note strict/lax version requirements in documentation
[p5sagit/p5-mst-13.2.git] / pod / perlfaq.pod
CommitLineData
68dc0745 1=head1 NAME
2
ac9dac7f 3perlfaq - frequently asked questions about Perl
68dc0745 4
5=head1 DESCRIPTION
6
fcd1fd07 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 11=head2 Where to get the perlfaq
12
fcd1fd07 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
fcd1fd07 19Besides your local system, you can find the perlfaq on the web, including
20at http://perldoc.perl.org/ .
197aec24 21
fcd1fd07 22The perlfaq is an evolving document and you can read the latest version
23at http://faq.perl.org/ . The perlfaq-workers periodically post extracts
24of the latest perlfaq to comp.lang.perl.misc.
197aec24 25
8d2e243f 26You can view the source tree at https://github.com/briandfoy/perlfaq
27(which is outside of the main Perl source tree). The git repository
28notes all changes to the FAQ and holds the latest version of the
29working documents and may vary significantly from the version
30distributed with the latest version of Perl. Check the repository
31before sending your corrections.
197aec24 32
fcd1fd07 33=head2 How to contribute to the perlfaq
197aec24 34
ac9dac7f 35You can mail corrections, additions, and suggestions to
fcd1fd07 36C<< <perlfaq-workers AT perl DOT org> >>. The perlfaq volunteers use this
37address to coordinate their efforts and track the perlfaq development.
38They appreciate your contributions to the FAQ but do not have time to
39provide individual help, so don't use this address to ask FAQs.
197aec24 40
fcd1fd07 41The perlfaq server posts extracts of the perlfaq to that newsgroup every
426 hours (or so), and the community of volunteers reviews and updates the
43answers. If you'd like to help review and update the answers, check out
44comp.lang.perl.misc.
197aec24 45
109f0441 46You can also fork the git repository for the perlfaq and send a pull
47request so the main repository can pull your changes. The repository
48is at:
49
8d2e243f 50 https://github.com/briandfoy/perlfaq
109f0441 51
fcd1fd07 52=head2 What will happen if you mail your Perl programming problems to the authors?
197aec24 53
fcd1fd07 54The perlfaq-workers like to keep all traffic on the perlfaq-workers list
55so that everyone can see the work being done (and the work that needs to
56be done). The mailing list serves as an official record. If you email the
57authors or maintainers directly, you'll probably get a reply asking you
58to post to the mailing list. If you don't get a reply, it probably means
59that the person never saw the message or didn't have time to deal with
60it. Posting to the list allows the volunteers with time to deal with it
61when others are busy.
197aec24 62
fcd1fd07 63If you have a question that isn't in the FAQ and you would like help with
64it, try the resources in L<perlfaq2>.
197aec24 65
fcd1fd07 66=head1 CREDITS
197aec24 67
fcd1fd07 68Tom Christiansen wrote the original perlfaq then expanded it with the
f12f5f55 69help of Nat Torkington. The perlfaq-workers maintain current document
8d2e243f 70and the dezinens of comp.lang.perl.misc regularly review and update the
fcd1fd07 71FAQ. Several people have contributed answers, corrections, and comments,
72and the perlfaq notes those contributions wherever appropriate.
197aec24 73
fcd1fd07 74=head1 AUTHOR AND COPYRIGHT
197aec24 75
8d2e243f 76Tom Christainsen wrote the original version of this document.
fcd1fd07 77brian d foy C<< <bdfoy@cpan.org> >> wrote this version. See the
78individual perlfaq documents for additional copyright information.
197aec24 79
fcd1fd07 80This document is available under the same terms as Perl itself. Code
81examples in all the perlfaq documents are in the public domain. Use
8d2e243f 82them as you see fit (and at your own risk with no warranty from anyone).
197aec24 83
84=head1 Table of Contents
68dc0745 85
5cd0b561 86=over 4
87
88=item perlfaq - this document
89
90=item perlfaq1 - General Questions About Perl
91
92=item perlfaq2 - Obtaining and Learning about Perl
93
94=item perlfaq3 - Programming Tools
95
96=item perlfaq4 - Data Manipulation
97
98=item perlfaq5 - Files and Formats
99
100=item perlfaq6 - Regular Expressions
101
102=item perlfaq7 - General Perl Language Issues
68dc0745 103
5cd0b561 104=item perlfaq8 - System Interaction
105
106=item perlfaq9 - Networking
107
5cd0b561 108=back
109
5cd0b561 110=head1 The Questions
68dc0745 111
40d4dc3e 112=head2 L<perlfaq1>: General Questions About Perl
68dc0745 113
ae3d0b9f 114Very general, high-level questions about Perl.
68dc0745 115
65acb1b1 116=over 4
117
40d4dc3e 118=item *
119
120What is Perl?
121
122=item *
123
124Who supports Perl? Who develops it? Why is it free?
125
126=item *
127
128Which version of Perl should I use?
129
130=item *
131
e9d185f8 132What are Perl 4, Perl 5, or Perl 6?
40d4dc3e 133
134=item *
135
322be77c 136What was Ponie?
c98c5709 137
138=item *
139
e9d185f8 140What is Perl 6?
65acb1b1 141
40d4dc3e 142=item *
65acb1b1 143
40d4dc3e 144How stable is Perl?
65acb1b1 145
40d4dc3e 146=item *
65acb1b1 147
40d4dc3e 148Is Perl difficult to learn?
65acb1b1 149
40d4dc3e 150=item *
65acb1b1 151
40d4dc3e 152How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
65acb1b1 153
40d4dc3e 154=item *
65acb1b1 155
40d4dc3e 156Can I do [task] in Perl?
65acb1b1 157
40d4dc3e 158=item *
65acb1b1 159
40d4dc3e 160When shouldn't I program in Perl?
65acb1b1 161
40d4dc3e 162=item *
65acb1b1 163
40d4dc3e 164What's the difference between "perl" and "Perl"?
65acb1b1 165
40d4dc3e 166=item *
65acb1b1 167
40d4dc3e 168Is it a Perl program or a Perl script?
169
170=item *
171
172What is a JAPH?
173
174=item *
175
176Where can I get a list of Larry Wall witticisms?
177
178=item *
179
ac9dac7f 180How can I convince others to use Perl?
65acb1b1 181
182=back
183
184
40d4dc3e 185=head2 L<perlfaq2>: Obtaining and Learning about Perl
68dc0745 186
c98c5709 187Where to find source and documentation for Perl, support, and related matters.
68dc0745 188
65acb1b1 189=over 4
190
40d4dc3e 191=item *
192
b68463f7 193What machines support perl? Where do I get it?
40d4dc3e 194
195=item *
196
b68463f7 197How can I get a binary version of perl?
65acb1b1 198
40d4dc3e 199=item *
65acb1b1 200
b68463f7 201I don't have a C compiler. How can I build my own Perl interpreter?
65acb1b1 202
40d4dc3e 203=item *
65acb1b1 204
b68463f7 205I copied the perl binary from one machine to another, but scripts don't work.
65acb1b1 206
40d4dc3e 207=item *
65acb1b1 208
40d4dc3e 209I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
65acb1b1 210
40d4dc3e 211=item *
65acb1b1 212
40d4dc3e 213What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
65acb1b1 214
40d4dc3e 215=item *
65acb1b1 216
40d4dc3e 217Is there an ISO or ANSI certified version of Perl?
65acb1b1 218
40d4dc3e 219=item *
65acb1b1 220
40d4dc3e 221Where can I get information on Perl?
65acb1b1 222
40d4dc3e 223=item *
65acb1b1 224
40d4dc3e 225What are the Perl newsgroups on Usenet? Where do I post questions?
65acb1b1 226
40d4dc3e 227=item *
65acb1b1 228
40d4dc3e 229Where should I post source code?
65acb1b1 230
40d4dc3e 231=item *
232
233Perl Books
234
235=item *
236
fcd1fd07 237Which magazines have Perl content?
40d4dc3e 238
239=item *
240
241What mailing lists are there for Perl?
242
243=item *
244
fcd1fd07 245Where are the archives for comp.lang.perl.misc?
40d4dc3e 246
247=item *
248
b68463f7 249Where can I buy a commercial version of perl?
40d4dc3e 250
251=item *
252
253Where do I send bug reports?
254
255=item *
256
ae3d0b9f 257What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org?
65acb1b1 258
259=back
260
261
40d4dc3e 262=head2 L<perlfaq3>: Programming Tools
68dc0745 263
264Programmer tools and programming support.
265
65acb1b1 266=over 4
267
40d4dc3e 268=item *
269
270How do I do (anything)?
271
272=item *
273
274How can I use Perl interactively?
275
276=item *
65acb1b1 277
40d4dc3e 278Is there a Perl shell?
65acb1b1 279
40d4dc3e 280=item *
65acb1b1 281
49d635f9 282How do I find which modules are installed on my system?
283
284=item *
285
40d4dc3e 286How do I debug my Perl programs?
65acb1b1 287
40d4dc3e 288=item *
65acb1b1 289
40d4dc3e 290How do I profile my Perl programs?
65acb1b1 291
40d4dc3e 292=item *
65acb1b1 293
40d4dc3e 294How do I cross-reference my Perl programs?
65acb1b1 295
40d4dc3e 296=item *
65acb1b1 297
40d4dc3e 298Is there a pretty-printer (formatter) for Perl?
65acb1b1 299
40d4dc3e 300=item *
65acb1b1 301
40d4dc3e 302Is there a ctags for Perl?
65acb1b1 303
40d4dc3e 304=item *
65acb1b1 305
40d4dc3e 306Is there an IDE or Windows Perl Editor?
65acb1b1 307
40d4dc3e 308=item *
65acb1b1 309
40d4dc3e 310Where can I get Perl macros for vi?
65acb1b1 311
40d4dc3e 312=item *
65acb1b1 313
40d4dc3e 314Where can I get perl-mode for emacs?
65acb1b1 315
40d4dc3e 316=item *
65acb1b1 317
40d4dc3e 318How can I use curses with Perl?
65acb1b1 319
40d4dc3e 320=item *
65acb1b1 321
c195e131 322How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
65acb1b1 323
40d4dc3e 324=item *
65acb1b1 325
40d4dc3e 326How can I make my Perl program run faster?
65acb1b1 327
40d4dc3e 328=item *
65acb1b1 329
40d4dc3e 330How can I make my Perl program take less memory?
331
332=item *
333
49d635f9 334Is it safe to return a reference to local or lexical data?
40d4dc3e 335
336=item *
337
338How can I free an array or hash so my program shrinks?
339
340=item *
341
342How can I make my CGI script more efficient?
343
344=item *
345
346How can I hide the source for my Perl program?
347
348=item *
349
350How can I compile my Perl program into byte code or C?
351
352=item *
353
40d4dc3e 354How can I get C<#!perl> to work on [MS-DOS,NT,...]?
355
356=item *
357
358Can I write useful Perl programs on the command line?
359
360=item *
361
362Why don't Perl one-liners work on my DOS/Mac/VMS system?
363
364=item *
365
366Where can I learn about CGI or Web programming in Perl?
367
368=item *
369
370Where can I learn about object-oriented Perl programming?
371
372=item *
373
b68463f7 374Where can I learn about linking C with Perl?
40d4dc3e 375
376=item *
377
7678cced 378I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
65acb1b1 379
40d4dc3e 380=item *
381
ae3d0b9f 382When I tried to run my script, I got this message. What does it mean?
65acb1b1 383
40d4dc3e 384=item *
385
386What's MakeMaker?
65acb1b1 387
388=back
389
390
40d4dc3e 391=head2 L<perlfaq4>: Data Manipulation
68dc0745 392
c98c5709 393Manipulating numbers, dates, strings, arrays, hashes, and miscellaneous data issues.
68dc0745 394
65acb1b1 395=over 4
396
40d4dc3e 397=item *
398
399Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?
400
401=item *
402
b68463f7 403Why is int() broken?
c98c5709 404
405=item *
406
40d4dc3e 407Why isn't my octal data interpreted correctly?
408
409=item *
410
b68463f7 411Does Perl have a round() function? What about ceil() and floor()? Trig functions?
40d4dc3e 412
413=item *
414
c98c5709 415How do I convert between numeric representations/bases/radixes?
40d4dc3e 416
417=item *
418
419Why doesn't & work the way I want it to?
65acb1b1 420
40d4dc3e 421=item *
65acb1b1 422
40d4dc3e 423How do I multiply matrices?
65acb1b1 424
40d4dc3e 425=item *
65acb1b1 426
40d4dc3e 427How do I perform an operation on a series of integers?
65acb1b1 428
40d4dc3e 429=item *
65acb1b1 430
40d4dc3e 431How can I output Roman numerals?
65acb1b1 432
40d4dc3e 433=item *
65acb1b1 434
40d4dc3e 435Why aren't my random numbers random?
65acb1b1 436
40d4dc3e 437=item *
65acb1b1 438
881bdbd4 439How do I get a random number between X and Y?
440
441=item *
442
5cd0b561 443How do I find the day or week of the year?
d92eb7b0 444
40d4dc3e 445=item *
65acb1b1 446
40d4dc3e 447How do I find the current century or millennium?
65acb1b1 448
40d4dc3e 449=item *
65acb1b1 450
40d4dc3e 451How can I compare two dates and find the difference?
65acb1b1 452
40d4dc3e 453=item *
65acb1b1 454
40d4dc3e 455How can I take a string and turn it into epoch seconds?
65acb1b1 456
40d4dc3e 457=item *
65acb1b1 458
40d4dc3e 459How can I find the Julian Day?
65acb1b1 460
40d4dc3e 461=item *
65acb1b1 462
40d4dc3e 463How do I find yesterday's date?
65acb1b1 464
40d4dc3e 465=item *
65acb1b1 466
8d2e243f 467Does Perl have a Year 2000 or 2038 problem? Is Perl Y2K compliant?
65acb1b1 468
40d4dc3e 469=item *
65acb1b1 470
40d4dc3e 471How do I validate input?
65acb1b1 472
40d4dc3e 473=item *
65acb1b1 474
40d4dc3e 475How do I unescape a string?
65acb1b1 476
40d4dc3e 477=item *
65acb1b1 478
40d4dc3e 479How do I remove consecutive pairs of characters?
480
481=item *
482
483How do I expand function calls in a string?
484
485=item *
486
487How do I find matching/nesting anything?
488
489=item *
490
491How do I reverse a string?
492
493=item *
494
495How do I expand tabs in a string?
496
497=item *
498
499How do I reformat a paragraph?
500
501=item *
502
49d635f9 503How can I access or change N characters of a string?
40d4dc3e 504
505=item *
506
507How do I change the Nth occurrence of something?
508
509=item *
510
511How can I count the number of occurrences of a substring within a string?
512
513=item *
514
515How do I capitalize all the words on one line?
516
517=item *
518
49d635f9 519How can I split a [character] delimited string except when inside [character]?
65acb1b1 520
40d4dc3e 521=item *
522
523How do I strip blank space from the beginning/end of a string?
524
525=item *
526
527How do I pad a string with blanks or pad a number with zeroes?
528
529=item *
530
531How do I extract selected columns from a string?
532
533=item *
534
535How do I find the soundex value of a string?
536
537=item *
538
539How can I expand variables in text strings?
540
541=item *
542
543What's wrong with always quoting "$vars"?
544
545=item *
546
04d666b1 547Why don't my E<lt>E<lt>HERE documents work?
40d4dc3e 548
549=item *
550
551What is the difference between a list and an array?
552
553=item *
554
b68463f7 555What is the difference between $array[1] and @array[1]?
40d4dc3e 556
557=item *
65acb1b1 558
40d4dc3e 559How can I remove duplicate elements from a list or array?
65acb1b1 560
40d4dc3e 561=item *
65acb1b1 562
ae3d0b9f 563How can I tell whether a certain element is contained in a list or array?
65acb1b1 564
40d4dc3e 565=item *
65acb1b1 566
40d4dc3e 567How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
65acb1b1 568
40d4dc3e 569=item *
65acb1b1 570
40d4dc3e 571How do I test whether two arrays or hashes are equal?
65acb1b1 572
40d4dc3e 573=item *
65acb1b1 574
40d4dc3e 575How do I find the first array element for which a condition is true?
65acb1b1 576
40d4dc3e 577=item *
65acb1b1 578
40d4dc3e 579How do I handle linked lists?
65acb1b1 580
40d4dc3e 581=item *
65acb1b1 582
40d4dc3e 583How do I handle circular lists?
65acb1b1 584
40d4dc3e 585=item *
65acb1b1 586
40d4dc3e 587How do I shuffle an array randomly?
65acb1b1 588
40d4dc3e 589=item *
65acb1b1 590
40d4dc3e 591How do I process/modify each element of an array?
65acb1b1 592
40d4dc3e 593=item *
65acb1b1 594
40d4dc3e 595How do I select a random element from an array?
65acb1b1 596
40d4dc3e 597=item *
65acb1b1 598
40d4dc3e 599How do I permute N elements of a list?
65acb1b1 600
40d4dc3e 601=item *
65acb1b1 602
40d4dc3e 603How do I sort an array by (anything)?
65acb1b1 604
40d4dc3e 605=item *
65acb1b1 606
40d4dc3e 607How do I manipulate arrays of bits?
65acb1b1 608
40d4dc3e 609=item *
65acb1b1 610
b68463f7 611Why does defined() return true on empty arrays and hashes?
65acb1b1 612
40d4dc3e 613=item *
65acb1b1 614
40d4dc3e 615How do I process an entire hash?
65acb1b1 616
40d4dc3e 617=item *
65acb1b1 618
109f0441 619How do I merge two hashes?
620
621=item *
622
40d4dc3e 623What happens if I add or remove keys from a hash while iterating over it?
65acb1b1 624
40d4dc3e 625=item *
65acb1b1 626
40d4dc3e 627How do I look up a hash element by value?
65acb1b1 628
40d4dc3e 629=item *
65acb1b1 630
40d4dc3e 631How can I know how many entries are in a hash?
65acb1b1 632
40d4dc3e 633=item *
65acb1b1 634
40d4dc3e 635How do I sort a hash (optionally by value instead of key)?
65acb1b1 636
40d4dc3e 637=item *
65acb1b1 638
40d4dc3e 639How can I always keep my hash sorted?
65acb1b1 640
40d4dc3e 641=item *
65acb1b1 642
40d4dc3e 643What's the difference between "delete" and "undef" with hashes?
65acb1b1 644
40d4dc3e 645=item *
65acb1b1 646
40d4dc3e 647Why don't my tied hashes make the defined/exists distinction?
65acb1b1 648
40d4dc3e 649=item *
650
b68463f7 651How do I reset an each() operation part-way through?
40d4dc3e 652
653=item *
654
655How can I get the unique keys from two hashes?
656
657=item *
658
659How can I store a multidimensional array in a DBM file?
660
661=item *
662
663How can I make my hash remember the order I put elements into it?
664
665=item *
666
667Why does passing a subroutine an undefined element in a hash create it?
668
669=item *
670
671How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?
672
673=item *
674
675How can I use a reference as a hash key?
676
677=item *
678
679How do I handle binary data correctly?
680
681=item *
682
683How do I determine whether a scalar is a number/whole/integer/float?
684
685=item *
686
687How do I keep persistent data across program calls?
688
689=item *
690
691How do I print out or copy a recursive data structure?
692
693=item *
694
695How do I define methods for every class/object?
696
697=item *
698
699How do I verify a credit card checksum?
700
701=item *
702
703How do I pack arrays of doubles or floats for XS code?
65acb1b1 704
705=back
706
707
40d4dc3e 708=head2 L<perlfaq5>: Files and Formats
68dc0745 709
ae3d0b9f 710I/O and the "f" issues: filehandles, flushing, formats, and footers.
68dc0745 711
65acb1b1 712=over 4
713
40d4dc3e 714=item *
715
716How do I flush/unbuffer an output filehandle? Why must I do this?
717
718=item *
719
e573f903 720How do I change, delete, or insert a line in a file, or append to the beginning of a file?
40d4dc3e 721
722=item *
723
724How do I count the number of lines in a file?
725
726=item *
727
8d2e243f 728How do I delete the last N lines from a file?
729
730=item *
731
49d635f9 732How can I use Perl's C<-i> option from within a program?
733
734=item *
735
7678cced 736How can I copy a file?
737
738=item *
739
40d4dc3e 740How do I make a temporary file name?
741
742=item *
743
744How can I manipulate fixed-record-length files?
745
746=item *
65acb1b1 747
40d4dc3e 748How 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 749
40d4dc3e 750=item *
65acb1b1 751
40d4dc3e 752How can I use a filehandle indirectly?
65acb1b1 753
40d4dc3e 754=item *
65acb1b1 755
b68463f7 756How can I set up a footer format to be used with write()?
65acb1b1 757
40d4dc3e 758=item *
65acb1b1 759
b68463f7 760How can I write() into a string?
65acb1b1 761
40d4dc3e 762=item *
65acb1b1 763
c195e131 764How can I open a filehandle to a string?
765
766=item *
767
40d4dc3e 768How can I output my numbers with commas added?
65acb1b1 769
40d4dc3e 770=item *
65acb1b1 771
40d4dc3e 772How can I translate tildes (~) in a filename?
65acb1b1 773
40d4dc3e 774=item *
65acb1b1 775
40d4dc3e 776How come when I open a file read-write it wipes it out?
65acb1b1 777
40d4dc3e 778=item *
65acb1b1 779
04d666b1 780Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
65acb1b1 781
40d4dc3e 782=item *
65acb1b1 783
b68463f7 784Is there a leak/bug in glob()?
65acb1b1 785
40d4dc3e 786=item *
65acb1b1 787
40d4dc3e 788How can I open a file with a leading ">" or trailing blanks?
65acb1b1 789
40d4dc3e 790=item *
65acb1b1 791
40d4dc3e 792How can I reliably rename a file?
65acb1b1 793
40d4dc3e 794=item *
65acb1b1 795
40d4dc3e 796How can I lock a file?
d92eb7b0 797
40d4dc3e 798=item *
65acb1b1 799
b68463f7 800Why can't I just open(FH, "E<gt>file.lock")?
65acb1b1 801
40d4dc3e 802=item *
65acb1b1 803
40d4dc3e 804I still don't get locking. I just want to increment the number in the file. How can I do this?
65acb1b1 805
40d4dc3e 806=item *
65acb1b1 807
f52f3be2 808All 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 809
810=item *
811
40d4dc3e 812How do I randomly update a binary file?
65acb1b1 813
40d4dc3e 814=item *
65acb1b1 815
40d4dc3e 816How do I get a file's timestamp in perl?
65acb1b1 817
40d4dc3e 818=item *
65acb1b1 819
40d4dc3e 820How do I set a file's timestamp in perl?
65acb1b1 821
40d4dc3e 822=item *
823
824How do I print to more than one file at once?
825
826=item *
827
828How can I read in an entire file all at once?
829
830=item *
831
832How can I read in a file by paragraphs?
833
834=item *
835
836How can I read a single character from a file? From the keyboard?
837
838=item *
839
840How can I tell whether there's a character waiting on a filehandle?
841
842=item *
843
844How do I do a C<tail -f> in perl?
845
846=item *
847
b68463f7 848How do I dup() a filehandle in Perl?
40d4dc3e 849
850=item *
851
852How do I close a file descriptor by number?
853
854=item *
855
c98c5709 856Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work?
40d4dc3e 857
858=item *
859
b68463f7 860Why doesn't glob("*.*") get all the files?
40d4dc3e 861
862=item *
863
864Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl?
865
866=item *
867
868How do I select a random line from a file?
869
870=item *
871
872Why do I get weird spaces when I print an array of lines?
65acb1b1 873
109f0441 874=item *
875
876How do I traverse a directory tree?
877
878=item *
879
880How do I delete a directory tree?
881
882=item *
883
884How do I copy an entire directory?
885
65acb1b1 886=back
887
888
ae3d0b9f 889=head2 L<perlfaq6>: Regular Expressions
68dc0745 890
b68463f7 891This 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 892
65acb1b1 893=over 4
894
40d4dc3e 895=item *
896
897How can I hope to use regular expressions without creating illegible and unmaintainable code?
898
899=item *
900
901I'm having trouble matching over more than one line. What's wrong?
902
903=item *
904
905How can I pull out lines between two patterns that are themselves on different lines?
906
907=item *
908
109f0441 909How do I match XML, HTML, or other nasty, ugly things with a regex?
910
911=item *
912
b68463f7 913I put a regular expression into $/ but it didn't work. What's wrong?
40d4dc3e 914
915=item *
916
917How do I substitute case insensitively on the LHS while preserving case on the RHS?
918
919=item *
920
921How can I make C<\w> match national character sets?
922
923=item *
924
925How can I match a locale-smart version of C</[a-zA-Z]/>?
65acb1b1 926
40d4dc3e 927=item *
65acb1b1 928
40d4dc3e 929How can I quote a variable to use in a regex?
65acb1b1 930
40d4dc3e 931=item *
65acb1b1 932
40d4dc3e 933What is C</o> really for?
65acb1b1 934
40d4dc3e 935=item *
65acb1b1 936
40d4dc3e 937How do I use a regular expression to strip C style comments from a file?
65acb1b1 938
40d4dc3e 939=item *
65acb1b1 940
40d4dc3e 941Can I use Perl regular expressions to match balanced text?
65acb1b1 942
40d4dc3e 943=item *
65acb1b1 944
40d4dc3e 945What does it mean that regexes are greedy? How can I get around it?
65acb1b1 946
40d4dc3e 947=item *
65acb1b1 948
40d4dc3e 949How do I process each word on each line?
65acb1b1 950
40d4dc3e 951=item *
65acb1b1 952
40d4dc3e 953How can I print out a word-frequency or line-frequency summary?
65acb1b1 954
40d4dc3e 955=item *
65acb1b1 956
40d4dc3e 957How can I do approximate matching?
65acb1b1 958
40d4dc3e 959=item *
65acb1b1 960
40d4dc3e 961How do I efficiently match many regular expressions at once?
65acb1b1 962
40d4dc3e 963=item *
65acb1b1 964
40d4dc3e 965Why don't word-boundary searches with C<\b> work for me?
65acb1b1 966
40d4dc3e 967=item *
65acb1b1 968
b68463f7 969Why does using $&, $`, or $' slow my program down?
40d4dc3e 970
971=item *
972
973What good is C<\G> in a regular expression?
974
975=item *
976
977Are Perl regexes DFAs or NFAs? Are they POSIX compliant?
978
979=item *
980
c98c5709 981What's wrong with using grep in a void context?
40d4dc3e 982
983=item *
984
985How can I match strings with multibyte characters?
986
987=item *
988
ac9dac7f 989How do I match a regular expression that's in a variable?
65acb1b1 990
991=back
992
993
40d4dc3e 994=head2 L<perlfaq7>: General Perl Language Issues
68dc0745 995
c98c5709 996General Perl language issues that don't clearly fit into any of the other sections.
68dc0745 997
65acb1b1 998=over 4
999
40d4dc3e 1000=item *
1001
1002Can I get a BNF/yacc/RE for the Perl language?
1003
1004=item *
1005
1006What are all these $@%&* punctuation signs, and how do I know when to use them?
1007
1008=item *
1009
1010Do I always/never have to quote my strings or use semicolons and commas?
1011
1012=item *
1013
1014How do I skip some return values?
1015
1016=item *
1017
1018How do I temporarily block warnings?
1019
1020=item *
1021
1022What's an extension?
1023
1024=item *
1025
1026Why do Perl operators have different precedence than C operators?
1027
1028=item *
1029
1030How do I declare/create a structure?
1031
1032=item *
1033
1034How do I create a module?
1035
1036=item *
1037
c195e131 1038How do I adopt or take over a module already on CPAN?
1039
1040=item *
1041
40d4dc3e 1042How do I create a class?
1043
1044=item *
1045
1046How can I tell if a variable is tainted?
1047
1048=item *
1049
1050What's a closure?
1051
1052=item *
1053
1054What is variable suicide and how can I prevent it?
1055
1056=item *
1057
1058How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
65acb1b1 1059
40d4dc3e 1060=item *
65acb1b1 1061
40d4dc3e 1062How do I create a static variable?
65acb1b1 1063
40d4dc3e 1064=item *
65acb1b1 1065
40d4dc3e 1066What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
65acb1b1 1067
40d4dc3e 1068=item *
65acb1b1 1069
40d4dc3e 1070How can I access a dynamic variable while a similarly named lexical is in scope?
65acb1b1 1071
40d4dc3e 1072=item *
65acb1b1 1073
40d4dc3e 1074What's the difference between deep and shallow binding?
65acb1b1 1075
40d4dc3e 1076=item *
65acb1b1 1077
b68463f7 1078Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right?
65acb1b1 1079
40d4dc3e 1080=item *
65acb1b1 1081
40d4dc3e 1082How do I redefine a builtin function, operator, or method?
65acb1b1 1083
40d4dc3e 1084=item *
65acb1b1 1085
b68463f7 1086What's the difference between calling a function as &foo and foo()?
65acb1b1 1087
40d4dc3e 1088=item *
65acb1b1 1089
40d4dc3e 1090How do I create a switch or case statement?
65acb1b1 1091
40d4dc3e 1092=item *
65acb1b1 1093
49d635f9 1094How can I catch accesses to undefined variables, functions, or methods?
65acb1b1 1095
40d4dc3e 1096=item *
65acb1b1 1097
40d4dc3e 1098Why can't a method included in this same file be found?
65acb1b1 1099
40d4dc3e 1100=item *
65acb1b1 1101
109f0441 1102How can I find out my current or calling package?
65acb1b1 1103
40d4dc3e 1104=item *
65acb1b1 1105
8d2e243f 1106How can I comment out a large block of Perl code?
65acb1b1 1107
40d4dc3e 1108=item *
65acb1b1 1109
40d4dc3e 1110How do I clear a package?
65acb1b1 1111
40d4dc3e 1112=item *
1113
1114How can I use a variable as a variable name?
d92eb7b0 1115
5cd0b561 1116=item *
1117
1118What does "bad interpreter" mean?
1119
65acb1b1 1120=back
1121
1122
40d4dc3e 1123=head2 L<perlfaq8>: System Interaction
68dc0745 1124
c98c5709 1125This 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 1126
65acb1b1 1127=over 4
1128
40d4dc3e 1129=item *
1130
1131How do I find out which operating system I'm running under?
1132
1133=item *
1134
b68463f7 1135How come exec() doesn't return?
40d4dc3e 1136
1137=item *
1138
1139How do I do fancy stuff with the keyboard/screen/mouse?
1140
1141=item *
1142
1143How do I print something out in color?
1144
1145=item *
1146
1147How do I read just one key without waiting for a return key?
1148
1149=item *
1150
1151How do I check whether input is ready on the keyboard?
1152
1153=item *
1154
1155How do I clear the screen?
1156
1157=item *
1158
1159How do I get the screen size?
1160
1161=item *
1162
1163How do I ask the user for a password?
1164
1165=item *
1166
1167How do I read and write the serial port?
1168
1169=item *
1170
1171How do I decode encrypted password files?
1172
1173=item *
1174
1175How do I start a process in the background?
1176
1177=item *
1178
1179How do I trap control characters/signals?
1180
1181=item *
1182
1183How do I modify the shadow password file on a Unix system?
1184
1185=item *
1186
1187How do I set the time and date?
1188
1189=item *
1190
b68463f7 1191How can I sleep() or alarm() for under a second?
40d4dc3e 1192
1193=item *
1194
1195How can I measure time under a second?
1196
1197=item *
1198
b68463f7 1199How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
40d4dc3e 1200
1201=item *
1202
1203Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
65acb1b1 1204
40d4dc3e 1205=item *
65acb1b1 1206
40d4dc3e 1207How can I call my system's unique C functions from Perl?
65acb1b1 1208
40d4dc3e 1209=item *
65acb1b1 1210
b68463f7 1211Where do I get the include files to do ioctl() or syscall()?
65acb1b1 1212
40d4dc3e 1213=item *
65acb1b1 1214
40d4dc3e 1215Why do setuid perl scripts complain about kernel problems?
65acb1b1 1216
40d4dc3e 1217=item *
65acb1b1 1218
40d4dc3e 1219How can I open a pipe both to and from a command?
65acb1b1 1220
40d4dc3e 1221=item *
65acb1b1 1222
b68463f7 1223Why can't I get the output of a command with system()?
65acb1b1 1224
40d4dc3e 1225=item *
65acb1b1 1226
40d4dc3e 1227How can I capture STDERR from an external command?
65acb1b1 1228
40d4dc3e 1229=item *
65acb1b1 1230
b68463f7 1231Why doesn't open() return an error when a pipe open fails?
65acb1b1 1232
40d4dc3e 1233=item *
65acb1b1 1234
40d4dc3e 1235What's wrong with using backticks in a void context?
65acb1b1 1236
40d4dc3e 1237=item *
65acb1b1 1238
40d4dc3e 1239How can I call backticks without shell processing?
65acb1b1 1240
40d4dc3e 1241=item *
65acb1b1 1242
40d4dc3e 1243Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
65acb1b1 1244
40d4dc3e 1245=item *
65acb1b1 1246
40d4dc3e 1247How can I convert my shell script to perl?
65acb1b1 1248
40d4dc3e 1249=item *
65acb1b1 1250
40d4dc3e 1251Can I use perl to run a telnet or ftp session?
65acb1b1 1252
40d4dc3e 1253=item *
65acb1b1 1254
40d4dc3e 1255How can I write expect in Perl?
65acb1b1 1256
40d4dc3e 1257=item *
65acb1b1 1258
40d4dc3e 1259Is there a way to hide perl's command line from programs such as "ps"?
65acb1b1 1260
40d4dc3e 1261=item *
65acb1b1 1262
b68463f7 1263I {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 1264
40d4dc3e 1265=item *
65acb1b1 1266
40d4dc3e 1267How do I close a process's filehandle without waiting for it to complete?
65acb1b1 1268
40d4dc3e 1269=item *
65acb1b1 1270
40d4dc3e 1271How do I fork a daemon process?
65acb1b1 1272
40d4dc3e 1273=item *
65acb1b1 1274
40d4dc3e 1275How do I find out if I'm running interactively or not?
65acb1b1 1276
40d4dc3e 1277=item *
65acb1b1 1278
40d4dc3e 1279How do I timeout a slow event?
65acb1b1 1280
40d4dc3e 1281=item *
65acb1b1 1282
40d4dc3e 1283How do I set CPU limits?
65acb1b1 1284
40d4dc3e 1285=item *
65acb1b1 1286
40d4dc3e 1287How do I avoid zombies on a Unix system?
65acb1b1 1288
40d4dc3e 1289=item *
65acb1b1 1290
40d4dc3e 1291How do I use an SQL database?
65acb1b1 1292
40d4dc3e 1293=item *
65acb1b1 1294
b68463f7 1295How do I make a system() exit on control-C?
65acb1b1 1296
40d4dc3e 1297=item *
65acb1b1 1298
40d4dc3e 1299How do I open a file without blocking?
1300
1301=item *
1302
c98c5709 1303How do I tell the difference between errors from the shell and perl?
1304
1305=item *
1306
40d4dc3e 1307How do I install a module from CPAN?
1308
1309=item *
1310
1311What's the difference between require and use?
1312
1313=item *
1314
1315How do I keep my own module/library directory?
1316
1317=item *
1318
1319How do I add the directory my program lives in to the module/library search path?
1320
1321=item *
1322
b68463f7 1323How do I add a directory to my include path (@INC) at runtime?
40d4dc3e 1324
1325=item *
1326
b68463f7 1327What is socket.ph and where do I get it?
65acb1b1 1328
1329=back
1330
1331
40d4dc3e 1332=head2 L<perlfaq9>: Networking
68dc0745 1333
ae3d0b9f 1334Networking, the internet, and a few on the web.
68dc0745 1335
65acb1b1 1336=over 4
1337
40d4dc3e 1338=item *
65acb1b1 1339
ae3d0b9f 1340What is the correct form of response from a CGI script?
1341
1342=item *
1343
40d4dc3e 1344My CGI script runs from the command line but not the browser. (500 Server Error)
65acb1b1 1345
40d4dc3e 1346=item *
65acb1b1 1347
40d4dc3e 1348How can I get better error messages from a CGI program?
65acb1b1 1349
40d4dc3e 1350=item *
65acb1b1 1351
40d4dc3e 1352How do I remove HTML from a string?
65acb1b1 1353
40d4dc3e 1354=item *
65acb1b1 1355
40d4dc3e 1356How do I extract URLs?
65acb1b1 1357
40d4dc3e 1358=item *
65acb1b1 1359
40d4dc3e 1360How do I download a file from the user's machine? How do I open a file on another machine?
65acb1b1 1361
40d4dc3e 1362=item *
65acb1b1 1363
e573f903 1364How do I make an HTML pop-up menu with Perl?
65acb1b1 1365
40d4dc3e 1366=item *
65acb1b1 1367
40d4dc3e 1368How do I fetch an HTML file?
65acb1b1 1369
40d4dc3e 1370=item *
65acb1b1 1371
40d4dc3e 1372How do I automate an HTML form submission?
65acb1b1 1373
40d4dc3e 1374=item *
65acb1b1 1375
40d4dc3e 1376How do I decode or create those %-encodings on the web?
65acb1b1 1377
40d4dc3e 1378=item *
65acb1b1 1379
40d4dc3e 1380How do I redirect to another page?
65acb1b1 1381
40d4dc3e 1382=item *
65acb1b1 1383
40d4dc3e 1384How do I put a password on my web pages?
65acb1b1 1385
40d4dc3e 1386=item *
65acb1b1 1387
b68463f7 1388How do I edit my .htpasswd and .htgroup files with Perl?
65acb1b1 1389
40d4dc3e 1390=item *
1391
1392How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
1393
1394=item *
1395
1396How do I parse a mail header?
1397
1398=item *
1399
1400How do I decode a CGI form?
1401
1402=item *
65acb1b1 1403
40d4dc3e 1404How do I check a valid mail address?
1405
1406=item *
1407
1408How do I decode a MIME/BASE64 string?
1409
1410=item *
1411
1412How do I return the user's mail address?
1413
1414=item *
1415
1416How do I send mail?
1417
1418=item *
1419
ae3d0b9f 1420How do I use MIME to make an attachment to a mail message?
1421
1422=item *
1423
40d4dc3e 1424How do I read mail?
1425
1426=item *
1427
a05e4845 1428How do I find out my hostname, domainname, or IP address?
40d4dc3e 1429
1430=item *
1431
1432How do I fetch a news article or the active newsgroups?
1433
1434=item *
1435
1436How do I fetch/put an FTP file?
1437
1438=item *
1439
1440How can I do RPC in Perl?
65acb1b1 1441
68dc0745 1442=back
1443
8d2e243f 1444