3 perlmodlib - constructing new Perl modules and finding existing ones
7 =head1 THE PERL MODULE LIBRARY
9 Many modules are included the Perl distribution. These are described
10 below, and all end in F<.pm>. You may discover compiled library
11 file (usually ending in F<.so>) or small pieces of modules to be
12 autoloaded (ending in F<.al>); these were automatically generated
13 by the installation process. You may also discover files in the
14 library directory that end in either F<.pl> or F<.ph>. These are
15 old libraries supplied so that old programs that use them still
16 run. The F<.pl> files will all eventually be converted into standard
17 modules, and the F<.ph> files made by B<h2ph> will probably end up
18 as extension modules made by B<h2xs>. (Some F<.ph> values may
19 already be available through the POSIX, Errno, or Fcntl modules.)
20 The B<pl2pm> file in the distribution may help in your conversion,
21 but it's just a mechanical process and therefore far from bulletproof.
23 =head2 Pragmatic Modules
25 They work somewhat like compiler directives (pragmata) in that they
26 tend to affect the compilation of your program, and thus will usually
27 work well only when used within a C<use>, or C<no>. Most of these
28 are lexically scoped, so an inner BLOCK may countermand them
35 which lasts until the end of that BLOCK.
37 Some pragmas are lexically scoped--typically those that affect the
38 C<$^H> hints variable. Others affect the current package instead,
39 like C<use vars> and C<use subs>, which allow you to predeclare a
40 variables or subroutines within a particular I<file> rather than
41 just a block. Such declarations are effective for the entire file
42 for which they were declared. You cannot rescind them with C<no
45 The following pragmas are defined (and have their own documentation).
51 Get/set subroutine or variable attributes
55 Set/get attributes of a subroutine (deprecated)
59 Postpone load of modules until a function is used
63 Establish IS-A relationship with base class at compile time
67 Use MakeMaker's uninstalled version of a package
71 Force byte semantics rather than character semantics
75 Define character names for C<\N{named}> string literal escape.
83 Perl compiler pragma to force verbose warning diagnostics
87 Compile-time class fields
91 Control the filetest permission operators
95 Compute arithmetic in integer instead of double
99 Request less of something from the compiler
103 Use and avoid POSIX locales for built-in operations
107 Set default disciplines for input and output
111 Restrict unsafe operations when compiling
115 Package for overloading perl operations
123 Alter regular expression behaviour
127 Enable simple signal handling
131 Restrict unsafe constructs
139 Enable/disable UTF-8 in source code
143 Predeclare global variable names (obsolete)
147 Control optional warnings
149 =item warnings::register
151 Warnings import function
155 =head2 Standard Modules
157 Standard, bundled modules are all expected to behave in a well-defined
158 manner with respect to namespace pollution because they use the
159 Exporter module. See their own documentation for details.
165 Provide framework for multiple DBMs
169 Load subroutines only on demand
173 Split a package for autoloading
181 Autogenerated data about Perl ops, used to generate bytecode
185 Assemble Perl bytecode
193 Perl compiler's bytecode backend
197 Perl compiler's C backend
201 Perl compiler's optimized C translation backend
205 Walk Perl syntax tree, printing debug info about ops
209 Perl compiler backend to produce perl code
211 =item B::Disassembler
213 Disassemble Perl bytecode
221 Show lexical variables used in functions or files
225 Helper module for CC backend
229 Show what stashes are loaded
233 Walk Perl syntax tree, printing terse info about ops
237 Generates cross reference reports for Perl programs
241 Benchmark running times of Perl code
245 Load byte compiled perl code
249 Simple Common Gateway Interface Class
253 Backward compatibility module for CGI.pm
257 CGI routines for writing to the HTTPD (or other) error log
261 Interface to Netscape Cookies
265 CGI Interface for Fast CGI
269 Module to produce nicely formatted HTML code
273 Simple Interface to Server Push
277 Backward compatibility module for defunct CGI::Switch
281 Query, download and build perl modules from CPAN sites
283 =item CPAN::FirstTime
285 Utility for CPAN::Config file Initialization
289 Wrapper around CPAN.pm without using any XS module
293 Warn of errors (from perspective of caller)
297 Declare struct-like datatypes as Perl classes
301 Get pathname of current working directory
305 Programmatic interface to the Perl debugging API (draft, subject to
309 Perl5 access to Berkeley DB version 1.x
311 =item Devel::SelfStubber
313 Generate stubs for a SelfLoading module
317 Supply object methods for directory handles
321 Provides screen dump of Perl data.
329 Use nice English (or awk) names for ugly punctuation variables
333 Perl module that imports environment variables as scalars or arrays
337 Implements default import method for modules
339 =item Exporter::Heavy
343 =item ExtUtils::Command
345 Utilities to replace common UNIX commands in Makefiles etc.
347 =item ExtUtils::Embed
349 Utilities for embedding Perl in C/C++ applications
351 =item ExtUtils::Install
353 Install files from here to there
355 =item ExtUtils::Installed
357 Inventory management of installed modules
359 =item ExtUtils::Liblist
361 Determine libraries to use and how to use them
363 =item ExtUtils::MM_Cygwin
365 Methods to override UN*X behaviour in ExtUtils::MakeMaker
367 =item ExtUtils::MM_OS2
369 Methods to override UN*X behaviour in ExtUtils::MakeMaker
371 =item ExtUtils::MM_Unix
373 Methods used by ExtUtils::MakeMaker
375 =item ExtUtils::MM_VMS
377 Methods to override UN*X behaviour in ExtUtils::MakeMaker
379 =item ExtUtils::MM_Win32
381 Methods to override UN*X behaviour in ExtUtils::MakeMaker
383 =item ExtUtils::MakeMaker
385 Create an extension Makefile
387 =item ExtUtils::Manifest
389 Utilities to write and check a MANIFEST file
391 =item ExtUtils::Mkbootstrap
393 Make a bootstrap file for use by DynaLoader
395 =item ExtUtils::Mksymlists
397 Write linker options files for dynamic extension
399 =item ExtUtils::Packlist
401 Manage .packlist files
403 =item ExtUtils::testlib
405 Add blib/* directories to @INC
409 Replace functions with equivalents which succeed or die
413 Load the C Fcntl.h defines
417 Split a pathname into pieces
419 =item File::CheckTree
421 Run many filetest checks on a tree
425 Compare files or filehandles
429 Copy files or filehandles
433 DOS like globbing and then some
441 Create or remove directory trees
445 Portably perform operations on file names
447 =item File::Spec::Epoc
449 Methods for Epoc file specs
451 =item File::Spec::Functions
453 Portably perform operations on file names
455 =item File::Spec::Mac
459 =item File::Spec::OS2
461 Methods for OS/2 file specs
463 =item File::Spec::Unix
465 Methods used by File::Spec
467 =item File::Spec::VMS
469 Methods for VMS file specs
471 =item File::Spec::Win32
473 Methods for Win32 file specs
477 Return name and handle of a temporary file safely
481 By-name interface to Perl's built-in stat() functions
485 Keep more files open than the system permits
489 Supply object methods for filehandles
493 Simplified source filtering
497 Locate directory of original perl script
501 Extended processing of command line options
505 Process single-character switches with switch clustering
509 Compare 8-bit scalar data according to the current locale
513 Load various IO modules
517 Open a process for both reading and writing
521 Open a process for reading, writing, and error handling
525 Arbitrary length float math package
529 Arbitrary size integer math package
533 Complex numbers and associated mathematical functions
537 Trigonometric functions
541 Tied access to ndbm files
545 Check a remote host for reachability
549 By-name interface to Perl's built-in gethost*() functions
553 By-name interface to Perl's built-in getnet*() functions
557 By-name interface to Perl's built-in getproto*() functions
561 By-name interface to Perl's built-in getserv*() functions
565 Generic interface to Perl Compiler backends
569 Tied access to odbm files
573 Disable named opcodes when compiling perl code
577 Check pod documents for syntax errors
581 Find POD documents in directory trees
585 Module to convert pod files to HTML
587 =item Pod::InputObjects
589 Objects representing POD input paragraphs, commands, etc.
593 Convert Pod data to formatted Latex
597 Convert POD data to formatted *roff input
599 =item Pod::ParseUtils
601 Helpers for POD parsing and conversion
605 Base class for creating POD filters and translators
609 Perl extension for converting Pod to old style Pod.
613 Extract selected sections of POD from input
617 Convert POD data to formatted ASCII text
619 =item Pod::Text::Color
621 Convert POD data to formatted color ASCII text
623 =item Pod::Text::Termcap
625 Convert POD data to ASCII text with format escapes
629 Print a usage message from embedded pod documentation
633 Tied access to sdbm files
637 Compile and execute code in restricted compartments
641 Search for key in dictionary file
645 Save and restore selected file handle
649 Load functions only on demand
653 Run shell commands transparently within perl
657 Load the C socket.h defines and structure manipulators
661 Persistency for perl data structures
665 Manipulate Perl symbols and their names
667 =item Term::ANSIColor
669 Color screen output using ANSI escape sequences
673 Perl termcap interface
677 Perl word completion module
681 Perl interface to various C<readline> packages. If
685 Provides a simple framework for writing test scripts
689 Run perl standard test scripts with statistics
693 Create an abbreviation table from a list
695 =item Text::ParseWords
697 Parse text into an array of tokens or array of arrays
701 Implementation of the Soundex Algorithm as Described by Knuth
705 Line wrapping to form simple paragraphs
709 Base class for tied arrays
713 Base class definitions for tied handles
717 Base class definitions for tied hashes
721 Use references as hash keys
725 Base class definitions for tied scalars
727 =item Tie::SubstrHash
729 Fixed-table-size, fixed-key-length hashing
733 Efficiently compute time from local and GMT time
737 By-name interface to Perl's built-in gmtime() function
739 =item Time::localtime
741 By-name interface to Perl's built-in localtime() function
745 Internal object used by Time::gmtime and Time::localtime
749 Base class for ALL classes (blessed references)
753 By-name interface to Perl's built-in getgr*() functions
757 By-name interface to Perl's built-in getpw*() functions
761 To find out I<all> modules installed on your system, including
762 those without documentation or outside the standard release,
765 % find `perl -e 'print "@INC"'` -name '*.pm' -print
767 They should all have their own documentation installed and accessible
768 via your system man(1) command. If you do not have a B<find>
769 program, you can use the Perl B<find2perl> program instead, which
770 generates Perl code as output you can run through perl. If you
771 have a B<man> program but it doesn't find your modules, you'll have
772 to fix your manpath. See L<perl> for details. If you have no
773 system B<man> command, you might try the B<perldoc> program.
775 =head2 Extension Modules
777 Extension modules are written in C (or a mix of Perl and C). They
778 are usually dynamically loaded into Perl if and when you need them,
779 but may also be be linked in statically. Supported extension modules
780 include Socket, Fcntl, and POSIX.
782 Many popular C extension modules do not come bundled (at least, not
783 completely) due to their sizes, volatility, or simply lack of time
784 for adequate testing and configuration across the multitude of
785 platforms on which Perl was beta-tested. You are encouraged to
786 look for them on CPAN (described below), or using web search engines
787 like Alta Vista or Deja News.
791 CPAN stands for Comprehensive Perl Archive Network; it's a globally
792 replicated trove of Perl materials, including documentation, style
793 guides, tricks and traps, alternate ports to non-Unix systems and
794 occasional binary distributions for these. Search engines for
795 CPAN can be found at http://cpan.perl.com/ and at
796 http://theory.uwinnipeg.ca/mod_perl/cpan-search.pl .
798 Most importantly, CPAN includes around a thousand unbundled modules,
799 some of which require a C compiler to build. Major categories of
805 Language Extensions and Documentation Tools
811 Operating System Interfaces
814 Networking, Device Control (modems) and InterProcess Communication
817 Data Types and Data Type Utilities
826 Interfaces to / Emulations of Other Programming Languages
829 File Names, File Systems and File Locking (see also File Handles)
832 String Processing, Language Text Processing, Parsing, and Searching
835 Option, Argument, Parameter, and Configuration File Processing
838 Internationalization and Locale
841 Authentication, Security, and Encryption
844 World Wide Web, HTML, HTTP, CGI, MIME
847 Server and Daemon Utilities
850 Archiving and Compression
853 Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
859 Control Flow Utilities (callbacks and exceptions etc)
862 File Handle and Input/Output Stream Utilities
865 Miscellaneous Modules
869 Registered CPAN sites as of this writing include the following.
870 You should try to choose one close to you:
876 South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
877 ftp://ftp.saix.net/pub/CPAN/
878 ftp://ftp.sun.ac.za/CPAN/
879 ftp://ftpza.co.za/pub/mirrors/cpan/
884 China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
885 Hong Kong ftp://ftp.pacific.net.hk/pub/mirror/CPAN/
886 Indonesia ftp://malone.piksi.itb.ac.id/pub/CPAN/
887 Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
888 Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
889 ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
890 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
891 ftp://ftp.meisei-u.ac.jp/pub/CPAN/
892 ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/
893 ftp://mirror.nucba.ac.jp/mirror/Perl/
894 Saudi-Arabia ftp://ftp.isu.net.sa/pub/CPAN/
895 Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
896 South Korea ftp://ftp.bora.net/pub/CPAN/
897 ftp://ftp.kornet.net/pub/CPAN/
898 ftp://ftp.nuri.net/pub/CPAN/
899 Taiwan ftp://coda.nctu.edu.tw/computer-languages/perl/CPAN/
900 ftp://ftp.ee.ncku.edu.tw/pub3/perl/CPAN/
901 ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
902 Thailand ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
907 Australia ftp://cpan.topend.com.au/pub/CPAN/
908 ftp://ftp.labyrinth.net.au/pub/perl-CPAN/
909 ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
910 ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
911 New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
912 ftp://sunsite.net.nz/pub/languages/perl/CPAN/
915 =item Central America
917 Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
922 Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
923 Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
924 Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
925 Croatia ftp://ftp.linux.hr/pub/CPAN/
926 Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
927 ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
928 Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
929 Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
930 Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
931 France ftp://ftp.grolier.fr/pub/perl/CPAN/
932 ftp://ftp.lip6.fr/pub/perl/CPAN/
933 ftp://ftp.oleane.net/pub/mirrors/CPAN/
934 ftp://ftp.pasteur.fr/pub/computing/CPAN/
935 ftp://ftp.uvsq.fr/pub/perl/CPAN/
936 German ftp://ftp.gigabell.net/pub/CPAN/
937 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
938 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
939 ftp://ftp.gmd.de/packages/CPAN/
940 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
942 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
943 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
944 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
945 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
946 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
947 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
948 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
949 ftp://ftp.gmd.de/packages/CPAN/
950 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
952 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
953 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
954 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
955 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
956 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
957 Greece ftp://ftp.ntua.gr/pub/lang/perl/
958 Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
959 Iceland ftp://ftp.gm.is/pub/CPAN/
960 Ireland ftp://cpan.indigo.ie/pub/CPAN/
961 ftp://sunsite.compapp.dcu.ie/pub/perl/
962 Italy ftp://cis.uniRoma2.it/CPAN/
963 ftp://ftp.flashnet.it/pub/CPAN/
964 ftp://ftp.unina.it/pub/Other/CPAN/
965 ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
966 Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
967 ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
968 Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
969 ftp://sunsite.uio.no/pub/languages/perl/CPAN/
970 Poland ftp://ftp.man.torun.pl/pub/CPAN/
971 ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
972 ftp://sunsite.icm.edu.pl/pub/CPAN/
973 Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
974 ftp://ftp.ist.utl.pt/pub/CPAN/
975 ftp://ftp.ua.pt/pub/CPAN/
976 Romania ftp://ftp.dnttm.ro/pub/CPAN/
977 Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/
978 ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
979 Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
980 Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
981 Spain ftp://ftp.etse.urv.es/pub/perl/
982 ftp://ftp.rediris.es/mirror/CPAN/
983 Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
984 Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
985 Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
986 United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
987 ftp://ftp.flirble.org/pub/languages/perl/CPAN/
989 ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/
990 ftp://ftp.plig.org/pub/CPAN/
991 ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
996 Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
997 California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
998 ftp://cpan.valueclick.com/CPAN/
999 ftp://ftp.cdrom.com/pub/perl/CPAN/
1000 http://download.sourceforge.net/mirrors/CPAN/
1001 Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
1002 Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
1003 Georgia ftp://ftp.twoguys.org/CPAN/
1004 Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
1005 Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
1006 ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
1007 Kentucky ftp://ftp.uky.edu/CPAN/
1008 Manitoba ftp://theoryx5.uwinnipeg.ca/pub/CPAN/
1010 ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
1011 ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
1012 Mexico ftp://ftp.msg.com.mx/pub/CPAN/
1013 New York ftp://ftp.deao.net/pub/CPAN/
1014 ftp://ftp.rge.com/pub/languages/perl/
1015 North Carolina ftp://ftp.duke.edu/pub/perl/
1016 Nova Scotia ftp://cpan.chebucto.ns.ca/pub/CPAN/
1017 Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
1018 Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/
1019 Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
1020 Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
1021 Tennessee ftp://ftp.sunsite.utk.edu/pub/CPAN/
1022 Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
1023 ftp://jhcloos.com/pub/mirror/CPAN/
1024 Utah ftp://mirror.xmission.com/CPAN/
1025 Virginia ftp://ftp.perl.org/pub/perl/CPAN/
1026 ftp://ruff.cs.jmu.edu/pub/CPAN/
1027 Washington ftp://ftp-mirror.internap.com/pub/CPAN/
1028 ftp://ftp.llarian.net/pub/CPAN/
1029 ftp://ftp.spu.edu/pub/CPAN/
1034 Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
1035 ftp://ftp.matrix.com.br/pub/perl/
1036 Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/PERL/
1040 For an up-to-date listing of CPAN sites,
1041 see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES .
1043 =head1 Modules: Creation, Use, and Abuse
1045 (The following section is borrowed directly from Tim Bunce's modules
1046 file, available at your nearest CPAN site.)
1048 Perl implements a class using a package, but the presence of a
1049 package doesn't imply the presence of a class. A package is just a
1050 namespace. A class is a package that provides subroutines that can be
1051 used as methods. A method is just a subroutine that expects, as its
1052 first argument, either the name of a package (for "static" methods),
1053 or a reference to something (for "virtual" methods).
1055 A module is a file that (by convention) provides a class of the same
1056 name (sans the .pm), plus an import method in that class that can be
1057 called to fetch exported symbols. This module may implement some of
1058 its methods by loading dynamic C or C++ objects, but that should be
1059 totally transparent to the user of the module. Likewise, the module
1060 might set up an AUTOLOAD function to slurp in subroutine definitions on
1061 demand, but this is also transparent. Only the F<.pm> file is required to
1062 exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
1063 the AUTOLOAD mechanism.
1065 =head2 Guidelines for Module Creation
1069 =item Do similar modules already exist in some form?
1071 If so, please try to reuse the existing modules either in whole or
1072 by inheriting useful features into a new class. If this is not
1073 practical try to get together with the module authors to work on
1074 extending or enhancing the functionality of the existing modules.
1075 A perfect example is the plethora of packages in perl4 for dealing
1076 with command line options.
1078 If you are writing a module to expand an already existing set of
1079 modules, please coordinate with the author of the package. It
1080 helps if you follow the same naming scheme and module interaction
1081 scheme as the original author.
1083 =item Try to design the new module to be easy to extend and reuse.
1085 Try to C<use warnings;> (or C<use warnings qw(...);>).
1086 Remember that you can add C<no warnings qw(...);> to individual blocks
1087 of code that need less warnings.
1089 Use blessed references. Use the two argument form of bless to bless
1090 into the class name given as the first parameter of the constructor,
1095 return bless {}, $class;
1098 or even this if you'd like it to be used as either a static
1099 or a virtual method.
1103 my $class = ref($self) || $self;
1104 return bless {}, $class;
1107 Pass arrays as references so more parameters can be added later
1108 (it's also faster). Convert functions into methods where
1109 appropriate. Split large methods into smaller more flexible ones.
1110 Inherit methods from other modules if appropriate.
1112 Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>.
1113 Generally you can delete the C<eq 'FOO'> part with no harm at all.
1114 Let the objects look after themselves! Generally, avoid hard-wired
1115 class names as far as possible.
1117 Avoid C<< $r->Class::func() >> where using C<@ISA=qw(... Class ...)> and
1118 C<< $r->func() >> would work (see L<perlbot> for more details).
1120 Use autosplit so little used or newly added functions won't be a
1121 burden to programs that don't use them. Add test functions to
1122 the module after __END__ either using AutoSplit or by saying:
1124 eval join('',<main::DATA>) || die $@ unless caller();
1126 Does your module pass the 'empty subclass' test? If you say
1127 C<@SUBCLASS::ISA = qw(YOURCLASS);> your applications should be able
1128 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
1129 does your application still work if you change: C<$obj = new YOURCLASS;>
1130 into: C<$obj = new SUBCLASS;> ?
1132 Avoid keeping any state information in your packages. It makes it
1133 difficult for multiple other packages to use yours. Keep state
1134 information in objects.
1138 Try to C<use strict;> (or C<use strict qw(...);>).
1139 Remember that you can add C<no strict qw(...);> to individual blocks
1140 of code that need less strictness.
1144 Follow the guidelines in the perlstyle(1) manual.
1148 =item Some simple style guidelines
1150 The perlstyle manual supplied with Perl has many helpful points.
1152 Coding style is a matter of personal taste. Many people evolve their
1153 style over several years as they learn what helps them write and
1154 maintain good code. Here's one set of assorted suggestions that
1155 seem to be widely used by experienced developers:
1157 Use underscores to separate words. It is generally easier to read
1158 $var_names_like_this than $VarNamesLikeThis, especially for
1159 non-native speakers of English. It's also a simple rule that works
1160 consistently with VAR_NAMES_LIKE_THIS.
1162 Package/Module names are an exception to this rule. Perl informally
1163 reserves lowercase module names for 'pragma' modules like integer
1164 and strict. Other modules normally begin with a capital letter and
1165 use mixed case with no underscores (need to be short and portable).
1167 You may find it helpful to use letter case to indicate the scope
1168 or nature of a variable. For example:
1170 $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
1171 $Some_Caps_Here package-wide global/static
1172 $no_caps_here function scope my() or local() variables
1174 Function and method names seem to work best as all lowercase.
1175 e.g., C<< $obj->as_string() >>.
1177 You can use a leading underscore to indicate that a variable or
1178 function should not be used outside the package that defined it.
1180 =item Select what to export.
1182 Do NOT export method names!
1184 Do NOT export anything else by default without a good reason!
1186 Exports pollute the namespace of the module user. If you must
1187 export try to use @EXPORT_OK in preference to @EXPORT and avoid
1188 short or common names to reduce the risk of name clashes.
1190 Generally anything not exported is still accessible from outside the
1191 module using the ModuleName::item_name (or C<< $blessed_ref->method >>)
1192 syntax. By convention you can use a leading underscore on names to
1193 indicate informally that they are 'internal' and not for public use.
1195 (It is actually possible to get private functions by saying:
1196 C<my $subref = sub { ... }; &$subref;>. But there's no way to call that
1197 directly as a method, because a method must have a name in the symbol
1200 As a general rule, if the module is trying to be object oriented
1201 then export nothing. If it's just a collection of functions then
1202 @EXPORT_OK anything but use @EXPORT with caution.
1204 =item Select a name for the module.
1206 This name should be as descriptive, accurate, and complete as
1207 possible. Avoid any risk of ambiguity. Always try to use two or
1208 more whole words. Generally the name should reflect what is special
1209 about what the module does rather than how it does it. Please use
1210 nested module names to group informally or categorize a module.
1211 There should be a very good reason for a module not to have a nested name.
1212 Module names should begin with a capital letter.
1214 Having 57 modules all called Sort will not make life easy for anyone
1215 (though having 23 called Sort::Quick is only marginally better :-).
1216 Imagine someone trying to install your module alongside many others.
1217 If in any doubt ask for suggestions in comp.lang.perl.misc.
1219 If you are developing a suite of related modules/classes it's good
1220 practice to use nested classes with a common prefix as this will
1221 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
1222 Xyz::Model etc. Use the modules in this list as a naming guide.
1224 If adding a new module to a set, follow the original author's
1225 standards for naming modules and the interface to methods in
1228 If developing modules for private internal or project specific use,
1229 that will never be released to the public, then you should ensure
1230 that their names will not clash with any future public module. You
1231 can do this either by using the reserved Local::* category or by
1232 using a category name that includes an underscore like Foo_Corp::*.
1234 To be portable each component of a module name should be limited to
1235 11 characters. If it might be used on MS-DOS then try to ensure each is
1236 unique in the first 8 characters. Nested modules make this easier.
1238 =item Have you got it right?
1240 How do you know that you've made the right decisions? Have you
1241 picked an interface design that will cause problems later? Have
1242 you picked the most appropriate name? Do you have any questions?
1244 The best way to know for sure, and pick up many helpful suggestions,
1245 is to ask someone who knows. Comp.lang.perl.misc is read by just about
1246 all the people who develop modules and it's the best place to ask.
1248 All you need to do is post a short summary of the module, its
1249 purpose and interfaces. A few lines on each of the main methods is
1250 probably enough. (If you post the whole module it might be ignored
1251 by busy people - generally the very people you want to read it!)
1253 Don't worry about posting if you can't say when the module will be
1254 ready - just say so in the message. It might be worth inviting
1255 others to help you, they may be able to complete it for you!
1257 =item README and other Additional Files.
1259 It's well known that software developers usually fully document the
1260 software they write. If, however, the world is in urgent need of
1261 your software and there is not enough time to write the full
1262 documentation please at least provide a README file containing:
1267 A description of the module/package/extension etc.
1270 A copyright notice - see below.
1273 Prerequisites - what else you may need to have.
1276 How to build it - possible changes to Makefile.PL etc.
1282 Recent changes in this release, especially incompatibilities
1285 Changes / enhancements you plan to make in the future.
1289 If the README file seems to be getting too large you may wish to
1290 split out some of the sections into separate files: INSTALL,
1295 =item Adding a Copyright Notice.
1297 How you choose to license your work is a personal decision.
1298 The general mechanism is to assert your Copyright and then make
1299 a declaration of how others may copy/use/modify your work.
1301 Perl, for example, is supplied with two types of licence: The GNU
1302 GPL and The Artistic Licence (see the files README, Copying, and
1303 Artistic). Larry has good reasons for NOT just using the GNU GPL.
1305 My personal recommendation, out of respect for Larry, Perl, and the
1306 Perl community at large is to state something simply like:
1308 Copyright (c) 1995 Your Name. All rights reserved.
1309 This program is free software; you can redistribute it and/or
1310 modify it under the same terms as Perl itself.
1312 This statement should at least appear in the README file. You may
1313 also wish to include it in a Copying file and your source files.
1314 Remember to include the other words in addition to the Copyright.
1316 =item Give the module a version/issue/release number.
1318 To be fully compatible with the Exporter and MakeMaker modules you
1319 should store your module's version number in a non-my package
1320 variable called $VERSION. This should be a floating point
1321 number with at least two digits after the decimal (i.e., hundredths,
1322 e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
1323 See L<Exporter> for details.
1325 It may be handy to add a function or method to retrieve the number.
1326 Use the number in announcements and archive file names when
1327 releasing the module (ModuleName-1.02.tar.Z).
1328 See perldoc ExtUtils::MakeMaker.pm for details.
1330 =item How to release and distribute a module.
1332 It's good idea to post an announcement of the availability of your
1333 module (or the module itself if small) to the comp.lang.perl.announce
1334 Usenet newsgroup. This will at least ensure very wide once-off
1337 If possible, register the module with CPAN. You should
1338 include details of its location in your announcement.
1340 Some notes about ftp archives: Please use a long descriptive file
1341 name that includes the version number. Most incoming directories
1342 will not be readable/listable, i.e., you won't be able to see your
1343 file after uploading it. Remember to send your email notification
1344 message as soon as possible after uploading else your file may get
1345 deleted automatically. Allow time for the file to be processed
1346 and/or check the file has been processed before announcing its
1349 FTP Archives for Perl Modules:
1351 Follow the instructions and links on:
1353 http://www.perl.com/CPAN/modules/00modlist.long.html
1354 http://www.perl.com/CPAN/modules/04pause.html
1356 or upload to one of these sites:
1358 https://pause.kbx.de/pause/
1359 http://pause.perl.org/pause/
1361 and notify <modules@perl.org>.
1363 By using the WWW interface you can ask the Upload Server to mirror
1364 your modules from your ftp or WWW site into your own directory on
1367 Please remember to send me an updated entry for the Module list!
1369 =item Take care when changing a released module.
1371 Always strive to remain compatible with previous released versions.
1372 Otherwise try to add a mechanism to revert to the
1373 old behavior if people rely on it. Document incompatible changes.
1379 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
1383 =item There is no requirement to convert anything.
1385 If it ain't broke, don't fix it! Perl 4 library scripts should
1386 continue to work with no problems. You may need to make some minor
1387 changes (like escaping non-array @'s in double quoted strings) but
1388 there is no need to convert a .pl file into a Module for just that.
1390 =item Consider the implications.
1392 All Perl applications that make use of the script will need to
1393 be changed (slightly) if the script is converted into a module. Is
1394 it worth it unless you plan to make other changes at the same time?
1396 =item Make the most of the opportunity.
1398 If you are going to convert the script to a module you can use the
1399 opportunity to redesign the interface. The guidelines for module
1400 creation above include many of the issues you should consider.
1402 =item The pl2pm utility will get you started.
1404 This utility will read *.pl files (given as parameters) and write
1405 corresponding *.pm files. The pl2pm utilities does the following:
1410 Adds the standard Module prologue lines
1413 Converts package specifiers from ' to ::
1416 Converts die(...) to croak(...)
1419 Several other minor changes
1423 Being a mechanical process pl2pm is not bullet proof. The converted
1424 code will need careful checking, especially any package statements.
1425 Don't delete the original .pl file till the new .pm one works!
1429 =head2 Guidelines for Reusing Application Code
1433 =item Complete applications rarely belong in the Perl Module Library.
1435 =item Many applications contain some Perl code that could be reused.
1437 Help save the world! Share your code in a form that makes it easy
1440 =item Break-out the reusable code into one or more separate module files.
1442 =item Take the opportunity to reconsider and redesign the interfaces.
1444 =item In some cases the 'application' can then be reduced to a small
1446 fragment of code built on top of the reusable modules. In these cases
1447 the application could invoked as:
1449 % perl -e 'use Module::Name; method(@ARGV)' ...
1451 % perl -mModule::Name ... (in perl5.002 or higher)
1457 Perl does not enforce private and public parts of its modules as you may
1458 have been used to in other languages like C++, Ada, or Modula-17. Perl
1459 doesn't have an infatuation with enforced privacy. It would prefer
1460 that you stayed out of its living room because you weren't invited, not
1461 because it has a shotgun.
1463 The module and its user have a contract, part of which is common law,
1464 and part of which is "written". Part of the common law contract is
1465 that a module doesn't pollute any namespace it wasn't asked to. The
1466 written contract for the module (A.K.A. documentation) may make other
1467 provisions. But then you know when you C<use RedefineTheWorld> that
1468 you're redefining the world and willing to take the consequences.