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
119 Alter regular expression behaviour
123 Enable simple signal handling
127 Restrict unsafe constructs
135 Enable/disable UTF-8 in source code
139 Predeclare global variable names (obsolete)
143 Control optional warnings
145 =item warnings::register
147 Warnings import function
151 =head2 Standard Modules
153 Standard, bundled modules are all expected to behave in a well-defined
154 manner with respect to namespace pollution because they use the
155 Exporter module. See their own documentation for details.
161 Provide framework for multiple DBMs
165 Load subroutines only on demand
169 Split a package for autoloading
177 Autogenerated data about Perl ops, used to generate bytecode
181 Assemble Perl bytecode
189 Perl compiler's bytecode backend
193 Perl compiler's C backend
197 Perl compiler's optimized C translation backend
201 Walk Perl syntax tree, printing debug info about ops
205 Perl compiler backend to produce perl code
207 =item B::Disassembler
209 Disassemble Perl bytecode
217 Show lexical variables used in functions or files
221 Helper module for CC backend
225 Show what stashes are loaded
229 Walk Perl syntax tree, printing terse info about ops
233 Generates cross reference reports for Perl programs
237 Benchmark running times of Perl code
241 Load byte compiled perl code
245 Simple Common Gateway Interface Class
249 Backward compatibility module for CGI.pm
253 CGI routines for writing to the HTTPD (or other) error log
257 Interface to Netscape Cookies
261 CGI Interface for Fast CGI
265 Module to produce nicely formatted HTML code
269 Simple Interface to Server Push
273 Backward compatibility module for defunct CGI::Switch
277 Query, download and build perl modules from CPAN sites
279 =item CPAN::FirstTime
281 Utility for CPAN::Config file Initialization
285 Wrapper around CPAN.pm without using any XS module
289 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::Functions
449 Portably perform operations on file names
451 =item File::Spec::Mac
455 =item File::Spec::OS2
457 Methods for OS/2 file specs
459 =item File::Spec::Unix
461 Methods used by File::Spec
463 =item File::Spec::VMS
465 Methods for VMS file specs
467 =item File::Spec::Win32
469 Methods for Win32 file specs
473 Return name and handle of a temporary file safely
477 By-name interface to Perl's built-in stat() functions
481 Keep more files open than the system permits
485 Supply object methods for filehandles
489 Locate directory of original perl script
493 Extended processing of command line options
497 Process single-character switches with switch clustering
501 Compare 8-bit scalar data according to the current locale
505 Load various IO modules
509 Open a process for both reading and writing
513 Open a process for reading, writing, and error handling
517 Arbitrary length float math package
521 Arbitrary size integer math package
525 Complex numbers and associated mathematical functions
529 Trigonometric functions
533 Tied access to ndbm files
537 Check a remote host for reachability
541 By-name interface to Perl's built-in gethost*() functions
545 By-name interface to Perl's built-in getnet*() functions
549 By-name interface to Perl's built-in getproto*() functions
553 By-name interface to Perl's built-in getserv*() functions
557 Generic interface to Perl Compiler backends
561 Tied access to odbm files
565 Disable named opcodes when compiling perl code
569 Check pod documents for syntax errors
573 Find POD documents in directory trees
577 Module to convert pod files to HTML
579 =item Pod::InputObjects
581 Objects representing POD input paragraphs, commands, etc.
585 Convert Pod data to formatted Latex
589 Convert POD data to formatted *roff input
591 =item Pod::ParseUtils
593 Helpers for POD parsing and conversion
597 Base class for creating POD filters and translators
601 Perl extension for converting Pod to old style Pod.
605 Extract selected sections of POD from input
609 Convert POD data to formatted ASCII text
611 =item Pod::Text::Color
613 Convert POD data to formatted color ASCII text
615 =item Pod::Text::Termcap
617 Convert POD data to ASCII text with format escapes
621 Print a usage message from embedded pod documentation
625 Tied access to sdbm files
629 Compile and execute code in restricted compartments
633 Search for key in dictionary file
637 Save and restore selected file handle
641 Load functions only on demand
645 Run shell commands transparently within perl
649 Load the C socket.h defines and structure manipulators
653 Persistency for perl data structures
657 Manipulate Perl symbols and their names
659 =item Term::ANSIColor
661 Color screen output using ANSI escape sequences
665 Perl termcap interface
669 Perl word completion module
673 Perl interface to various C<readline> packages. If
677 Provides a simple framework for writing test scripts
681 Run perl standard test scripts with statistics
685 Create an abbreviation table from a list
687 =item Text::ParseWords
689 Parse text into an array of tokens or array of arrays
693 Implementation of the Soundex Algorithm as Described by Knuth
697 Line wrapping to form simple paragraphs
701 Base class for tied arrays
705 Base class definitions for tied handles
709 Base class definitions for tied hashes
713 Use references as hash keys
717 Base class definitions for tied scalars
719 =item Tie::SubstrHash
721 Fixed-table-size, fixed-key-length hashing
725 Efficiently compute time from local and GMT time
729 By-name interface to Perl's built-in gmtime() function
731 =item Time::localtime
733 By-name interface to Perl's built-in localtime() function
737 Internal object used by Time::gmtime and Time::localtime
741 Base class for ALL classes (blessed references)
745 By-name interface to Perl's built-in getgr*() functions
749 By-name interface to Perl's built-in getpw*() functions
753 To find out I<all> modules installed on your system, including
754 those without documentation or outside the standard release,
757 % find `perl -e 'print "@INC"'` -name '*.pm' -print
759 They should all have their own documentation installed and accessible
760 via your system man(1) command. If you do not have a B<find>
761 program, you can use the Perl B<find2perl> program instead, which
762 generates Perl code as output you can run through perl. If you
763 have a B<man> program but it doesn't find your modules, you'll have
764 to fix your manpath. See L<perl> for details. If you have no
765 system B<man> command, you might try the B<perldoc> program.
767 =head2 Extension Modules
769 Extension modules are written in C (or a mix of Perl and C). They
770 are usually dynamically loaded into Perl if and when you need them,
771 but may also be be linked in statically. Supported extension modules
772 include Socket, Fcntl, and POSIX.
774 Many popular C extension modules do not come bundled (at least, not
775 completely) due to their sizes, volatility, or simply lack of time
776 for adequate testing and configuration across the multitude of
777 platforms on which Perl was beta-tested. You are encouraged to
778 look for them on CPAN (described below), or using web search engines
779 like Alta Vista or Deja News.
783 CPAN stands for Comprehensive Perl Archive Network; it's a globally
784 replicated trove of Perl materials, including documentation, style
785 guides, tricks and traps, alternate ports to non-Unix systems and
786 occasional binary distributions for these. Search engines for
787 CPAN can be found at http://cpan.perl.com/ and at
788 http://theory.uwinnipeg.ca/mod_perl/cpan-search.pl .
790 Most importantly, CPAN includes around a thousand unbundled modules,
791 some of which require a C compiler to build. Major categories of
797 Language Extensions and Documentation Tools
803 Operating System Interfaces
806 Networking, Device Control (modems) and InterProcess Communication
809 Data Types and Data Type Utilities
818 Interfaces to / Emulations of Other Programming Languages
821 File Names, File Systems and File Locking (see also File Handles)
824 String Processing, Language Text Processing, Parsing, and Searching
827 Option, Argument, Parameter, and Configuration File Processing
830 Internationalization and Locale
833 Authentication, Security, and Encryption
836 World Wide Web, HTML, HTTP, CGI, MIME
839 Server and Daemon Utilities
842 Archiving and Compression
845 Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
851 Control Flow Utilities (callbacks and exceptions etc)
854 File Handle and Input/Output Stream Utilities
857 Miscellaneous Modules
861 Registered CPAN sites as of this writing include the following.
862 You should try to choose one close to you:
868 South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
869 ftp://ftp.saix.net/pub/CPAN/
870 ftp://ftp.sun.ac.za/CPAN/
871 ftp://ftpza.co.za/pub/mirrors/cpan/
876 China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
877 Hong Kong ftp://ftp.pacific.net.hk/pub/mirror/CPAN/
878 Indonesia ftp://malone.piksi.itb.ac.id/pub/CPAN/
879 Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
880 Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
881 ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
882 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
883 ftp://ftp.meisei-u.ac.jp/pub/CPAN/
884 ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/
885 ftp://mirror.nucba.ac.jp/mirror/Perl/
886 Saudi-Arabia ftp://ftp.isu.net.sa/pub/CPAN/
887 Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
888 South Korea ftp://ftp.bora.net/pub/CPAN/
889 ftp://ftp.kornet.net/pub/CPAN/
890 ftp://ftp.nuri.net/pub/CPAN/
891 Taiwan ftp://coda.nctu.edu.tw/computer-languages/perl/CPAN/
892 ftp://ftp.ee.ncku.edu.tw/pub3/perl/CPAN/
893 ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
894 Thailand ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
899 Australia ftp://cpan.topend.com.au/pub/CPAN/
900 ftp://ftp.labyrinth.net.au/pub/perl-CPAN/
901 ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
902 ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
903 New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
904 ftp://sunsite.net.nz/pub/languages/perl/CPAN/
907 =item Central America
909 Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
914 Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
915 Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
916 Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
917 Croatia ftp://ftp.linux.hr/pub/CPAN/
918 Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
919 ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
920 Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
921 Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
922 Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
923 France ftp://ftp.grolier.fr/pub/perl/CPAN/
924 ftp://ftp.lip6.fr/pub/perl/CPAN/
925 ftp://ftp.oleane.net/pub/mirrors/CPAN/
926 ftp://ftp.pasteur.fr/pub/computing/CPAN/
927 ftp://ftp.uvsq.fr/pub/perl/CPAN/
928 German ftp://ftp.gigabell.net/pub/CPAN/
929 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
930 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
931 ftp://ftp.gmd.de/packages/CPAN/
932 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
934 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
935 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
936 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
937 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
938 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
939 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
940 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
941 ftp://ftp.gmd.de/packages/CPAN/
942 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
944 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
945 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
946 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
947 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
948 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
949 Greece ftp://ftp.ntua.gr/pub/lang/perl/
950 Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
951 Iceland ftp://ftp.gm.is/pub/CPAN/
952 Ireland ftp://cpan.indigo.ie/pub/CPAN/
953 ftp://sunsite.compapp.dcu.ie/pub/perl/
954 Italy ftp://cis.uniRoma2.it/CPAN/
955 ftp://ftp.flashnet.it/pub/CPAN/
956 ftp://ftp.unina.it/pub/Other/CPAN/
957 ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
958 Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
959 ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
960 Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
961 ftp://sunsite.uio.no/pub/languages/perl/CPAN/
962 Poland ftp://ftp.man.torun.pl/pub/CPAN/
963 ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
964 ftp://sunsite.icm.edu.pl/pub/CPAN/
965 Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
966 ftp://ftp.ist.utl.pt/pub/CPAN/
967 ftp://ftp.ua.pt/pub/CPAN/
968 Romania ftp://ftp.dnttm.ro/pub/CPAN/
969 Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/
970 ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
971 Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
972 Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
973 Spain ftp://ftp.etse.urv.es/pub/perl/
974 ftp://ftp.rediris.es/mirror/CPAN/
975 Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
976 Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
977 Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
978 United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
979 ftp://ftp.flirble.org/pub/languages/perl/CPAN/
981 ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/
982 ftp://ftp.plig.org/pub/CPAN/
983 ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
988 Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
989 California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
990 ftp://cpan.valueclick.com/CPAN/
991 ftp://ftp.cdrom.com/pub/perl/CPAN/
992 http://download.sourceforge.net/mirrors/CPAN/
993 Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
994 Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
995 Georgia ftp://ftp.twoguys.org/CPAN/
996 Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
997 Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
998 ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
999 Kentucky ftp://ftp.uky.edu/CPAN/
1000 Manitoba ftp://theoryx5.uwinnipeg.ca/pub/CPAN/
1002 ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
1003 ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
1004 Mexico ftp://ftp.msg.com.mx/pub/CPAN/
1005 New York ftp://ftp.deao.net/pub/CPAN/
1006 ftp://ftp.rge.com/pub/languages/perl/
1007 North Carolina ftp://ftp.duke.edu/pub/perl/
1008 Nova Scotia ftp://cpan.chebucto.ns.ca/pub/CPAN/
1009 Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
1010 Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/
1011 Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
1012 Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
1013 Tennessee ftp://ftp.sunsite.utk.edu/pub/CPAN/
1014 Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
1015 ftp://jhcloos.com/pub/mirror/CPAN/
1016 Utah ftp://mirror.xmission.com/CPAN/
1017 Virginia ftp://ftp.perl.org/pub/perl/CPAN/
1018 ftp://ruff.cs.jmu.edu/pub/CPAN/
1019 Washington ftp://ftp-mirror.internap.com/pub/CPAN/
1020 ftp://ftp.llarian.net/pub/CPAN/
1021 ftp://ftp.spu.edu/pub/CPAN/
1026 Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
1027 ftp://ftp.matrix.com.br/pub/perl/
1028 Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/PERL/
1032 For an up-to-date listing of CPAN sites,
1033 see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES .
1035 =head1 Modules: Creation, Use, and Abuse
1037 (The following section is borrowed directly from Tim Bunce's modules
1038 file, available at your nearest CPAN site.)
1040 Perl implements a class using a package, but the presence of a
1041 package doesn't imply the presence of a class. A package is just a
1042 namespace. A class is a package that provides subroutines that can be
1043 used as methods. A method is just a subroutine that expects, as its
1044 first argument, either the name of a package (for "static" methods),
1045 or a reference to something (for "virtual" methods).
1047 A module is a file that (by convention) provides a class of the same
1048 name (sans the .pm), plus an import method in that class that can be
1049 called to fetch exported symbols. This module may implement some of
1050 its methods by loading dynamic C or C++ objects, but that should be
1051 totally transparent to the user of the module. Likewise, the module
1052 might set up an AUTOLOAD function to slurp in subroutine definitions on
1053 demand, but this is also transparent. Only the F<.pm> file is required to
1054 exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
1055 the AUTOLOAD mechanism.
1057 =head2 Guidelines for Module Creation
1061 =item Do similar modules already exist in some form?
1063 If so, please try to reuse the existing modules either in whole or
1064 by inheriting useful features into a new class. If this is not
1065 practical try to get together with the module authors to work on
1066 extending or enhancing the functionality of the existing modules.
1067 A perfect example is the plethora of packages in perl4 for dealing
1068 with command line options.
1070 If you are writing a module to expand an already existing set of
1071 modules, please coordinate with the author of the package. It
1072 helps if you follow the same naming scheme and module interaction
1073 scheme as the original author.
1075 =item Try to design the new module to be easy to extend and reuse.
1077 Try to C<use warnings;> (or C<use warnings qw(...);>).
1078 Remember that you can add C<no warnings qw(...);> to individual blocks
1079 of code that need less warnings.
1081 Use blessed references. Use the two argument form of bless to bless
1082 into the class name given as the first parameter of the constructor,
1087 return bless {}, $class;
1090 or even this if you'd like it to be used as either a static
1091 or a virtual method.
1095 my $class = ref($self) || $self;
1096 return bless {}, $class;
1099 Pass arrays as references so more parameters can be added later
1100 (it's also faster). Convert functions into methods where
1101 appropriate. Split large methods into smaller more flexible ones.
1102 Inherit methods from other modules if appropriate.
1104 Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>.
1105 Generally you can delete the C<eq 'FOO'> part with no harm at all.
1106 Let the objects look after themselves! Generally, avoid hard-wired
1107 class names as far as possible.
1109 Avoid C<< $r->Class::func() >> where using C<@ISA=qw(... Class ...)> and
1110 C<< $r->func() >> would work (see L<perlbot> for more details).
1112 Use autosplit so little used or newly added functions won't be a
1113 burden to programs that don't use them. Add test functions to
1114 the module after __END__ either using AutoSplit or by saying:
1116 eval join('',<main::DATA>) || die $@ unless caller();
1118 Does your module pass the 'empty subclass' test? If you say
1119 C<@SUBCLASS::ISA = qw(YOURCLASS);> your applications should be able
1120 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
1121 does your application still work if you change: C<$obj = new YOURCLASS;>
1122 into: C<$obj = new SUBCLASS;> ?
1124 Avoid keeping any state information in your packages. It makes it
1125 difficult for multiple other packages to use yours. Keep state
1126 information in objects.
1130 Try to C<use strict;> (or C<use strict qw(...);>).
1131 Remember that you can add C<no strict qw(...);> to individual blocks
1132 of code that need less strictness.
1136 Follow the guidelines in the perlstyle(1) manual.
1140 =item Some simple style guidelines
1142 The perlstyle manual supplied with Perl has many helpful points.
1144 Coding style is a matter of personal taste. Many people evolve their
1145 style over several years as they learn what helps them write and
1146 maintain good code. Here's one set of assorted suggestions that
1147 seem to be widely used by experienced developers:
1149 Use underscores to separate words. It is generally easier to read
1150 $var_names_like_this than $VarNamesLikeThis, especially for
1151 non-native speakers of English. It's also a simple rule that works
1152 consistently with VAR_NAMES_LIKE_THIS.
1154 Package/Module names are an exception to this rule. Perl informally
1155 reserves lowercase module names for 'pragma' modules like integer
1156 and strict. Other modules normally begin with a capital letter and
1157 use mixed case with no underscores (need to be short and portable).
1159 You may find it helpful to use letter case to indicate the scope
1160 or nature of a variable. For example:
1162 $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
1163 $Some_Caps_Here package-wide global/static
1164 $no_caps_here function scope my() or local() variables
1166 Function and method names seem to work best as all lowercase.
1167 e.g., C<< $obj->as_string() >>.
1169 You can use a leading underscore to indicate that a variable or
1170 function should not be used outside the package that defined it.
1172 =item Select what to export.
1174 Do NOT export method names!
1176 Do NOT export anything else by default without a good reason!
1178 Exports pollute the namespace of the module user. If you must
1179 export try to use @EXPORT_OK in preference to @EXPORT and avoid
1180 short or common names to reduce the risk of name clashes.
1182 Generally anything not exported is still accessible from outside the
1183 module using the ModuleName::item_name (or C<< $blessed_ref->method >>)
1184 syntax. By convention you can use a leading underscore on names to
1185 indicate informally that they are 'internal' and not for public use.
1187 (It is actually possible to get private functions by saying:
1188 C<my $subref = sub { ... }; &$subref;>. But there's no way to call that
1189 directly as a method, because a method must have a name in the symbol
1192 As a general rule, if the module is trying to be object oriented
1193 then export nothing. If it's just a collection of functions then
1194 @EXPORT_OK anything but use @EXPORT with caution.
1196 =item Select a name for the module.
1198 This name should be as descriptive, accurate, and complete as
1199 possible. Avoid any risk of ambiguity. Always try to use two or
1200 more whole words. Generally the name should reflect what is special
1201 about what the module does rather than how it does it. Please use
1202 nested module names to group informally or categorize a module.
1203 There should be a very good reason for a module not to have a nested name.
1204 Module names should begin with a capital letter.
1206 Having 57 modules all called Sort will not make life easy for anyone
1207 (though having 23 called Sort::Quick is only marginally better :-).
1208 Imagine someone trying to install your module alongside many others.
1209 If in any doubt ask for suggestions in comp.lang.perl.misc.
1211 If you are developing a suite of related modules/classes it's good
1212 practice to use nested classes with a common prefix as this will
1213 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
1214 Xyz::Model etc. Use the modules in this list as a naming guide.
1216 If adding a new module to a set, follow the original author's
1217 standards for naming modules and the interface to methods in
1220 To be portable each component of a module name should be limited to
1221 11 characters. If it might be used on MS-DOS then try to ensure each is
1222 unique in the first 8 characters. Nested modules make this easier.
1224 =item Have you got it right?
1226 How do you know that you've made the right decisions? Have you
1227 picked an interface design that will cause problems later? Have
1228 you picked the most appropriate name? Do you have any questions?
1230 The best way to know for sure, and pick up many helpful suggestions,
1231 is to ask someone who knows. Comp.lang.perl.misc is read by just about
1232 all the people who develop modules and it's the best place to ask.
1234 All you need to do is post a short summary of the module, its
1235 purpose and interfaces. A few lines on each of the main methods is
1236 probably enough. (If you post the whole module it might be ignored
1237 by busy people - generally the very people you want to read it!)
1239 Don't worry about posting if you can't say when the module will be
1240 ready - just say so in the message. It might be worth inviting
1241 others to help you, they may be able to complete it for you!
1243 =item README and other Additional Files.
1245 It's well known that software developers usually fully document the
1246 software they write. If, however, the world is in urgent need of
1247 your software and there is not enough time to write the full
1248 documentation please at least provide a README file containing:
1253 A description of the module/package/extension etc.
1256 A copyright notice - see below.
1259 Prerequisites - what else you may need to have.
1262 How to build it - possible changes to Makefile.PL etc.
1268 Recent changes in this release, especially incompatibilities
1271 Changes / enhancements you plan to make in the future.
1275 If the README file seems to be getting too large you may wish to
1276 split out some of the sections into separate files: INSTALL,
1281 =item Adding a Copyright Notice.
1283 How you choose to license your work is a personal decision.
1284 The general mechanism is to assert your Copyright and then make
1285 a declaration of how others may copy/use/modify your work.
1287 Perl, for example, is supplied with two types of licence: The GNU
1288 GPL and The Artistic Licence (see the files README, Copying, and
1289 Artistic). Larry has good reasons for NOT just using the GNU GPL.
1291 My personal recommendation, out of respect for Larry, Perl, and the
1292 Perl community at large is to state something simply like:
1294 Copyright (c) 1995 Your Name. All rights reserved.
1295 This program is free software; you can redistribute it and/or
1296 modify it under the same terms as Perl itself.
1298 This statement should at least appear in the README file. You may
1299 also wish to include it in a Copying file and your source files.
1300 Remember to include the other words in addition to the Copyright.
1302 =item Give the module a version/issue/release number.
1304 To be fully compatible with the Exporter and MakeMaker modules you
1305 should store your module's version number in a non-my package
1306 variable called $VERSION. This should be a floating point
1307 number with at least two digits after the decimal (i.e., hundredths,
1308 e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
1309 See L<Exporter> for details.
1311 It may be handy to add a function or method to retrieve the number.
1312 Use the number in announcements and archive file names when
1313 releasing the module (ModuleName-1.02.tar.Z).
1314 See perldoc ExtUtils::MakeMaker.pm for details.
1316 =item How to release and distribute a module.
1318 It's good idea to post an announcement of the availability of your
1319 module (or the module itself if small) to the comp.lang.perl.announce
1320 Usenet newsgroup. This will at least ensure very wide once-off
1323 If possible, register the module with CPAN. You should
1324 include details of its location in your announcement.
1326 Some notes about ftp archives: Please use a long descriptive file
1327 name that includes the version number. Most incoming directories
1328 will not be readable/listable, i.e., you won't be able to see your
1329 file after uploading it. Remember to send your email notification
1330 message as soon as possible after uploading else your file may get
1331 deleted automatically. Allow time for the file to be processed
1332 and/or check the file has been processed before announcing its
1335 FTP Archives for Perl Modules:
1337 Follow the instructions and links on:
1339 http://www.perl.com/CPAN/modules/00modlist.long.html
1340 http://www.perl.com/CPAN/modules/04pause.html
1342 or upload to one of these sites:
1344 https://pause.kbx.de/pause/
1345 http://pause.perl.org/pause/
1347 and notify <modules@perl.org>.
1349 By using the WWW interface you can ask the Upload Server to mirror
1350 your modules from your ftp or WWW site into your own directory on
1353 Please remember to send me an updated entry for the Module list!
1355 =item Take care when changing a released module.
1357 Always strive to remain compatible with previous released versions.
1358 Otherwise try to add a mechanism to revert to the
1359 old behavior if people rely on it. Document incompatible changes.
1365 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
1369 =item There is no requirement to convert anything.
1371 If it ain't broke, don't fix it! Perl 4 library scripts should
1372 continue to work with no problems. You may need to make some minor
1373 changes (like escaping non-array @'s in double quoted strings) but
1374 there is no need to convert a .pl file into a Module for just that.
1376 =item Consider the implications.
1378 All Perl applications that make use of the script will need to
1379 be changed (slightly) if the script is converted into a module. Is
1380 it worth it unless you plan to make other changes at the same time?
1382 =item Make the most of the opportunity.
1384 If you are going to convert the script to a module you can use the
1385 opportunity to redesign the interface. The guidelines for module
1386 creation above include many of the issues you should consider.
1388 =item The pl2pm utility will get you started.
1390 This utility will read *.pl files (given as parameters) and write
1391 corresponding *.pm files. The pl2pm utilities does the following:
1396 Adds the standard Module prologue lines
1399 Converts package specifiers from ' to ::
1402 Converts die(...) to croak(...)
1405 Several other minor changes
1409 Being a mechanical process pl2pm is not bullet proof. The converted
1410 code will need careful checking, especially any package statements.
1411 Don't delete the original .pl file till the new .pm one works!
1415 =head2 Guidelines for Reusing Application Code
1419 =item Complete applications rarely belong in the Perl Module Library.
1421 =item Many applications contain some Perl code that could be reused.
1423 Help save the world! Share your code in a form that makes it easy
1426 =item Break-out the reusable code into one or more separate module files.
1428 =item Take the opportunity to reconsider and redesign the interfaces.
1430 =item In some cases the 'application' can then be reduced to a small
1432 fragment of code built on top of the reusable modules. In these cases
1433 the application could invoked as:
1435 % perl -e 'use Module::Name; method(@ARGV)' ...
1437 % perl -mModule::Name ... (in perl5.002 or higher)
1443 Perl does not enforce private and public parts of its modules as you may
1444 have been used to in other languages like C++, Ada, or Modula-17. Perl
1445 doesn't have an infatuation with enforced privacy. It would prefer
1446 that you stayed out of its living room because you weren't invited, not
1447 because it has a shotgun.
1449 The module and its user have a contract, part of which is common law,
1450 and part of which is "written". Part of the common law contract is
1451 that a module doesn't pollute any namespace it wasn't asked to. The
1452 written contract for the module (A.K.A. documentation) may make other
1453 provisions. But then you know when you C<use RedefineTheWorld> that
1454 you're redefining the world and willing to take the consequences.