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
806 Language Extensions and Documentation Tools
814 Operating System Interfaces
818 Networking, Device Control (modems) and InterProcess Communication
822 Data Types and Data Type Utilities
834 Interfaces to / Emulations of Other Programming Languages
838 File Names, File Systems and File Locking (see also File Handles)
842 String Processing, Language Text Processing, Parsing, and Searching
846 Option, Argument, Parameter, and Configuration File Processing
850 Internationalization and Locale
854 Authentication, Security, and Encryption
858 World Wide Web, HTML, HTTP, CGI, MIME
862 Server and Daemon Utilities
866 Archiving and Compression
870 Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
878 Control Flow Utilities (callbacks and exceptions etc)
882 File Handle and Input/Output Stream Utilities
886 Miscellaneous Modules
890 Registered CPAN sites as of this writing include the following.
891 You should try to choose one close to you:
897 South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
898 ftp://ftp.saix.net/pub/CPAN/
899 ftp://ftp.sun.ac.za/CPAN/
900 ftp://ftpza.co.za/pub/mirrors/cpan/
905 China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
906 Hong Kong ftp://ftp.pacific.net.hk/pub/mirror/CPAN/
907 Indonesia ftp://malone.piksi.itb.ac.id/pub/CPAN/
908 Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
909 Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
910 ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
911 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
912 ftp://ftp.meisei-u.ac.jp/pub/CPAN/
913 ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/
914 ftp://mirror.nucba.ac.jp/mirror/Perl/
915 Saudi-Arabia ftp://ftp.isu.net.sa/pub/CPAN/
916 Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
917 South Korea ftp://ftp.bora.net/pub/CPAN/
918 ftp://ftp.kornet.net/pub/CPAN/
919 ftp://ftp.nuri.net/pub/CPAN/
920 Taiwan ftp://coda.nctu.edu.tw/computer-languages/perl/CPAN/
921 ftp://ftp.ee.ncku.edu.tw/pub3/perl/CPAN/
922 ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
923 Thailand ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
928 Australia ftp://cpan.topend.com.au/pub/CPAN/
929 ftp://ftp.labyrinth.net.au/pub/perl-CPAN/
930 ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
931 ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
932 New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
933 ftp://sunsite.net.nz/pub/languages/perl/CPAN/
936 =item Central America
938 Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
943 Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
944 Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
945 Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
946 Croatia ftp://ftp.linux.hr/pub/CPAN/
947 Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
948 ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
949 Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
950 Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
951 Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
952 France ftp://ftp.grolier.fr/pub/perl/CPAN/
953 ftp://ftp.lip6.fr/pub/perl/CPAN/
954 ftp://ftp.oleane.net/pub/mirrors/CPAN/
955 ftp://ftp.pasteur.fr/pub/computing/CPAN/
956 ftp://ftp.uvsq.fr/pub/perl/CPAN/
957 German ftp://ftp.gigabell.net/pub/CPAN/
958 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
959 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
960 ftp://ftp.gmd.de/packages/CPAN/
961 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
963 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
964 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
965 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
966 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
967 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
968 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
969 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
970 ftp://ftp.gmd.de/packages/CPAN/
971 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
973 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
974 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
975 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
976 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
977 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
978 Greece ftp://ftp.ntua.gr/pub/lang/perl/
979 Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
980 Iceland ftp://ftp.gm.is/pub/CPAN/
981 Ireland ftp://cpan.indigo.ie/pub/CPAN/
982 ftp://sunsite.compapp.dcu.ie/pub/perl/
983 Italy ftp://cis.uniRoma2.it/CPAN/
984 ftp://ftp.flashnet.it/pub/CPAN/
985 ftp://ftp.unina.it/pub/Other/CPAN/
986 ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
987 Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
988 ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
989 Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
990 ftp://sunsite.uio.no/pub/languages/perl/CPAN/
991 Poland ftp://ftp.man.torun.pl/pub/CPAN/
992 ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
993 ftp://sunsite.icm.edu.pl/pub/CPAN/
994 Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
995 ftp://ftp.ist.utl.pt/pub/CPAN/
996 ftp://ftp.ua.pt/pub/CPAN/
997 Romania ftp://ftp.dnttm.ro/pub/CPAN/
998 Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/
999 ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
1000 Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
1001 Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
1002 Spain ftp://ftp.etse.urv.es/pub/perl/
1003 ftp://ftp.rediris.es/mirror/CPAN/
1004 Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
1005 Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
1006 Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
1007 United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
1008 ftp://ftp.flirble.org/pub/languages/perl/CPAN/
1010 ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/
1011 ftp://ftp.plig.org/pub/CPAN/
1012 ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
1017 Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
1018 California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
1019 ftp://cpan.valueclick.com/CPAN/
1020 ftp://ftp.cdrom.com/pub/perl/CPAN/
1021 http://download.sourceforge.net/mirrors/CPAN/
1022 Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
1023 Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
1024 Georgia ftp://ftp.twoguys.org/CPAN/
1025 Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
1026 Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
1027 ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
1028 Kentucky ftp://ftp.uky.edu/CPAN/
1029 Manitoba ftp://theoryx5.uwinnipeg.ca/pub/CPAN/
1031 ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
1032 ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
1033 Mexico ftp://ftp.msg.com.mx/pub/CPAN/
1034 New York ftp://ftp.deao.net/pub/CPAN/
1035 ftp://ftp.rge.com/pub/languages/perl/
1036 North Carolina ftp://ftp.duke.edu/pub/perl/
1037 Nova Scotia ftp://cpan.chebucto.ns.ca/pub/CPAN/
1038 Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
1039 Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/
1040 Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
1041 Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
1042 Tennessee ftp://ftp.sunsite.utk.edu/pub/CPAN/
1043 Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
1044 ftp://jhcloos.com/pub/mirror/CPAN/
1045 Utah ftp://mirror.xmission.com/CPAN/
1046 Virginia ftp://ftp.perl.org/pub/perl/CPAN/
1047 ftp://ruff.cs.jmu.edu/pub/CPAN/
1048 Washington ftp://ftp-mirror.internap.com/pub/CPAN/
1049 ftp://ftp.llarian.net/pub/CPAN/
1050 ftp://ftp.spu.edu/pub/CPAN/
1055 Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
1056 ftp://ftp.matrix.com.br/pub/perl/
1057 Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/PERL/
1061 For an up-to-date listing of CPAN sites,
1062 see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES .
1064 =head1 Modules: Creation, Use, and Abuse
1066 (The following section is borrowed directly from Tim Bunce's modules
1067 file, available at your nearest CPAN site.)
1069 Perl implements a class using a package, but the presence of a
1070 package doesn't imply the presence of a class. A package is just a
1071 namespace. A class is a package that provides subroutines that can be
1072 used as methods. A method is just a subroutine that expects, as its
1073 first argument, either the name of a package (for "static" methods),
1074 or a reference to something (for "virtual" methods).
1076 A module is a file that (by convention) provides a class of the same
1077 name (sans the .pm), plus an import method in that class that can be
1078 called to fetch exported symbols. This module may implement some of
1079 its methods by loading dynamic C or C++ objects, but that should be
1080 totally transparent to the user of the module. Likewise, the module
1081 might set up an AUTOLOAD function to slurp in subroutine definitions on
1082 demand, but this is also transparent. Only the F<.pm> file is required to
1083 exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
1084 the AUTOLOAD mechanism.
1086 =head2 Guidelines for Module Creation
1090 =item Do similar modules already exist in some form?
1092 If so, please try to reuse the existing modules either in whole or
1093 by inheriting useful features into a new class. If this is not
1094 practical try to get together with the module authors to work on
1095 extending or enhancing the functionality of the existing modules.
1096 A perfect example is the plethora of packages in perl4 for dealing
1097 with command line options.
1099 If you are writing a module to expand an already existing set of
1100 modules, please coordinate with the author of the package. It
1101 helps if you follow the same naming scheme and module interaction
1102 scheme as the original author.
1104 =item Try to design the new module to be easy to extend and reuse.
1106 Try to C<use warnings;> (or C<use warnings qw(...);>).
1107 Remember that you can add C<no warnings qw(...);> to individual blocks
1108 of code that need less warnings.
1110 Use blessed references. Use the two argument form of bless to bless
1111 into the class name given as the first parameter of the constructor,
1116 return bless {}, $class;
1119 or even this if you'd like it to be used as either a static
1120 or a virtual method.
1124 my $class = ref($self) || $self;
1125 return bless {}, $class;
1128 Pass arrays as references so more parameters can be added later
1129 (it's also faster). Convert functions into methods where
1130 appropriate. Split large methods into smaller more flexible ones.
1131 Inherit methods from other modules if appropriate.
1133 Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>.
1134 Generally you can delete the C<eq 'FOO'> part with no harm at all.
1135 Let the objects look after themselves! Generally, avoid hard-wired
1136 class names as far as possible.
1138 Avoid C<< $r->Class::func() >> where using C<@ISA=qw(... Class ...)> and
1139 C<< $r->func() >> would work (see L<perlbot> for more details).
1141 Use autosplit so little used or newly added functions won't be a
1142 burden to programs that don't use them. Add test functions to
1143 the module after __END__ either using AutoSplit or by saying:
1145 eval join('',<main::DATA>) || die $@ unless caller();
1147 Does your module pass the 'empty subclass' test? If you say
1148 C<@SUBCLASS::ISA = qw(YOURCLASS);> your applications should be able
1149 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
1150 does your application still work if you change: C<$obj = new YOURCLASS;>
1151 into: C<$obj = new SUBCLASS;> ?
1153 Avoid keeping any state information in your packages. It makes it
1154 difficult for multiple other packages to use yours. Keep state
1155 information in objects.
1159 Try to C<use strict;> (or C<use strict qw(...);>).
1160 Remember that you can add C<no strict qw(...);> to individual blocks
1161 of code that need less strictness.
1165 Follow the guidelines in the perlstyle(1) manual.
1169 =item Some simple style guidelines
1171 The perlstyle manual supplied with Perl has many helpful points.
1173 Coding style is a matter of personal taste. Many people evolve their
1174 style over several years as they learn what helps them write and
1175 maintain good code. Here's one set of assorted suggestions that
1176 seem to be widely used by experienced developers:
1178 Use underscores to separate words. It is generally easier to read
1179 $var_names_like_this than $VarNamesLikeThis, especially for
1180 non-native speakers of English. It's also a simple rule that works
1181 consistently with VAR_NAMES_LIKE_THIS.
1183 Package/Module names are an exception to this rule. Perl informally
1184 reserves lowercase module names for 'pragma' modules like integer
1185 and strict. Other modules normally begin with a capital letter and
1186 use mixed case with no underscores (need to be short and portable).
1188 You may find it helpful to use letter case to indicate the scope
1189 or nature of a variable. For example:
1191 $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
1192 $Some_Caps_Here package-wide global/static
1193 $no_caps_here function scope my() or local() variables
1195 Function and method names seem to work best as all lowercase.
1196 e.g., C<< $obj->as_string() >>.
1198 You can use a leading underscore to indicate that a variable or
1199 function should not be used outside the package that defined it.
1201 =item Select what to export.
1203 Do NOT export method names!
1205 Do NOT export anything else by default without a good reason!
1207 Exports pollute the namespace of the module user. If you must
1208 export try to use @EXPORT_OK in preference to @EXPORT and avoid
1209 short or common names to reduce the risk of name clashes.
1211 Generally anything not exported is still accessible from outside the
1212 module using the ModuleName::item_name (or C<< $blessed_ref->method >>)
1213 syntax. By convention you can use a leading underscore on names to
1214 indicate informally that they are 'internal' and not for public use.
1216 (It is actually possible to get private functions by saying:
1217 C<my $subref = sub { ... }; &$subref;>. But there's no way to call that
1218 directly as a method, because a method must have a name in the symbol
1221 As a general rule, if the module is trying to be object oriented
1222 then export nothing. If it's just a collection of functions then
1223 @EXPORT_OK anything but use @EXPORT with caution.
1225 =item Select a name for the module.
1227 This name should be as descriptive, accurate, and complete as
1228 possible. Avoid any risk of ambiguity. Always try to use two or
1229 more whole words. Generally the name should reflect what is special
1230 about what the module does rather than how it does it. Please use
1231 nested module names to group informally or categorize a module.
1232 There should be a very good reason for a module not to have a nested name.
1233 Module names should begin with a capital letter.
1235 Having 57 modules all called Sort will not make life easy for anyone
1236 (though having 23 called Sort::Quick is only marginally better :-).
1237 Imagine someone trying to install your module alongside many others.
1238 If in any doubt ask for suggestions in comp.lang.perl.misc.
1240 If you are developing a suite of related modules/classes it's good
1241 practice to use nested classes with a common prefix as this will
1242 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
1243 Xyz::Model etc. Use the modules in this list as a naming guide.
1245 If adding a new module to a set, follow the original author's
1246 standards for naming modules and the interface to methods in
1249 If developing modules for private internal or project specific use,
1250 that will never be released to the public, then you should ensure
1251 that their names will not clash with any future public module. You
1252 can do this either by using the reserved Local::* category or by
1253 using a category name that includes an underscore like Foo_Corp::*.
1255 To be portable each component of a module name should be limited to
1256 11 characters. If it might be used on MS-DOS then try to ensure each is
1257 unique in the first 8 characters. Nested modules make this easier.
1259 =item Have you got it right?
1261 How do you know that you've made the right decisions? Have you
1262 picked an interface design that will cause problems later? Have
1263 you picked the most appropriate name? Do you have any questions?
1265 The best way to know for sure, and pick up many helpful suggestions,
1266 is to ask someone who knows. Comp.lang.perl.misc is read by just about
1267 all the people who develop modules and it's the best place to ask.
1269 All you need to do is post a short summary of the module, its
1270 purpose and interfaces. A few lines on each of the main methods is
1271 probably enough. (If you post the whole module it might be ignored
1272 by busy people - generally the very people you want to read it!)
1274 Don't worry about posting if you can't say when the module will be
1275 ready - just say so in the message. It might be worth inviting
1276 others to help you, they may be able to complete it for you!
1278 =item README and other Additional Files.
1280 It's well known that software developers usually fully document the
1281 software they write. If, however, the world is in urgent need of
1282 your software and there is not enough time to write the full
1283 documentation please at least provide a README file containing:
1288 A description of the module/package/extension etc.
1291 A copyright notice - see below.
1294 Prerequisites - what else you may need to have.
1297 How to build it - possible changes to Makefile.PL etc.
1303 Recent changes in this release, especially incompatibilities
1306 Changes / enhancements you plan to make in the future.
1310 If the README file seems to be getting too large you may wish to
1311 split out some of the sections into separate files: INSTALL,
1316 =item Adding a Copyright Notice.
1318 How you choose to license your work is a personal decision.
1319 The general mechanism is to assert your Copyright and then make
1320 a declaration of how others may copy/use/modify your work.
1322 Perl, for example, is supplied with two types of licence: The GNU
1323 GPL and The Artistic Licence (see the files README, Copying, and
1324 Artistic). Larry has good reasons for NOT just using the GNU GPL.
1326 My personal recommendation, out of respect for Larry, Perl, and the
1327 Perl community at large is to state something simply like:
1329 Copyright (c) 1995 Your Name. All rights reserved.
1330 This program is free software; you can redistribute it and/or
1331 modify it under the same terms as Perl itself.
1333 This statement should at least appear in the README file. You may
1334 also wish to include it in a Copying file and your source files.
1335 Remember to include the other words in addition to the Copyright.
1337 =item Give the module a version/issue/release number.
1339 To be fully compatible with the Exporter and MakeMaker modules you
1340 should store your module's version number in a non-my package
1341 variable called $VERSION. This should be a floating point
1342 number with at least two digits after the decimal (i.e., hundredths,
1343 e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
1344 See L<Exporter> for details.
1346 It may be handy to add a function or method to retrieve the number.
1347 Use the number in announcements and archive file names when
1348 releasing the module (ModuleName-1.02.tar.Z).
1349 See perldoc ExtUtils::MakeMaker.pm for details.
1351 =item How to release and distribute a module.
1353 It's good idea to post an announcement of the availability of your
1354 module (or the module itself if small) to the comp.lang.perl.announce
1355 Usenet newsgroup. This will at least ensure very wide once-off
1358 If possible, register the module with CPAN. You should
1359 include details of its location in your announcement.
1361 Some notes about ftp archives: Please use a long descriptive file
1362 name that includes the version number. Most incoming directories
1363 will not be readable/listable, i.e., you won't be able to see your
1364 file after uploading it. Remember to send your email notification
1365 message as soon as possible after uploading else your file may get
1366 deleted automatically. Allow time for the file to be processed
1367 and/or check the file has been processed before announcing its
1370 FTP Archives for Perl Modules:
1372 Follow the instructions and links on:
1374 http://www.perl.com/CPAN/modules/00modlist.long.html
1375 http://www.perl.com/CPAN/modules/04pause.html
1377 or upload to one of these sites:
1379 https://pause.kbx.de/pause/
1380 http://pause.perl.org/pause/
1382 and notify <modules@perl.org>.
1384 By using the WWW interface you can ask the Upload Server to mirror
1385 your modules from your ftp or WWW site into your own directory on
1388 Please remember to send me an updated entry for the Module list!
1390 =item Take care when changing a released module.
1392 Always strive to remain compatible with previous released versions.
1393 Otherwise try to add a mechanism to revert to the
1394 old behavior if people rely on it. Document incompatible changes.
1400 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
1404 =item There is no requirement to convert anything.
1406 If it ain't broke, don't fix it! Perl 4 library scripts should
1407 continue to work with no problems. You may need to make some minor
1408 changes (like escaping non-array @'s in double quoted strings) but
1409 there is no need to convert a .pl file into a Module for just that.
1411 =item Consider the implications.
1413 All Perl applications that make use of the script will need to
1414 be changed (slightly) if the script is converted into a module. Is
1415 it worth it unless you plan to make other changes at the same time?
1417 =item Make the most of the opportunity.
1419 If you are going to convert the script to a module you can use the
1420 opportunity to redesign the interface. The guidelines for module
1421 creation above include many of the issues you should consider.
1423 =item The pl2pm utility will get you started.
1425 This utility will read *.pl files (given as parameters) and write
1426 corresponding *.pm files. The pl2pm utilities does the following:
1431 Adds the standard Module prologue lines
1434 Converts package specifiers from ' to ::
1437 Converts die(...) to croak(...)
1440 Several other minor changes
1444 Being a mechanical process pl2pm is not bullet proof. The converted
1445 code will need careful checking, especially any package statements.
1446 Don't delete the original .pl file till the new .pm one works!
1450 =head2 Guidelines for Reusing Application Code
1456 Complete applications rarely belong in the Perl Module Library.
1460 Many applications contain some Perl code that could be reused.
1462 Help save the world! Share your code in a form that makes it easy
1467 Break-out the reusable code into one or more separate module files.
1471 Take the opportunity to reconsider and redesign the interfaces.
1475 In some cases the 'application' can then be reduced to a small
1477 fragment of code built on top of the reusable modules. In these cases
1478 the application could invoked as:
1480 % perl -e 'use Module::Name; method(@ARGV)' ...
1482 % perl -mModule::Name ... (in perl5.002 or higher)
1488 Perl does not enforce private and public parts of its modules as you may
1489 have been used to in other languages like C++, Ada, or Modula-17. Perl
1490 doesn't have an infatuation with enforced privacy. It would prefer
1491 that you stayed out of its living room because you weren't invited, not
1492 because it has a shotgun.
1494 The module and its user have a contract, part of which is common law,
1495 and part of which is "written". Part of the common law contract is
1496 that a module doesn't pollute any namespace it wasn't asked to. The
1497 written contract for the module (A.K.A. documentation) may make other
1498 provisions. But then you know when you C<use RedefineTheWorld> that
1499 you're redefining the world and willing to take the consequences.