC\fR contains the list of places that the \f(CW\*(C`do EXPR\*(C'\fR, | |
1463 | \&\f(CW\*(C`require\*(C'\fR, or \f(CW\*(C`use\*(C'\fR constructs look for their library files. It | |
1464 | initially consists of the arguments to any \fB\-I\fR command-line | |
1465 | switches, followed by the default Perl library, probably | |
1466 | \&\fI/usr/local/lib/perl\fR, followed by \*(L".\*(R", to represent the current | |
1467 | directory. (\*(L".\*(R" will not be appended if taint checks are enabled, either by | |
1468 | \&\f(CW\*(C`\-T\*(C'\fR or by \f(CW\*(C`\-t\*(C'\fR.) If you need to modify this at runtime, you should use | |
1469 | the \f(CW\*(C`use lib\*(C'\fR pragma to get the machine-dependent library properly | |
1470 | loaded also: | |
1471 | .Sp | |
1472 | .Vb 2 | |
1473 | \& use lib '/mypath/libdir/'; | |
1474 | \& use SomeMod; | |
1475 | .Ve | |
1476 | .Sp | |
1477 | You can also insert hooks into the file inclusion system by putting Perl | |
1478 | code directly into \f(CW@INC\fR. Those hooks may be subroutine references, array | |
1479 | references or blessed objects. See \*(L"require\*(R" in perlfunc for details. | |
1480 | .IP "@_" 8 | |
1481 | .IX Item "@_" | |
1482 | Within a subroutine the array \f(CW@_\fR contains the parameters passed to that | |
1483 | subroutine. See perlsub. | |
1484 | .IP "%INC" 8 | |
1485 | .IX Item "%INC" | |
1486 | The hash \f(CW%INC\fR contains entries for each filename included via the | |
1487 | \&\f(CW\*(C`do\*(C'\fR, \f(CW\*(C`require\*(C'\fR, or \f(CW\*(C`use\*(C'\fR operators. The key is the filename | |
1488 | you specified (with module names converted to pathnames), and the | |
1489 | value is the location of the file found. The \f(CW\*(C`require\*(C'\fR | |
1490 | operator uses this hash to determine whether a particular file has | |
1491 | already been included. | |
1492 | .Sp | |
1493 | If the file was loaded via a hook (e.g. a subroutine reference, see | |
1494 | \&\*(L"require\*(R" in perlfunc for a description of these hooks), this hook is | |
1495 | by default inserted into \f(CW%INC\fR in place of a filename. Note, however, | |
1496 | that the hook may have set the \f(CW%INC\fR entry by itself to provide some more | |
1497 | specific info. | |
1498 | .IP "%ENV" 8 | |
1499 | .IX Item "%ENV" | |
1500 | .PD 0 | |
1501 | .IP "$ENV{expr}" 8 | |
1502 | .IX Item "$ENV{expr}" | |
1503 | .PD | |
1504 | The hash \f(CW%ENV\fR contains your current environment. Setting a | |
1505 | value in \f(CW\*(C`ENV\*(C'\fR changes the environment for any child processes | |
1506 | you subsequently \fIfork()\fR off. | |
1507 | .IP "%SIG" 8 | |
1508 | .IX Item "%SIG" | |
1509 | .PD 0 | |
1510 | .IP "$SIG{expr}" 8 | |
1511 | .IX Item "$SIG{expr}" | |
1512 | .PD | |
1513 | The hash \f(CW%SIG\fR contains signal handlers for signals. For example: | |
1514 | .Sp | |
1515 | .Vb 6 | |
1516 | \& sub handler { # 1st argument is signal name | |
1517 | \& my($sig) = @_; | |
1518 | \& print "Caught a SIG$sig--shutting down\en"; | |
1519 | \& close(LOG); | |
1520 | \& exit(0); | |
1521 | \& } | |
1522 | .Ve | |
1523 | .Sp | |
1524 | .Vb 5 | |
1525 | \& $SIG{'INT'} = \e&handler; | |
1526 | \& $SIG{'QUIT'} = \e&handler; | |
1527 | \& ... | |
1528 | \& $SIG{'INT'} = 'DEFAULT'; # restore default action | |
1529 | \& $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT | |
1530 | .Ve | |
1531 | .Sp | |
1532 | Using a value of \f(CW'IGNORE'\fR usually has the effect of ignoring the | |
1533 | signal, except for the \f(CW\*(C`CHLD\*(C'\fR signal. See perlipc for more about | |
1534 | this special case. | |
1535 | .Sp | |
1536 | Here are some other examples: | |
1537 | .Sp | |
1538 | .Vb 4 | |
1539 | \& $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not recommended) | |
1540 | \& $SIG{"PIPE"} = \e&Plumber; # just fine; assume current Plumber | |
1541 | \& $SIG{"PIPE"} = *Plumber; # somewhat esoteric | |
1542 | \& $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return?? | |
1543 | .Ve | |
1544 | .Sp | |
1545 | Be sure not to use a bareword as the name of a signal handler, | |
1546 | lest you inadvertently call it. | |
1547 | .Sp | |
1548 | If your system has the \fIsigaction()\fR function then signal handlers are | |
1549 | installed using it. This means you get reliable signal handling. | |
1550 | .Sp | |
1551 | The default delivery policy of signals changed in Perl 5.8.0 from | |
1552 | immediate (also known as \*(L"unsafe\*(R") to deferred, also known as | |
1553 | \&\*(L"safe signals\*(R". See perlipc for more information. | |
1554 | .Sp | |
1555 | Certain internal hooks can be also set using the \f(CW%SIG\fR hash. The | |
1556 | routine indicated by \f(CW$SIG{_\|_WARN_\|_}\fR is called when a warning message is | |
1557 | about to be printed. The warning message is passed as the first | |
1558 | argument. The presence of a _\|_WARN_\|_ hook causes the ordinary printing | |
1559 | of warnings to \s-1STDERR\s0 to be suppressed. You can use this to save warnings | |
1560 | in a variable, or turn warnings into fatal errors, like this: | |
1561 | .Sp | |
1562 | .Vb 2 | |
1563 | \& local $SIG{__WARN__} = sub { die $_[0] }; | |
1564 | \& eval $proggie; | |
1565 | .Ve | |
1566 | .Sp | |
1567 | The routine indicated by \f(CW$SIG{_\|_DIE_\|_}\fR is called when a fatal exception | |
1568 | is about to be thrown. The error message is passed as the first | |
1569 | argument. When a _\|_DIE_\|_ hook routine returns, the exception | |
1570 | processing continues as it would have in the absence of the hook, | |
1571 | unless the hook routine itself exits via a \f(CW\*(C`goto\*(C'\fR, a loop exit, or a \fIdie()\fR. | |
1572 | The \f(CW\*(C`_\|_DIE_\|_\*(C'\fR handler is explicitly disabled during the call, so that you | |
1573 | can die from a \f(CW\*(C`_\|_DIE_\|_\*(C'\fR handler. Similarly for \f(CW\*(C`_\|_WARN_\|_\*(C'\fR. | |
1574 | .Sp | |
1575 | Due to an implementation glitch, the \f(CW$SIG{_\|_DIE_\|_}\fR hook is called | |
1576 | even inside an \fIeval()\fR. Do not use this to rewrite a pending exception | |
1577 | in \f(CW$@\fR, or as a bizarre substitute for overriding \fICORE::GLOBAL::die()\fR. | |
1578 | This strange action at a distance may be fixed in a future release | |
1579 | so that \f(CW$SIG{_\|_DIE_\|_}\fR is only called if your program is about | |
1580 | to exit, as was the original intent. Any other use is deprecated. | |
1581 | .Sp | |
1582 | \&\f(CW\*(C`_\|_DIE_\|_\*(C'\fR/\f(CW\*(C`_\|_WARN_\|_\*(C'\fR handlers are very special in one respect: | |
1583 | they may be called to report (probable) errors found by the parser. | |
1584 | In such a case the parser may be in inconsistent state, so any | |
1585 | attempt to evaluate Perl code from such a handler will probably | |
1586 | result in a segfault. This means that warnings or errors that | |
1587 | result from parsing Perl should be used with extreme caution, like | |
1588 | this: | |
1589 | .Sp | |
1590 | .Vb 4 | |
1591 | \& require Carp if defined $^S; | |
1592 | \& Carp::confess("Something wrong") if defined &Carp::confess; | |
1593 | \& die "Something wrong, but could not load Carp to give backtrace... | |
1594 | \& To see backtrace try starting Perl with -MCarp switch"; | |
1595 | .Ve | |
1596 | .Sp | |
1597 | Here the first line will load Carp \fIunless\fR it is the parser who | |
1598 | called the handler. The second line will print backtrace and die if | |
1599 | Carp was available. The third line will be executed only if Carp was | |
1600 | not available. | |
1601 | .Sp | |
1602 | See \*(L"die\*(R" in perlfunc, \*(L"warn\*(R" in perlfunc, \*(L"eval\*(R" in perlfunc, and | |
1603 | warnings for additional information. | |
1604 | .Sh "Error Indicators" | |
1605 | .IX Subsection "Error Indicators" | |
1606 | The variables \f(CW$@\fR, \f(CW$!\fR, \f(CW$^E\fR, and \f(CW$?\fR contain information | |
1607 | about different types of error conditions that may appear during | |
1608 | execution of a Perl program. The variables are shown ordered by | |
1609 | the \*(L"distance\*(R" between the subsystem which reported the error and | |
1610 | the Perl process. They correspond to errors detected by the Perl | |
1611 | interpreter, C library, operating system, or an external program, | |
1612 | respectively. | |
1613 | .PP | |
1614 | To illustrate the differences between these variables, consider the | |
1615 | following Perl expression, which uses a single-quoted string: | |
1616 | .PP | |
1617 | .Vb 5 | |
1618 | \& eval q{ | |
1619 | \& open my $pipe, "/cdrom/install |" or die $!; | |
1620 | \& my @res = <$pipe>; | |
1621 | \& close $pipe or die "bad pipe: $?, $!"; | |
1622 | \& }; | |
1623 | .Ve | |
1624 | .PP | |
1625 | After execution of this statement all 4 variables may have been set. | |
1626 | .PP | |
1627 | \&\f(CW$@\fR is set if the string to be \f(CW\*(C`eval\*(C'\fR\-ed did not compile (this | |
1628 | may happen if \f(CW\*(C`open\*(C'\fR or \f(CW\*(C`close\*(C'\fR were imported with bad prototypes), | |
1629 | or if Perl code executed during evaluation \fIdie()\fRd . In these cases | |
1630 | the value of $@ is the compile error, or the argument to \f(CW\*(C`die\*(C'\fR | |
1631 | (which will interpolate \f(CW$!\fR and \f(CW$?\fR). (See also Fatal, | |
1632 | though.) | |
1633 | .PP | |
1634 | When the \fIeval()\fR expression above is executed, \fIopen()\fR, \f(CW\*(C`<PIPE>\*(C'\fR, | |
1635 | and \f(CW\*(C`close\*(C'\fR are translated to calls in the C run-time library and | |
1636 | thence to the operating system kernel. \f(CW$!\fR is set to the C library's | |
1637 | \&\f(CW\*(C`errno\*(C'\fR if one of these calls fails. | |
1638 | .PP | |
1639 | Under a few operating systems, \f(CW$^E\fR may contain a more verbose | |
1640 | error indicator, such as in this case, \*(L"\s-1CDROM\s0 tray not closed.\*(R" | |
1641 | Systems that do not support extended error messages leave \f(CW$^E\fR | |
1642 | the same as \f(CW$!\fR. | |
1643 | .PP | |
1644 | Finally, \f(CW$?\fR may be set to non\-0 value if the external program | |
1645 | \&\fI/cdrom/install\fR fails. The upper eight bits reflect specific | |
1646 | error conditions encountered by the program (the program's \fIexit()\fR | |
1647 | value). The lower eight bits reflect mode of failure, like signal | |
1648 | death and core dump information See \fIwait\fR\|(2) for details. In | |
1649 | contrast to \f(CW$!\fR and \f(CW$^E\fR, which are set only if error condition | |
1650 | is detected, the variable \f(CW$?\fR is set on each \f(CW\*(C`wait\*(C'\fR or pipe | |
1651 | \&\f(CW\*(C`close\*(C'\fR, overwriting the old value. This is more like \f(CW$@\fR, which | |
1652 | on every \fIeval()\fR is always set on failure and cleared on success. | |
1653 | .PP | |
1654 | For more details, see the individual descriptions at \f(CW$@\fR, \f(CW$!\fR, \f(CW$^E\fR, | |
1655 | and \f(CW$?\fR. | |
1656 | .Sh "Technical Note on the Syntax of Variable Names" | |
1657 | .IX Subsection "Technical Note on the Syntax of Variable Names" | |
1658 | Variable names in Perl can have several formats. Usually, they | |
1659 | must begin with a letter or underscore, in which case they can be | |
1660 | arbitrarily long (up to an internal limit of 251 characters) and | |
1661 | may contain letters, digits, underscores, or the special sequence | |
1662 | \&\f(CW\*(C`::\*(C'\fR or \f(CW\*(C`'\*(C'\fR. In this case, the part before the last \f(CW\*(C`::\*(C'\fR or | |
1663 | \&\f(CW\*(C`'\*(C'\fR is taken to be a \fIpackage qualifier\fR; see perlmod. | |
1664 | .PP | |
1665 | Perl variable names may also be a sequence of digits or a single | |
1666 | punctuation or control character. These names are all reserved for | |
1667 | special uses by Perl; for example, the all-digits names are used | |
1668 | to hold data captured by backreferences after a regular expression | |
1669 | match. Perl has a special syntax for the single-control-character | |
1670 | names: It understands \f(CW\*(C`^X\*(C'\fR (caret \f(CW\*(C`X\*(C'\fR) to mean the control\-\f(CW\*(C`X\*(C'\fR | |
1671 | character. For example, the notation \f(CW$^W\fR (dollar\-sign caret | |
1672 | \&\f(CW\*(C`W\*(C'\fR) is the scalar variable whose name is the single character | |
1673 | control\-\f(CW\*(C`W\*(C'\fR. This is better than typing a literal control\-\f(CW\*(C`W\*(C'\fR | |
1674 | into your program. | |
1675 | .PP | |
1676 | Finally, new in Perl 5.6, Perl variable names may be alphanumeric | |
1677 | strings that begin with control characters (or better yet, a caret). | |
1678 | These variables must be written in the form \f(CW\*(C`${^Foo}\*(C'\fR; the braces | |
1679 | are not optional. \f(CW\*(C`${^Foo}\*(C'\fR denotes the scalar variable whose | |
1680 | name is a control\-\f(CW\*(C`F\*(C'\fR followed by two \f(CW\*(C`o\*(C'\fR's. These variables are | |
1681 | reserved for future special uses by Perl, except for the ones that | |
1682 | begin with \f(CW\*(C`^_\*(C'\fR (control\-underscore or caret\-underscore). No | |
1683 | control-character name that begins with \f(CW\*(C`^_\*(C'\fR will acquire a special | |
1684 | meaning in any future version of Perl; such names may therefore be | |
1685 | used safely in programs. \f(CW$^_\fR itself, however, \fIis\fR reserved. | |
1686 | .PP | |
1687 | Perl identifiers that begin with digits, control characters, or | |
1688 | punctuation characters are exempt from the effects of the \f(CW\*(C`package\*(C'\fR | |
1689 | declaration and are always forced to be in package \f(CW\*(C`main\*(C'\fR; they are | |
1690 | also exempt from \f(CW\*(C`strict 'vars'\*(C'\fR errors. A few other names are also | |
1691 | exempt in these ways: | |
1692 | .PP | |
1693 | .Vb 5 | |
1694 | \& ENV STDIN | |
1695 | \& INC STDOUT | |
1696 | \& ARGV STDERR | |
1697 | \& ARGVOUT _ | |
1698 | \& SIG | |
1699 | .Ve | |
1700 | .PP | |
1701 | In particular, the new special \f(CW\*(C`${^_XYZ}\*(C'\fR variables are always taken | |
1702 | to be in package \f(CW\*(C`main\*(C'\fR, regardless of any \f(CW\*(C`package\*(C'\fR declarations | |
1703 | presently in scope. | |
1704 | .SH "BUGS" | |
1705 | .IX Header "BUGS" | |
1706 | Due to an unfortunate accident of Perl's implementation, \f(CW\*(C`use | |
1707 | English\*(C'\fR imposes a considerable performance penalty on all regular | |
1708 | expression matches in a program, regardless of whether they occur | |
1709 | in the scope of \f(CW\*(C`use English\*(C'\fR. For that reason, saying \f(CW\*(C`use | |
1710 | English\*(C'\fR in libraries is strongly discouraged. See the | |
1711 | Devel::SawAmpersand module documentation from \s-1CPAN\s0 | |
1712 | ( http://www.cpan.org/modules/by\-module/Devel/ ) | |
1713 | for more information. | |
1714 | .PP | |
1715 | Having to even think about the \f(CW$^S\fR variable in your exception | |
1716 | handlers is simply wrong. \f(CW$SIG{_\|_DIE_\|_}\fR as currently implemented | |
1717 | invites grievous and difficult to track down errors. Avoid it | |
1718 | and use an \f(CW\*(C`END{}\*(C'\fR or CORE::GLOBAL::die override instead. |