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
137 =item unicode::distinct
139 Strictly distinguish UTF8 data and non-UTF data.
143 Enable/disable UTF-8 in source code
147 Predeclare global variable names (obsolete)
151 Control optional warnings
153 =item warnings::register
155 Warnings import function
159 =head2 Standard Modules
161 Standard, bundled modules are all expected to behave in a well-defined
162 manner with respect to namespace pollution because they use the
163 Exporter module. See their own documentation for details.
169 Provide framework for multiple DBMs
173 Load subroutines only on demand
177 Split a package for autoloading
185 Autogenerated data about Perl ops, used to generate bytecode
189 Assemble Perl bytecode
197 Perl compiler's bytecode backend
201 Perl compiler's C backend
205 Perl compiler's optimized C translation backend
209 Walk Perl syntax tree, printing concise info about ops
213 Walk Perl syntax tree, printing debug info about ops
217 Perl compiler backend to produce perl code
219 =item B::Disassembler
221 Disassemble Perl bytecode
229 Show lexical variables used in functions or files
233 Helper module for CC backend
237 Show what stashes are loaded
241 Walk Perl syntax tree, printing terse info about ops
245 Generates cross reference reports for Perl programs
249 Benchmark running times of Perl code
253 Load byte compiled perl code
257 Simple Common Gateway Interface Class
261 Backward compatibility module for CGI.pm
265 CGI routines for writing to the HTTPD (or other) error log
269 Interface to Netscape Cookies
273 CGI Interface for Fast CGI
277 Module to produce nicely formatted HTML code
281 Simple Interface to Server Push
285 Backward compatibility module for defunct CGI::Switch
289 Query, download and build perl modules from CPAN sites
291 =item CPAN::FirstTime
293 Utility for CPAN::Config file Initialization
297 Wrapper around CPAN.pm without using any XS module
301 Warn of errors (from perspective of caller)
305 No user serviceable parts inside
309 Declare struct-like datatypes as Perl classes
313 Get pathname of current working directory
317 Programmatic interface to the Perl debugging API (draft, subject to
321 Perl5 access to Berkeley DB version 1.x
323 =item Devel::SelfStubber
325 Generate stubs for a SelfLoading module
329 Supply object methods for directory handles
333 Provides screen dump of Perl data.
341 Use nice English (or awk) names for ugly punctuation variables
345 Perl module that imports environment variables as scalars or arrays
349 Implements default import method for modules
351 =item Exporter::Heavy
355 =item ExtUtils::Command
357 Utilities to replace common UNIX commands in Makefiles etc.
359 =item ExtUtils::Embed
361 Utilities for embedding Perl in C/C++ applications
363 =item ExtUtils::Install
365 Install files from here to there
367 =item ExtUtils::Installed
369 Inventory management of installed modules
371 =item ExtUtils::Liblist
373 Determine libraries to use and how to use them
375 =item ExtUtils::MM_Cygwin
377 Methods to override UN*X behaviour in ExtUtils::MakeMaker
379 =item ExtUtils::MM_OS2
381 Methods to override UN*X behaviour in ExtUtils::MakeMaker
383 =item ExtUtils::MM_Unix
385 Methods used by ExtUtils::MakeMaker
387 =item ExtUtils::MM_VMS
389 Methods to override UN*X behaviour in ExtUtils::MakeMaker
391 =item ExtUtils::MM_Win32
393 Methods to override UN*X behaviour in ExtUtils::MakeMaker
395 =item ExtUtils::MakeMaker
397 Create an extension Makefile
399 =item ExtUtils::Manifest
401 Utilities to write and check a MANIFEST file
403 =item ExtUtils::Mkbootstrap
405 Make a bootstrap file for use by DynaLoader
407 =item ExtUtils::Mksymlists
409 Write linker options files for dynamic extension
411 =item ExtUtils::Packlist
413 Manage .packlist files
415 =item ExtUtils::testlib
417 Add blib/* directories to @INC
421 Replace functions with equivalents which succeed or die
425 Load the C Fcntl.h defines
429 Split a pathname into pieces
431 =item File::CheckTree
433 Run many filetest checks on a tree
437 Compare files or filehandles
441 Copy files or filehandles
445 DOS like globbing and then some
453 Create or remove directory trees
457 Portably perform operations on file names
459 =item File::Spec::Epoc
461 Methods for Epoc file specs
463 =item File::Spec::Functions
465 Portably perform operations on file names
467 =item File::Spec::Mac
471 =item File::Spec::OS2
473 Methods for OS/2 file specs
475 =item File::Spec::Unix
477 Methods used by File::Spec
479 =item File::Spec::VMS
481 Methods for VMS file specs
483 =item File::Spec::Win32
485 Methods for Win32 file specs
489 Return name and handle of a temporary file safely
493 By-name interface to Perl's built-in stat() functions
497 Keep more files open than the system permits
501 Supply object methods for filehandles
505 Simplified source filtering
509 Locate directory of original perl script
513 Perl5 access to the gdbm library.
517 Extended processing of command line options
521 Process single-character switches with switch clustering
525 Compare 8-bit scalar data according to the current locale
529 Load various IO modules
533 Open a process for both reading and writing
537 Open a process for reading, writing, and error handling
541 Arbitrary length float math package
545 Arbitrary size integer math package
549 Complex numbers and associated mathematical functions
553 Trigonometric functions
557 Tied access to ndbm files
561 Check a remote host for reachability
565 By-name interface to Perl's built-in gethost*() functions
569 By-name interface to Perl's built-in getnet*() functions
573 By-name interface to Perl's built-in getproto*() functions
577 By-name interface to Perl's built-in getserv*() functions
581 Generic interface to Perl Compiler backends
585 Tied access to odbm files
589 Disable named opcodes when compiling perl code
593 Check pod documents for syntax errors
597 Find POD documents in directory trees
601 Module to convert pod files to HTML
603 =item Pod::InputObjects
605 Objects representing POD input paragraphs, commands, etc.
609 Convert Pod data to formatted Latex
613 Convert POD data to formatted *roff input
615 =item Pod::ParseUtils
617 Helpers for POD parsing and conversion
621 Base class for creating POD filters and translators
625 Perl extension for converting Pod to old style Pod.
629 Extract selected sections of POD from input
633 Convert POD data to formatted ASCII text
635 =item Pod::Text::Color
637 Convert POD data to formatted color ASCII text
639 =item Pod::Text::Overstrike
641 Convert POD data to formatted overstrike text
643 =item Pod::Text::Termcap
645 Convert POD data to ASCII text with format escapes
649 Print a usage message from embedded pod documentation
653 Tied access to sdbm files
657 Compile and execute code in restricted compartments
661 Search for key in dictionary file
665 Save and restore selected file handle
669 Load functions only on demand
673 Run shell commands transparently within perl
677 Load the C socket.h defines and structure manipulators
681 Persistency for perl data structures
685 Manipulate Perl symbols and their names
687 =item Term::ANSIColor
689 Color screen output using ANSI escape sequences
693 Perl termcap interface
697 Perl word completion module
701 Perl interface to various C<readline> packages. If
705 Provides a simple framework for writing test scripts
709 Run perl standard test scripts with statistics
713 Create an abbreviation table from a list
715 =item Text::ParseWords
717 Parse text into an array of tokens or array of arrays
721 Implementation of the Soundex Algorithm as Described by Knuth
725 Line wrapping to form simple paragraphs
729 Base class for tied arrays
733 Base class definitions for tied handles
737 Base class definitions for tied hashes
741 Use references as hash keys
745 Base class definitions for tied scalars
747 =item Tie::SubstrHash
749 Fixed-table-size, fixed-key-length hashing
753 Efficiently compute time from local and GMT time
757 By-name interface to Perl's built-in gmtime() function
759 =item Time::localtime
761 By-name interface to Perl's built-in localtime() function
765 Internal object used by Time::gmtime and Time::localtime
769 Base class for ALL classes (blessed references)
773 By-name interface to Perl's built-in getgr*() functions
777 By-name interface to Perl's built-in getpw*() functions
781 To find out I<all> modules installed on your system, including
782 those without documentation or outside the standard release,
785 % find `perl -e 'print "@INC"'` -name '*.pm' -print
787 They should all have their own documentation installed and accessible
788 via your system man(1) command. If you do not have a B<find>
789 program, you can use the Perl B<find2perl> program instead, which
790 generates Perl code as output you can run through perl. If you
791 have a B<man> program but it doesn't find your modules, you'll have
792 to fix your manpath. See L<perl> for details. If you have no
793 system B<man> command, you might try the B<perldoc> program.
795 =head2 Extension Modules
797 Extension modules are written in C (or a mix of Perl and C). They
798 are usually dynamically loaded into Perl if and when you need them,
799 but may also be be linked in statically. Supported extension modules
800 include Socket, Fcntl, and POSIX.
802 Many popular C extension modules do not come bundled (at least, not
803 completely) due to their sizes, volatility, or simply lack of time
804 for adequate testing and configuration across the multitude of
805 platforms on which Perl was beta-tested. You are encouraged to
806 look for them on CPAN (described below), or using web search engines
807 like Alta Vista or Deja News.
811 CPAN stands for Comprehensive Perl Archive Network; it's a globally
812 replicated trove of Perl materials, including documentation, style
813 guides, tricks and traps, alternate ports to non-Unix systems and
814 occasional binary distributions for these. Search engines for
815 CPAN can be found at http://cpan.perl.com/ and at
816 http://theory.uwinnipeg.ca/mod_perl/cpan-search.pl .
818 Most importantly, CPAN includes around a thousand unbundled modules,
819 some of which require a C compiler to build. Major categories of
825 Language Extensions and Documentation Tools
831 Operating System Interfaces
834 Networking, Device Control (modems) and InterProcess Communication
837 Data Types and Data Type Utilities
846 Interfaces to / Emulations of Other Programming Languages
849 File Names, File Systems and File Locking (see also File Handles)
852 String Processing, Language Text Processing, Parsing, and Searching
855 Option, Argument, Parameter, and Configuration File Processing
858 Internationalization and Locale
861 Authentication, Security, and Encryption
864 World Wide Web, HTML, HTTP, CGI, MIME
867 Server and Daemon Utilities
870 Archiving and Compression
873 Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
879 Control Flow Utilities (callbacks and exceptions etc)
882 File Handle and Input/Output Stream Utilities
885 Miscellaneous Modules
889 Registered CPAN sites as of this writing include the following.
890 You should try to choose one close to you:
896 South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
897 ftp://ftp.saix.net/pub/CPAN/
898 ftp://ftp.sun.ac.za/CPAN/
899 ftp://ftpza.co.za/pub/mirrors/cpan/
904 China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
905 Hong Kong ftp://ftp.pacific.net.hk/pub/mirror/CPAN/
906 Indonesia ftp://malone.piksi.itb.ac.id/pub/CPAN/
907 Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
908 Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
909 ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
910 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
911 ftp://ftp.meisei-u.ac.jp/pub/CPAN/
912 ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/
913 ftp://mirror.nucba.ac.jp/mirror/Perl/
914 Saudi-Arabia ftp://ftp.isu.net.sa/pub/CPAN/
915 Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
916 South Korea ftp://ftp.bora.net/pub/CPAN/
917 ftp://ftp.kornet.net/pub/CPAN/
918 ftp://ftp.nuri.net/pub/CPAN/
919 Taiwan ftp://coda.nctu.edu.tw/computer-languages/perl/CPAN/
920 ftp://ftp.ee.ncku.edu.tw/pub3/perl/CPAN/
921 ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
922 Thailand ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
927 Australia ftp://cpan.topend.com.au/pub/CPAN/
928 ftp://ftp.labyrinth.net.au/pub/perl-CPAN/
929 ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
930 ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
931 New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
932 ftp://sunsite.net.nz/pub/languages/perl/CPAN/
935 =item Central America
937 Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
942 Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
943 Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
944 Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
945 Croatia ftp://ftp.linux.hr/pub/CPAN/
946 Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
947 ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
948 Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
949 Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
950 Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
951 France ftp://ftp.grolier.fr/pub/perl/CPAN/
952 ftp://ftp.lip6.fr/pub/perl/CPAN/
953 ftp://ftp.oleane.net/pub/mirrors/CPAN/
954 ftp://ftp.pasteur.fr/pub/computing/CPAN/
955 ftp://ftp.uvsq.fr/pub/perl/CPAN/
956 German ftp://ftp.gigabell.net/pub/CPAN/
957 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
958 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
959 ftp://ftp.gmd.de/packages/CPAN/
960 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
962 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
963 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
964 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
965 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
966 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
967 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
968 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
969 ftp://ftp.gmd.de/packages/CPAN/
970 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
972 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
973 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
974 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
975 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
976 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
977 Greece ftp://ftp.ntua.gr/pub/lang/perl/
978 Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
979 Iceland ftp://ftp.gm.is/pub/CPAN/
980 Ireland ftp://cpan.indigo.ie/pub/CPAN/
981 ftp://sunsite.compapp.dcu.ie/pub/perl/
982 Italy ftp://cis.uniRoma2.it/CPAN/
983 ftp://ftp.flashnet.it/pub/CPAN/
984 ftp://ftp.unina.it/pub/Other/CPAN/
985 ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
986 Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
987 ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
988 Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
989 ftp://sunsite.uio.no/pub/languages/perl/CPAN/
990 Poland ftp://ftp.man.torun.pl/pub/CPAN/
991 ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
992 ftp://sunsite.icm.edu.pl/pub/CPAN/
993 Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
994 ftp://ftp.ist.utl.pt/pub/CPAN/
995 ftp://ftp.ua.pt/pub/CPAN/
996 Romania ftp://ftp.dnttm.ro/pub/CPAN/
997 Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/
998 ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
999 Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
1000 Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
1001 Spain ftp://ftp.etse.urv.es/pub/perl/
1002 ftp://ftp.rediris.es/mirror/CPAN/
1003 Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
1004 Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
1005 Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
1006 United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
1007 ftp://ftp.flirble.org/pub/languages/perl/CPAN/
1009 ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/
1010 ftp://ftp.plig.org/pub/CPAN/
1011 ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
1016 Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
1017 California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
1018 ftp://cpan.valueclick.com/CPAN/
1019 ftp://ftp.cdrom.com/pub/perl/CPAN/
1020 http://download.sourceforge.net/mirrors/CPAN/
1021 Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
1022 Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
1023 Georgia ftp://ftp.twoguys.org/CPAN/
1024 Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
1025 Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
1026 ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
1027 Kentucky ftp://ftp.uky.edu/CPAN/
1028 Manitoba ftp://theoryx5.uwinnipeg.ca/pub/CPAN/
1030 ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
1031 ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
1032 Mexico ftp://ftp.msg.com.mx/pub/CPAN/
1033 New York ftp://ftp.deao.net/pub/CPAN/
1034 ftp://ftp.rge.com/pub/languages/perl/
1035 North Carolina ftp://ftp.duke.edu/pub/perl/
1036 Nova Scotia ftp://cpan.chebucto.ns.ca/pub/CPAN/
1037 Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
1038 Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/
1039 Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
1040 Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
1041 Tennessee ftp://ftp.sunsite.utk.edu/pub/CPAN/
1042 Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
1043 ftp://jhcloos.com/pub/mirror/CPAN/
1044 Utah ftp://mirror.xmission.com/CPAN/
1045 Virginia ftp://ftp.perl.org/pub/perl/CPAN/
1046 ftp://ruff.cs.jmu.edu/pub/CPAN/
1047 Washington ftp://ftp-mirror.internap.com/pub/CPAN/
1048 ftp://ftp.llarian.net/pub/CPAN/
1049 ftp://ftp.spu.edu/pub/CPAN/
1054 Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
1055 ftp://ftp.matrix.com.br/pub/perl/
1056 Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/PERL/
1060 For an up-to-date listing of CPAN sites,
1061 see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES .
1063 =head1 Modules: Creation, Use, and Abuse
1065 (The following section is borrowed directly from Tim Bunce's modules
1066 file, available at your nearest CPAN site.)
1068 Perl implements a class using a package, but the presence of a
1069 package doesn't imply the presence of a class. A package is just a
1070 namespace. A class is a package that provides subroutines that can be
1071 used as methods. A method is just a subroutine that expects, as its
1072 first argument, either the name of a package (for "static" methods),
1073 or a reference to something (for "virtual" methods).
1075 A module is a file that (by convention) provides a class of the same
1076 name (sans the .pm), plus an import method in that class that can be
1077 called to fetch exported symbols. This module may implement some of
1078 its methods by loading dynamic C or C++ objects, but that should be
1079 totally transparent to the user of the module. Likewise, the module
1080 might set up an AUTOLOAD function to slurp in subroutine definitions on
1081 demand, but this is also transparent. Only the F<.pm> file is required to
1082 exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
1083 the AUTOLOAD mechanism.
1085 =head2 Guidelines for Module Creation
1089 =item Do similar modules already exist in some form?
1091 If so, please try to reuse the existing modules either in whole or
1092 by inheriting useful features into a new class. If this is not
1093 practical try to get together with the module authors to work on
1094 extending or enhancing the functionality of the existing modules.
1095 A perfect example is the plethora of packages in perl4 for dealing
1096 with command line options.
1098 If you are writing a module to expand an already existing set of
1099 modules, please coordinate with the author of the package. It
1100 helps if you follow the same naming scheme and module interaction
1101 scheme as the original author.
1103 =item Try to design the new module to be easy to extend and reuse.
1105 Try to C<use warnings;> (or C<use warnings qw(...);>).
1106 Remember that you can add C<no warnings qw(...);> to individual blocks
1107 of code that need less warnings.
1109 Use blessed references. Use the two argument form of bless to bless
1110 into the class name given as the first parameter of the constructor,
1115 return bless {}, $class;
1118 or even this if you'd like it to be used as either a static
1119 or a virtual method.
1123 my $class = ref($self) || $self;
1124 return bless {}, $class;
1127 Pass arrays as references so more parameters can be added later
1128 (it's also faster). Convert functions into methods where
1129 appropriate. Split large methods into smaller more flexible ones.
1130 Inherit methods from other modules if appropriate.
1132 Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>.
1133 Generally you can delete the C<eq 'FOO'> part with no harm at all.
1134 Let the objects look after themselves! Generally, avoid hard-wired
1135 class names as far as possible.
1137 Avoid C<< $r->Class::func() >> where using C<@ISA=qw(... Class ...)> and
1138 C<< $r->func() >> would work (see L<perlbot> for more details).
1140 Use autosplit so little used or newly added functions won't be a
1141 burden to programs that don't use them. Add test functions to
1142 the module after __END__ either using AutoSplit or by saying:
1144 eval join('',<main::DATA>) || die $@ unless caller();
1146 Does your module pass the 'empty subclass' test? If you say
1147 C<@SUBCLASS::ISA = qw(YOURCLASS);> your applications should be able
1148 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
1149 does your application still work if you change: C<$obj = new YOURCLASS;>
1150 into: C<$obj = new SUBCLASS;> ?
1152 Avoid keeping any state information in your packages. It makes it
1153 difficult for multiple other packages to use yours. Keep state
1154 information in objects.
1158 Try to C<use strict;> (or C<use strict qw(...);>).
1159 Remember that you can add C<no strict qw(...);> to individual blocks
1160 of code that need less strictness.
1164 Follow the guidelines in the perlstyle(1) manual.
1168 =item Some simple style guidelines
1170 The perlstyle manual supplied with Perl has many helpful points.
1172 Coding style is a matter of personal taste. Many people evolve their
1173 style over several years as they learn what helps them write and
1174 maintain good code. Here's one set of assorted suggestions that
1175 seem to be widely used by experienced developers:
1177 Use underscores to separate words. It is generally easier to read
1178 $var_names_like_this than $VarNamesLikeThis, especially for
1179 non-native speakers of English. It's also a simple rule that works
1180 consistently with VAR_NAMES_LIKE_THIS.
1182 Package/Module names are an exception to this rule. Perl informally
1183 reserves lowercase module names for 'pragma' modules like integer
1184 and strict. Other modules normally begin with a capital letter and
1185 use mixed case with no underscores (need to be short and portable).
1187 You may find it helpful to use letter case to indicate the scope
1188 or nature of a variable. For example:
1190 $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
1191 $Some_Caps_Here package-wide global/static
1192 $no_caps_here function scope my() or local() variables
1194 Function and method names seem to work best as all lowercase.
1195 e.g., C<< $obj->as_string() >>.
1197 You can use a leading underscore to indicate that a variable or
1198 function should not be used outside the package that defined it.
1200 =item Select what to export.
1202 Do NOT export method names!
1204 Do NOT export anything else by default without a good reason!
1206 Exports pollute the namespace of the module user. If you must
1207 export try to use @EXPORT_OK in preference to @EXPORT and avoid
1208 short or common names to reduce the risk of name clashes.
1210 Generally anything not exported is still accessible from outside the
1211 module using the ModuleName::item_name (or C<< $blessed_ref->method >>)
1212 syntax. By convention you can use a leading underscore on names to
1213 indicate informally that they are 'internal' and not for public use.
1215 (It is actually possible to get private functions by saying:
1216 C<my $subref = sub { ... }; &$subref;>. But there's no way to call that
1217 directly as a method, because a method must have a name in the symbol
1220 As a general rule, if the module is trying to be object oriented
1221 then export nothing. If it's just a collection of functions then
1222 @EXPORT_OK anything but use @EXPORT with caution.
1224 =item Select a name for the module.
1226 This name should be as descriptive, accurate, and complete as
1227 possible. Avoid any risk of ambiguity. Always try to use two or
1228 more whole words. Generally the name should reflect what is special
1229 about what the module does rather than how it does it. Please use
1230 nested module names to group informally or categorize a module.
1231 There should be a very good reason for a module not to have a nested name.
1232 Module names should begin with a capital letter.
1234 Having 57 modules all called Sort will not make life easy for anyone
1235 (though having 23 called Sort::Quick is only marginally better :-).
1236 Imagine someone trying to install your module alongside many others.
1237 If in any doubt ask for suggestions in comp.lang.perl.misc.
1239 If you are developing a suite of related modules/classes it's good
1240 practice to use nested classes with a common prefix as this will
1241 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
1242 Xyz::Model etc. Use the modules in this list as a naming guide.
1244 If adding a new module to a set, follow the original author's
1245 standards for naming modules and the interface to methods in
1248 If developing modules for private internal or project specific use,
1249 that will never be released to the public, then you should ensure
1250 that their names will not clash with any future public module. You
1251 can do this either by using the reserved Local::* category or by
1252 using a category name that includes an underscore like Foo_Corp::*.
1254 To be portable each component of a module name should be limited to
1255 11 characters. If it might be used on MS-DOS then try to ensure each is
1256 unique in the first 8 characters. Nested modules make this easier.
1258 =item Have you got it right?
1260 How do you know that you've made the right decisions? Have you
1261 picked an interface design that will cause problems later? Have
1262 you picked the most appropriate name? Do you have any questions?
1264 The best way to know for sure, and pick up many helpful suggestions,
1265 is to ask someone who knows. Comp.lang.perl.misc is read by just about
1266 all the people who develop modules and it's the best place to ask.
1268 All you need to do is post a short summary of the module, its
1269 purpose and interfaces. A few lines on each of the main methods is
1270 probably enough. (If you post the whole module it might be ignored
1271 by busy people - generally the very people you want to read it!)
1273 Don't worry about posting if you can't say when the module will be
1274 ready - just say so in the message. It might be worth inviting
1275 others to help you, they may be able to complete it for you!
1277 =item README and other Additional Files.
1279 It's well known that software developers usually fully document the
1280 software they write. If, however, the world is in urgent need of
1281 your software and there is not enough time to write the full
1282 documentation please at least provide a README file containing:
1287 A description of the module/package/extension etc.
1290 A copyright notice - see below.
1293 Prerequisites - what else you may need to have.
1296 How to build it - possible changes to Makefile.PL etc.
1302 Recent changes in this release, especially incompatibilities
1305 Changes / enhancements you plan to make in the future.
1309 If the README file seems to be getting too large you may wish to
1310 split out some of the sections into separate files: INSTALL,
1315 =item Adding a Copyright Notice.
1317 How you choose to license your work is a personal decision.
1318 The general mechanism is to assert your Copyright and then make
1319 a declaration of how others may copy/use/modify your work.
1321 Perl, for example, is supplied with two types of licence: The GNU
1322 GPL and The Artistic Licence (see the files README, Copying, and
1323 Artistic). Larry has good reasons for NOT just using the GNU GPL.
1325 My personal recommendation, out of respect for Larry, Perl, and the
1326 Perl community at large is to state something simply like:
1328 Copyright (c) 1995 Your Name. All rights reserved.
1329 This program is free software; you can redistribute it and/or
1330 modify it under the same terms as Perl itself.
1332 This statement should at least appear in the README file. You may
1333 also wish to include it in a Copying file and your source files.
1334 Remember to include the other words in addition to the Copyright.
1336 =item Give the module a version/issue/release number.
1338 To be fully compatible with the Exporter and MakeMaker modules you
1339 should store your module's version number in a non-my package
1340 variable called $VERSION. This should be a floating point
1341 number with at least two digits after the decimal (i.e., hundredths,
1342 e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
1343 See L<Exporter> for details.
1345 It may be handy to add a function or method to retrieve the number.
1346 Use the number in announcements and archive file names when
1347 releasing the module (ModuleName-1.02.tar.Z).
1348 See perldoc ExtUtils::MakeMaker.pm for details.
1350 =item How to release and distribute a module.
1352 It's good idea to post an announcement of the availability of your
1353 module (or the module itself if small) to the comp.lang.perl.announce
1354 Usenet newsgroup. This will at least ensure very wide once-off
1357 If possible, register the module with CPAN. You should
1358 include details of its location in your announcement.
1360 Some notes about ftp archives: Please use a long descriptive file
1361 name that includes the version number. Most incoming directories
1362 will not be readable/listable, i.e., you won't be able to see your
1363 file after uploading it. Remember to send your email notification
1364 message as soon as possible after uploading else your file may get
1365 deleted automatically. Allow time for the file to be processed
1366 and/or check the file has been processed before announcing its
1369 FTP Archives for Perl Modules:
1371 Follow the instructions and links on:
1373 http://www.perl.com/CPAN/modules/00modlist.long.html
1374 http://www.perl.com/CPAN/modules/04pause.html
1376 or upload to one of these sites:
1378 https://pause.kbx.de/pause/
1379 http://pause.perl.org/pause/
1381 and notify <modules@perl.org>.
1383 By using the WWW interface you can ask the Upload Server to mirror
1384 your modules from your ftp or WWW site into your own directory on
1387 Please remember to send me an updated entry for the Module list!
1389 =item Take care when changing a released module.
1391 Always strive to remain compatible with previous released versions.
1392 Otherwise try to add a mechanism to revert to the
1393 old behavior if people rely on it. Document incompatible changes.
1399 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
1403 =item There is no requirement to convert anything.
1405 If it ain't broke, don't fix it! Perl 4 library scripts should
1406 continue to work with no problems. You may need to make some minor
1407 changes (like escaping non-array @'s in double quoted strings) but
1408 there is no need to convert a .pl file into a Module for just that.
1410 =item Consider the implications.
1412 All Perl applications that make use of the script will need to
1413 be changed (slightly) if the script is converted into a module. Is
1414 it worth it unless you plan to make other changes at the same time?
1416 =item Make the most of the opportunity.
1418 If you are going to convert the script to a module you can use the
1419 opportunity to redesign the interface. The guidelines for module
1420 creation above include many of the issues you should consider.
1422 =item The pl2pm utility will get you started.
1424 This utility will read *.pl files (given as parameters) and write
1425 corresponding *.pm files. The pl2pm utilities does the following:
1430 Adds the standard Module prologue lines
1433 Converts package specifiers from ' to ::
1436 Converts die(...) to croak(...)
1439 Several other minor changes
1443 Being a mechanical process pl2pm is not bullet proof. The converted
1444 code will need careful checking, especially any package statements.
1445 Don't delete the original .pl file till the new .pm one works!
1449 =head2 Guidelines for Reusing Application Code
1453 =item Complete applications rarely belong in the Perl Module Library.
1455 =item Many applications contain some Perl code that could be reused.
1457 Help save the world! Share your code in a form that makes it easy
1460 =item Break-out the reusable code into one or more separate module files.
1462 =item Take the opportunity to reconsider and redesign the interfaces.
1464 =item In some cases the 'application' can then be reduced to a small
1466 fragment of code built on top of the reusable modules. In these cases
1467 the application could invoked as:
1469 % perl -e 'use Module::Name; method(@ARGV)' ...
1471 % perl -mModule::Name ... (in perl5.002 or higher)
1477 Perl does not enforce private and public parts of its modules as you may
1478 have been used to in other languages like C++, Ada, or Modula-17. Perl
1479 doesn't have an infatuation with enforced privacy. It would prefer
1480 that you stayed out of its living room because you weren't invited, not
1481 because it has a shotgun.
1483 The module and its user have a contract, part of which is common law,
1484 and part of which is "written". Part of the common law contract is
1485 that a module doesn't pollute any namespace it wasn't asked to. The
1486 written contract for the module (A.K.A. documentation) may make other
1487 provisions. But then you know when you C<use RedefineTheWorld> that
1488 you're redefining the world and willing to take the consequences.