Revert "show -E in error message when called with -E"
[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
7ba19369 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
fcd1fd07 26You can view the source tree at
e573f903 27https://svn.perl.org/modules/perlfaq/trunk/ (which is outside of the
28main Perl source tree). The SVN repository notes all changes to the FAQ
fcd1fd07 29and holds the latest version of the working documents and may vary
30significantly from the version distributed with the latest version of
31Perl. Check the repository before 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
fcd1fd07 46=head2 What will happen if you mail your Perl programming problems to the authors?
197aec24 47
fcd1fd07 48The perlfaq-workers like to keep all traffic on the perlfaq-workers list
49so that everyone can see the work being done (and the work that needs to
50be done). The mailing list serves as an official record. If you email the
51authors or maintainers directly, you'll probably get a reply asking you
52to post to the mailing list. If you don't get a reply, it probably means
53that the person never saw the message or didn't have time to deal with
54it. Posting to the list allows the volunteers with time to deal with it
55when others are busy.
197aec24 56
fcd1fd07 57If you have a question that isn't in the FAQ and you would like help with
58it, try the resources in L<perlfaq2>.
197aec24 59
fcd1fd07 60=head1 CREDITS
197aec24 61
fcd1fd07 62Tom Christiansen wrote the original perlfaq then expanded it with the
63help of Nat Torkington. The perlfaq-workers maintain current document
c195e131 64and the denizens of comp.lang.perl.misc regularly review and update the
fcd1fd07 65FAQ. Several people have contributed answers, corrections, and comments,
66and the perlfaq notes those contributions wherever appropriate.
197aec24 67
fcd1fd07 68=head1 AUTHOR AND COPYRIGHT
197aec24 69
c195e131 70Tom Christiansen wrote the original version of this document.
fcd1fd07 71brian d foy C<< <bdfoy@cpan.org> >> wrote this version. See the
72individual perlfaq documents for additional copyright information.
197aec24 73
fcd1fd07 74This document is available under the same terms as Perl itself. Code
75examples in all the perlfaq documents are in the public domain. Use
76them as you see fit (and at your own risk with no warranty from anyone).
197aec24 77
78=head1 Table of Contents
68dc0745 79
5cd0b561 80=over 4
81
82=item perlfaq - this document
83
84=item perlfaq1 - General Questions About Perl
85
86=item perlfaq2 - Obtaining and Learning about Perl
87
88=item perlfaq3 - Programming Tools
89
90=item perlfaq4 - Data Manipulation
91
92=item perlfaq5 - Files and Formats
93
94=item perlfaq6 - Regular Expressions
95
96=item perlfaq7 - General Perl Language Issues
68dc0745 97
5cd0b561 98=item perlfaq8 - System Interaction
99
100=item perlfaq9 - Networking
101
5cd0b561 102=back
103
5cd0b561 104=head1 The Questions
68dc0745 105
40d4dc3e 106=head2 L<perlfaq1>: General Questions About Perl
68dc0745 107
ae3d0b9f 108Very general, high-level questions about Perl.
68dc0745 109
65acb1b1 110=over 4
111
40d4dc3e 112=item *
113
114What is Perl?
115
116=item *
117
118Who supports Perl? Who develops it? Why is it free?
119
120=item *
121
122Which version of Perl should I use?
123
124=item *
125
e9d185f8 126What are Perl 4, Perl 5, or Perl 6?
40d4dc3e 127
128=item *
129
322be77c 130What was Ponie?
c98c5709 131
132=item *
133
e9d185f8 134What is Perl 6?
65acb1b1 135
40d4dc3e 136=item *
65acb1b1 137
40d4dc3e 138How stable is Perl?
65acb1b1 139
40d4dc3e 140=item *
65acb1b1 141
40d4dc3e 142Is Perl difficult to learn?
65acb1b1 143
40d4dc3e 144=item *
65acb1b1 145
40d4dc3e 146How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
65acb1b1 147
40d4dc3e 148=item *
65acb1b1 149
40d4dc3e 150Can I do [task] in Perl?
65acb1b1 151
40d4dc3e 152=item *
65acb1b1 153
40d4dc3e 154When shouldn't I program in Perl?
65acb1b1 155
40d4dc3e 156=item *
65acb1b1 157
40d4dc3e 158What's the difference between "perl" and "Perl"?
65acb1b1 159
40d4dc3e 160=item *
65acb1b1 161
40d4dc3e 162Is it a Perl program or a Perl script?
163
164=item *
165
166What is a JAPH?
167
168=item *
169
170Where can I get a list of Larry Wall witticisms?
171
172=item *
173
ac9dac7f 174How can I convince others to use Perl?
65acb1b1 175
176=back
177
178
40d4dc3e 179=head2 L<perlfaq2>: Obtaining and Learning about Perl
68dc0745 180
c98c5709 181Where to find source and documentation for Perl, support, and related matters.
68dc0745 182
65acb1b1 183=over 4
184
40d4dc3e 185=item *
186
b68463f7 187What machines support perl? Where do I get it?
40d4dc3e 188
189=item *
190
b68463f7 191How can I get a binary version of perl?
65acb1b1 192
40d4dc3e 193=item *
65acb1b1 194
b68463f7 195I don't have a C compiler. How can I build my own Perl interpreter?
65acb1b1 196
40d4dc3e 197=item *
65acb1b1 198
b68463f7 199I copied the perl binary from one machine to another, but scripts don't work.
65acb1b1 200
40d4dc3e 201=item *
65acb1b1 202
40d4dc3e 203I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
65acb1b1 204
40d4dc3e 205=item *
65acb1b1 206
40d4dc3e 207What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
65acb1b1 208
40d4dc3e 209=item *
65acb1b1 210
40d4dc3e 211Is there an ISO or ANSI certified version of Perl?
65acb1b1 212
40d4dc3e 213=item *
65acb1b1 214
40d4dc3e 215Where can I get information on Perl?
65acb1b1 216
40d4dc3e 217=item *
65acb1b1 218
40d4dc3e 219What are the Perl newsgroups on Usenet? Where do I post questions?
65acb1b1 220
40d4dc3e 221=item *
65acb1b1 222
40d4dc3e 223Where should I post source code?
65acb1b1 224
40d4dc3e 225=item *
226
227Perl Books
228
229=item *
230
fcd1fd07 231Which magazines have Perl content?
40d4dc3e 232
233=item *
234
235What mailing lists are there for Perl?
236
237=item *
238
fcd1fd07 239Where are the archives for comp.lang.perl.misc?
40d4dc3e 240
241=item *
242
b68463f7 243Where can I buy a commercial version of perl?
40d4dc3e 244
245=item *
246
247Where do I send bug reports?
248
249=item *
250
ae3d0b9f 251What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org?
65acb1b1 252
253=back
254
255
40d4dc3e 256=head2 L<perlfaq3>: Programming Tools
68dc0745 257
258Programmer tools and programming support.
259
65acb1b1 260=over 4
261
40d4dc3e 262=item *
263
264How do I do (anything)?
265
266=item *
267
268How can I use Perl interactively?
269
270=item *
65acb1b1 271
40d4dc3e 272Is there a Perl shell?
65acb1b1 273
40d4dc3e 274=item *
65acb1b1 275
49d635f9 276How do I find which modules are installed on my system?
277
278=item *
279
40d4dc3e 280How do I debug my Perl programs?
65acb1b1 281
40d4dc3e 282=item *
65acb1b1 283
40d4dc3e 284How do I profile my Perl programs?
65acb1b1 285
40d4dc3e 286=item *
65acb1b1 287
40d4dc3e 288How do I cross-reference my Perl programs?
65acb1b1 289
40d4dc3e 290=item *
65acb1b1 291
40d4dc3e 292Is there a pretty-printer (formatter) for Perl?
65acb1b1 293
40d4dc3e 294=item *
65acb1b1 295
40d4dc3e 296Is there a ctags for Perl?
65acb1b1 297
40d4dc3e 298=item *
65acb1b1 299
40d4dc3e 300Is there an IDE or Windows Perl Editor?
65acb1b1 301
40d4dc3e 302=item *
65acb1b1 303
40d4dc3e 304Where can I get Perl macros for vi?
65acb1b1 305
40d4dc3e 306=item *
65acb1b1 307
40d4dc3e 308Where can I get perl-mode for emacs?
65acb1b1 309
40d4dc3e 310=item *
65acb1b1 311
40d4dc3e 312How can I use curses with Perl?
65acb1b1 313
40d4dc3e 314=item *
65acb1b1 315
c195e131 316How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
65acb1b1 317
40d4dc3e 318=item *
65acb1b1 319
40d4dc3e 320How can I make my Perl program run faster?
65acb1b1 321
40d4dc3e 322=item *
65acb1b1 323
40d4dc3e 324How can I make my Perl program take less memory?
325
326=item *
327
49d635f9 328Is it safe to return a reference to local or lexical data?
40d4dc3e 329
330=item *
331
332How can I free an array or hash so my program shrinks?
333
334=item *
335
336How can I make my CGI script more efficient?
337
338=item *
339
340How can I hide the source for my Perl program?
341
342=item *
343
344How can I compile my Perl program into byte code or C?
345
346=item *
347
40d4dc3e 348How can I get C<#!perl> to work on [MS-DOS,NT,...]?
349
350=item *
351
352Can I write useful Perl programs on the command line?
353
354=item *
355
356Why don't Perl one-liners work on my DOS/Mac/VMS system?
357
358=item *
359
360Where can I learn about CGI or Web programming in Perl?
361
362=item *
363
364Where can I learn about object-oriented Perl programming?
365
366=item *
367
b68463f7 368Where can I learn about linking C with Perl?
40d4dc3e 369
370=item *
371
7678cced 372I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
65acb1b1 373
40d4dc3e 374=item *
375
ae3d0b9f 376When I tried to run my script, I got this message. What does it mean?
65acb1b1 377
40d4dc3e 378=item *
379
380What's MakeMaker?
65acb1b1 381
382=back
383
384
40d4dc3e 385=head2 L<perlfaq4>: Data Manipulation
68dc0745 386
c98c5709 387Manipulating numbers, dates, strings, arrays, hashes, and miscellaneous data issues.
68dc0745 388
65acb1b1 389=over 4
390
40d4dc3e 391=item *
392
393Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?
394
395=item *
396
b68463f7 397Why is int() broken?
c98c5709 398
399=item *
400
40d4dc3e 401Why isn't my octal data interpreted correctly?
402
403=item *
404
b68463f7 405Does Perl have a round() function? What about ceil() and floor()? Trig functions?
40d4dc3e 406
407=item *
408
c98c5709 409How do I convert between numeric representations/bases/radixes?
40d4dc3e 410
411=item *
412
413Why doesn't & work the way I want it to?
65acb1b1 414
40d4dc3e 415=item *
65acb1b1 416
40d4dc3e 417How do I multiply matrices?
65acb1b1 418
40d4dc3e 419=item *
65acb1b1 420
40d4dc3e 421How do I perform an operation on a series of integers?
65acb1b1 422
40d4dc3e 423=item *
65acb1b1 424
40d4dc3e 425How can I output Roman numerals?
65acb1b1 426
40d4dc3e 427=item *
65acb1b1 428
40d4dc3e 429Why aren't my random numbers random?
65acb1b1 430
40d4dc3e 431=item *
65acb1b1 432
881bdbd4 433How do I get a random number between X and Y?
434
435=item *
436
5cd0b561 437How do I find the day or week of the year?
d92eb7b0 438
40d4dc3e 439=item *
65acb1b1 440
40d4dc3e 441How do I find the current century or millennium?
65acb1b1 442
40d4dc3e 443=item *
65acb1b1 444
40d4dc3e 445How can I compare two dates and find the difference?
65acb1b1 446
40d4dc3e 447=item *
65acb1b1 448
40d4dc3e 449How can I take a string and turn it into epoch seconds?
65acb1b1 450
40d4dc3e 451=item *
65acb1b1 452
40d4dc3e 453How can I find the Julian Day?
65acb1b1 454
40d4dc3e 455=item *
65acb1b1 456
40d4dc3e 457How do I find yesterday's date?
65acb1b1 458
40d4dc3e 459=item *
65acb1b1 460
e573f903 461Does Perl have a Year 2000 problem? Is Perl Y2K compliant?
65acb1b1 462
40d4dc3e 463=item *
65acb1b1 464
40d4dc3e 465How do I validate input?
65acb1b1 466
40d4dc3e 467=item *
65acb1b1 468
40d4dc3e 469How do I unescape a string?
65acb1b1 470
40d4dc3e 471=item *
65acb1b1 472
40d4dc3e 473How do I remove consecutive pairs of characters?
474
475=item *
476
477How do I expand function calls in a string?
478
479=item *
480
481How do I find matching/nesting anything?
482
483=item *
484
485How do I reverse a string?
486
487=item *
488
489How do I expand tabs in a string?
490
491=item *
492
493How do I reformat a paragraph?
494
495=item *
496
49d635f9 497How can I access or change N characters of a string?
40d4dc3e 498
499=item *
500
501How do I change the Nth occurrence of something?
502
503=item *
504
505How can I count the number of occurrences of a substring within a string?
506
507=item *
508
509How do I capitalize all the words on one line?
510
511=item *
512
49d635f9 513How can I split a [character] delimited string except when inside [character]?
65acb1b1 514
40d4dc3e 515=item *
516
517How do I strip blank space from the beginning/end of a string?
518
519=item *
520
521How do I pad a string with blanks or pad a number with zeroes?
522
523=item *
524
525How do I extract selected columns from a string?
526
527=item *
528
529How do I find the soundex value of a string?
530
531=item *
532
533How can I expand variables in text strings?
534
535=item *
536
537What's wrong with always quoting "$vars"?
538
539=item *
540
04d666b1 541Why don't my E<lt>E<lt>HERE documents work?
40d4dc3e 542
543=item *
544
545What is the difference between a list and an array?
546
547=item *
548
b68463f7 549What is the difference between $array[1] and @array[1]?
40d4dc3e 550
551=item *
65acb1b1 552
40d4dc3e 553How can I remove duplicate elements from a list or array?
65acb1b1 554
40d4dc3e 555=item *
65acb1b1 556
ae3d0b9f 557How can I tell whether a certain element is contained in a list or array?
65acb1b1 558
40d4dc3e 559=item *
65acb1b1 560
40d4dc3e 561How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
65acb1b1 562
40d4dc3e 563=item *
65acb1b1 564
40d4dc3e 565How do I test whether two arrays or hashes are equal?
65acb1b1 566
40d4dc3e 567=item *
65acb1b1 568
40d4dc3e 569How do I find the first array element for which a condition is true?
65acb1b1 570
40d4dc3e 571=item *
65acb1b1 572
40d4dc3e 573How do I handle linked lists?
65acb1b1 574
40d4dc3e 575=item *
65acb1b1 576
40d4dc3e 577How do I handle circular lists?
65acb1b1 578
40d4dc3e 579=item *
65acb1b1 580
40d4dc3e 581How do I shuffle an array randomly?
65acb1b1 582
40d4dc3e 583=item *
65acb1b1 584
40d4dc3e 585How do I process/modify each element of an array?
65acb1b1 586
40d4dc3e 587=item *
65acb1b1 588
40d4dc3e 589How do I select a random element from an array?
65acb1b1 590
40d4dc3e 591=item *
65acb1b1 592
40d4dc3e 593How do I permute N elements of a list?
65acb1b1 594
40d4dc3e 595=item *
65acb1b1 596
40d4dc3e 597How do I sort an array by (anything)?
65acb1b1 598
40d4dc3e 599=item *
65acb1b1 600
40d4dc3e 601How do I manipulate arrays of bits?
65acb1b1 602
40d4dc3e 603=item *
65acb1b1 604
b68463f7 605Why does defined() return true on empty arrays and hashes?
65acb1b1 606
40d4dc3e 607=item *
65acb1b1 608
40d4dc3e 609How do I process an entire hash?
65acb1b1 610
40d4dc3e 611=item *
65acb1b1 612
40d4dc3e 613What happens if I add or remove keys from a hash while iterating over it?
65acb1b1 614
40d4dc3e 615=item *
65acb1b1 616
40d4dc3e 617How do I look up a hash element by value?
65acb1b1 618
40d4dc3e 619=item *
65acb1b1 620
40d4dc3e 621How can I know how many entries are in a hash?
65acb1b1 622
40d4dc3e 623=item *
65acb1b1 624
40d4dc3e 625How do I sort a hash (optionally by value instead of key)?
65acb1b1 626
40d4dc3e 627=item *
65acb1b1 628
40d4dc3e 629How can I always keep my hash sorted?
65acb1b1 630
40d4dc3e 631=item *
65acb1b1 632
40d4dc3e 633What's the difference between "delete" and "undef" with hashes?
65acb1b1 634
40d4dc3e 635=item *
65acb1b1 636
40d4dc3e 637Why don't my tied hashes make the defined/exists distinction?
65acb1b1 638
40d4dc3e 639=item *
640
b68463f7 641How do I reset an each() operation part-way through?
40d4dc3e 642
643=item *
644
645How can I get the unique keys from two hashes?
646
647=item *
648
649How can I store a multidimensional array in a DBM file?
650
651=item *
652
653How can I make my hash remember the order I put elements into it?
654
655=item *
656
657Why does passing a subroutine an undefined element in a hash create it?
658
659=item *
660
661How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?
662
663=item *
664
665How can I use a reference as a hash key?
666
667=item *
668
669How do I handle binary data correctly?
670
671=item *
672
673How do I determine whether a scalar is a number/whole/integer/float?
674
675=item *
676
677How do I keep persistent data across program calls?
678
679=item *
680
681How do I print out or copy a recursive data structure?
682
683=item *
684
685How do I define methods for every class/object?
686
687=item *
688
689How do I verify a credit card checksum?
690
691=item *
692
693How do I pack arrays of doubles or floats for XS code?
65acb1b1 694
695=back
696
697
40d4dc3e 698=head2 L<perlfaq5>: Files and Formats
68dc0745 699
ae3d0b9f 700I/O and the "f" issues: filehandles, flushing, formats, and footers.
68dc0745 701
65acb1b1 702=over 4
703
40d4dc3e 704=item *
705
706How do I flush/unbuffer an output filehandle? Why must I do this?
707
708=item *
709
e573f903 710How do I change, delete, or insert a line in a file, or append to the beginning of a file?
40d4dc3e 711
712=item *
713
714How do I count the number of lines in a file?
715
716=item *
717
49d635f9 718How can I use Perl's C<-i> option from within a program?
719
720=item *
721
7678cced 722How can I copy a file?
723
724=item *
725
40d4dc3e 726How do I make a temporary file name?
727
728=item *
729
730How can I manipulate fixed-record-length files?
731
732=item *
65acb1b1 733
40d4dc3e 734How 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 735
40d4dc3e 736=item *
65acb1b1 737
40d4dc3e 738How can I use a filehandle indirectly?
65acb1b1 739
40d4dc3e 740=item *
65acb1b1 741
b68463f7 742How can I set up a footer format to be used with write()?
65acb1b1 743
40d4dc3e 744=item *
65acb1b1 745
b68463f7 746How can I write() into a string?
65acb1b1 747
40d4dc3e 748=item *
65acb1b1 749
c195e131 750How can I open a filehandle to a string?
751
752=item *
753
40d4dc3e 754How can I output my numbers with commas added?
65acb1b1 755
40d4dc3e 756=item *
65acb1b1 757
40d4dc3e 758How can I translate tildes (~) in a filename?
65acb1b1 759
40d4dc3e 760=item *
65acb1b1 761
40d4dc3e 762How come when I open a file read-write it wipes it out?
65acb1b1 763
40d4dc3e 764=item *
65acb1b1 765
04d666b1 766Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
65acb1b1 767
40d4dc3e 768=item *
65acb1b1 769
b68463f7 770Is there a leak/bug in glob()?
65acb1b1 771
40d4dc3e 772=item *
65acb1b1 773
40d4dc3e 774How can I open a file with a leading ">" or trailing blanks?
65acb1b1 775
40d4dc3e 776=item *
65acb1b1 777
40d4dc3e 778How can I reliably rename a file?
65acb1b1 779
40d4dc3e 780=item *
65acb1b1 781
40d4dc3e 782How can I lock a file?
d92eb7b0 783
40d4dc3e 784=item *
65acb1b1 785
b68463f7 786Why can't I just open(FH, "E<gt>file.lock")?
65acb1b1 787
40d4dc3e 788=item *
65acb1b1 789
40d4dc3e 790I still don't get locking. I just want to increment the number in the file. How can I do this?
65acb1b1 791
40d4dc3e 792=item *
65acb1b1 793
f52f3be2 794All 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 795
796=item *
797
40d4dc3e 798How do I randomly update a binary file?
65acb1b1 799
40d4dc3e 800=item *
65acb1b1 801
40d4dc3e 802How do I get a file's timestamp in perl?
65acb1b1 803
40d4dc3e 804=item *
65acb1b1 805
40d4dc3e 806How do I set a file's timestamp in perl?
65acb1b1 807
40d4dc3e 808=item *
809
810How do I print to more than one file at once?
811
812=item *
813
814How can I read in an entire file all at once?
815
816=item *
817
818How can I read in a file by paragraphs?
819
820=item *
821
822How can I read a single character from a file? From the keyboard?
823
824=item *
825
826How can I tell whether there's a character waiting on a filehandle?
827
828=item *
829
830How do I do a C<tail -f> in perl?
831
832=item *
833
b68463f7 834How do I dup() a filehandle in Perl?
40d4dc3e 835
836=item *
837
838How do I close a file descriptor by number?
839
840=item *
841
c98c5709 842Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work?
40d4dc3e 843
844=item *
845
b68463f7 846Why doesn't glob("*.*") get all the files?
40d4dc3e 847
848=item *
849
850Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl?
851
852=item *
853
854How do I select a random line from a file?
855
856=item *
857
858Why do I get weird spaces when I print an array of lines?
65acb1b1 859
860=back
861
862
ae3d0b9f 863=head2 L<perlfaq6>: Regular Expressions
68dc0745 864
b68463f7 865This 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 866
65acb1b1 867=over 4
868
40d4dc3e 869=item *
870
871How can I hope to use regular expressions without creating illegible and unmaintainable code?
872
873=item *
874
875I'm having trouble matching over more than one line. What's wrong?
876
877=item *
878
879How can I pull out lines between two patterns that are themselves on different lines?
880
881=item *
882
b68463f7 883I put a regular expression into $/ but it didn't work. What's wrong?
40d4dc3e 884
885=item *
886
887How do I substitute case insensitively on the LHS while preserving case on the RHS?
888
889=item *
890
891How can I make C<\w> match national character sets?
892
893=item *
894
895How can I match a locale-smart version of C</[a-zA-Z]/>?
65acb1b1 896
40d4dc3e 897=item *
65acb1b1 898
40d4dc3e 899How can I quote a variable to use in a regex?
65acb1b1 900
40d4dc3e 901=item *
65acb1b1 902
40d4dc3e 903What is C</o> really for?
65acb1b1 904
40d4dc3e 905=item *
65acb1b1 906
40d4dc3e 907How do I use a regular expression to strip C style comments from a file?
65acb1b1 908
40d4dc3e 909=item *
65acb1b1 910
40d4dc3e 911Can I use Perl regular expressions to match balanced text?
65acb1b1 912
40d4dc3e 913=item *
65acb1b1 914
40d4dc3e 915What does it mean that regexes are greedy? How can I get around it?
65acb1b1 916
40d4dc3e 917=item *
65acb1b1 918
40d4dc3e 919How do I process each word on each line?
65acb1b1 920
40d4dc3e 921=item *
65acb1b1 922
40d4dc3e 923How can I print out a word-frequency or line-frequency summary?
65acb1b1 924
40d4dc3e 925=item *
65acb1b1 926
40d4dc3e 927How can I do approximate matching?
65acb1b1 928
40d4dc3e 929=item *
65acb1b1 930
40d4dc3e 931How do I efficiently match many regular expressions at once?
65acb1b1 932
40d4dc3e 933=item *
65acb1b1 934
40d4dc3e 935Why don't word-boundary searches with C<\b> work for me?
65acb1b1 936
40d4dc3e 937=item *
65acb1b1 938
b68463f7 939Why does using $&, $`, or $' slow my program down?
40d4dc3e 940
941=item *
942
943What good is C<\G> in a regular expression?
944
945=item *
946
947Are Perl regexes DFAs or NFAs? Are they POSIX compliant?
948
949=item *
950
c98c5709 951What's wrong with using grep in a void context?
40d4dc3e 952
953=item *
954
955How can I match strings with multibyte characters?
956
957=item *
958
ac9dac7f 959How do I match a regular expression that's in a variable?
65acb1b1 960
961=back
962
963
40d4dc3e 964=head2 L<perlfaq7>: General Perl Language Issues
68dc0745 965
c98c5709 966General Perl language issues that don't clearly fit into any of the other sections.
68dc0745 967
65acb1b1 968=over 4
969
40d4dc3e 970=item *
971
972Can I get a BNF/yacc/RE for the Perl language?
973
974=item *
975
976What are all these $@%&* punctuation signs, and how do I know when to use them?
977
978=item *
979
980Do I always/never have to quote my strings or use semicolons and commas?
981
982=item *
983
984How do I skip some return values?
985
986=item *
987
988How do I temporarily block warnings?
989
990=item *
991
992What's an extension?
993
994=item *
995
996Why do Perl operators have different precedence than C operators?
997
998=item *
999
1000How do I declare/create a structure?
1001
1002=item *
1003
1004How do I create a module?
1005
1006=item *
1007
c195e131 1008How do I adopt or take over a module already on CPAN?
1009
1010=item *
1011
40d4dc3e 1012How do I create a class?
1013
1014=item *
1015
1016How can I tell if a variable is tainted?
1017
1018=item *
1019
1020What's a closure?
1021
1022=item *
1023
1024What is variable suicide and how can I prevent it?
1025
1026=item *
1027
1028How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
65acb1b1 1029
40d4dc3e 1030=item *
65acb1b1 1031
40d4dc3e 1032How do I create a static variable?
65acb1b1 1033
40d4dc3e 1034=item *
65acb1b1 1035
40d4dc3e 1036What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
65acb1b1 1037
40d4dc3e 1038=item *
65acb1b1 1039
40d4dc3e 1040How can I access a dynamic variable while a similarly named lexical is in scope?
65acb1b1 1041
40d4dc3e 1042=item *
65acb1b1 1043
40d4dc3e 1044What's the difference between deep and shallow binding?
65acb1b1 1045
40d4dc3e 1046=item *
65acb1b1 1047
b68463f7 1048Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right?
65acb1b1 1049
40d4dc3e 1050=item *
65acb1b1 1051
40d4dc3e 1052How do I redefine a builtin function, operator, or method?
65acb1b1 1053
40d4dc3e 1054=item *
65acb1b1 1055
b68463f7 1056What's the difference between calling a function as &foo and foo()?
65acb1b1 1057
40d4dc3e 1058=item *
65acb1b1 1059
40d4dc3e 1060How do I create a switch or case statement?
65acb1b1 1061
40d4dc3e 1062=item *
65acb1b1 1063
49d635f9 1064How can I catch accesses to undefined variables, functions, or methods?
65acb1b1 1065
40d4dc3e 1066=item *
65acb1b1 1067
40d4dc3e 1068Why can't a method included in this same file be found?
65acb1b1 1069
40d4dc3e 1070=item *
65acb1b1 1071
40d4dc3e 1072How can I find out my current package?
65acb1b1 1073
40d4dc3e 1074=item *
65acb1b1 1075
40d4dc3e 1076How can I comment out a large block of perl code?
65acb1b1 1077
40d4dc3e 1078=item *
65acb1b1 1079
40d4dc3e 1080How do I clear a package?
65acb1b1 1081
40d4dc3e 1082=item *
1083
1084How can I use a variable as a variable name?
d92eb7b0 1085
5cd0b561 1086=item *
1087
1088What does "bad interpreter" mean?
1089
65acb1b1 1090=back
1091
1092
40d4dc3e 1093=head2 L<perlfaq8>: System Interaction
68dc0745 1094
c98c5709 1095This 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 1096
65acb1b1 1097=over 4
1098
40d4dc3e 1099=item *
1100
1101How do I find out which operating system I'm running under?
1102
1103=item *
1104
b68463f7 1105How come exec() doesn't return?
40d4dc3e 1106
1107=item *
1108
1109How do I do fancy stuff with the keyboard/screen/mouse?
1110
1111=item *
1112
1113How do I print something out in color?
1114
1115=item *
1116
1117How do I read just one key without waiting for a return key?
1118
1119=item *
1120
1121How do I check whether input is ready on the keyboard?
1122
1123=item *
1124
1125How do I clear the screen?
1126
1127=item *
1128
1129How do I get the screen size?
1130
1131=item *
1132
1133How do I ask the user for a password?
1134
1135=item *
1136
1137How do I read and write the serial port?
1138
1139=item *
1140
1141How do I decode encrypted password files?
1142
1143=item *
1144
1145How do I start a process in the background?
1146
1147=item *
1148
1149How do I trap control characters/signals?
1150
1151=item *
1152
1153How do I modify the shadow password file on a Unix system?
1154
1155=item *
1156
1157How do I set the time and date?
1158
1159=item *
1160
b68463f7 1161How can I sleep() or alarm() for under a second?
40d4dc3e 1162
1163=item *
1164
1165How can I measure time under a second?
1166
1167=item *
1168
b68463f7 1169How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
40d4dc3e 1170
1171=item *
1172
1173Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
65acb1b1 1174
40d4dc3e 1175=item *
65acb1b1 1176
40d4dc3e 1177How can I call my system's unique C functions from Perl?
65acb1b1 1178
40d4dc3e 1179=item *
65acb1b1 1180
b68463f7 1181Where do I get the include files to do ioctl() or syscall()?
65acb1b1 1182
40d4dc3e 1183=item *
65acb1b1 1184
40d4dc3e 1185Why do setuid perl scripts complain about kernel problems?
65acb1b1 1186
40d4dc3e 1187=item *
65acb1b1 1188
40d4dc3e 1189How can I open a pipe both to and from a command?
65acb1b1 1190
40d4dc3e 1191=item *
65acb1b1 1192
b68463f7 1193Why can't I get the output of a command with system()?
65acb1b1 1194
40d4dc3e 1195=item *
65acb1b1 1196
40d4dc3e 1197How can I capture STDERR from an external command?
65acb1b1 1198
40d4dc3e 1199=item *
65acb1b1 1200
b68463f7 1201Why doesn't open() return an error when a pipe open fails?
65acb1b1 1202
40d4dc3e 1203=item *
65acb1b1 1204
40d4dc3e 1205What's wrong with using backticks in a void context?
65acb1b1 1206
40d4dc3e 1207=item *
65acb1b1 1208
40d4dc3e 1209How can I call backticks without shell processing?
65acb1b1 1210
40d4dc3e 1211=item *
65acb1b1 1212
40d4dc3e 1213Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
65acb1b1 1214
40d4dc3e 1215=item *
65acb1b1 1216
40d4dc3e 1217How can I convert my shell script to perl?
65acb1b1 1218
40d4dc3e 1219=item *
65acb1b1 1220
40d4dc3e 1221Can I use perl to run a telnet or ftp session?
65acb1b1 1222
40d4dc3e 1223=item *
65acb1b1 1224
40d4dc3e 1225How can I write expect in Perl?
65acb1b1 1226
40d4dc3e 1227=item *
65acb1b1 1228
40d4dc3e 1229Is there a way to hide perl's command line from programs such as "ps"?
65acb1b1 1230
40d4dc3e 1231=item *
65acb1b1 1232
b68463f7 1233I {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 1234
40d4dc3e 1235=item *
65acb1b1 1236
40d4dc3e 1237How do I close a process's filehandle without waiting for it to complete?
65acb1b1 1238
40d4dc3e 1239=item *
65acb1b1 1240
40d4dc3e 1241How do I fork a daemon process?
65acb1b1 1242
40d4dc3e 1243=item *
65acb1b1 1244
40d4dc3e 1245How do I find out if I'm running interactively or not?
65acb1b1 1246
40d4dc3e 1247=item *
65acb1b1 1248
40d4dc3e 1249How do I timeout a slow event?
65acb1b1 1250
40d4dc3e 1251=item *
65acb1b1 1252
40d4dc3e 1253How do I set CPU limits?
65acb1b1 1254
40d4dc3e 1255=item *
65acb1b1 1256
40d4dc3e 1257How do I avoid zombies on a Unix system?
65acb1b1 1258
40d4dc3e 1259=item *
65acb1b1 1260
40d4dc3e 1261How do I use an SQL database?
65acb1b1 1262
40d4dc3e 1263=item *
65acb1b1 1264
b68463f7 1265How do I make a system() exit on control-C?
65acb1b1 1266
40d4dc3e 1267=item *
65acb1b1 1268
40d4dc3e 1269How do I open a file without blocking?
1270
1271=item *
1272
c98c5709 1273How do I tell the difference between errors from the shell and perl?
1274
1275=item *
1276
40d4dc3e 1277How do I install a module from CPAN?
1278
1279=item *
1280
1281What's the difference between require and use?
1282
1283=item *
1284
1285How do I keep my own module/library directory?
1286
1287=item *
1288
1289How do I add the directory my program lives in to the module/library search path?
1290
1291=item *
1292
b68463f7 1293How do I add a directory to my include path (@INC) at runtime?
40d4dc3e 1294
1295=item *
1296
b68463f7 1297What is socket.ph and where do I get it?
65acb1b1 1298
1299=back
1300
1301
40d4dc3e 1302=head2 L<perlfaq9>: Networking
68dc0745 1303
ae3d0b9f 1304Networking, the internet, and a few on the web.
68dc0745 1305
65acb1b1 1306=over 4
1307
40d4dc3e 1308=item *
65acb1b1 1309
ae3d0b9f 1310What is the correct form of response from a CGI script?
1311
1312=item *
1313
40d4dc3e 1314My CGI script runs from the command line but not the browser. (500 Server Error)
65acb1b1 1315
40d4dc3e 1316=item *
65acb1b1 1317
40d4dc3e 1318How can I get better error messages from a CGI program?
65acb1b1 1319
40d4dc3e 1320=item *
65acb1b1 1321
40d4dc3e 1322How do I remove HTML from a string?
65acb1b1 1323
40d4dc3e 1324=item *
65acb1b1 1325
40d4dc3e 1326How do I extract URLs?
65acb1b1 1327
40d4dc3e 1328=item *
65acb1b1 1329
40d4dc3e 1330How do I download a file from the user's machine? How do I open a file on another machine?
65acb1b1 1331
40d4dc3e 1332=item *
65acb1b1 1333
e573f903 1334How do I make an HTML pop-up menu with Perl?
65acb1b1 1335
40d4dc3e 1336=item *
65acb1b1 1337
40d4dc3e 1338How do I fetch an HTML file?
65acb1b1 1339
40d4dc3e 1340=item *
65acb1b1 1341
40d4dc3e 1342How do I automate an HTML form submission?
65acb1b1 1343
40d4dc3e 1344=item *
65acb1b1 1345
40d4dc3e 1346How do I decode or create those %-encodings on the web?
65acb1b1 1347
40d4dc3e 1348=item *
65acb1b1 1349
40d4dc3e 1350How do I redirect to another page?
65acb1b1 1351
40d4dc3e 1352=item *
65acb1b1 1353
40d4dc3e 1354How do I put a password on my web pages?
65acb1b1 1355
40d4dc3e 1356=item *
65acb1b1 1357
b68463f7 1358How do I edit my .htpasswd and .htgroup files with Perl?
65acb1b1 1359
40d4dc3e 1360=item *
1361
1362How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
1363
1364=item *
1365
1366How do I parse a mail header?
1367
1368=item *
1369
1370How do I decode a CGI form?
1371
1372=item *
65acb1b1 1373
40d4dc3e 1374How do I check a valid mail address?
1375
1376=item *
1377
1378How do I decode a MIME/BASE64 string?
1379
1380=item *
1381
1382How do I return the user's mail address?
1383
1384=item *
1385
1386How do I send mail?
1387
1388=item *
1389
ae3d0b9f 1390How do I use MIME to make an attachment to a mail message?
1391
1392=item *
1393
40d4dc3e 1394How do I read mail?
1395
1396=item *
1397
a05e4845 1398How do I find out my hostname, domainname, or IP address?
40d4dc3e 1399
1400=item *
1401
1402How do I fetch a news article or the active newsgroups?
1403
1404=item *
1405
1406How do I fetch/put an FTP file?
1407
1408=item *
1409
1410How can I do RPC in Perl?
65acb1b1 1411
68dc0745 1412=back
1413
40d4dc3e 1414