This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
Add quick note to perlfaq main page about searching the perlfaq
[perl5.git] / dist / perlfaq / lib / perlfaq.pod
CommitLineData
68dc0745
PP
1=head1 NAME
2
ac9dac7f 3perlfaq - frequently asked questions about Perl
68dc0745
PP
4
5=head1 DESCRIPTION
6
fcd1fd07
RGS
7The perlfaq comprises several documents that answer the most commonly
8asked questions about Perl and Perl programming. It's divided by topic
9into nine major sections outlined in this document.
68dc0745 10
197aec24
RGS
11=head2 Where to get the perlfaq
12
fcd1fd07
RGS
13The perlfaq comes with the standard Perl distribution, so if you have Perl
14you should have the perlfaq. You should also have the C<perldoc> tool
e1020413 15that lets you read the L<perlfaq>:
197aec24 16
fcd1fd07 17 $ perldoc perlfaq
197aec24 18
ce46a400
MH
19or search the L<perlfaq> question headings:
20
21 $ perldoc -q open
22
23See C<perldoc> for more information.
24
fcd1fd07
RGS
25Besides your local system, you can find the perlfaq on the web, including
26at http://perldoc.perl.org/ .
197aec24 27
fcd1fd07
RGS
28The perlfaq is an evolving document and you can read the latest version
29at http://faq.perl.org/ . The perlfaq-workers periodically post extracts
30of the latest perlfaq to comp.lang.perl.misc.
197aec24 31
67126c1b 32The perlfaq documents are in the perl source tree (see
c222ef46 33L<perlgit>). The git repository notes all changes to the FAQ and
67126c1b 34holds the latest version of the working documents and may vary
35significantly from the version distributed with the latest version of
36Perl. Check the repository before sending your corrections.
197aec24 37
fcd1fd07 38=head2 How to contribute to the perlfaq
197aec24 39
ac9dac7f 40You can mail corrections, additions, and suggestions to
fcd1fd07
RGS
41C<< <perlfaq-workers AT perl DOT org> >>. The perlfaq volunteers use this
42address to coordinate their efforts and track the perlfaq development.
43They appreciate your contributions to the FAQ but do not have time to
44provide individual help, so don't use this address to ask FAQs.
197aec24 45
a1bbdff3 46The perlfaq server posts extracts of the perlfaq to that newsgroup
47every 6 hours (or so), and the community of volunteers reviews and
48updates the answers. If you'd like to help review and update the
49answers, check out comp.lang.perl.misc.
50
51You can also fork the perl repository, make your changes, and send them
c222ef46 52to Perl 5 Porters. See L<perlgit>.
197aec24 53
fcd1fd07 54=head2 What will happen if you mail your Perl programming problems to the authors?
197aec24 55
fcd1fd07
RGS
56The perlfaq-workers like to keep all traffic on the perlfaq-workers list
57so that everyone can see the work being done (and the work that needs to
58be done). The mailing list serves as an official record. If you email the
59authors or maintainers directly, you'll probably get a reply asking you
60to post to the mailing list. If you don't get a reply, it probably means
61that the person never saw the message or didn't have time to deal with
62it. Posting to the list allows the volunteers with time to deal with it
63when others are busy.
197aec24 64
fcd1fd07
RGS
65If you have a question that isn't in the FAQ and you would like help with
66it, try the resources in L<perlfaq2>.
197aec24 67
fcd1fd07 68=head1 CREDITS
197aec24 69
fcd1fd07 70Tom Christiansen wrote the original perlfaq then expanded it with the
f12f5f55 71help of Nat Torkington. The perlfaq-workers maintain current document
a1bbdff3 72and the denizens of comp.lang.perl.misc regularly review and update the
fcd1fd07
RGS
73FAQ. Several people have contributed answers, corrections, and comments,
74and the perlfaq notes those contributions wherever appropriate.
197aec24 75
fcd1fd07 76=head1 AUTHOR AND COPYRIGHT
197aec24 77
a1bbdff3 78Tom Christiansen wrote the original version of this document.
fcd1fd07
RGS
79brian d foy C<< <bdfoy@cpan.org> >> wrote this version. See the
80individual perlfaq documents for additional copyright information.
197aec24 81
fcd1fd07
RGS
82This document is available under the same terms as Perl itself. Code
83examples in all the perlfaq documents are in the public domain. Use
8d2e243f 84them as you see fit (and at your own risk with no warranty from anyone).
197aec24
RGS
85
86=head1 Table of Contents
68dc0745 87
5cd0b561
RGS
88=over 4
89
90=item perlfaq - this document
91
92=item perlfaq1 - General Questions About Perl
93
94=item perlfaq2 - Obtaining and Learning about Perl
95
96=item perlfaq3 - Programming Tools
97
98=item perlfaq4 - Data Manipulation
99
100=item perlfaq5 - Files and Formats
101
102=item perlfaq6 - Regular Expressions
103
104=item perlfaq7 - General Perl Language Issues
68dc0745 105
5cd0b561
RGS
106=item perlfaq8 - System Interaction
107
108=item perlfaq9 - Networking
109
5cd0b561
RGS
110=back
111
5cd0b561 112=head1 The Questions
68dc0745 113
40d4dc3e 114=head2 L<perlfaq1>: General Questions About Perl
68dc0745 115
ae3d0b9f 116Very general, high-level questions about Perl.
68dc0745 117
65acb1b1
TC
118=over 4
119
40d4dc3e
RB
120=item *
121
122What is Perl?
123
124=item *
125
a1bbdff3 126Who supports Perl? Who develops it? Why is it free?
40d4dc3e
RB
127
128=item *
129
130Which version of Perl should I use?
131
132=item *
133
e9d185f8 134What are Perl 4, Perl 5, or Perl 6?
40d4dc3e
RB
135
136=item *
137
e9d185f8 138What is Perl 6?
65acb1b1 139
40d4dc3e 140=item *
65acb1b1 141
40d4dc3e 142How stable is Perl?
65acb1b1 143
40d4dc3e 144=item *
65acb1b1 145
40d4dc3e 146Is Perl difficult to learn?
65acb1b1 147
40d4dc3e 148=item *
65acb1b1 149
40d4dc3e 150How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
65acb1b1 151
40d4dc3e 152=item *
65acb1b1 153
40d4dc3e 154Can I do [task] in Perl?
65acb1b1 155
40d4dc3e 156=item *
65acb1b1 157
40d4dc3e 158When shouldn't I program in Perl?
65acb1b1 159
40d4dc3e 160=item *
65acb1b1 161
40d4dc3e 162What's the difference between "perl" and "Perl"?
65acb1b1 163
40d4dc3e 164=item *
65acb1b1 165
40d4dc3e
RB
166Is it a Perl program or a Perl script?
167
168=item *
169
170What is a JAPH?
171
172=item *
173
174Where can I get a list of Larry Wall witticisms?
175
176=item *
177
ac9dac7f 178How can I convince others to use Perl?
65acb1b1
TC
179
180=back
181
182
40d4dc3e 183=head2 L<perlfaq2>: Obtaining and Learning about Perl
68dc0745 184
c98c5709 185Where to find source and documentation for Perl, support, and related matters.
68dc0745 186
65acb1b1
TC
187=over 4
188
40d4dc3e
RB
189=item *
190
b68463f7 191What machines support perl? Where do I get it?
40d4dc3e
RB
192
193=item *
194
b68463f7 195How can I get a binary version of perl?
65acb1b1 196
40d4dc3e 197=item *
65acb1b1 198
b68463f7 199I don't have a C compiler. How can I build my own Perl interpreter?
65acb1b1 200
40d4dc3e 201=item *
65acb1b1 202
b68463f7 203I copied the perl binary from one machine to another, but scripts don't work.
65acb1b1 204
40d4dc3e 205=item *
65acb1b1 206
40d4dc3e 207I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
65acb1b1 208
40d4dc3e 209=item *
65acb1b1 210
40d4dc3e 211What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
65acb1b1 212
40d4dc3e 213=item *
65acb1b1 214
40d4dc3e 215Is there an ISO or ANSI certified version of Perl?
65acb1b1 216
40d4dc3e 217=item *
65acb1b1 218
40d4dc3e 219Where can I get information on Perl?
65acb1b1 220
40d4dc3e 221=item *
65acb1b1 222
40d4dc3e 223What are the Perl newsgroups on Usenet? Where do I post questions?
65acb1b1 224
40d4dc3e 225=item *
65acb1b1 226
40d4dc3e 227Where should I post source code?
65acb1b1 228
40d4dc3e
RB
229=item *
230
231Perl Books
232
233=item *
234
fcd1fd07 235Which magazines have Perl content?
40d4dc3e
RB
236
237=item *
238
239What mailing lists are there for Perl?
240
241=item *
242
fcd1fd07 243Where are the archives for comp.lang.perl.misc?
40d4dc3e
RB
244
245=item *
246
b68463f7 247Where can I buy a commercial version of perl?
40d4dc3e
RB
248
249=item *
250
251Where do I send bug reports?
252
253=item *
254
ae3d0b9f 255What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org?
65acb1b1
TC
256
257=back
258
259
40d4dc3e 260=head2 L<perlfaq3>: Programming Tools
68dc0745
PP
261
262Programmer tools and programming support.
263
65acb1b1
TC
264=over 4
265
40d4dc3e
RB
266=item *
267
268How do I do (anything)?
269
270=item *
271
272How can I use Perl interactively?
273
274=item *
65acb1b1 275
40d4dc3e 276Is there a Perl shell?
65acb1b1 277
40d4dc3e 278=item *
65acb1b1 279
49d635f9
RGS
280How do I find which modules are installed on my system?
281
282=item *
283
40d4dc3e 284How do I debug my Perl programs?
65acb1b1 285
40d4dc3e 286=item *
65acb1b1 287
40d4dc3e 288How do I profile my Perl programs?
65acb1b1 289
40d4dc3e 290=item *
65acb1b1 291
40d4dc3e 292How do I cross-reference my Perl programs?
65acb1b1 293
40d4dc3e 294=item *
65acb1b1 295
40d4dc3e 296Is there a pretty-printer (formatter) for Perl?
65acb1b1 297
40d4dc3e 298=item *
65acb1b1 299
40d4dc3e 300Is there a ctags for Perl?
65acb1b1 301
40d4dc3e 302=item *
65acb1b1 303
40d4dc3e 304Is there an IDE or Windows Perl Editor?
65acb1b1 305
40d4dc3e 306=item *
65acb1b1 307
40d4dc3e 308Where can I get Perl macros for vi?
65acb1b1 309
40d4dc3e 310=item *
65acb1b1 311
a1bbdff3 312Where can I get perl-mode or cperl-mode for emacs?
65acb1b1 313
40d4dc3e 314=item *
65acb1b1 315
40d4dc3e 316How can I use curses with Perl?
65acb1b1 317
40d4dc3e 318=item *
65acb1b1 319
c195e131 320How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
65acb1b1 321
40d4dc3e 322=item *
65acb1b1 323
40d4dc3e 324How can I make my Perl program run faster?
65acb1b1 325
40d4dc3e 326=item *
65acb1b1 327
40d4dc3e
RB
328How can I make my Perl program take less memory?
329
330=item *
331
49d635f9 332Is it safe to return a reference to local or lexical data?
40d4dc3e
RB
333
334=item *
335
336How can I free an array or hash so my program shrinks?
337
338=item *
339
340How can I make my CGI script more efficient?
341
342=item *
343
344How can I hide the source for my Perl program?
345
346=item *
347
348How can I compile my Perl program into byte code or C?
349
350=item *
351
40d4dc3e
RB
352How can I get C<#!perl> to work on [MS-DOS,NT,...]?
353
354=item *
355
356Can I write useful Perl programs on the command line?
357
358=item *
359
360Why don't Perl one-liners work on my DOS/Mac/VMS system?
361
362=item *
363
364Where can I learn about CGI or Web programming in Perl?
365
366=item *
367
368Where can I learn about object-oriented Perl programming?
369
370=item *
371
b68463f7 372Where can I learn about linking C with Perl?
40d4dc3e
RB
373
374=item *
375
7678cced 376I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
65acb1b1 377
40d4dc3e
RB
378=item *
379
ae3d0b9f 380When I tried to run my script, I got this message. What does it mean?
65acb1b1 381
40d4dc3e
RB
382=item *
383
384What's MakeMaker?
65acb1b1
TC
385
386=back
387
388
40d4dc3e 389=head2 L<perlfaq4>: Data Manipulation
68dc0745 390
c98c5709 391Manipulating numbers, dates, strings, arrays, hashes, and miscellaneous data issues.
68dc0745 392
65acb1b1
TC
393=over 4
394
40d4dc3e
RB
395=item *
396
397Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?
398
399=item *
400
b68463f7 401Why is int() broken?
c98c5709
RGS
402
403=item *
404
40d4dc3e
RB
405Why isn't my octal data interpreted correctly?
406
407=item *
408
b68463f7 409Does Perl have a round() function? What about ceil() and floor()? Trig functions?
40d4dc3e
RB
410
411=item *
412
c98c5709 413How do I convert between numeric representations/bases/radixes?
40d4dc3e
RB
414
415=item *
416
417Why doesn't & work the way I want it to?
65acb1b1 418
40d4dc3e 419=item *
65acb1b1 420
40d4dc3e 421How do I multiply matrices?
65acb1b1 422
40d4dc3e 423=item *
65acb1b1 424
40d4dc3e 425How do I perform an operation on a series of integers?
65acb1b1 426
40d4dc3e 427=item *
65acb1b1 428
40d4dc3e 429How can I output Roman numerals?
65acb1b1 430
40d4dc3e 431=item *
65acb1b1 432
40d4dc3e 433Why aren't my random numbers random?
65acb1b1 434
40d4dc3e 435=item *
65acb1b1 436
881bdbd4
JH
437How do I get a random number between X and Y?
438
439=item *
440
5cd0b561 441How do I find the day or week of the year?
d92eb7b0 442
40d4dc3e 443=item *
65acb1b1 444
40d4dc3e 445How do I find the current century or millennium?
65acb1b1 446
40d4dc3e 447=item *
65acb1b1 448
40d4dc3e 449How can I compare two dates and find the difference?
65acb1b1 450
40d4dc3e 451=item *
65acb1b1 452
40d4dc3e 453How can I take a string and turn it into epoch seconds?
65acb1b1 454
40d4dc3e 455=item *
65acb1b1 456
40d4dc3e 457How can I find the Julian Day?
65acb1b1 458
40d4dc3e 459=item *
65acb1b1 460
40d4dc3e 461How do I find yesterday's date?
65acb1b1 462
40d4dc3e 463=item *
65acb1b1 464
8d2e243f 465Does Perl have a Year 2000 or 2038 problem? Is Perl Y2K compliant?
65acb1b1 466
40d4dc3e 467=item *
65acb1b1 468
40d4dc3e 469How do I validate input?
65acb1b1 470
40d4dc3e 471=item *
65acb1b1 472
40d4dc3e 473How do I unescape a string?
65acb1b1 474
40d4dc3e 475=item *
65acb1b1 476
40d4dc3e
RB
477How do I remove consecutive pairs of characters?
478
479=item *
480
481How do I expand function calls in a string?
482
483=item *
484
485How do I find matching/nesting anything?
486
487=item *
488
489How do I reverse a string?
490
491=item *
492
493How do I expand tabs in a string?
494
495=item *
496
497How do I reformat a paragraph?
498
499=item *
500
49d635f9 501How can I access or change N characters of a string?
40d4dc3e
RB
502
503=item *
504
505How do I change the Nth occurrence of something?
506
507=item *
508
509How can I count the number of occurrences of a substring within a string?
510
511=item *
512
513How do I capitalize all the words on one line?
514
515=item *
516
c905bd84 517How can I split a [character]-delimited string except when inside [character]?
65acb1b1 518
40d4dc3e
RB
519=item *
520
521How do I strip blank space from the beginning/end of a string?
522
523=item *
524
525How do I pad a string with blanks or pad a number with zeroes?
526
527=item *
528
529How do I extract selected columns from a string?
530
531=item *
532
533How do I find the soundex value of a string?
534
535=item *
536
537How can I expand variables in text strings?
538
539=item *
540
541What's wrong with always quoting "$vars"?
542
543=item *
544
04d666b1 545Why don't my E<lt>E<lt>HERE documents work?
40d4dc3e
RB
546
547=item *
548
549What is the difference between a list and an array?
550
551=item *
552
b68463f7 553What is the difference between $array[1] and @array[1]?
40d4dc3e
RB
554
555=item *
65acb1b1 556
40d4dc3e 557How can I remove duplicate elements from a list or array?
65acb1b1 558
40d4dc3e 559=item *
65acb1b1 560
ae3d0b9f 561How can I tell whether a certain element is contained in a list or array?
65acb1b1 562
40d4dc3e 563=item *
65acb1b1 564
40d4dc3e 565How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
65acb1b1 566
40d4dc3e 567=item *
65acb1b1 568
40d4dc3e 569How do I test whether two arrays or hashes are equal?
65acb1b1 570
40d4dc3e 571=item *
65acb1b1 572
40d4dc3e 573How do I find the first array element for which a condition is true?
65acb1b1 574
40d4dc3e 575=item *
65acb1b1 576
40d4dc3e 577How do I handle linked lists?
65acb1b1 578
40d4dc3e 579=item *
65acb1b1 580
40d4dc3e 581How do I handle circular lists?
65acb1b1 582
40d4dc3e 583=item *
65acb1b1 584
40d4dc3e 585How do I shuffle an array randomly?
65acb1b1 586
40d4dc3e 587=item *
65acb1b1 588
40d4dc3e 589How do I process/modify each element of an array?
65acb1b1 590
40d4dc3e 591=item *
65acb1b1 592
40d4dc3e 593How do I select a random element from an array?
65acb1b1 594
40d4dc3e 595=item *
65acb1b1 596
40d4dc3e 597How do I permute N elements of a list?
65acb1b1 598
40d4dc3e 599=item *
65acb1b1 600
40d4dc3e 601How do I sort an array by (anything)?
65acb1b1 602
40d4dc3e 603=item *
65acb1b1 604
40d4dc3e 605How do I manipulate arrays of bits?
65acb1b1 606
40d4dc3e 607=item *
65acb1b1 608
b68463f7 609Why does defined() return true on empty arrays and hashes?
65acb1b1 610
40d4dc3e 611=item *
65acb1b1 612
40d4dc3e 613How do I process an entire hash?
65acb1b1 614
40d4dc3e 615=item *
65acb1b1 616
109f0441
SM
617How do I merge two hashes?
618
619=item *
620
40d4dc3e 621What happens if I add or remove keys from a hash while iterating over it?
65acb1b1 622
40d4dc3e 623=item *
65acb1b1 624
40d4dc3e 625How do I look up a hash element by value?
65acb1b1 626
40d4dc3e 627=item *
65acb1b1 628
40d4dc3e 629How can I know how many entries are in a hash?
65acb1b1 630
40d4dc3e 631=item *
65acb1b1 632
40d4dc3e 633How do I sort a hash (optionally by value instead of key)?
65acb1b1 634
40d4dc3e 635=item *
65acb1b1 636
40d4dc3e 637How can I always keep my hash sorted?
65acb1b1 638
40d4dc3e 639=item *
65acb1b1 640
40d4dc3e 641What's the difference between "delete" and "undef" with hashes?
65acb1b1 642
40d4dc3e 643=item *
65acb1b1 644
40d4dc3e 645Why don't my tied hashes make the defined/exists distinction?
65acb1b1 646
40d4dc3e
RB
647=item *
648
b68463f7 649How do I reset an each() operation part-way through?
40d4dc3e
RB
650
651=item *
652
653How can I get the unique keys from two hashes?
654
655=item *
656
657How can I store a multidimensional array in a DBM file?
658
659=item *
660
661How can I make my hash remember the order I put elements into it?
662
663=item *
664
665Why does passing a subroutine an undefined element in a hash create it?
666
667=item *
668
669How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?
670
671=item *
672
673How can I use a reference as a hash key?
674
675=item *
676
ebeb11a2 677How can I check if a key exists in a multilevel hash?
a1bbdff3 678
679=item *
680
40d4dc3e
RB
681How do I handle binary data correctly?
682
683=item *
684
685How do I determine whether a scalar is a number/whole/integer/float?
686
687=item *
688
689How do I keep persistent data across program calls?
690
691=item *
692
693How do I print out or copy a recursive data structure?
694
695=item *
696
697How do I define methods for every class/object?
698
699=item *
700
701How do I verify a credit card checksum?
702
703=item *
704
705How do I pack arrays of doubles or floats for XS code?
65acb1b1
TC
706
707=back
708
709
40d4dc3e 710=head2 L<perlfaq5>: Files and Formats
68dc0745 711
ae3d0b9f 712I/O and the "f" issues: filehandles, flushing, formats, and footers.
68dc0745 713
65acb1b1
TC
714=over 4
715
40d4dc3e
RB
716=item *
717
718How do I flush/unbuffer an output filehandle? Why must I do this?
719
720=item *
721
e573f903 722How do I change, delete, or insert a line in a file, or append to the beginning of a file?
40d4dc3e
RB
723
724=item *
725
726How do I count the number of lines in a file?
727
728=item *
729
8d2e243f 730How do I delete the last N lines from a file?
731
732=item *
733
49d635f9
RGS
734How can I use Perl's C<-i> option from within a program?
735
736=item *
737
7678cced
RGS
738How can I copy a file?
739
740=item *
741
40d4dc3e
RB
742How do I make a temporary file name?
743
744=item *
745
746How can I manipulate fixed-record-length files?
747
748=item *
65acb1b1 749
40d4dc3e 750How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles?
65acb1b1 751
40d4dc3e 752=item *
65acb1b1 753
40d4dc3e 754How can I use a filehandle indirectly?
65acb1b1 755
40d4dc3e 756=item *
65acb1b1 757
b68463f7 758How can I set up a footer format to be used with write()?
65acb1b1 759
40d4dc3e 760=item *
65acb1b1 761
b68463f7 762How can I write() into a string?
65acb1b1 763
40d4dc3e 764=item *
65acb1b1 765
c195e131
RGS
766How can I open a filehandle to a string?
767
768=item *
769
40d4dc3e 770How can I output my numbers with commas added?
65acb1b1 771
40d4dc3e 772=item *
65acb1b1 773
40d4dc3e 774How can I translate tildes (~) in a filename?
65acb1b1 775
40d4dc3e 776=item *
65acb1b1 777
40d4dc3e 778How come when I open a file read-write it wipes it out?
65acb1b1 779
40d4dc3e 780=item *
65acb1b1 781
04d666b1 782Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
65acb1b1 783
40d4dc3e 784=item *
65acb1b1 785
b68463f7 786Is there a leak/bug in glob()?
65acb1b1 787
40d4dc3e 788=item *
65acb1b1 789
40d4dc3e 790How can I open a file with a leading ">" or trailing blanks?
65acb1b1 791
40d4dc3e 792=item *
65acb1b1 793
40d4dc3e 794How can I reliably rename a file?
65acb1b1 795
40d4dc3e 796=item *
65acb1b1 797
40d4dc3e 798How can I lock a file?
d92eb7b0 799
40d4dc3e 800=item *
65acb1b1 801
b68463f7 802Why can't I just open(FH, "E<gt>file.lock")?
65acb1b1 803
40d4dc3e 804=item *
65acb1b1 805
a1bbdff3 806I still don't get locking. I just want to increment the number in the file. How can I do this?
65acb1b1 807
40d4dc3e 808=item *
65acb1b1 809
a1bbdff3 810All I want to do is append a small amount of text to the end of a file. Do I still have to use locking?
05caf3a7
GJ
811
812=item *
813
40d4dc3e 814How do I randomly update a binary file?
65acb1b1 815
40d4dc3e 816=item *
65acb1b1 817
40d4dc3e 818How do I get a file's timestamp in perl?
65acb1b1 819
40d4dc3e 820=item *
65acb1b1 821
40d4dc3e 822How do I set a file's timestamp in perl?
65acb1b1 823
40d4dc3e
RB
824=item *
825
826How do I print to more than one file at once?
827
828=item *
829
830How can I read in an entire file all at once?
831
832=item *
833
834How can I read in a file by paragraphs?
835
836=item *
837
838How can I read a single character from a file? From the keyboard?
839
840=item *
841
842How can I tell whether there's a character waiting on a filehandle?
843
844=item *
845
846How do I do a C<tail -f> in perl?
847
848=item *
849
b68463f7 850How do I dup() a filehandle in Perl?
40d4dc3e
RB
851
852=item *
853
854How do I close a file descriptor by number?
855
856=item *
857
c98c5709 858Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work?
40d4dc3e
RB
859
860=item *
861
b68463f7 862Why doesn't glob("*.*") get all the files?
40d4dc3e
RB
863
864=item *
865
866Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl?
867
868=item *
869
870How do I select a random line from a file?
871
872=item *
873
874Why do I get weird spaces when I print an array of lines?
65acb1b1 875
109f0441
SM
876=item *
877
878How do I traverse a directory tree?
879
880=item *
881
882How do I delete a directory tree?
883
884=item *
885
886How do I copy an entire directory?
887
65acb1b1
TC
888=back
889
890
ae3d0b9f 891=head2 L<perlfaq6>: Regular Expressions
68dc0745 892
b68463f7 893This section is surprisingly small because the rest of the FAQ is littered with answers involving regular expressions. For example, decoding a URL and checking whether something is a number are handled with regular expressions, but those answers are found elsewhere in this document (in L<perlfaq9>: "How do I decode or create those %-encodings on the web" and L<perlfaq4>: "How do I determine whether a scalar is a number/whole/integer/float", to be precise).
68dc0745 894
65acb1b1
TC
895=over 4
896
40d4dc3e
RB
897=item *
898
899How can I hope to use regular expressions without creating illegible and unmaintainable code?
900
901=item *
902
a1bbdff3 903I'm having trouble matching over more than one line. What's wrong?
40d4dc3e
RB
904
905=item *
906
907How can I pull out lines between two patterns that are themselves on different lines?
908
909=item *
910
109f0441
SM
911How do I match XML, HTML, or other nasty, ugly things with a regex?
912
913=item *
914
b68463f7 915I put a regular expression into $/ but it didn't work. What's wrong?
40d4dc3e
RB
916
917=item *
918
a3cdda95 919How do I substitute case-insensitively on the LHS while preserving case on the RHS?
40d4dc3e
RB
920
921=item *
922
923How can I make C<\w> match national character sets?
924
925=item *
926
927How can I match a locale-smart version of C</[a-zA-Z]/>?
65acb1b1 928
40d4dc3e 929=item *
65acb1b1 930
40d4dc3e 931How can I quote a variable to use in a regex?
65acb1b1 932
40d4dc3e 933=item *
65acb1b1 934
40d4dc3e 935What is C</o> really for?
65acb1b1 936
40d4dc3e 937=item *
65acb1b1 938
c905bd84 939How do I use a regular expression to strip C-style comments from a file?
65acb1b1 940
40d4dc3e 941=item *
65acb1b1 942
40d4dc3e 943Can I use Perl regular expressions to match balanced text?
65acb1b1 944
40d4dc3e 945=item *
65acb1b1 946
a1bbdff3 947What does it mean that regexes are greedy? How can I get around it?
65acb1b1 948
40d4dc3e 949=item *
65acb1b1 950
40d4dc3e 951How do I process each word on each line?
65acb1b1 952
40d4dc3e 953=item *
65acb1b1 954
40d4dc3e 955How can I print out a word-frequency or line-frequency summary?
65acb1b1 956
40d4dc3e 957=item *
65acb1b1 958
40d4dc3e 959How can I do approximate matching?
65acb1b1 960
40d4dc3e 961=item *
65acb1b1 962
40d4dc3e 963How do I efficiently match many regular expressions at once?
65acb1b1 964
40d4dc3e 965=item *
65acb1b1 966
40d4dc3e 967Why don't word-boundary searches with C<\b> work for me?
65acb1b1 968
40d4dc3e 969=item *
65acb1b1 970
b68463f7 971Why does using $&, $`, or $' slow my program down?
40d4dc3e
RB
972
973=item *
974
975What good is C<\G> in a regular expression?
976
977=item *
978
a1bbdff3 979Are Perl regexes DFAs or NFAs? Are they POSIX compliant?
40d4dc3e
RB
980
981=item *
982
c98c5709 983What's wrong with using grep in a void context?
40d4dc3e
RB
984
985=item *
986
987How can I match strings with multibyte characters?
988
989=item *
990
ac9dac7f 991How do I match a regular expression that's in a variable?
65acb1b1
TC
992
993=back
994
995
40d4dc3e 996=head2 L<perlfaq7>: General Perl Language Issues
68dc0745 997
c98c5709 998General Perl language issues that don't clearly fit into any of the other sections.
68dc0745 999
65acb1b1
TC
1000=over 4
1001
40d4dc3e
RB
1002=item *
1003
1004Can I get a BNF/yacc/RE for the Perl language?
1005
1006=item *
1007
1008What are all these $@%&* punctuation signs, and how do I know when to use them?
1009
1010=item *
1011
1012Do I always/never have to quote my strings or use semicolons and commas?
1013
1014=item *
1015
1016How do I skip some return values?
1017
1018=item *
1019
1020How do I temporarily block warnings?
1021
1022=item *
1023
1024What's an extension?
1025
1026=item *
1027
1028Why do Perl operators have different precedence than C operators?
1029
1030=item *
1031
1032How do I declare/create a structure?
1033
1034=item *
1035
1036How do I create a module?
1037
1038=item *
1039
c195e131
RGS
1040How do I adopt or take over a module already on CPAN?
1041
1042=item *
1043
40d4dc3e
RB
1044How do I create a class?
1045
1046=item *
1047
1048How can I tell if a variable is tainted?
1049
1050=item *
1051
1052What's a closure?
1053
1054=item *
1055
1056What is variable suicide and how can I prevent it?
1057
1058=item *
1059
1060How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
65acb1b1 1061
40d4dc3e 1062=item *
65acb1b1 1063
40d4dc3e 1064How do I create a static variable?
65acb1b1 1065
40d4dc3e 1066=item *
65acb1b1 1067
40d4dc3e 1068What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
65acb1b1 1069
40d4dc3e 1070=item *
65acb1b1 1071
40d4dc3e 1072How can I access a dynamic variable while a similarly named lexical is in scope?
65acb1b1 1073
40d4dc3e 1074=item *
65acb1b1 1075
40d4dc3e 1076What's the difference between deep and shallow binding?
65acb1b1 1077
40d4dc3e 1078=item *
65acb1b1 1079
b68463f7 1080Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right?
65acb1b1 1081
40d4dc3e 1082=item *
65acb1b1 1083
40d4dc3e 1084How do I redefine a builtin function, operator, or method?
65acb1b1 1085
40d4dc3e 1086=item *
65acb1b1 1087
b68463f7 1088What's the difference between calling a function as &foo and foo()?
65acb1b1 1089
40d4dc3e 1090=item *
65acb1b1 1091
40d4dc3e 1092How do I create a switch or case statement?
65acb1b1 1093
40d4dc3e 1094=item *
65acb1b1 1095
49d635f9 1096How can I catch accesses to undefined variables, functions, or methods?
65acb1b1 1097
40d4dc3e 1098=item *
65acb1b1 1099
40d4dc3e 1100Why can't a method included in this same file be found?
65acb1b1 1101
40d4dc3e 1102=item *
65acb1b1 1103
109f0441 1104How can I find out my current or calling package?
65acb1b1 1105
40d4dc3e 1106=item *
65acb1b1 1107
8d2e243f 1108How can I comment out a large block of Perl code?
65acb1b1 1109
40d4dc3e 1110=item *
65acb1b1 1111
40d4dc3e 1112How do I clear a package?
65acb1b1 1113
40d4dc3e
RB
1114=item *
1115
1116How can I use a variable as a variable name?
d92eb7b0 1117
5cd0b561
RGS
1118=item *
1119
1120What does "bad interpreter" mean?
1121
65acb1b1
TC
1122=back
1123
1124
40d4dc3e 1125=head2 L<perlfaq8>: System Interaction
68dc0745 1126
c98c5709 1127This section of the Perl FAQ covers questions involving operating system interaction. Topics include interprocess communication (IPC), control over the user-interface (keyboard, screen and pointing devices), and most anything else not related to data manipulation. Read the FAQs and documentation specific to the port of perl to your operating system (eg, L<perlvms>, L<perlplan9>, ...). These should contain more detailed information on the vagaries of your perl.
68dc0745 1128
65acb1b1
TC
1129=over 4
1130
40d4dc3e
RB
1131=item *
1132
1133How do I find out which operating system I'm running under?
1134
1135=item *
1136
b68463f7 1137How come exec() doesn't return?
40d4dc3e
RB
1138
1139=item *
1140
1141How do I do fancy stuff with the keyboard/screen/mouse?
1142
1143=item *
1144
1145How do I print something out in color?
1146
1147=item *
1148
1149How do I read just one key without waiting for a return key?
1150
1151=item *
1152
1153How do I check whether input is ready on the keyboard?
1154
1155=item *
1156
1157How do I clear the screen?
1158
1159=item *
1160
1161How do I get the screen size?
1162
1163=item *
1164
1165How do I ask the user for a password?
1166
1167=item *
1168
1169How do I read and write the serial port?
1170
1171=item *
1172
1173How do I decode encrypted password files?
1174
1175=item *
1176
1177How do I start a process in the background?
1178
1179=item *
1180
1181How do I trap control characters/signals?
1182
1183=item *
1184
1185How do I modify the shadow password file on a Unix system?
1186
1187=item *
1188
1189How do I set the time and date?
1190
1191=item *
1192
b68463f7 1193How can I sleep() or alarm() for under a second?
40d4dc3e
RB
1194
1195=item *
1196
1197How can I measure time under a second?
1198
1199=item *
1200
b68463f7 1201How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
40d4dc3e
RB
1202
1203=item *
1204
1205Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
65acb1b1 1206
40d4dc3e 1207=item *
65acb1b1 1208
40d4dc3e 1209How can I call my system's unique C functions from Perl?
65acb1b1 1210
40d4dc3e 1211=item *
65acb1b1 1212
b68463f7 1213Where do I get the include files to do ioctl() or syscall()?
65acb1b1 1214
40d4dc3e 1215=item *
65acb1b1 1216
40d4dc3e 1217Why do setuid perl scripts complain about kernel problems?
65acb1b1 1218
40d4dc3e 1219=item *
65acb1b1 1220
40d4dc3e 1221How can I open a pipe both to and from a command?
65acb1b1 1222
40d4dc3e 1223=item *
65acb1b1 1224
b68463f7 1225Why can't I get the output of a command with system()?
65acb1b1 1226
40d4dc3e 1227=item *
65acb1b1 1228
40d4dc3e 1229How can I capture STDERR from an external command?
65acb1b1 1230
40d4dc3e 1231=item *
65acb1b1 1232
b68463f7 1233Why doesn't open() return an error when a pipe open fails?
65acb1b1 1234
40d4dc3e 1235=item *
65acb1b1 1236
40d4dc3e 1237What's wrong with using backticks in a void context?
65acb1b1 1238
40d4dc3e 1239=item *
65acb1b1 1240
40d4dc3e 1241How can I call backticks without shell processing?
65acb1b1 1242
40d4dc3e 1243=item *
65acb1b1 1244
40d4dc3e 1245Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
65acb1b1 1246
40d4dc3e 1247=item *
65acb1b1 1248
40d4dc3e 1249How can I convert my shell script to perl?
65acb1b1 1250
40d4dc3e 1251=item *
65acb1b1 1252
40d4dc3e 1253Can I use perl to run a telnet or ftp session?
65acb1b1 1254
40d4dc3e 1255=item *
65acb1b1 1256
40d4dc3e 1257How can I write expect in Perl?
65acb1b1 1258
40d4dc3e 1259=item *
65acb1b1 1260
40d4dc3e 1261Is there a way to hide perl's command line from programs such as "ps"?
65acb1b1 1262
40d4dc3e 1263=item *
65acb1b1 1264
b68463f7 1265I {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?
65acb1b1 1266
40d4dc3e 1267=item *
65acb1b1 1268
40d4dc3e 1269How do I close a process's filehandle without waiting for it to complete?
65acb1b1 1270
40d4dc3e 1271=item *
65acb1b1 1272
40d4dc3e 1273How do I fork a daemon process?
65acb1b1 1274
40d4dc3e 1275=item *
65acb1b1 1276
40d4dc3e 1277How do I find out if I'm running interactively or not?
65acb1b1 1278
40d4dc3e 1279=item *
65acb1b1 1280
40d4dc3e 1281How do I timeout a slow event?
65acb1b1 1282
40d4dc3e 1283=item *
65acb1b1 1284
40d4dc3e 1285How do I set CPU limits?
65acb1b1 1286
40d4dc3e 1287=item *
65acb1b1 1288
40d4dc3e 1289How do I avoid zombies on a Unix system?
65acb1b1 1290
40d4dc3e 1291=item *
65acb1b1 1292
40d4dc3e 1293How do I use an SQL database?
65acb1b1 1294
40d4dc3e 1295=item *
65acb1b1 1296
b68463f7 1297How do I make a system() exit on control-C?
65acb1b1 1298
40d4dc3e 1299=item *
65acb1b1 1300
40d4dc3e
RB
1301How do I open a file without blocking?
1302
1303=item *
1304
c98c5709
RGS
1305How do I tell the difference between errors from the shell and perl?
1306
1307=item *
1308
40d4dc3e
RB
1309How do I install a module from CPAN?
1310
1311=item *
1312
1313What's the difference between require and use?
1314
1315=item *
1316
1317How do I keep my own module/library directory?
1318
1319=item *
1320
1321How do I add the directory my program lives in to the module/library search path?
1322
1323=item *
1324
b68463f7 1325How do I add a directory to my include path (@INC) at runtime?
40d4dc3e
RB
1326
1327=item *
1328
b68463f7 1329What is socket.ph and where do I get it?
65acb1b1
TC
1330
1331=back
1332
1333
40d4dc3e 1334=head2 L<perlfaq9>: Networking
68dc0745 1335
ae3d0b9f 1336Networking, the internet, and a few on the web.
68dc0745 1337
65acb1b1
TC
1338=over 4
1339
40d4dc3e 1340=item *
65acb1b1 1341
ae3d0b9f
JH
1342What is the correct form of response from a CGI script?
1343
1344=item *
1345
a1bbdff3 1346My CGI script runs from the command line but not the browser. (500 Server Error)
65acb1b1 1347
40d4dc3e 1348=item *
65acb1b1 1349
40d4dc3e 1350How can I get better error messages from a CGI program?
65acb1b1 1351
40d4dc3e 1352=item *
65acb1b1 1353
40d4dc3e 1354How do I remove HTML from a string?
65acb1b1 1355
40d4dc3e 1356=item *
65acb1b1 1357
40d4dc3e 1358How do I extract URLs?
65acb1b1 1359
40d4dc3e 1360=item *
65acb1b1 1361
40d4dc3e 1362How do I download a file from the user's machine? How do I open a file on another machine?
65acb1b1 1363
40d4dc3e 1364=item *
65acb1b1 1365
e573f903 1366How do I make an HTML pop-up menu with Perl?
65acb1b1 1367
40d4dc3e 1368=item *
65acb1b1 1369
40d4dc3e 1370How do I fetch an HTML file?
65acb1b1 1371
40d4dc3e 1372=item *
65acb1b1 1373
40d4dc3e 1374How do I automate an HTML form submission?
65acb1b1 1375
40d4dc3e 1376=item *
65acb1b1 1377
40d4dc3e 1378How do I decode or create those %-encodings on the web?
65acb1b1 1379
40d4dc3e 1380=item *
65acb1b1 1381
40d4dc3e 1382How do I redirect to another page?
65acb1b1 1383
40d4dc3e 1384=item *
65acb1b1 1385
40d4dc3e 1386How do I put a password on my web pages?
65acb1b1 1387
40d4dc3e 1388=item *
65acb1b1 1389
b68463f7 1390How do I edit my .htpasswd and .htgroup files with Perl?
65acb1b1 1391
40d4dc3e
RB
1392=item *
1393
1394How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
1395
1396=item *
1397
1398How do I parse a mail header?
1399
1400=item *
1401
1402How do I decode a CGI form?
1403
1404=item *
65acb1b1 1405
40d4dc3e
RB
1406How do I check a valid mail address?
1407
1408=item *
1409
1410How do I decode a MIME/BASE64 string?
1411
1412=item *
1413
1414How do I return the user's mail address?
1415
1416=item *
1417
1418How do I send mail?
1419
1420=item *
1421
ae3d0b9f
JH
1422How do I use MIME to make an attachment to a mail message?
1423
1424=item *
1425
40d4dc3e
RB
1426How do I read mail?
1427
1428=item *
1429
a05e4845 1430How do I find out my hostname, domainname, or IP address?
40d4dc3e
RB
1431
1432=item *
1433
1434How do I fetch a news article or the active newsgroups?
1435
1436=item *
1437
1438How do I fetch/put an FTP file?
1439
1440=item *
1441
1442How can I do RPC in Perl?
65acb1b1 1443
68dc0745 1444=back