3 perlmodlib - constructing new Perl modules and finding existing ones
7 =head1 THE PERL MODULE LIBRARY
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
20 =head2 Pragmatic Modules
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 lexically scoped, so an inner BLOCK
25 may countermand any of these by saying:
30 which lasts until the end of that BLOCK.
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>.
39 The following pragmas are defined (and have their own documentation).
43 =item use autouse MODULE => qw(sub1 sub2 sub3)
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.
51 manipulate @INC at compile time to use MakeMaker's uninstalled version
56 force verbose warning diagnostics
60 compute arithmetic in integer instead of double
64 request less of something from the compiler
68 manipulate @INC at compile time
72 use or ignore current locale for builtin operations (see L<perllocale>)
76 restrict named opcodes when compiling or running Perl code
80 overload basic Perl operations
84 alter behaviour of regular expressions
88 enable simple signal handling
92 restrict unsafe constructs
100 adopt certain VMS-specific behaviors
104 predeclare global variable names
108 =head2 Standard Modules
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.
118 provide framework for multiple DBMs
122 load functions only on demand
126 split a package for autoloading
130 benchmark running times of code
134 interface to Comprehensive Perl Archive Network
136 =item CPAN::FirstTime
138 create a CPAN configuration file
142 run CPAN while avoiding compiled extensions
146 warn of errors (from perspective of caller)
150 declare struct-like datatypes
154 access Perl configuration information
158 get pathname of current working directory
162 access to Berkeley DB
166 data debugging tool for the XS programmer
168 =item Devel::SelfStubber
170 generate stubs for a SelfLoading module
174 supply object methods for directory handles
178 dynamically load C libraries into Perl code
182 use nice English (or awk) names for ugly punctuation variables
186 import environment variables
190 implements default import method for modules
192 =item ExtUtils::Embed
194 utilities for embedding Perl in C/C++ applications
196 =item ExtUtils::Install
198 install files from here to there
200 =item ExtUtils::Liblist
202 determine libraries to use and how to use them
204 =item ExtUtils::MM_OS2
206 methods to override Unix behaviour in ExtUtils::MakeMaker
208 =item ExtUtils::MM_Unix
210 methods used by ExtUtils::MakeMaker
212 =item ExtUtils::MM_VMS
214 methods to override Unix behaviour in ExtUtils::MakeMaker
216 =item ExtUtils::MakeMaker
218 create an extension Makefile
220 =item ExtUtils::Manifest
222 utilities to write and check a MANIFEST file
224 =item ExtUtils::Mkbootstrap
226 make a bootstrap file for use by DynaLoader
228 =item ExtUtils::Mksymlists
230 write linker options files for dynamic extension
232 =item ExtUtils::testlib
234 add blib/* directories to @INC
238 make errors in builtins or Perl functions fatal
242 load the C Fcntl.h defines
246 split a pathname into pieces
248 =item File::CheckTree
250 run many filetest checks on a tree
254 compare files or filehandles
258 copy files or filehandles
266 create or remove a series of directories
270 portably perform operations on file names
272 =item File::Spec::Functions
274 function call interface to File::Spec module
278 by-name interface to Perl's builtin stat() functions
282 keep more files open than the system permits
286 supply object methods for filehandles
290 locate directory of original Perl script
294 access to the gdbm library
298 extended processing of command line options
302 process single-character switches with switch clustering
306 compare 8-bit scalar data according to the current locale
310 load various IO modules
314 supply object methods for filehandles
318 supply object methods for I/O handles
322 supply object methods for pipes
326 supply seek based methods for I/O objects
330 OO interface to the select system call
334 object interface to socket communications
338 open a process for both reading and writing
342 open a process for reading, writing, and error handling
346 arbitrary length float math package
350 arbitrary size integer math package
354 complex numbers and associated mathematical functions
358 simple interface to parts of Math::Complex for those who
359 need trigonometric functions only for real numbers
363 tied access to ndbm files
371 by-name interface to Perl's builtin gethost*() functions
375 by-name interface to Perl's builtin getnet*() functions
379 by-name interface to Perl's builtin getproto*() functions
383 by-name interface to Perl's builtin getserv*() functions
387 disable named opcodes when compiling or running Perl code
391 convert POD data to formatted ASCII text
395 interface to IEEE Standard 1003.1
399 tied access to sdbm files
403 compile and execute code in restricted compartments
407 search for key in dictionary file
411 save and restore selected file handle
415 load functions only on demand
419 run shell commands transparently within Perl
423 load the C socket.h defines and structure manipulators
427 manipulate Perl symbols and their names
431 try every conceivable way to get hostname
435 interface to the Unix syslog(3) calls
443 word completion module
447 interface to various C<readline> packages
451 run Perl standard test scripts with statistics
455 create an abbreviation table from a list
457 =item Text::ParseWords
459 parse text into an array of tokens
463 implementation of the Soundex Algorithm as described by Knuth
467 expand and unexpand tabs per the Unix expand(1) and unexpand(1)
471 line wrapping to form simple paragraphs
475 base class definitions for tied hashes
479 base class definitions for tied hashes with references as keys
483 base class definitions for tied scalars
485 =item Tie::SubstrHash
487 fixed-table-size, fixed-key-length hashing
491 efficiently compute time from local and GMT time
495 by-name interface to Perl's builtin gmtime() function
497 =item Time::localtime
499 by-name interface to Perl's builtin localtime() function
503 internal object used by Time::gmtime and Time::localtime
507 base class for ALL classes (blessed references)
511 by-name interface to Perl's builtin getgr*() functions
515 by-name interface to Perl's builtin getpw*() functions
519 To find out I<all> the modules installed on your system, including
520 those without documentation or outside the standard release, do this:
522 % find `perl -e 'print "@INC"'` -name '*.pm' -print
524 They should all have their own documentation installed and accessible via
525 your system man(1) command. If that fails, try the I<perldoc> program.
527 =head2 Extension Modules
529 Extension modules are written in C (or a mix of Perl and C) and may be
530 statically linked or in general are
531 dynamically loaded into Perl if and when you need them. Supported
532 extension modules include the Socket, Fcntl, and POSIX modules.
534 Many popular C extension modules do not come bundled (at least, not
535 completely) due to their sizes, volatility, or simply lack of time for
536 adequate testing and configuration across the multitude of platforms on
537 which Perl was beta-tested. You are encouraged to look for them in
538 archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their
539 authors before randomly posting asking for their present condition and
544 CPAN stands for the Comprehensive Perl Archive Network. This is a globally
545 replicated collection of all known Perl materials, including hundreds
546 of unbundled modules. Here are the major categories of modules:
551 Language Extensions and Documentation Tools
557 Operating System Interfaces
560 Networking, Device Control (modems) and InterProcess Communication
563 Data Types and Data Type Utilities
572 Interfaces to / Emulations of Other Programming Languages
575 File Names, File Systems and File Locking (see also File Handles)
578 String Processing, Language Text Processing, Parsing, and Searching
581 Option, Argument, Parameter, and Configuration File Processing
584 Internationalization and Locale
587 Authentication, Security, and Encryption
590 World Wide Web, HTML, HTTP, CGI, MIME
593 Server and Daemon Utilities
596 Archiving and Compression
599 Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
605 Control Flow Utilities (callbacks and exceptions etc)
608 File Handle and Input/Output Stream Utilities
611 Miscellaneous Modules
615 The registered CPAN sites as of this writing include the following.
616 You should try to choose one close to you:
623 South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
624 ftp://ftpza.co.za/pub/mirrors/cpan/
629 Armenia ftp://sunsite.aua.am/pub/CPAN/
630 China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
631 Hong Kong ftp://ftp.hkstar.com/pub/CPAN/
632 Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
633 Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
634 ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
635 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
636 ftp://ftp.meisei-u.ac.jp/pub/CPAN/
637 ftp://mirror.nucba.ac.jp/mirror/Perl/
638 Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
639 South Korea ftp://ftp.bora.net/pub/CPAN/
640 ftp://ftp.nuri.net/pub/CPAN/
641 Taiwan ftp://ftp.wownet.net/pub2/PERL/
642 ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
643 Thailand ftp://ftp.cs.riubon.ac.th/pub/mirrors/CPAN/
644 ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
649 Australia ftp://cpan.topend.com.au/pub/CPAN/
650 ftp://ftp.labyrinth.net.au/pub/perl/CPAN/
651 ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
652 ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
653 New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
654 ftp://sunsite.net.nz/pub/languages/perl/CPAN/
659 Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
664 Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
665 Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
666 Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
667 Croatia ftp://ftp.linux.hr/pub/CPAN/
668 Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
669 ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
670 Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
671 Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
672 Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
673 France ftp://ftp.lip6.fr/pub/perl/CPAN/
674 ftp://ftp.oleane.net/pub/mirrors/CPAN/
675 ftp://ftp.pasteur.fr/pub/computing/CPAN/
676 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
677 ftp://ftp.gmd.de/packages/CPAN/
678 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
679 ftp://ftp.leo.org/pub/comp/programming/languages/script/perl/CPAN/
680 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
681 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
682 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
683 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
684 Greece ftp://ftp.ntua.gr/pub/lang/perl/
685 Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
686 Ireland ftp://sunsite.compapp.dcu.ie/pub/perl/
687 Italy ftp://cis.uniRoma2.it/CPAN/
688 ftp://ftp.flashnet.it/pub/CPAN/
689 ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
690 Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
691 ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
692 Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
693 ftp://sunsite.uio.no/pub/languages/perl/CPAN/
694 Poland ftp://ftp.man.szczecin.pl/pub/perl/CPAN/
695 ftp://ftp.man.torun.pl/pub/doc/CPAN/
696 ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
697 ftp://sunsite.icm.edu.pl/pub/CPAN/
698 Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
699 ftp://ftp.ua.pt/pub/CPAN/
700 Romania ftp://ftp.dntis.ro/pub/mirrors/perl-cpan/
701 ftp://ftp.dnttm.ro/pub/CPAN/
702 Russia ftp://cpan.npi.msu.su/CPAN/
703 ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
704 Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
705 Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
706 Spain ftp://ftp.etse.urv.es/pub/perl/
707 ftp://ftp.rediris.es/mirror/CPAN/
708 Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
709 Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
710 Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
711 United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
712 ftp://ftp.flirble.org/pub/languages/perl/CPAN/
713 ftp://ftp.plig.org/pub/CPAN/
714 ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
715 ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/
720 Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
721 California ftp://ftp.cdrom.com/pub/perl/CPAN/
722 ftp://ftp.digital.com/pub/plan/perl/CPAN/
723 Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
724 Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
725 Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
726 Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
727 ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
728 Manitoba ftp://theory.uwinnipeg.ca/pub/CPAN/
729 Massachusetts ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
730 ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
731 Mexico D.F. ftp://ftp.msg.com.mx/pub/CPAN/
732 New York ftp://ftp.rge.com/pub/languages/perl/
733 North Carolina ftp://ftp.duke.edu/pub/perl/
734 Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
735 Ontario ftp://ftp.crc.ca/pub/packages/perl/CPAN/
736 Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
737 Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
738 Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
739 Utah ftp://mirror.xmission.com/CPAN/
740 Virginia ftp://ftp.perl.org/pub/perl/CPAN/
741 ftp://ruff.cs.jmu.edu/pub/CPAN/
742 Washington ftp://ftp.spu.edu/pub/CPAN/
747 Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
748 Chile ftp://ftp.ing.puc.cl/pub/unix/perl/CPAN/
749 ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/
753 For an up-to-date listing of CPAN sites,
754 see F<http://www.perl.com/perl/CPAN> or F<ftp://ftp.perl.com/perl/>.
756 =head1 Modules: Creation, Use, and Abuse
758 (The following section is borrowed directly from Tim Bunce's modules
759 file, available at your nearest CPAN site.)
761 Perl implements a class using a package, but the presence of a
762 package doesn't imply the presence of a class. A package is just a
763 namespace. A class is a package that provides subroutines that can be
764 used as methods. A method is just a subroutine that expects, as its
765 first argument, either the name of a package (for "static" methods),
766 or a reference to something (for "virtual" methods).
768 A module is a file that (by convention) provides a class of the same
769 name (sans the .pm), plus an import method in that class that can be
770 called to fetch exported symbols. This module may implement some of
771 its methods by loading dynamic C or C++ objects, but that should be
772 totally transparent to the user of the module. Likewise, the module
773 might set up an AUTOLOAD function to slurp in subroutine definitions on
774 demand, but this is also transparent. Only the F<.pm> file is required to
775 exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
776 the AUTOLOAD mechanism.
778 =head2 Guidelines for Module Creation
782 =item Do similar modules already exist in some form?
784 If so, please try to reuse the existing modules either in whole or
785 by inheriting useful features into a new class. If this is not
786 practical try to get together with the module authors to work on
787 extending or enhancing the functionality of the existing modules.
788 A perfect example is the plethora of packages in perl4 for dealing
789 with command line options.
791 If you are writing a module to expand an already existing set of
792 modules, please coordinate with the author of the package. It
793 helps if you follow the same naming scheme and module interaction
794 scheme as the original author.
796 =item Try to design the new module to be easy to extend and reuse.
798 Use blessed references. Use the two argument form of bless to bless
799 into the class name given as the first parameter of the constructor,
804 return bless {}, $class;
807 or even this if you'd like it to be used as either a static
812 my $class = ref($self) || $self;
813 return bless {}, $class;
816 Pass arrays as references so more parameters can be added later
817 (it's also faster). Convert functions into methods where
818 appropriate. Split large methods into smaller more flexible ones.
819 Inherit methods from other modules if appropriate.
821 Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>.
822 Generally you can delete the "C<eq 'FOO'>" part with no harm at all.
823 Let the objects look after themselves! Generally, avoid hard-wired
824 class names as far as possible.
826 Avoid C<$r-E<gt>Class::func()> where using C<@ISA=qw(... Class ...)> and
827 C<$r-E<gt>func()> would work (see L<perlbot> for more details).
829 Use autosplit so little used or newly added functions won't be a
830 burden to programs that don't use them. Add test functions to
831 the module after __END__ either using AutoSplit or by saying:
833 eval join('',<main::DATA>) || die $@ unless caller();
835 Does your module pass the 'empty subclass' test? If you say
836 "C<@SUBCLASS::ISA = qw(YOURCLASS);>" your applications should be able
837 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
838 does your application still work if you change: C<$obj = new YOURCLASS;>
839 into: C<$obj = new SUBCLASS;> ?
841 Avoid keeping any state information in your packages. It makes it
842 difficult for multiple other packages to use yours. Keep state
843 information in objects.
845 Always use B<-w>. Try to C<use strict;> (or C<use strict qw(...);>).
846 Remember that you can add C<no strict qw(...);> to individual blocks
847 of code that need less strictness. Always use B<-w>. Always use B<-w>!
848 Follow the guidelines in the perlstyle(1) manual.
850 =item Some simple style guidelines
852 The perlstyle manual supplied with Perl has many helpful points.
854 Coding style is a matter of personal taste. Many people evolve their
855 style over several years as they learn what helps them write and
856 maintain good code. Here's one set of assorted suggestions that
857 seem to be widely used by experienced developers:
859 Use underscores to separate words. It is generally easier to read
860 $var_names_like_this than $VarNamesLikeThis, especially for
861 non-native speakers of English. It's also a simple rule that works
862 consistently with VAR_NAMES_LIKE_THIS.
864 Package/Module names are an exception to this rule. Perl informally
865 reserves lowercase module names for 'pragma' modules like integer
866 and strict. Other modules normally begin with a capital letter and
867 use mixed case with no underscores (need to be short and portable).
869 You may find it helpful to use letter case to indicate the scope
870 or nature of a variable. For example:
872 $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
873 $Some_Caps_Here package-wide global/static
874 $no_caps_here function scope my() or local() variables
876 Function and method names seem to work best as all lowercase.
877 e.g., C<$obj-E<gt>as_string()>.
879 You can use a leading underscore to indicate that a variable or
880 function should not be used outside the package that defined it.
882 =item Select what to export.
884 Do NOT export method names!
886 Do NOT export anything else by default without a good reason!
888 Exports pollute the namespace of the module user. If you must
889 export try to use @EXPORT_OK in preference to @EXPORT and avoid
890 short or common names to reduce the risk of name clashes.
892 Generally anything not exported is still accessible from outside the
893 module using the ModuleName::item_name (or C<$blessed_ref-E<gt>method>)
894 syntax. By convention you can use a leading underscore on names to
895 indicate informally that they are 'internal' and not for public use.
897 (It is actually possible to get private functions by saying:
898 C<my $subref = sub { ... }; &$subref;>. But there's no way to call that
899 directly as a method, because a method must have a name in the symbol
902 As a general rule, if the module is trying to be object oriented
903 then export nothing. If it's just a collection of functions then
904 @EXPORT_OK anything but use @EXPORT with caution.
906 =item Select a name for the module.
908 This name should be as descriptive, accurate, and complete as
909 possible. Avoid any risk of ambiguity. Always try to use two or
910 more whole words. Generally the name should reflect what is special
911 about what the module does rather than how it does it. Please use
912 nested module names to group informally or categorize a module.
913 There should be a very good reason for a module not to have a nested name.
914 Module names should begin with a capital letter.
916 Having 57 modules all called Sort will not make life easy for anyone
917 (though having 23 called Sort::Quick is only marginally better :-).
918 Imagine someone trying to install your module alongside many others.
919 If in any doubt ask for suggestions in comp.lang.perl.misc.
921 If you are developing a suite of related modules/classes it's good
922 practice to use nested classes with a common prefix as this will
923 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
924 Xyz::Model etc. Use the modules in this list as a naming guide.
926 If adding a new module to a set, follow the original author's
927 standards for naming modules and the interface to methods in
930 To be portable each component of a module name should be limited to
931 11 characters. If it might be used on MS-DOS then try to ensure each is
932 unique in the first 8 characters. Nested modules make this easier.
934 =item Have you got it right?
936 How do you know that you've made the right decisions? Have you
937 picked an interface design that will cause problems later? Have
938 you picked the most appropriate name? Do you have any questions?
940 The best way to know for sure, and pick up many helpful suggestions,
941 is to ask someone who knows. Comp.lang.perl.misc is read by just about
942 all the people who develop modules and it's the best place to ask.
944 All you need to do is post a short summary of the module, its
945 purpose and interfaces. A few lines on each of the main methods is
946 probably enough. (If you post the whole module it might be ignored
947 by busy people - generally the very people you want to read it!)
949 Don't worry about posting if you can't say when the module will be
950 ready - just say so in the message. It might be worth inviting
951 others to help you, they may be able to complete it for you!
953 =item README and other Additional Files.
955 It's well known that software developers usually fully document the
956 software they write. If, however, the world is in urgent need of
957 your software and there is not enough time to write the full
958 documentation please at least provide a README file containing:
963 A description of the module/package/extension etc.
966 A copyright notice - see below.
969 Prerequisites - what else you may need to have.
972 How to build it - possible changes to Makefile.PL etc.
978 Recent changes in this release, especially incompatibilities
981 Changes / enhancements you plan to make in the future.
985 If the README file seems to be getting too large you may wish to
986 split out some of the sections into separate files: INSTALL,
991 =item Adding a Copyright Notice.
993 How you choose to license your work is a personal decision.
994 The general mechanism is to assert your Copyright and then make
995 a declaration of how others may copy/use/modify your work.
997 Perl, for example, is supplied with two types of licence: The GNU
998 GPL and The Artistic Licence (see the files README, Copying, and
999 Artistic). Larry has good reasons for NOT just using the GNU GPL.
1001 My personal recommendation, out of respect for Larry, Perl, and the
1002 Perl community at large is to state something simply like:
1004 Copyright (c) 1995 Your Name. All rights reserved.
1005 This program is free software; you can redistribute it and/or
1006 modify it under the same terms as Perl itself.
1008 This statement should at least appear in the README file. You may
1009 also wish to include it in a Copying file and your source files.
1010 Remember to include the other words in addition to the Copyright.
1012 =item Give the module a version/issue/release number.
1014 To be fully compatible with the Exporter and MakeMaker modules you
1015 should store your module's version number in a non-my package
1016 variable called $VERSION. This should be a floating point
1017 number with at least two digits after the decimal (i.e., hundredths,
1018 e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
1019 See Exporter.pm in Perl5.001m or later for details.
1021 It may be handy to add a function or method to retrieve the number.
1022 Use the number in announcements and archive file names when
1023 releasing the module (ModuleName-1.02.tar.Z).
1024 See perldoc ExtUtils::MakeMaker.pm for details.
1026 =item How to release and distribute a module.
1028 It's good idea to post an announcement of the availability of your
1029 module (or the module itself if small) to the comp.lang.perl.announce
1030 Usenet newsgroup. This will at least ensure very wide once-off
1033 If possible you should place the module into a major ftp archive and
1034 include details of its location in your announcement.
1036 Some notes about ftp archives: Please use a long descriptive file
1037 name that includes the version number. Most incoming directories
1038 will not be readable/listable, i.e., you won't be able to see your
1039 file after uploading it. Remember to send your email notification
1040 message as soon as possible after uploading else your file may get
1041 deleted automatically. Allow time for the file to be processed
1042 and/or check the file has been processed before announcing its
1045 FTP Archives for Perl Modules:
1047 Follow the instructions and links on
1049 http://franz.ww.tu-berlin.de/modulelist
1051 or upload to one of these sites:
1053 ftp://franz.ww.tu-berlin.de/incoming
1054 ftp://ftp.cis.ufl.edu/incoming
1056 and notify <F<upload@franz.ww.tu-berlin.de>>.
1058 By using the WWW interface you can ask the Upload Server to mirror
1059 your modules from your ftp or WWW site into your own directory on
1062 Please remember to send me an updated entry for the Module list!
1064 =item Take care when changing a released module.
1066 Always strive to remain compatible with previous released versions.
1067 Otherwise try to add a mechanism to revert to the
1068 old behaviour if people rely on it. Document incompatible changes.
1074 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
1078 =item There is no requirement to convert anything.
1080 If it ain't broke, don't fix it! Perl 4 library scripts should
1081 continue to work with no problems. You may need to make some minor
1082 changes (like escaping non-array @'s in double quoted strings) but
1083 there is no need to convert a .pl file into a Module for just that.
1085 =item Consider the implications.
1087 All Perl applications that make use of the script will need to
1088 be changed (slightly) if the script is converted into a module. Is
1089 it worth it unless you plan to make other changes at the same time?
1091 =item Make the most of the opportunity.
1093 If you are going to convert the script to a module you can use the
1094 opportunity to redesign the interface. The 'Guidelines for Module
1095 Creation' above include many of the issues you should consider.
1097 =item The pl2pm utility will get you started.
1099 This utility will read *.pl files (given as parameters) and write
1100 corresponding *.pm files. The pl2pm utilities does the following:
1105 Adds the standard Module prologue lines
1108 Converts package specifiers from ' to ::
1111 Converts die(...) to croak(...)
1114 Several other minor changes
1118 Being a mechanical process pl2pm is not bullet proof. The converted
1119 code will need careful checking, especially any package statements.
1120 Don't delete the original .pl file till the new .pm one works!
1124 =head2 Guidelines for Reusing Application Code
1128 =item Complete applications rarely belong in the Perl Module Library.
1130 =item Many applications contain some Perl code that could be reused.
1132 Help save the world! Share your code in a form that makes it easy
1135 =item Break-out the reusable code into one or more separate module files.
1137 =item Take the opportunity to reconsider and redesign the interfaces.
1139 =item In some cases the 'application' can then be reduced to a small
1141 fragment of code built on top of the reusable modules. In these cases
1142 the application could invoked as:
1144 % perl -e 'use Module::Name; method(@ARGV)' ...
1146 % perl -mModule::Name ... (in perl5.002 or higher)
1152 Perl does not enforce private and public parts of its modules as you may
1153 have been used to in other languages like C++, Ada, or Modula-17. Perl
1154 doesn't have an infatuation with enforced privacy. It would prefer
1155 that you stayed out of its living room because you weren't invited, not
1156 because it has a shotgun.
1158 The module and its user have a contract, part of which is common law,
1159 and part of which is "written". Part of the common law contract is
1160 that a module doesn't pollute any namespace it wasn't asked to. The
1161 written contract for the module (A.K.A. documentation) may make other
1162 provisions. But then you know when you C<use RedefineTheWorld> that
1163 you're redefining the world and willing to take the consequences.