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1 | =head1 NAME |
2 | ||
3 | perlfaq - frequently asked questions about Perl ($Date: 2002/03/11 21:32:23 $) | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | The perlfaq is structured into the following documents: | |
8 | ||
9 | ||
10 | =head2 perlfaq: Structural overview of the FAQ. | |
11 | ||
12 | This document. | |
13 | ||
14 | =head2 L<perlfaq1>: General Questions About Perl | |
15 | ||
16 | Very general, high-level questions about Perl. | |
17 | ||
18 | =over 4 | |
19 | ||
20 | =item * | |
21 | ||
22 | What is Perl? | |
23 | ||
24 | =item * | |
25 | ||
26 | Who supports Perl? Who develops it? Why is it free? | |
27 | ||
28 | =item * | |
29 | ||
30 | Which version of Perl should I use? | |
31 | ||
32 | =item * | |
33 | ||
34 | What are perl4 and perl5? | |
35 | ||
36 | =item * | |
37 | ||
38 | What is perl6? | |
39 | ||
40 | =item * | |
41 | ||
42 | How stable is Perl? | |
43 | ||
44 | =item * | |
45 | ||
46 | Is Perl difficult to learn? | |
47 | ||
48 | =item * | |
49 | ||
50 | How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? | |
51 | ||
52 | =item * | |
53 | ||
54 | Can I do [task] in Perl? | |
55 | ||
56 | =item * | |
57 | ||
58 | When shouldn't I program in Perl? | |
59 | ||
60 | =item * | |
61 | ||
62 | What's the difference between "perl" and "Perl"? | |
63 | ||
64 | =item * | |
65 | ||
66 | Is it a Perl program or a Perl script? | |
67 | ||
68 | =item * | |
69 | ||
70 | What is a JAPH? | |
71 | ||
72 | =item * | |
73 | ||
74 | Where can I get a list of Larry Wall witticisms? | |
75 | ||
76 | =item * | |
77 | ||
78 | How can I convince my sysadmin/supervisor/employees to use version 5/5.6.1/Perl instead of some other language? | |
79 | ||
80 | =back | |
81 | ||
82 | ||
83 | =head2 L<perlfaq2>: Obtaining and Learning about Perl | |
84 | ||
85 | Where to find source and documentation for Perl, support, | |
86 | and related matters. | |
87 | ||
88 | =over 4 | |
89 | ||
90 | =item * | |
91 | ||
92 | What machines support Perl? Where do I get it? | |
93 | ||
94 | =item * | |
95 | ||
96 | How can I get a binary version of Perl? | |
97 | ||
98 | =item * | |
99 | ||
100 | I don't have a C compiler on my system. How can I compile perl? | |
101 | ||
102 | =item * | |
103 | ||
104 | I copied the Perl binary from one machine to another, but scripts don't work. | |
105 | ||
106 | =item * | |
107 | ||
108 | I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work? | |
109 | ||
110 | =item * | |
111 | ||
112 | What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean? | |
113 | ||
114 | =item * | |
115 | ||
116 | Is there an ISO or ANSI certified version of Perl? | |
117 | ||
118 | =item * | |
119 | ||
120 | Where can I get information on Perl? | |
121 | ||
122 | =item * | |
123 | ||
124 | What are the Perl newsgroups on Usenet? Where do I post questions? | |
125 | ||
126 | =item * | |
127 | ||
128 | Where should I post source code? | |
129 | ||
130 | =item * | |
131 | ||
132 | Perl Books | |
133 | ||
134 | =item * | |
135 | ||
136 | Perl in Magazines | |
137 | ||
138 | =item * | |
139 | ||
140 | Perl on the Net: FTP and WWW Access | |
141 | ||
142 | =item * | |
143 | ||
144 | What mailing lists are there for Perl? | |
145 | ||
146 | =item * | |
147 | ||
148 | Archives of comp.lang.perl.misc | |
149 | ||
150 | =item * | |
151 | ||
152 | Where can I buy a commercial version of Perl? | |
153 | ||
154 | =item * | |
155 | ||
156 | Where do I send bug reports? | |
157 | ||
158 | =item * | |
159 | ||
160 | What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org? | |
161 | ||
162 | =back | |
163 | ||
164 | ||
165 | =head2 L<perlfaq3>: Programming Tools | |
166 | ||
167 | Programmer tools and programming support. | |
168 | ||
169 | =over 4 | |
170 | ||
171 | =item * | |
172 | ||
173 | How do I do (anything)? | |
174 | ||
175 | =item * | |
176 | ||
177 | How can I use Perl interactively? | |
178 | ||
179 | =item * | |
180 | ||
181 | Is there a Perl shell? | |
182 | ||
183 | =item * | |
184 | ||
185 | How do I debug my Perl programs? | |
186 | ||
187 | =item * | |
188 | ||
189 | How do I profile my Perl programs? | |
190 | ||
191 | =item * | |
192 | ||
193 | How do I cross-reference my Perl programs? | |
194 | ||
195 | =item * | |
196 | ||
197 | Is there a pretty-printer (formatter) for Perl? | |
198 | ||
199 | =item * | |
200 | ||
201 | Is there a ctags for Perl? | |
202 | ||
203 | =item * | |
204 | ||
205 | Is there an IDE or Windows Perl Editor? | |
206 | ||
207 | =item * | |
208 | ||
209 | Where can I get Perl macros for vi? | |
210 | ||
211 | =item * | |
212 | ||
213 | Where can I get perl-mode for emacs? | |
214 | ||
215 | =item * | |
216 | ||
217 | How can I use curses with Perl? | |
218 | ||
219 | =item * | |
220 | ||
221 | How can I use X or Tk with Perl? | |
222 | ||
223 | =item * | |
224 | ||
225 | How can I generate simple menus without using CGI or Tk? | |
226 | ||
227 | =item * | |
228 | ||
229 | How can I make my Perl program run faster? | |
230 | ||
231 | =item * | |
232 | ||
233 | How can I make my Perl program take less memory? | |
234 | ||
235 | =item * | |
236 | ||
237 | Is it unsafe to return a pointer to local data? | |
238 | ||
239 | =item * | |
240 | ||
241 | How can I free an array or hash so my program shrinks? | |
242 | ||
243 | =item * | |
244 | ||
245 | How can I make my CGI script more efficient? | |
246 | ||
247 | =item * | |
248 | ||
249 | How can I hide the source for my Perl program? | |
250 | ||
251 | =item * | |
252 | ||
253 | How can I compile my Perl program into byte code or C? | |
254 | ||
255 | =item * | |
256 | ||
257 | How can I compile Perl into Java? | |
258 | ||
259 | =item * | |
260 | ||
261 | How can I get C<#!perl> to work on [MS-DOS,NT,...]? | |
262 | ||
263 | =item * | |
264 | ||
265 | Can I write useful Perl programs on the command line? | |
266 | ||
267 | =item * | |
268 | ||
269 | Why don't Perl one-liners work on my DOS/Mac/VMS system? | |
270 | ||
271 | =item * | |
272 | ||
273 | Where can I learn about CGI or Web programming in Perl? | |
274 | ||
275 | =item * | |
276 | ||
277 | Where can I learn about object-oriented Perl programming? | |
278 | ||
279 | =item * | |
280 | ||
281 | Where can I learn about linking C with Perl? [h2xs, xsubpp] | |
282 | ||
283 | =item * | |
284 | ||
285 | I've read perlembed, perlguts, etc., but I can't embed perl in | |
286 | my C program; what am I doing wrong? | |
287 | ||
288 | =item * | |
289 | ||
290 | When I tried to run my script, I got this message. What does it mean? | |
291 | ||
292 | =item * | |
293 | ||
294 | What's MakeMaker? | |
295 | ||
296 | =back | |
297 | ||
298 | ||
299 | =head2 L<perlfaq4>: Data Manipulation | |
300 | ||
301 | Manipulating numbers, dates, strings, arrays, hashes, and | |
302 | miscellaneous data issues. | |
303 | ||
304 | =over 4 | |
305 | ||
306 | =item * | |
307 | ||
308 | Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)? | |
309 | ||
310 | =item * | |
311 | ||
312 | Why isn't my octal data interpreted correctly? | |
313 | ||
314 | =item * | |
315 | ||
316 | Does Perl have a round() function? What about ceil() and floor()? Trig functions? | |
317 | ||
318 | =item * | |
319 | ||
320 | How do I convert between numeric representations? | |
321 | ||
322 | =item * | |
323 | ||
324 | Why doesn't & work the way I want it to? | |
325 | ||
326 | =item * | |
327 | ||
328 | How do I multiply matrices? | |
329 | ||
330 | =item * | |
331 | ||
332 | How do I perform an operation on a series of integers? | |
333 | ||
334 | =item * | |
335 | ||
336 | How can I output Roman numerals? | |
337 | ||
338 | =item * | |
339 | ||
340 | Why aren't my random numbers random? | |
341 | ||
342 | =item * | |
343 | ||
344 | How do I get a random number between X and Y? | |
345 | ||
346 | =item * | |
347 | ||
348 | How do I find the week-of-the-year/day-of-the-year? | |
349 | ||
350 | =item * | |
351 | ||
352 | How do I find the current century or millennium? | |
353 | ||
354 | =item * | |
355 | ||
356 | How can I compare two dates and find the difference? | |
357 | ||
358 | =item * | |
359 | ||
360 | How can I take a string and turn it into epoch seconds? | |
361 | ||
362 | =item * | |
363 | ||
364 | How can I find the Julian Day? | |
365 | ||
366 | =item * | |
367 | ||
368 | How do I find yesterday's date? | |
369 | ||
370 | =item * | |
371 | ||
372 | Does Perl have a Year 2000 problem? Is Perl Y2K compliant? | |
373 | ||
374 | =item * | |
375 | ||
376 | How do I validate input? | |
377 | ||
378 | =item * | |
379 | ||
380 | How do I unescape a string? | |
381 | ||
382 | =item * | |
383 | ||
384 | How do I remove consecutive pairs of characters? | |
385 | ||
386 | =item * | |
387 | ||
388 | How do I expand function calls in a string? | |
389 | ||
390 | =item * | |
391 | ||
392 | How do I find matching/nesting anything? | |
393 | ||
394 | =item * | |
395 | ||
396 | How do I reverse a string? | |
397 | ||
398 | =item * | |
399 | ||
400 | How do I expand tabs in a string? | |
401 | ||
402 | =item * | |
403 | ||
404 | How do I reformat a paragraph? | |
405 | ||
406 | =item * | |
407 | ||
408 | How can I access/change the first N letters of a string? | |
409 | ||
410 | =item * | |
411 | ||
412 | How do I change the Nth occurrence of something? | |
413 | ||
414 | =item * | |
415 | ||
416 | How can I count the number of occurrences of a substring within a string? | |
417 | ||
418 | =item * | |
419 | ||
420 | How do I capitalize all the words on one line? | |
421 | ||
422 | =item * | |
423 | ||
424 | How can I split a [character] delimited string except when inside | |
425 | [character]? (Comma-separated files) | |
426 | ||
427 | =item * | |
428 | ||
429 | How do I strip blank space from the beginning/end of a string? | |
430 | ||
431 | =item * | |
432 | ||
433 | How do I pad a string with blanks or pad a number with zeroes? | |
434 | ||
435 | =item * | |
436 | ||
437 | How do I extract selected columns from a string? | |
438 | ||
439 | =item * | |
440 | ||
441 | How do I find the soundex value of a string? | |
442 | ||
443 | =item * | |
444 | ||
445 | How can I expand variables in text strings? | |
446 | ||
447 | =item * | |
448 | ||
449 | What's wrong with always quoting "$vars"? | |
450 | ||
451 | =item * | |
452 | ||
453 | Why don't my <<HERE documents work? | |
454 | ||
455 | =item * | |
456 | ||
457 | What is the difference between a list and an array? | |
458 | ||
459 | =item * | |
460 | ||
461 | What is the difference between $array[1] and @array[1]? | |
462 | ||
463 | =item * | |
464 | ||
465 | How can I remove duplicate elements from a list or array? | |
466 | ||
467 | =item * | |
468 | ||
469 | How can I tell whether a certain element is contained in a list or array? | |
470 | ||
471 | =item * | |
472 | ||
473 | How do I compute the difference of two arrays? How do I compute the intersection of two arrays? | |
474 | ||
475 | =item * | |
476 | ||
477 | How do I test whether two arrays or hashes are equal? | |
478 | ||
479 | =item * | |
480 | ||
481 | How do I find the first array element for which a condition is true? | |
482 | ||
483 | =item * | |
484 | ||
485 | How do I handle linked lists? | |
486 | ||
487 | =item * | |
488 | ||
489 | How do I handle circular lists? | |
490 | ||
491 | =item * | |
492 | ||
493 | How do I shuffle an array randomly? | |
494 | ||
495 | =item * | |
496 | ||
497 | How do I process/modify each element of an array? | |
498 | ||
499 | =item * | |
500 | ||
501 | How do I select a random element from an array? | |
502 | ||
503 | =item * | |
504 | ||
505 | How do I permute N elements of a list? | |
506 | ||
507 | =item * | |
508 | ||
509 | How do I sort an array by (anything)? | |
510 | ||
511 | =item * | |
512 | ||
513 | How do I manipulate arrays of bits? | |
514 | ||
515 | =item * | |
516 | ||
517 | Why does defined() return true on empty arrays and hashes? | |
518 | ||
519 | =item * | |
520 | ||
521 | How do I process an entire hash? | |
522 | ||
523 | =item * | |
524 | ||
525 | What happens if I add or remove keys from a hash while iterating over it? | |
526 | ||
527 | =item * | |
528 | ||
529 | How do I look up a hash element by value? | |
530 | ||
531 | =item * | |
532 | ||
533 | How can I know how many entries are in a hash? | |
534 | ||
535 | =item * | |
536 | ||
537 | How do I sort a hash (optionally by value instead of key)? | |
538 | ||
539 | =item * | |
540 | ||
541 | How can I always keep my hash sorted? | |
542 | ||
543 | =item * | |
544 | ||
545 | What's the difference between "delete" and "undef" with hashes? | |
546 | ||
547 | =item * | |
548 | ||
549 | Why don't my tied hashes make the defined/exists distinction? | |
550 | ||
551 | =item * | |
552 | ||
553 | How do I reset an each() operation part-way through? | |
554 | ||
555 | =item * | |
556 | ||
557 | How can I get the unique keys from two hashes? | |
558 | ||
559 | =item * | |
560 | ||
561 | How can I store a multidimensional array in a DBM file? | |
562 | ||
563 | =item * | |
564 | ||
565 | How can I make my hash remember the order I put elements into it? | |
566 | ||
567 | =item * | |
568 | ||
569 | Why does passing a subroutine an undefined element in a hash create it? | |
570 | ||
571 | =item * | |
572 | ||
573 | How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays? | |
574 | ||
575 | =item * | |
576 | ||
577 | How can I use a reference as a hash key? | |
578 | ||
579 | =item * | |
580 | ||
581 | How do I handle binary data correctly? | |
582 | ||
583 | =item * | |
584 | ||
585 | How do I determine whether a scalar is a number/whole/integer/float? | |
586 | ||
587 | =item * | |
588 | ||
589 | How do I keep persistent data across program calls? | |
590 | ||
591 | =item * | |
592 | ||
593 | How do I print out or copy a recursive data structure? | |
594 | ||
595 | =item * | |
596 | ||
597 | How do I define methods for every class/object? | |
598 | ||
599 | =item * | |
600 | ||
601 | How do I verify a credit card checksum? | |
602 | ||
603 | =item * | |
604 | ||
605 | How do I pack arrays of doubles or floats for XS code? | |
606 | ||
607 | =back | |
608 | ||
609 | ||
610 | =head2 L<perlfaq5>: Files and Formats | |
611 | ||
612 | I/O and the "f" issues: filehandles, flushing, formats, and footers. | |
613 | ||
614 | =over 4 | |
615 | ||
616 | =item * | |
617 | ||
618 | How do I flush/unbuffer an output filehandle? Why must I do this? | |
619 | ||
620 | =item * | |
621 | ||
622 | How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file? | |
623 | ||
624 | =item * | |
625 | ||
626 | How do I count the number of lines in a file? | |
627 | ||
628 | =item * | |
629 | ||
630 | How do I make a temporary file name? | |
631 | ||
632 | =item * | |
633 | ||
634 | How can I manipulate fixed-record-length files? | |
635 | ||
636 | =item * | |
637 | ||
638 | How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles? | |
639 | ||
640 | =item * | |
641 | ||
642 | How can I use a filehandle indirectly? | |
643 | ||
644 | =item * | |
645 | ||
646 | How can I set up a footer format to be used with write()? | |
647 | ||
648 | =item * | |
649 | ||
650 | How can I write() into a string? | |
651 | ||
652 | =item * | |
653 | ||
654 | How can I output my numbers with commas added? | |
655 | ||
656 | =item * | |
657 | ||
658 | How can I translate tildes (~) in a filename? | |
659 | ||
660 | =item * | |
661 | ||
662 | How come when I open a file read-write it wipes it out? | |
663 | ||
664 | =item * | |
665 | ||
666 | Why do I sometimes get an "Argument list too long" when I use <*>? | |
667 | ||
668 | =item * | |
669 | ||
670 | Is there a leak/bug in glob()? | |
671 | ||
672 | =item * | |
673 | ||
674 | How can I open a file with a leading ">" or trailing blanks? | |
675 | ||
676 | =item * | |
677 | ||
678 | How can I reliably rename a file? | |
679 | ||
680 | =item * | |
681 | ||
682 | How can I lock a file? | |
683 | ||
684 | =item * | |
685 | ||
686 | Why can't I just open(FH, ">file.lock")? | |
687 | ||
688 | =item * | |
689 | ||
690 | I still don't get locking. I just want to increment the number in the file. How can I do this? | |
691 | ||
692 | =item * | |
693 | ||
694 | All I want to do is append a small amount of text to the end of a file. Do I still have to use locking? | |
695 | ||
696 | =item * | |
697 | ||
698 | How do I randomly update a binary file? | |
699 | ||
700 | =item * | |
701 | ||
702 | How do I get a file's timestamp in perl? | |
703 | ||
704 | =item * | |
705 | ||
706 | How do I set a file's timestamp in perl? | |
707 | ||
708 | =item * | |
709 | ||
710 | How do I print to more than one file at once? | |
711 | ||
712 | =item * | |
713 | ||
714 | How can I read in an entire file all at once? | |
715 | ||
716 | =item * | |
717 | ||
718 | How can I read in a file by paragraphs? | |
719 | ||
720 | =item * | |
721 | ||
722 | How can I read a single character from a file? From the keyboard? | |
723 | ||
724 | =item * | |
725 | ||
726 | How can I tell whether there's a character waiting on a filehandle? | |
727 | ||
728 | =item * | |
729 | ||
730 | How do I do a C<tail -f> in perl? | |
731 | ||
732 | =item * | |
733 | ||
734 | How do I dup() a filehandle in Perl? | |
735 | ||
736 | =item * | |
737 | ||
738 | How do I close a file descriptor by number? | |
739 | ||
740 | =item * | |
741 | ||
742 | Why can't I use "C:\temp\foo" in DOS paths? What doesn't `C:\temp\foo.exe` work? | |
743 | ||
744 | =item * | |
745 | ||
746 | Why doesn't glob("*.*") get all the files? | |
747 | ||
748 | =item * | |
749 | ||
750 | Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl? | |
751 | ||
752 | =item * | |
753 | ||
754 | How do I select a random line from a file? | |
755 | ||
756 | =item * | |
757 | ||
758 | Why do I get weird spaces when I print an array of lines? | |
759 | ||
760 | =back | |
761 | ||
762 | ||
763 | =head2 L<perlfaq6>: Regular Expressions | |
764 | ||
765 | Pattern matching and regular expressions. | |
766 | ||
767 | =over 4 | |
768 | ||
769 | =item * | |
770 | ||
771 | How can I hope to use regular expressions without creating illegible and unmaintainable code? | |
772 | ||
773 | =item * | |
774 | ||
775 | I'm having trouble matching over more than one line. What's wrong? | |
776 | ||
777 | =item * | |
778 | ||
779 | How can I pull out lines between two patterns that are themselves on different lines? | |
780 | ||
781 | =item * | |
782 | ||
783 | I put a regular expression into $/ but it didn't work. What's wrong? | |
784 | ||
785 | =item * | |
786 | ||
787 | How do I substitute case insensitively on the LHS while preserving case on the RHS? | |
788 | ||
789 | =item * | |
790 | ||
791 | How can I make C<\w> match national character sets? | |
792 | ||
793 | =item * | |
794 | ||
795 | How can I match a locale-smart version of C</[a-zA-Z]/>? | |
796 | ||
797 | =item * | |
798 | ||
799 | How can I quote a variable to use in a regex? | |
800 | ||
801 | =item * | |
802 | ||
803 | What is C</o> really for? | |
804 | ||
805 | =item * | |
806 | ||
807 | How do I use a regular expression to strip C style comments from a file? | |
808 | ||
809 | =item * | |
810 | ||
811 | Can I use Perl regular expressions to match balanced text? | |
812 | ||
813 | =item * | |
814 | ||
815 | What does it mean that regexes are greedy? How can I get around it? | |
816 | ||
817 | =item * | |
818 | ||
819 | How do I process each word on each line? | |
820 | ||
821 | =item * | |
822 | ||
823 | How can I print out a word-frequency or line-frequency summary? | |
824 | ||
825 | =item * | |
826 | ||
827 | How can I do approximate matching? | |
828 | ||
829 | =item * | |
830 | ||
831 | How do I efficiently match many regular expressions at once? | |
832 | ||
833 | =item * | |
834 | ||
835 | Why don't word-boundary searches with C<\b> work for me? | |
836 | ||
837 | =item * | |
838 | ||
839 | Why does using $&, $`, or $' slow my program down? | |
840 | ||
841 | =item * | |
842 | ||
843 | What good is C<\G> in a regular expression? | |
844 | ||
845 | =item * | |
846 | ||
847 | Are Perl regexes DFAs or NFAs? Are they POSIX compliant? | |
848 | ||
849 | =item * | |
850 | ||
851 | What's wrong with using grep or map in a void context? | |
852 | ||
853 | =item * | |
854 | ||
855 | How can I match strings with multibyte characters? | |
856 | ||
857 | =item * | |
858 | ||
859 | How do I match a pattern that is supplied by the user? | |
860 | ||
861 | =back | |
862 | ||
863 | ||
864 | =head2 L<perlfaq7>: General Perl Language Issues | |
865 | ||
866 | General Perl language issues that don't clearly fit into any of the | |
867 | other sections. | |
868 | ||
869 | =over 4 | |
870 | ||
871 | =item * | |
872 | ||
873 | Can I get a BNF/yacc/RE for the Perl language? | |
874 | ||
875 | =item * | |
876 | ||
877 | What are all these $@%&* punctuation signs, and how do I know when to use them? | |
878 | ||
879 | =item * | |
880 | ||
881 | Do I always/never have to quote my strings or use semicolons and commas? | |
882 | ||
883 | =item * | |
884 | ||
885 | How do I skip some return values? | |
886 | ||
887 | =item * | |
888 | ||
889 | How do I temporarily block warnings? | |
890 | ||
891 | =item * | |
892 | ||
893 | What's an extension? | |
894 | ||
895 | =item * | |
896 | ||
897 | Why do Perl operators have different precedence than C operators? | |
898 | ||
899 | =item * | |
900 | ||
901 | How do I declare/create a structure? | |
902 | ||
903 | =item * | |
904 | ||
905 | How do I create a module? | |
906 | ||
907 | =item * | |
908 | ||
909 | How do I create a class? | |
910 | ||
911 | =item * | |
912 | ||
913 | How can I tell if a variable is tainted? | |
914 | ||
915 | =item * | |
916 | ||
917 | What's a closure? | |
918 | ||
919 | =item * | |
920 | ||
921 | What is variable suicide and how can I prevent it? | |
922 | ||
923 | =item * | |
924 | ||
925 | How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}? | |
926 | ||
927 | =item * | |
928 | ||
929 | How do I create a static variable? | |
930 | ||
931 | =item * | |
932 | ||
933 | What's the difference between dynamic and lexical (static) scoping? Between local() and my()? | |
934 | ||
935 | =item * | |
936 | ||
937 | How can I access a dynamic variable while a similarly named lexical is in scope? | |
938 | ||
939 | =item * | |
940 | ||
941 | What's the difference between deep and shallow binding? | |
942 | ||
943 | =item * | |
944 | ||
945 | Why doesn't "my($foo) = <FILE>;" work right? | |
946 | ||
947 | =item * | |
948 | ||
949 | How do I redefine a builtin function, operator, or method? | |
950 | ||
951 | =item * | |
952 | ||
953 | What's the difference between calling a function as &foo and foo()? | |
954 | ||
955 | =item * | |
956 | ||
957 | How do I create a switch or case statement? | |
958 | ||
959 | =item * | |
960 | ||
961 | How can I catch accesses to undefined variables/functions/methods? | |
962 | ||
963 | =item * | |
964 | ||
965 | Why can't a method included in this same file be found? | |
966 | ||
967 | =item * | |
968 | ||
969 | How can I find out my current package? | |
970 | ||
971 | =item * | |
972 | ||
973 | How can I comment out a large block of perl code? | |
974 | ||
975 | =item * | |
976 | ||
977 | How do I clear a package? | |
978 | ||
979 | =item * | |
980 | ||
981 | How can I use a variable as a variable name? | |
982 | ||
983 | =back | |
984 | ||
985 | ||
986 | =head2 L<perlfaq8>: System Interaction | |
987 | ||
988 | Interprocess communication (IPC), control over the user-interface | |
989 | (keyboard, screen and pointing devices). | |
990 | ||
991 | =over 4 | |
992 | ||
993 | =item * | |
994 | ||
995 | How do I find out which operating system I'm running under? | |
996 | ||
997 | =item * | |
998 | ||
999 | How come exec() doesn't return? | |
1000 | ||
1001 | =item * | |
1002 | ||
1003 | How do I do fancy stuff with the keyboard/screen/mouse? | |
1004 | ||
1005 | =item * | |
1006 | ||
1007 | How do I print something out in color? | |
1008 | ||
1009 | =item * | |
1010 | ||
1011 | How do I read just one key without waiting for a return key? | |
1012 | ||
1013 | =item * | |
1014 | ||
1015 | How do I check whether input is ready on the keyboard? | |
1016 | ||
1017 | =item * | |
1018 | ||
1019 | How do I clear the screen? | |
1020 | ||
1021 | =item * | |
1022 | ||
1023 | How do I get the screen size? | |
1024 | ||
1025 | =item * | |
1026 | ||
1027 | How do I ask the user for a password? | |
1028 | ||
1029 | =item * | |
1030 | ||
1031 | How do I read and write the serial port? | |
1032 | ||
1033 | =item * | |
1034 | ||
1035 | How do I decode encrypted password files? | |
1036 | ||
1037 | =item * | |
1038 | ||
1039 | How do I start a process in the background? | |
1040 | ||
1041 | =item * | |
1042 | ||
1043 | How do I trap control characters/signals? | |
1044 | ||
1045 | =item * | |
1046 | ||
1047 | How do I modify the shadow password file on a Unix system? | |
1048 | ||
1049 | =item * | |
1050 | ||
1051 | How do I set the time and date? | |
1052 | ||
1053 | =item * | |
1054 | ||
1055 | How can I sleep() or alarm() for under a second? | |
1056 | ||
1057 | =item * | |
1058 | ||
1059 | How can I measure time under a second? | |
1060 | ||
1061 | =item * | |
1062 | ||
1063 | How can I do an atexit() or setjmp()/longjmp()? (Exception handling) | |
1064 | ||
1065 | =item * | |
1066 | ||
1067 | Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean? | |
1068 | ||
1069 | =item * | |
1070 | ||
1071 | How can I call my system's unique C functions from Perl? | |
1072 | ||
1073 | =item * | |
1074 | ||
1075 | Where do I get the include files to do ioctl() or syscall()? | |
1076 | ||
1077 | =item * | |
1078 | ||
1079 | Why do setuid perl scripts complain about kernel problems? | |
1080 | ||
1081 | =item * | |
1082 | ||
1083 | How can I open a pipe both to and from a command? | |
1084 | ||
1085 | =item * | |
1086 | ||
1087 | Why can't I get the output of a command with system()? | |
1088 | ||
1089 | =item * | |
1090 | ||
1091 | How can I capture STDERR from an external command? | |
1092 | ||
1093 | =item * | |
1094 | ||
1095 | Why doesn't open() return an error when a pipe open fails? | |
1096 | ||
1097 | =item * | |
1098 | ||
1099 | What's wrong with using backticks in a void context? | |
1100 | ||
1101 | =item * | |
1102 | ||
1103 | How can I call backticks without shell processing? | |
1104 | ||
1105 | =item * | |
1106 | ||
1107 | Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)? | |
1108 | ||
1109 | =item * | |
1110 | ||
1111 | How can I convert my shell script to perl? | |
1112 | ||
1113 | =item * | |
1114 | ||
1115 | Can I use perl to run a telnet or ftp session? | |
1116 | ||
1117 | =item * | |
1118 | ||
1119 | How can I write expect in Perl? | |
1120 | ||
1121 | =item * | |
1122 | ||
1123 | Is there a way to hide perl's command line from programs such as "ps"? | |
1124 | ||
1125 | =item * | |
1126 | ||
1127 | I {changed directory, modified my environment} in a perl script. How come the change disappeared when I exited the script? How do I get my changes to be visible? | |
1128 | ||
1129 | =item * | |
1130 | ||
1131 | How do I close a process's filehandle without waiting for it to complete? | |
1132 | ||
1133 | =item * | |
1134 | ||
1135 | How do I fork a daemon process? | |
1136 | ||
1137 | =item * | |
1138 | ||
1139 | How do I find out if I'm running interactively or not? | |
1140 | ||
1141 | =item * | |
1142 | ||
1143 | How do I timeout a slow event? | |
1144 | ||
1145 | =item * | |
1146 | ||
1147 | How do I set CPU limits? | |
1148 | ||
1149 | =item * | |
1150 | ||
1151 | How do I avoid zombies on a Unix system? | |
1152 | ||
1153 | =item * | |
1154 | ||
1155 | How do I use an SQL database? | |
1156 | ||
1157 | =item * | |
1158 | ||
1159 | How do I make a system() exit on control-C? | |
1160 | ||
1161 | =item * | |
1162 | ||
1163 | How do I open a file without blocking? | |
1164 | ||
1165 | =item * | |
1166 | ||
1167 | How do I install a module from CPAN? | |
1168 | ||
1169 | =item * | |
1170 | ||
1171 | What's the difference between require and use? | |
1172 | ||
1173 | =item * | |
1174 | ||
1175 | How do I keep my own module/library directory? | |
1176 | ||
1177 | =item * | |
1178 | ||
1179 | How do I add the directory my program lives in to the module/library search path? | |
1180 | ||
1181 | =item * | |
1182 | ||
1183 | How do I add a directory to my include path at runtime? | |
1184 | ||
1185 | =item * | |
1186 | ||
1187 | What is socket.ph and where do I get it? | |
1188 | ||
1189 | =back | |
1190 | ||
1191 | ||
1192 | =head2 L<perlfaq9>: Networking | |
1193 | ||
1194 | Networking, the internet, and a few on the web. | |
1195 | ||
1196 | =over 4 | |
1197 | ||
1198 | =item * | |
1199 | ||
1200 | What is the correct form of response from a CGI script? | |
1201 | ||
1202 | =item * | |
1203 | ||
1204 | My CGI script runs from the command line but not the browser. (500 Server Error) | |
1205 | ||
1206 | =item * | |
1207 | ||
1208 | How can I get better error messages from a CGI program? | |
1209 | ||
1210 | =item * | |
1211 | ||
1212 | How do I remove HTML from a string? | |
1213 | ||
1214 | =item * | |
1215 | ||
1216 | How do I extract URLs? | |
1217 | ||
1218 | =item * | |
1219 | ||
1220 | How do I download a file from the user's machine? How do I open a file on another machine? | |
1221 | ||
1222 | =item * | |
1223 | ||
1224 | How do I make a pop-up menu in HTML? | |
1225 | ||
1226 | =item * | |
1227 | ||
1228 | How do I fetch an HTML file? | |
1229 | ||
1230 | =item * | |
1231 | ||
1232 | How do I automate an HTML form submission? | |
1233 | ||
1234 | =item * | |
1235 | ||
1236 | How do I decode or create those %-encodings on the web? | |
1237 | ||
1238 | =item * | |
1239 | ||
1240 | How do I redirect to another page? | |
1241 | ||
1242 | =item * | |
1243 | ||
1244 | How do I put a password on my web pages? | |
1245 | ||
1246 | =item * | |
1247 | ||
1248 | How do I edit my .htpasswd and .htgroup files with Perl? | |
1249 | ||
1250 | =item * | |
1251 | ||
1252 | How do I make sure users can't enter values into a form that cause my CGI script to do bad things? | |
1253 | ||
1254 | =item * | |
1255 | ||
1256 | How do I parse a mail header? | |
1257 | ||
1258 | =item * | |
1259 | ||
1260 | How do I decode a CGI form? | |
1261 | ||
1262 | =item * | |
1263 | ||
1264 | How do I check a valid mail address? | |
1265 | ||
1266 | =item * | |
1267 | ||
1268 | How do I decode a MIME/BASE64 string? | |
1269 | ||
1270 | =item * | |
1271 | ||
1272 | How do I return the user's mail address? | |
1273 | ||
1274 | =item * | |
1275 | ||
1276 | How do I send mail? | |
1277 | ||
1278 | =item * | |
1279 | ||
1280 | How do I use MIME to make an attachment to a mail message? | |
1281 | ||
1282 | =item * | |
1283 | ||
1284 | How do I read mail? | |
1285 | ||
1286 | =item * | |
1287 | ||
1288 | How do I find out my hostname/domainname/IP address? | |
1289 | ||
1290 | =item * | |
1291 | ||
1292 | How do I fetch a news article or the active newsgroups? | |
1293 | ||
1294 | =item * | |
1295 | ||
1296 | How do I fetch/put an FTP file? | |
1297 | ||
1298 | =item * | |
1299 | ||
1300 | How can I do RPC in Perl? | |
1301 | ||
1302 | =back | |
1303 | ||
1304 | ||
1305 | =head1 About the perlfaq documents | |
1306 | ||
1307 | =head2 Where to get the perlfaq | |
1308 | ||
1309 | This document is posted regularly to comp.lang.perl.announce and | |
1310 | several other related newsgroups. It is available on many | |
1311 | web sites: http://www.perldoc.com/ and http://perlfaq.cpan.org/ . | |
1312 | ||
1313 | =head2 How to contribute to the perlfaq | |
1314 | ||
1315 | You may mail corrections, additions, and suggestions to | |
1316 | perlfaq-workers@perl.org . This alias should not be | |
1317 | used to I<ask> FAQs. It's for fixing the current FAQ. | |
1318 | Send questions to the comp.lang.perl.misc newsgroup. | |
1319 | ||
1320 | =head2 What will happen if you mail your Perl programming problems to the authors | |
1321 | ||
1322 | Your questions will probably go unread, unless they're suggestions of | |
1323 | new questions to add to the FAQ, in which case they should have gone | |
1324 | to the perlfaq-workers@perl.org instead. | |
1325 | ||
1326 | You should have read section 2 of this faq. There you would have | |
1327 | learned that comp.lang.perl.misc is the appropriate place to go for | |
1328 | free advice. If your question is really important and you require a | |
1329 | prompt and correct answer, you should hire a consultant. | |
1330 | ||
1331 | =head1 Credits | |
1332 | ||
1333 | When I first began the Perl FAQ in the late 80s, I never realized it | |
1334 | would have grown to over a hundred pages, nor that Perl would ever become | |
1335 | so popular and widespread. This document could not have been written | |
1336 | without the tremendous help provided by Larry Wall and the rest of the | |
1337 | Perl Porters. | |
1338 | ||
1339 | =head1 Author and Copyright Information | |
1340 | ||
1341 | Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington. | |
1342 | All rights reserved. | |
1343 | ||
1344 | =head2 Bundled Distributions | |
1345 | ||
1346 | This documentation is free; you can redistribute it and/or modify it | |
1347 | under the same terms as Perl itself. | |
1348 | ||
1349 | Irrespective of its distribution, all code examples in these files | |
1350 | are hereby placed into the public domain. You are permitted and | |
1351 | encouraged to use this code in your own programs for fun | |
1352 | or for profit as you see fit. A simple comment in the code giving | |
1353 | credit would be courteous but is not required. | |
1354 | ||
1355 | =head2 Disclaimer | |
1356 | ||
1357 | This information is offered in good faith and in the hope that it may | |
1358 | be of use, but is not guaranteed to be correct, up to date, or suitable | |
1359 | for any particular purpose whatsoever. The authors accept no liability | |
1360 | in respect of this information or its use. | |
1361 | ||
1362 | =head1 Changes | |
1363 | ||
1364 | =over 4 | |
1365 | ||
1366 | =item 1/November/2000 | |
1367 | ||
1368 | A few grammatical fixes and updates implemented by John Borwick. | |
1369 | ||
1370 | =item 23/May/99 | |
1371 | ||
1372 | Extensive updates from the net in preparation for 5.6 release. | |
1373 | ||
1374 | =item 13/April/99 | |
1375 | ||
1376 | More minor touch-ups. Added new question at the end | |
1377 | of perlfaq7 on variable names within variables. | |
1378 | ||
1379 | =item 7/January/99 | |
1380 | ||
1381 | Small touch ups here and there. Added all questions in this | |
1382 | document as a sort of table of contents. | |
1383 | ||
1384 | =item 22/June/98 | |
1385 | ||
1386 | Significant changes throughout in preparation for the 5.005 | |
1387 | release. | |
1388 | ||
1389 | =item 24/April/97 | |
1390 | ||
1391 | Style and whitespace changes from Chip, new question on reading one | |
1392 | character at a time from a terminal using POSIX from Tom. | |
1393 | ||
1394 | =item 23/April/97 | |
1395 | ||
1396 | Added http://www.oasis.leo.org/perl/ to L<perlfaq2>. Style fix to | |
1397 | L<perlfaq3>. Added floating point precision, fixed complex number | |
1398 | arithmetic, cross-references, caveat for Text::Wrap, alternative | |
1399 | answer for initial capitalizing, fixed incorrect regexp, added example | |
1400 | of Tie::IxHash to L<perlfaq4>. Added example of passing and storing | |
1401 | filehandles, added commify to L<perlfaq5>. Restored variable suicide, | |
1402 | and added mass commenting to L<perlfaq7>. Added Net::Telnet, fixed | |
1403 | backticks, added reader/writer pair to telnet question, added FindBin, | |
1404 | grouped module questions together in L<perlfaq8>. Expanded caveats | |
1405 | for the simple URL extractor, gave LWP example, added CGI security | |
1406 | question, expanded on the mail address answer in L<perlfaq9>. | |
1407 | ||
1408 | =item 25/March/97 | |
1409 | ||
1410 | Added more info to the binary distribution section of L<perlfaq2>. | |
1411 | Added Net::Telnet to L<perlfaq6>. Fixed typos in L<perlfaq8>. Added | |
1412 | mail sending example to L<perlfaq9>. Added Merlyn's columns to | |
1413 | L<perlfaq2>. | |
1414 | ||
1415 | =item 18/March/97 | |
1416 | ||
1417 | Added the DATE to the NAME section, indicating which sections have | |
1418 | changed. | |
1419 | ||
1420 | Mentioned SIGPIPE and L<perlipc> in the forking open answer in | |
1421 | L<perlfaq8>. | |
1422 | ||
1423 | Fixed description of a regular expression in L<perlfaq4>. | |
1424 | ||
1425 | =item 17/March/97 Version | |
1426 | ||
1427 | Various typos fixed throughout. | |
1428 | ||
1429 | Added new question on Perl BNF on L<perlfaq7>. | |
1430 | ||
1431 | =item Initial Release: 11/March/97 | |
1432 | ||
1433 | This is the initial release of version 3 of the FAQ; consequently there | |
1434 | have been no changes since its initial release. | |
1435 | ||
1436 | =back |