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1 | =head1 NAME |
2 | |
3 | perlmodlib - constructing new Perl modules and finding existing ones |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | =head1 THE PERL MODULE LIBRARY |
8 | |
9 | A number of modules are included the Perl distribution. These are |
10 | described below, and all end in F<.pm>. You may also discover files in |
11 | the library directory that end in either F<.pl> or F<.ph>. These are old |
12 | libraries supplied so that old programs that use them still run. The |
13 | F<.pl> files will all eventually be converted into standard modules, and |
14 | the F<.ph> files made by B<h2ph> will probably end up as extension modules |
15 | made by B<h2xs>. (Some F<.ph> values may already be available through the |
16 | POSIX module.) The B<pl2pm> file in the distribution may help in your |
17 | conversion, but it's just a mechanical process and therefore far from |
18 | bulletproof. |
19 | |
20 | =head2 Pragmatic Modules |
21 | |
22 | They work somewhat like pragmas in that they tend to affect the compilation of |
23 | your program, and thus will usually work well only when used within a |
24 | C<use>, or C<no>. Most of these are locally scoped, so an inner BLOCK |
25 | may countermand any of these by saying: |
26 | |
27 | no integer; |
28 | no strict 'refs'; |
29 | |
30 | which lasts until the end of that BLOCK. |
31 | |
32 | Unlike the pragmas that effect the C<$^H> hints variable, the C<use |
33 | vars> and C<use subs> declarations are not BLOCK-scoped. They allow |
34 | you to predeclare a variables or subroutines within a particular |
35 | I<file> rather than just a block. Such declarations are effective |
36 | for the entire file for which they were declared. You cannot rescind |
37 | them with C<no vars> or C<no subs>. |
38 | |
39 | The following pragmas are defined (and have their own documentation). |
40 | |
41 | =over 12 |
42 | |
43 | =item use autouse MODULE => qw(sub1 sub2 sub3) |
44 | |
45 | Defers C<require MODULE> until someone calls one of the specified |
46 | subroutines (which must be exported by MODULE). This pragma should be |
47 | used with caution, and only when necessary. |
48 | |
49 | =item blib |
50 | |
51 | manipulate @INC at compile time to use MakeMaker's uninstalled version |
52 | of a package |
53 | |
54 | =item diagnostics |
55 | |
56 | force verbose warning diagnostics |
57 | |
58 | =item integer |
59 | |
60 | compute arithmetic in integer instead of double |
61 | |
62 | =item less |
63 | |
64 | request less of something from the compiler |
65 | |
66 | =item lib |
67 | |
68 | manipulate @INC at compile time |
69 | |
70 | =item locale |
71 | |
72 | use or ignore current locale for builtin operations (see L<perllocale>) |
73 | |
74 | =item ops |
75 | |
76 | restrict named opcodes when compiling or running Perl code |
77 | |
78 | =item overload |
79 | |
80 | overload basic Perl operations |
81 | |
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82 | =item re |
83 | |
84 | alter behaviour of regular expressions |
85 | |
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86 | =item sigtrap |
87 | |
88 | enable simple signal handling |
89 | |
90 | =item strict |
91 | |
92 | restrict unsafe constructs |
93 | |
94 | =item subs |
95 | |
96 | predeclare sub names |
97 | |
98 | =item vmsish |
99 | |
100 | adopt certain VMS-specific behaviors |
101 | |
102 | =item vars |
103 | |
104 | predeclare global variable names |
105 | |
106 | =back |
107 | |
108 | =head2 Standard Modules |
109 | |
110 | Standard, bundled modules are all expected to behave in a well-defined |
111 | manner with respect to namespace pollution because they use the |
112 | Exporter module. See their own documentation for details. |
113 | |
114 | =over 12 |
115 | |
116 | =item AnyDBM_File |
117 | |
118 | provide framework for multiple DBMs |
119 | |
120 | =item AutoLoader |
121 | |
122 | load functions only on demand |
123 | |
124 | =item AutoSplit |
125 | |
126 | split a package for autoloading |
127 | |
128 | =item Benchmark |
129 | |
130 | benchmark running times of code |
131 | |
132 | =item CPAN |
133 | |
134 | interface to Comprehensive Perl Archive Network |
135 | |
136 | =item CPAN::FirstTime |
137 | |
138 | create a CPAN configuration file |
139 | |
140 | =item CPAN::Nox |
141 | |
142 | run CPAN while avoiding compiled extensions |
143 | |
144 | =item Carp |
145 | |
146 | warn of errors (from perspective of caller) |
147 | |
148 | =item Class::Struct |
149 | |
150 | declare struct-like datatypes |
151 | |
152 | =item Config |
153 | |
154 | access Perl configuration information |
155 | |
156 | =item Cwd |
157 | |
158 | get pathname of current working directory |
159 | |
160 | =item DB_File |
161 | |
162 | access to Berkeley DB |
163 | |
164 | =item Devel::SelfStubber |
165 | |
166 | generate stubs for a SelfLoading module |
167 | |
168 | =item DirHandle |
169 | |
170 | supply object methods for directory handles |
171 | |
172 | =item DynaLoader |
173 | |
174 | dynamically load C libraries into Perl code |
175 | |
176 | =item English |
177 | |
178 | use nice English (or awk) names for ugly punctuation variables |
179 | |
180 | =item Env |
181 | |
182 | import environment variables |
183 | |
184 | =item Exporter |
185 | |
186 | implements default import method for modules |
187 | |
188 | =item ExtUtils::Embed |
189 | |
190 | utilities for embedding Perl in C/C++ applications |
191 | |
192 | =item ExtUtils::Install |
193 | |
194 | install files from here to there |
195 | |
196 | =item ExtUtils::Liblist |
197 | |
198 | determine libraries to use and how to use them |
199 | |
200 | =item ExtUtils::MM_OS2 |
201 | |
202 | methods to override Unix behaviour in ExtUtils::MakeMaker |
203 | |
204 | =item ExtUtils::MM_Unix |
205 | |
206 | methods used by ExtUtils::MakeMaker |
207 | |
208 | =item ExtUtils::MM_VMS |
209 | |
210 | methods to override Unix behaviour in ExtUtils::MakeMaker |
211 | |
212 | =item ExtUtils::MakeMaker |
213 | |
214 | create an extension Makefile |
215 | |
216 | =item ExtUtils::Manifest |
217 | |
218 | utilities to write and check a MANIFEST file |
219 | |
220 | =item ExtUtils::Mkbootstrap |
221 | |
222 | make a bootstrap file for use by DynaLoader |
223 | |
224 | =item ExtUtils::Mksymlists |
225 | |
226 | write linker options files for dynamic extension |
227 | |
228 | =item ExtUtils::testlib |
229 | |
230 | add blib/* directories to @INC |
231 | |
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232 | =item Fatal |
233 | |
234 | make errors in builtins or Perl functions fatal |
235 | |
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236 | =item Fcntl |
237 | |
238 | load the C Fcntl.h defines |
239 | |
240 | =item File::Basename |
241 | |
242 | split a pathname into pieces |
243 | |
244 | =item File::CheckTree |
245 | |
246 | run many filetest checks on a tree |
247 | |
248 | =item File::Compare |
249 | |
250 | compare files or filehandles |
251 | |
252 | =item File::Copy |
253 | |
254 | copy files or filehandles |
255 | |
256 | =item File::Find |
257 | |
258 | traverse a file tree |
259 | |
260 | =item File::Path |
261 | |
262 | create or remove a series of directories |
263 | |
264 | =item File::stat |
265 | |
266 | by-name interface to Perl's builtin stat() functions |
267 | |
268 | =item FileCache |
269 | |
270 | keep more files open than the system permits |
271 | |
272 | =item FileHandle |
273 | |
274 | supply object methods for filehandles |
275 | |
276 | =item FindBin |
277 | |
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278 | locate directory of original Perl script |
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279 | |
280 | =item GDBM_File |
281 | |
282 | access to the gdbm library |
283 | |
284 | =item Getopt::Long |
285 | |
286 | extended processing of command line options |
287 | |
288 | =item Getopt::Std |
289 | |
290 | process single-character switches with switch clustering |
291 | |
292 | =item I18N::Collate |
293 | |
294 | compare 8-bit scalar data according to the current locale |
295 | |
296 | =item IO |
297 | |
298 | load various IO modules |
299 | |
300 | =item IO::File |
301 | |
302 | supply object methods for filehandles |
303 | |
304 | =item IO::Handle |
305 | |
306 | supply object methods for I/O handles |
307 | |
308 | =item IO::Pipe |
309 | |
310 | supply object methods for pipes |
311 | |
312 | =item IO::Seekable |
313 | |
314 | supply seek based methods for I/O objects |
315 | |
316 | =item IO::Select |
317 | |
318 | OO interface to the select system call |
319 | |
320 | =item IO::Socket |
321 | |
322 | object interface to socket communications |
323 | |
324 | =item IPC::Open2 |
325 | |
326 | open a process for both reading and writing |
327 | |
328 | =item IPC::Open3 |
329 | |
330 | open a process for reading, writing, and error handling |
331 | |
332 | =item Math::BigFloat |
333 | |
334 | arbitrary length float math package |
335 | |
336 | =item Math::BigInt |
337 | |
338 | arbitrary size integer math package |
339 | |
340 | =item Math::Complex |
341 | |
342 | complex numbers and associated mathematical functions |
343 | |
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344 | =item Math::Trig |
345 | |
346 | simple interface to parts of Math::Complex for those who |
347 | need trigonometric functions only for real numbers |
348 | |
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349 | =item NDBM_File |
350 | |
351 | tied access to ndbm files |
352 | |
353 | =item Net::Ping |
354 | |
355 | Hello, anybody home? |
356 | |
357 | =item Net::hostent |
358 | |
359 | by-name interface to Perl's builtin gethost*() functions |
360 | |
361 | =item Net::netent |
362 | |
363 | by-name interface to Perl's builtin getnet*() functions |
364 | |
365 | =item Net::protoent |
366 | |
367 | by-name interface to Perl's builtin getproto*() functions |
368 | |
369 | =item Net::servent |
370 | |
371 | by-name interface to Perl's builtin getserv*() functions |
372 | |
373 | =item Opcode |
374 | |
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375 | disable named opcodes when compiling or running Perl code |
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376 | |
377 | =item Pod::Text |
378 | |
379 | convert POD data to formatted ASCII text |
380 | |
381 | =item POSIX |
382 | |
383 | interface to IEEE Standard 1003.1 |
384 | |
385 | =item SDBM_File |
386 | |
387 | tied access to sdbm files |
388 | |
389 | =item Safe |
390 | |
391 | compile and execute code in restricted compartments |
392 | |
393 | =item Search::Dict |
394 | |
395 | search for key in dictionary file |
396 | |
397 | =item SelectSaver |
398 | |
399 | save and restore selected file handle |
400 | |
401 | =item SelfLoader |
402 | |
403 | load functions only on demand |
404 | |
405 | =item Shell |
406 | |
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407 | run shell commands transparently within Perl |
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408 | |
409 | =item Socket |
410 | |
411 | load the C socket.h defines and structure manipulators |
412 | |
413 | =item Symbol |
414 | |
415 | manipulate Perl symbols and their names |
416 | |
417 | =item Sys::Hostname |
418 | |
419 | try every conceivable way to get hostname |
420 | |
421 | =item Sys::Syslog |
422 | |
423 | interface to the Unix syslog(3) calls |
424 | |
425 | =item Term::Cap |
426 | |
427 | termcap interface |
428 | |
429 | =item Term::Complete |
430 | |
431 | word completion module |
432 | |
433 | =item Term::ReadLine |
434 | |
435 | interface to various C<readline> packages |
436 | |
437 | =item Test::Harness |
438 | |
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439 | run Perl standard test scripts with statistics |
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440 | |
441 | =item Text::Abbrev |
442 | |
443 | create an abbreviation table from a list |
444 | |
445 | =item Text::ParseWords |
446 | |
447 | parse text into an array of tokens |
448 | |
449 | =item Text::Soundex |
450 | |
451 | implementation of the Soundex Algorithm as described by Knuth |
452 | |
453 | =item Text::Tabs |
454 | |
455 | expand and unexpand tabs per the Unix expand(1) and unexpand(1) |
456 | |
457 | =item Text::Wrap |
458 | |
459 | line wrapping to form simple paragraphs |
460 | |
461 | =item Tie::Hash |
462 | |
463 | base class definitions for tied hashes |
464 | |
465 | =item Tie::RefHash |
466 | |
467 | base class definitions for tied hashes with references as keys |
468 | |
469 | =item Tie::Scalar |
470 | |
471 | base class definitions for tied scalars |
472 | |
473 | =item Tie::SubstrHash |
474 | |
475 | fixed-table-size, fixed-key-length hashing |
476 | |
477 | =item Time::Local |
478 | |
479 | efficiently compute time from local and GMT time |
480 | |
481 | =item Time::gmtime |
482 | |
483 | by-name interface to Perl's builtin gmtime() function |
484 | |
485 | =item Time::localtime |
486 | |
487 | by-name interface to Perl's builtin localtime() function |
488 | |
489 | =item Time::tm |
490 | |
491 | internal object used by Time::gmtime and Time::localtime |
492 | |
493 | =item UNIVERSAL |
494 | |
495 | base class for ALL classes (blessed references) |
496 | |
497 | =item User::grent |
498 | |
499 | by-name interface to Perl's builtin getgr*() functions |
500 | |
501 | =item User::pwent |
502 | |
503 | by-name interface to Perl's builtin getpw*() functions |
504 | |
505 | =back |
506 | |
507 | To find out I<all> the modules installed on your system, including |
508 | those without documentation or outside the standard release, do this: |
509 | |
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510 | % find `perl -e 'print "@INC"'` -name '*.pm' -print |
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511 | |
512 | They should all have their own documentation installed and accessible via |
513 | your system man(1) command. If that fails, try the I<perldoc> program. |
514 | |
515 | =head2 Extension Modules |
516 | |
517 | Extension modules are written in C (or a mix of Perl and C) and may be |
518 | statically linked or in general are |
519 | dynamically loaded into Perl if and when you need them. Supported |
520 | extension modules include the Socket, Fcntl, and POSIX modules. |
521 | |
522 | Many popular C extension modules do not come bundled (at least, not |
523 | completely) due to their sizes, volatility, or simply lack of time for |
524 | adequate testing and configuration across the multitude of platforms on |
525 | which Perl was beta-tested. You are encouraged to look for them in |
526 | archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their |
527 | authors before randomly posting asking for their present condition and |
528 | disposition. |
529 | |
530 | =head1 CPAN |
531 | |
532 | CPAN stands for the Comprehensive Perl Archive Network. This is a globally |
533 | replicated collection of all known Perl materials, including hundreds |
534 | of unbundled modules. Here are the major categories of modules: |
535 | |
536 | =over |
537 | |
538 | =item * |
539 | Language Extensions and Documentation Tools |
540 | |
541 | =item * |
542 | Development Support |
543 | |
544 | =item * |
545 | Operating System Interfaces |
546 | |
547 | =item * |
548 | Networking, Device Control (modems) and InterProcess Communication |
549 | |
550 | =item * |
551 | Data Types and Data Type Utilities |
552 | |
553 | =item * |
554 | Database Interfaces |
555 | |
556 | =item * |
557 | User Interfaces |
558 | |
559 | =item * |
560 | Interfaces to / Emulations of Other Programming Languages |
561 | |
562 | =item * |
563 | File Names, File Systems and File Locking (see also File Handles) |
564 | |
565 | =item * |
566 | String Processing, Language Text Processing, Parsing, and Searching |
567 | |
568 | =item * |
569 | Option, Argument, Parameter, and Configuration File Processing |
570 | |
571 | =item * |
572 | Internationalization and Locale |
573 | |
574 | =item * |
575 | Authentication, Security, and Encryption |
576 | |
577 | =item * |
578 | World Wide Web, HTML, HTTP, CGI, MIME |
579 | |
580 | =item * |
581 | Server and Daemon Utilities |
582 | |
583 | =item * |
584 | Archiving and Compression |
585 | |
586 | =item * |
587 | Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing |
588 | |
589 | =item * |
590 | Mail and Usenet News |
591 | |
592 | =item * |
593 | Control Flow Utilities (callbacks and exceptions etc) |
594 | |
595 | =item * |
596 | File Handle and Input/Output Stream Utilities |
597 | |
598 | =item * |
599 | Miscellaneous Modules |
600 | |
601 | =back |
602 | |
603 | The registered CPAN sites as of this writing include the following. |
604 | You should try to choose one close to you: |
605 | |
606 | =over |
607 | |
608 | =item * |
609 | Africa |
610 | |
611 | South Africa ftp://ftp.is.co.za/programming/perl/CPAN/ |
612 | |
613 | =item * |
614 | Asia |
615 | |
616 | Hong Kong ftp://ftp.hkstar.com/pub/CPAN/ |
617 | Japan ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/ |
618 | ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/ |
619 | South Korea ftp://ftp.nuri.net/pub/CPAN/ |
620 | Taiwan ftp://dongpo.math.ncu.edu.tw/perl/CPAN/ |
621 | ftp://ftp.wownet.net/pub2/PERL/ |
622 | |
623 | =item * |
624 | Australasia |
625 | |
626 | Australia ftp://ftp.netinfo.com.au/pub/perl/CPAN/ |
627 | New Zealand ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/ |
628 | |
629 | =item * |
630 | Europe |
631 | |
632 | Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/ |
633 | Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/ |
634 | Czech Republic ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/ |
635 | Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/ |
636 | Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/ |
637 | France ftp://ftp.ibp.fr/pub/perl/CPAN/ |
638 | ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/ |
639 | Germany ftp://ftp.gmd.de/packages/CPAN/ |
640 | ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/ |
641 | ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/ |
642 | ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/ |
643 | ftp://ftp.uni-erlangen.de/pub/source/Perl/CPAN/ |
644 | ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/ |
645 | Greece ftp://ftp.ntua.gr/pub/lang/perl/ |
646 | Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/ |
647 | Italy ftp://cis.utovrm.it/CPAN/ |
648 | the Netherlands ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/ |
649 | ftp://ftp.EU.net/packages/cpan/ |
650 | Norway ftp://ftp.uit.no/pub/languages/perl/cpan/ |
651 | Poland ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/ |
652 | ftp://sunsite.icm.edu.pl/pub/CPAN/ |
653 | Portugal ftp://ftp.ci.uminho.pt/pub/lang/perl/ |
654 | ftp://ftp.telepac.pt/pub/CPAN/ |
655 | Russia ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/ |
656 | Slovenia ftp://ftp.arnes.si/software/perl/CPAN/ |
657 | Spain ftp://ftp.etse.urv.es/pub/mirror/perl/ |
658 | ftp://ftp.rediris.es/mirror/CPAN/ |
659 | Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/ |
660 | UK ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/ |
661 | ftp://sunsite.doc.ic.ac.uk/packages/CPAN/ |
662 | ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/ |
663 | |
664 | =item * |
665 | North America |
666 | |
667 | Ontario ftp://ftp.utilis.com/public/CPAN/ |
668 | ftp://enterprise.ic.gc.ca/pub/perl/CPAN/ |
669 | Manitoba ftp://theory.uwinnipeg.ca/pub/CPAN/ |
670 | California ftp://ftp.digital.com/pub/plan/perl/CPAN/ |
671 | ftp://ftp.cdrom.com/pub/perl/CPAN/ |
672 | Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/ |
673 | Florida ftp://ftp.cis.ufl.edu/pub/perl/CPAN/ |
674 | Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/ |
675 | Massachusetts ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/ |
676 | New York ftp://ftp.rge.com/pub/languages/perl/ |
677 | North Carolina ftp://ftp.duke.edu/pub/perl/ |
678 | Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/ |
679 | Oregon http://www.perl.org/CPAN/ |
680 | ftp://ftp.orst.edu/pub/packages/CPAN/ |
681 | Pennsylvania ftp://ftp.epix.net/pub/languages/perl/ |
682 | Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/ |
683 | ftp://ftp.metronet.com/pub/perl/ |
684 | |
685 | =item * |
686 | South America |
687 | |
688 | Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/ |
689 | |
690 | =back |
691 | |
692 | For an up-to-date listing of CPAN sites, |
693 | see F<http://www.perl.com/perl/CPAN> or F<ftp://ftp.perl.com/perl/>. |
694 | |
695 | =head1 Modules: Creation, Use, and Abuse |
696 | |
697 | (The following section is borrowed directly from Tim Bunce's modules |
698 | file, available at your nearest CPAN site.) |
699 | |
700 | Perl implements a class using a package, but the presence of a |
701 | package doesn't imply the presence of a class. A package is just a |
702 | namespace. A class is a package that provides subroutines that can be |
703 | used as methods. A method is just a subroutine that expects, as its |
704 | first argument, either the name of a package (for "static" methods), |
705 | or a reference to something (for "virtual" methods). |
706 | |
707 | A module is a file that (by convention) provides a class of the same |
708 | name (sans the .pm), plus an import method in that class that can be |
709 | called to fetch exported symbols. This module may implement some of |
710 | its methods by loading dynamic C or C++ objects, but that should be |
711 | totally transparent to the user of the module. Likewise, the module |
712 | might set up an AUTOLOAD function to slurp in subroutine definitions on |
713 | demand, but this is also transparent. Only the F<.pm> file is required to |
714 | exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about |
715 | the AUTOLOAD mechanism. |
716 | |
717 | =head2 Guidelines for Module Creation |
718 | |
719 | =over 4 |
720 | |
721 | =item Do similar modules already exist in some form? |
722 | |
723 | If so, please try to reuse the existing modules either in whole or |
724 | by inheriting useful features into a new class. If this is not |
725 | practical try to get together with the module authors to work on |
726 | extending or enhancing the functionality of the existing modules. |
727 | A perfect example is the plethora of packages in perl4 for dealing |
728 | with command line options. |
729 | |
730 | If you are writing a module to expand an already existing set of |
731 | modules, please coordinate with the author of the package. It |
732 | helps if you follow the same naming scheme and module interaction |
733 | scheme as the original author. |
734 | |
735 | =item Try to design the new module to be easy to extend and reuse. |
736 | |
737 | Use blessed references. Use the two argument form of bless to bless |
738 | into the class name given as the first parameter of the constructor, |
739 | e.g.,: |
740 | |
741 | sub new { |
742 | my $class = shift; |
743 | return bless {}, $class; |
744 | } |
745 | |
746 | or even this if you'd like it to be used as either a static |
747 | or a virtual method. |
748 | |
749 | sub new { |
750 | my $self = shift; |
751 | my $class = ref($self) || $self; |
752 | return bless {}, $class; |
753 | } |
754 | |
755 | Pass arrays as references so more parameters can be added later |
756 | (it's also faster). Convert functions into methods where |
757 | appropriate. Split large methods into smaller more flexible ones. |
758 | Inherit methods from other modules if appropriate. |
759 | |
760 | Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>. |
761 | Generally you can delete the "C<eq 'FOO'>" part with no harm at all. |
762 | Let the objects look after themselves! Generally, avoid hard-wired |
763 | class names as far as possible. |
764 | |
765 | Avoid C<$r-E<gt>Class::func()> where using C<@ISA=qw(... Class ...)> and |
766 | C<$r-E<gt>func()> would work (see L<perlbot> for more details). |
767 | |
768 | Use autosplit so little used or newly added functions won't be a |
5a964f20 |
769 | burden to programs that don't use them. Add test functions to |
f102b883 |
770 | the module after __END__ either using AutoSplit or by saying: |
771 | |
772 | eval join('',<main::DATA>) || die $@ unless caller(); |
773 | |
774 | Does your module pass the 'empty subclass' test? If you say |
775 | "C<@SUBCLASS::ISA = qw(YOURCLASS);>" your applications should be able |
776 | to use SUBCLASS in exactly the same way as YOURCLASS. For example, |
777 | does your application still work if you change: C<$obj = new YOURCLASS;> |
778 | into: C<$obj = new SUBCLASS;> ? |
779 | |
780 | Avoid keeping any state information in your packages. It makes it |
781 | difficult for multiple other packages to use yours. Keep state |
782 | information in objects. |
783 | |
784 | Always use B<-w>. Try to C<use strict;> (or C<use strict qw(...);>). |
785 | Remember that you can add C<no strict qw(...);> to individual blocks |
5a964f20 |
786 | of code that need less strictness. Always use B<-w>. Always use B<-w>! |
f102b883 |
787 | Follow the guidelines in the perlstyle(1) manual. |
788 | |
789 | =item Some simple style guidelines |
790 | |
5a964f20 |
791 | The perlstyle manual supplied with Perl has many helpful points. |
f102b883 |
792 | |
793 | Coding style is a matter of personal taste. Many people evolve their |
794 | style over several years as they learn what helps them write and |
795 | maintain good code. Here's one set of assorted suggestions that |
796 | seem to be widely used by experienced developers: |
797 | |
798 | Use underscores to separate words. It is generally easier to read |
799 | $var_names_like_this than $VarNamesLikeThis, especially for |
800 | non-native speakers of English. It's also a simple rule that works |
801 | consistently with VAR_NAMES_LIKE_THIS. |
802 | |
803 | Package/Module names are an exception to this rule. Perl informally |
804 | reserves lowercase module names for 'pragma' modules like integer |
805 | and strict. Other modules normally begin with a capital letter and |
806 | use mixed case with no underscores (need to be short and portable). |
807 | |
808 | You may find it helpful to use letter case to indicate the scope |
809 | or nature of a variable. For example: |
810 | |
5a964f20 |
811 | $ALL_CAPS_HERE constants only (beware clashes with Perl vars) |
f102b883 |
812 | $Some_Caps_Here package-wide global/static |
813 | $no_caps_here function scope my() or local() variables |
814 | |
815 | Function and method names seem to work best as all lowercase. |
816 | e.g., C<$obj-E<gt>as_string()>. |
817 | |
818 | You can use a leading underscore to indicate that a variable or |
819 | function should not be used outside the package that defined it. |
820 | |
821 | =item Select what to export. |
822 | |
823 | Do NOT export method names! |
824 | |
825 | Do NOT export anything else by default without a good reason! |
826 | |
827 | Exports pollute the namespace of the module user. If you must |
828 | export try to use @EXPORT_OK in preference to @EXPORT and avoid |
829 | short or common names to reduce the risk of name clashes. |
830 | |
831 | Generally anything not exported is still accessible from outside the |
832 | module using the ModuleName::item_name (or C<$blessed_ref-E<gt>method>) |
833 | syntax. By convention you can use a leading underscore on names to |
834 | indicate informally that they are 'internal' and not for public use. |
835 | |
836 | (It is actually possible to get private functions by saying: |
837 | C<my $subref = sub { ... }; &$subref;>. But there's no way to call that |
838 | directly as a method, because a method must have a name in the symbol |
839 | table.) |
840 | |
841 | As a general rule, if the module is trying to be object oriented |
842 | then export nothing. If it's just a collection of functions then |
843 | @EXPORT_OK anything but use @EXPORT with caution. |
844 | |
845 | =item Select a name for the module. |
846 | |
847 | This name should be as descriptive, accurate, and complete as |
848 | possible. Avoid any risk of ambiguity. Always try to use two or |
849 | more whole words. Generally the name should reflect what is special |
850 | about what the module does rather than how it does it. Please use |
851 | nested module names to group informally or categorize a module. |
852 | There should be a very good reason for a module not to have a nested name. |
853 | Module names should begin with a capital letter. |
854 | |
855 | Having 57 modules all called Sort will not make life easy for anyone |
856 | (though having 23 called Sort::Quick is only marginally better :-). |
857 | Imagine someone trying to install your module alongside many others. |
858 | If in any doubt ask for suggestions in comp.lang.perl.misc. |
859 | |
860 | If you are developing a suite of related modules/classes it's good |
861 | practice to use nested classes with a common prefix as this will |
862 | avoid namespace clashes. For example: Xyz::Control, Xyz::View, |
863 | Xyz::Model etc. Use the modules in this list as a naming guide. |
864 | |
865 | If adding a new module to a set, follow the original author's |
866 | standards for naming modules and the interface to methods in |
867 | those modules. |
868 | |
869 | To be portable each component of a module name should be limited to |
870 | 11 characters. If it might be used on MS-DOS then try to ensure each is |
871 | unique in the first 8 characters. Nested modules make this easier. |
872 | |
873 | =item Have you got it right? |
874 | |
875 | How do you know that you've made the right decisions? Have you |
876 | picked an interface design that will cause problems later? Have |
877 | you picked the most appropriate name? Do you have any questions? |
878 | |
879 | The best way to know for sure, and pick up many helpful suggestions, |
880 | is to ask someone who knows. Comp.lang.perl.misc is read by just about |
881 | all the people who develop modules and it's the best place to ask. |
882 | |
883 | All you need to do is post a short summary of the module, its |
884 | purpose and interfaces. A few lines on each of the main methods is |
885 | probably enough. (If you post the whole module it might be ignored |
886 | by busy people - generally the very people you want to read it!) |
887 | |
888 | Don't worry about posting if you can't say when the module will be |
889 | ready - just say so in the message. It might be worth inviting |
890 | others to help you, they may be able to complete it for you! |
891 | |
892 | =item README and other Additional Files. |
893 | |
894 | It's well known that software developers usually fully document the |
895 | software they write. If, however, the world is in urgent need of |
896 | your software and there is not enough time to write the full |
897 | documentation please at least provide a README file containing: |
898 | |
899 | =over 10 |
900 | |
901 | =item * |
902 | A description of the module/package/extension etc. |
903 | |
904 | =item * |
905 | A copyright notice - see below. |
906 | |
907 | =item * |
908 | Prerequisites - what else you may need to have. |
909 | |
910 | =item * |
911 | How to build it - possible changes to Makefile.PL etc. |
912 | |
913 | =item * |
914 | How to install it. |
915 | |
916 | =item * |
917 | Recent changes in this release, especially incompatibilities |
918 | |
919 | =item * |
920 | Changes / enhancements you plan to make in the future. |
921 | |
922 | =back |
923 | |
924 | If the README file seems to be getting too large you may wish to |
925 | split out some of the sections into separate files: INSTALL, |
926 | Copying, ToDo etc. |
927 | |
928 | =over 4 |
929 | |
930 | =item Adding a Copyright Notice. |
931 | |
932 | How you choose to license your work is a personal decision. |
933 | The general mechanism is to assert your Copyright and then make |
934 | a declaration of how others may copy/use/modify your work. |
935 | |
936 | Perl, for example, is supplied with two types of licence: The GNU |
937 | GPL and The Artistic Licence (see the files README, Copying, and |
938 | Artistic). Larry has good reasons for NOT just using the GNU GPL. |
939 | |
940 | My personal recommendation, out of respect for Larry, Perl, and the |
5a964f20 |
941 | Perl community at large is to state something simply like: |
f102b883 |
942 | |
943 | Copyright (c) 1995 Your Name. All rights reserved. |
944 | This program is free software; you can redistribute it and/or |
945 | modify it under the same terms as Perl itself. |
946 | |
947 | This statement should at least appear in the README file. You may |
948 | also wish to include it in a Copying file and your source files. |
949 | Remember to include the other words in addition to the Copyright. |
950 | |
951 | =item Give the module a version/issue/release number. |
952 | |
953 | To be fully compatible with the Exporter and MakeMaker modules you |
954 | should store your module's version number in a non-my package |
955 | variable called $VERSION. This should be a floating point |
956 | number with at least two digits after the decimal (i.e., hundredths, |
957 | e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version. |
958 | See Exporter.pm in Perl5.001m or later for details. |
959 | |
960 | It may be handy to add a function or method to retrieve the number. |
961 | Use the number in announcements and archive file names when |
962 | releasing the module (ModuleName-1.02.tar.Z). |
963 | See perldoc ExtUtils::MakeMaker.pm for details. |
964 | |
965 | =item How to release and distribute a module. |
966 | |
967 | It's good idea to post an announcement of the availability of your |
968 | module (or the module itself if small) to the comp.lang.perl.announce |
969 | Usenet newsgroup. This will at least ensure very wide once-off |
970 | distribution. |
971 | |
972 | If possible you should place the module into a major ftp archive and |
973 | include details of its location in your announcement. |
974 | |
975 | Some notes about ftp archives: Please use a long descriptive file |
5a964f20 |
976 | name that includes the version number. Most incoming directories |
f102b883 |
977 | will not be readable/listable, i.e., you won't be able to see your |
978 | file after uploading it. Remember to send your email notification |
979 | message as soon as possible after uploading else your file may get |
980 | deleted automatically. Allow time for the file to be processed |
981 | and/or check the file has been processed before announcing its |
982 | location. |
983 | |
984 | FTP Archives for Perl Modules: |
985 | |
986 | Follow the instructions and links on |
987 | |
988 | http://franz.ww.tu-berlin.de/modulelist |
989 | |
990 | or upload to one of these sites: |
991 | |
992 | ftp://franz.ww.tu-berlin.de/incoming |
993 | ftp://ftp.cis.ufl.edu/incoming |
994 | |
995 | and notify <F<upload@franz.ww.tu-berlin.de>>. |
996 | |
997 | By using the WWW interface you can ask the Upload Server to mirror |
998 | your modules from your ftp or WWW site into your own directory on |
999 | CPAN! |
1000 | |
1001 | Please remember to send me an updated entry for the Module list! |
1002 | |
1003 | =item Take care when changing a released module. |
1004 | |
7b8d334a |
1005 | Always strive to remain compatible with previous released versions. |
1006 | Otherwise try to add a mechanism to revert to the |
f102b883 |
1007 | old behaviour if people rely on it. Document incompatible changes. |
1008 | |
1009 | =back |
1010 | |
1011 | =back |
1012 | |
1013 | =head2 Guidelines for Converting Perl 4 Library Scripts into Modules |
1014 | |
1015 | =over 4 |
1016 | |
1017 | =item There is no requirement to convert anything. |
1018 | |
1019 | If it ain't broke, don't fix it! Perl 4 library scripts should |
1020 | continue to work with no problems. You may need to make some minor |
1021 | changes (like escaping non-array @'s in double quoted strings) but |
1022 | there is no need to convert a .pl file into a Module for just that. |
1023 | |
1024 | =item Consider the implications. |
1025 | |
5a964f20 |
1026 | All Perl applications that make use of the script will need to |
f102b883 |
1027 | be changed (slightly) if the script is converted into a module. Is |
1028 | it worth it unless you plan to make other changes at the same time? |
1029 | |
1030 | =item Make the most of the opportunity. |
1031 | |
1032 | If you are going to convert the script to a module you can use the |
1033 | opportunity to redesign the interface. The 'Guidelines for Module |
1034 | Creation' above include many of the issues you should consider. |
1035 | |
1036 | =item The pl2pm utility will get you started. |
1037 | |
1038 | This utility will read *.pl files (given as parameters) and write |
1039 | corresponding *.pm files. The pl2pm utilities does the following: |
1040 | |
1041 | =over 10 |
1042 | |
1043 | =item * |
1044 | Adds the standard Module prologue lines |
1045 | |
1046 | =item * |
1047 | Converts package specifiers from ' to :: |
1048 | |
1049 | =item * |
1050 | Converts die(...) to croak(...) |
1051 | |
1052 | =item * |
1053 | Several other minor changes |
1054 | |
1055 | =back |
1056 | |
1057 | Being a mechanical process pl2pm is not bullet proof. The converted |
1058 | code will need careful checking, especially any package statements. |
1059 | Don't delete the original .pl file till the new .pm one works! |
1060 | |
1061 | =back |
1062 | |
1063 | =head2 Guidelines for Reusing Application Code |
1064 | |
1065 | =over 4 |
1066 | |
1067 | =item Complete applications rarely belong in the Perl Module Library. |
1068 | |
5a964f20 |
1069 | =item Many applications contain some Perl code that could be reused. |
f102b883 |
1070 | |
1071 | Help save the world! Share your code in a form that makes it easy |
1072 | to reuse. |
1073 | |
1074 | =item Break-out the reusable code into one or more separate module files. |
1075 | |
1076 | =item Take the opportunity to reconsider and redesign the interfaces. |
1077 | |
1078 | =item In some cases the 'application' can then be reduced to a small |
1079 | |
1080 | fragment of code built on top of the reusable modules. In these cases |
1081 | the application could invoked as: |
1082 | |
5a964f20 |
1083 | % perl -e 'use Module::Name; method(@ARGV)' ... |
f102b883 |
1084 | or |
5a964f20 |
1085 | % perl -mModule::Name ... (in perl5.002 or higher) |
f102b883 |
1086 | |
1087 | =back |
1088 | |
1089 | =head1 NOTE |
1090 | |
1091 | Perl does not enforce private and public parts of its modules as you may |
1092 | have been used to in other languages like C++, Ada, or Modula-17. Perl |
1093 | doesn't have an infatuation with enforced privacy. It would prefer |
1094 | that you stayed out of its living room because you weren't invited, not |
1095 | because it has a shotgun. |
1096 | |
1097 | The module and its user have a contract, part of which is common law, |
1098 | and part of which is "written". Part of the common law contract is |
1099 | that a module doesn't pollute any namespace it wasn't asked to. The |
1100 | written contract for the module (A.K.A. documentation) may make other |
1101 | provisions. But then you know when you C<use RedefineTheWorld> that |
1102 | you're redefining the world and willing to take the consequences. |