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 Inherit pragmatic attributes from caller's context
75 Define character names for C<\N{named}> string literal escape.
83 Force verbose warning diagnostics
87 Declare a class's attribute fields at compile-time
91 Control the filetest operators like C<-r>, C<-w> for AFS, etc.
95 Compute arithmetic in integer instead of double
99 Request less of something from the compiler (unimplemented)
103 Manipulate @INC at compile time
107 Use or avoid POSIX locales for built-in operations
111 Restrict unsafe operations when compiling
115 Overload Perl operations
119 Alter regular expression behavior
123 Enable simple signal handling
127 Restrict unsafe constructs
131 Predeclare subroutine names
135 Turn on UTF-8 and Unicode support
139 Predeclare global variable names (obsoleted by our())
143 Control optional warnings
147 =head2 Standard Modules
149 Standard, bundled modules are all expected to behave in a well-defined
150 manner with respect to namespace pollution because they use the
151 Exporter module. See their own documentation for details.
157 Provide framework for multiple DBM libraries
161 Load subroutines only on demand
165 Split a package for autoloading
169 Guts of the Perl code generator (aka compiler)
173 Autogenerated data about Perl ops, used to generate bytecode
177 Assemble Perl bytecode
185 Perl compiler's bytecode backend
189 Perl compiler's C backend
193 Perl compiler's optimized C translation backend
197 Walk Perl syntax tree, printing debug info about ops
201 Perl compiler backend to produce Perl code
203 =item B::Disassembler
205 Disassemble Perl bytecode
209 Module to catch dubious constructs
213 Show lexical variables used in functions or files
217 Helper module for CC backend
219 B::Stash -- XXX NFI XXX
223 Walk Perl syntax tree, printing terse info about ops
227 Generates cross reference reports for Perl programs
231 Benchmark running times of code
235 Load byte-compiled Perl code
239 Simple Common Gateway Interface class
243 Make things work with CGI.pm against Perl-Apache API
247 CGI routines for writing to the HTTPD (or other) error log
251 Interface to Netscape Cookies
255 CGI Interface for Fast CGI
259 Module to produce nicely formatted HTML code
263 Simple Interface to Server Push
267 Try more than one constructors and return the first object available
271 Query, download, and build Perl modules from CPAN sites
273 =item CPAN::FirstTime
275 Utility for CPAN::Config file initialization
279 Wrapper around CPAN.pm without using any XS module
283 Act like warn/die from perspective of caller
291 Declare struct-like datatypes as Perl classes
295 Access Perl configuration information
299 Get pathname of current working directory
303 Programmatic interface to the Perl debugging API (experimental)
307 Perl5 access to Berkeley DB version 1.x
311 Serialize Perl data structures
315 A Perl execution profiler
319 A data debugging tool for the XS programmer
321 =item Devel::SelfStubber
323 Generate stubs for a SelfLoading module
327 Supply object methods for directory handles
331 Provide screen dump of Perl data
335 Dynamically load C libraries into Perl code
339 Use English (or awk) names for ugly punctuation variables
343 Access environment variables as regular ones
347 Load the libc errno.h defines
351 Implement default import method for modules
353 =item Exporter::Heavy
357 =item ExtUtils::Command
359 Utilities to replace common Unix commands in Makefiles etc.
361 =item ExtUtils::Embed
363 Utilities for embedding Perl in C/C++ programs
365 =item ExtUtils::Install
367 Install files from here to there
369 =item ExtUtils::Installed
371 Inventory management of installed modules
373 =item ExtUtils::Liblist
375 Determine libraries to use and how to use them
377 =item ExtUtils::MM_Cygwin
379 Methods to override Unix behavior in ExtUtils::MakeMaker
381 =item ExtUtils::MM_OS2
383 Methods to override Unix behavior in ExtUtils::MakeMaker
385 =item ExtUtils::MM_Unix
387 Methods used by ExtUtils::MakeMaker
389 =item ExtUtils::MM_VMS
391 Methods to override Unix behavior in ExtUtils::MakeMaker
393 =item ExtUtils::MM_Win32
395 Methods to override Unix behavior in ExtUtils::MakeMaker
397 =item ExtUtils::MakeMaker
399 Create an extension Makefile
401 =item ExtUtils::Manifest
403 Utilities to write and check a MANIFEST file
405 ExtUtils::Miniperl, writemain - Write the C code for perlmain.c
407 =item ExtUtils::Mkbootstrap
409 Make a bootstrap file for use by DynaLoader
411 =item ExtUtils::Mksymlists
413 Write linker options files for dynamic extension
415 =item ExtUtils::Packlist
417 Manage .packlist files
419 =item ExtUtils::testlib
421 Add blib/* directories to @INC
425 Replace functions with equivalents which succeed or die
429 Load the libc fcntl.h defines
433 Split a pathname into pieces
435 =item File::CheckTree
437 Run many filetest checks on a tree
441 Compare files or filehandles
445 Copy files or filehandles
449 DOS-like globbing and then some
457 Perl extension for BSD filename globbing
461 Create or remove a series of directories
465 Portably perform operations on file names
467 =item File::Spec::Functions
469 Portably perform operations on file names
471 =item File::Spec::Mac
475 =item File::Spec::OS2
477 Methods for OS/2 file specs
479 =item File::Spec::Unix
481 Methods used by File::Spec
483 =item File::Spec::VMS
485 Methods for VMS file specs
487 =item File::Spec::Win32
489 Methods for Win32 file specs
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 Locate installation directory of running Perl program
509 Access to the gdbm library
513 Extended processing of command line options
517 Process single-character switches with switch clustering
521 Compare 8-bit scalar data according to current locale
525 Front-end to load various IO modules
529 Supply object methods for directory handles
533 Supply object methods for filehandles
537 Supply object methods for I/O handles
541 Supply object methods for pipes
545 Object interface to system poll call
549 Supply seek based methods for I/O objects
553 OO interface to the select system call
557 Object interface to socket communications
559 =item IO::Socket::INET
561 Object interface for AF_INET domain sockets
563 =item IO::Socket::UNIX
565 Object interface for AF_UNIX domain sockets
569 SysV Msg IPC object class
573 Open a process for both reading and writing
577 Open a process for reading, writing, and error handling
581 SysV Semaphore IPC object class
589 Arbitrary length float math package
593 Arbitrary size integer math package
597 Complex numbers and associated mathematical functions
601 Trigonometric functions
605 Check a remote host for reachability
609 By-name interface to Perl's built-in gethost*() functions
613 By-name interface to Perl's built-in getnet*() functions
617 By-name interface to Perl's built-in getproto*() functions
621 By-name interface to Perl's built-in getserv*() functions
625 Generic interface to Perl Compiler backends
629 Disable named opcodes when compiling Perl code
633 Perl interface to IEEE Std 1003.1
637 Check pod documents for syntax errors
641 Module to convert pod files to HTML
643 =item Pod::InputObjects
649 Convert POD data to formatted *roff input
653 Base class for creating POD filters and translators
657 Extract selected sections of POD from input
661 Convert POD data to formatted ASCII text
663 =item Pod::Text::Color
665 Convert POD data to formatted color ASCII text
669 Print a usage message from embedded pod documentation
673 Tied access to sdbm files
677 Compile and execute code in restricted compartments
681 Search for key in dictionary file
685 Save and restore selected file handle
689 Load functions only on demand
693 Run shell commands transparently within Perl
697 Load the libc socket.h defines and structure manipulators
701 Manipulate Perl symbols and their names
705 Try every conceivable way to get hostname
709 Interface to the libc syslog(3) calls
717 Word completion module
721 Interface to various `readline' packages.
725 Provides a simple framework for writing test scripts
729 Run Perl standard test scripts with statistics
733 Create an abbreviation table from a list
735 =item Text::ParseWords
737 Parse text into a list of tokens or array of arrays
741 Implementation of the Soundex Algorithm as described by Knuth
743 Text::Tabs -- expand and unexpand tabs per expand(1) and unexpand(1)
747 Line wrapping to form simple paragraphs
751 Base class for tied arrays
755 Base class definitions for tied handles
759 Base class definitions for tied hashes
763 Use references as hash keys
767 Base class definitions for tied scalars
769 =item Tie::SubstrHash
771 Fixed-table-size, fixed-key-length hashing
775 Efficiently compute time from local and GMT time
779 By-name interface to Perl's built-in gmtime() function
781 =item Time::localtime
783 By-name interface to Perl's built-in localtime() function
787 Internal object used by Time::gmtime and Time::localtime
791 Base class for ALL classes (blessed references)
795 By-name interface to Perl's built-in getgr*() functions
799 By-name interface to Perl's built-in getpw*() functions
803 To find out I<all> modules installed on your system, including
804 those without documentation or outside the standard release,
807 % find `perl -e 'print "@INC"'` -name '*.pm' -print
809 To get a log of all module distributions which have been installed
810 since perl was installed, just do:
814 Modules should all have their own documentation installed and accessible
815 via your system man(1) command, or via the C<perldoc> program. If you do
817 program, you can use the Perl B<find2perl> program instead, which
818 generates Perl code as output you can run through perl. If you
819 have a B<man> program but it doesn't find your modules, you'll have
820 to fix your manpath. See L<perl> for details.
822 =head2 Extension Modules
824 Extension modules are written in C (or a mix of Perl and C). They
825 are usually dynamically loaded into Perl if and when you need them,
826 but may also be be linked in statically. Supported extension modules
827 include Socket, Fcntl, and POSIX.
829 Many popular C extension modules do not come bundled (at least, not
830 completely) due to their sizes, volatility, or simply lack of time
831 for adequate testing and configuration across the multitude of
832 platforms on which Perl was beta-tested. You are encouraged to
833 look for them on CPAN (described below), or using web search engines
834 like Alta Vista or Deja News.
838 CPAN stands for Comprehensive Perl Archive Network; it's a globally
839 replicated trove of Perl materials, including documentation, style
840 guides, tricks and trap, alternate ports to non-Unix systems and
841 occasional binary distributions for these. Search engines for
842 CPAN can be found at http://cpan.perl.com/ and at
843 http://theory.uwinnipeg.ca/mod_perl/cpan-search.pl .
845 Most importantly, CPAN includes around a thousand unbundled modules,
846 some of which require a C compiler to build. Major categories of
852 Language Extensions and Documentation Tools
858 Operating System Interfaces
861 Networking, Device Control (modems) and InterProcess Communication
864 Data Types and Data Type Utilities
873 Interfaces to / Emulations of Other Programming Languages
876 File Names, File Systems and File Locking (see also File Handles)
879 String Processing, Language Text Processing, Parsing, and Searching
882 Option, Argument, Parameter, and Configuration File Processing
885 Internationalization and Locale
888 Authentication, Security, and Encryption
891 World Wide Web, HTML, HTTP, CGI, MIME
894 Server and Daemon Utilities
897 Archiving and Compression
900 Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
906 Control Flow Utilities (callbacks and exceptions etc)
909 File Handle and Input/Output Stream Utilities
912 Miscellaneous Modules
916 Registered CPAN sites as of this writing include the following.
917 You should try to choose one close to you:
923 South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
924 ftp://ftp.saix.net/pub/CPAN/
925 ftp://ftp.sun.ac.za/CPAN/
926 ftp://ftpza.co.za/pub/mirrors/cpan/
931 China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
932 Hong Kong ftp://ftp.pacific.net.hk/pub/mirror/CPAN/
933 Indonesia ftp://malone.piksi.itb.ac.id/pub/CPAN/
934 Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
935 Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
936 ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
937 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
938 ftp://ftp.meisei-u.ac.jp/pub/CPAN/
939 ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/
940 ftp://mirror.nucba.ac.jp/mirror/Perl/
941 Saudi-Arabia ftp://ftp.isu.net.sa/pub/CPAN/
942 Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
943 South Korea ftp://ftp.bora.net/pub/CPAN/
944 ftp://ftp.kornet.net/pub/CPAN/
945 ftp://ftp.nuri.net/pub/CPAN/
946 Taiwan ftp://coda.nctu.edu.tw/computer-languages/perl/CPAN/
947 ftp://ftp.ee.ncku.edu.tw/pub3/perl/CPAN/
948 ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
949 Thailand ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
954 Australia ftp://cpan.topend.com.au/pub/CPAN/
955 ftp://ftp.labyrinth.net.au/pub/perl-CPAN/
956 ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
957 ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
958 New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
959 ftp://sunsite.net.nz/pub/languages/perl/CPAN/
962 =item Central America
964 Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
969 Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
970 Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
971 Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
972 Croatia ftp://ftp.linux.hr/pub/CPAN/
973 Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
974 ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
975 Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
976 Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
977 Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
978 France ftp://ftp.grolier.fr/pub/perl/CPAN/
979 ftp://ftp.lip6.fr/pub/perl/CPAN/
980 ftp://ftp.oleane.net/pub/mirrors/CPAN/
981 ftp://ftp.pasteur.fr/pub/computing/CPAN/
982 ftp://ftp.uvsq.fr/pub/perl/CPAN/
983 German ftp://ftp.gigabell.net/pub/CPAN/
984 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
985 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
986 ftp://ftp.gmd.de/packages/CPAN/
987 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
988 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
989 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
990 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
991 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
992 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
993 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
994 ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
995 ftp://ftp.gmd.de/packages/CPAN/
996 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
997 ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
998 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
999 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
1000 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
1001 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
1002 Greece ftp://ftp.ntua.gr/pub/lang/perl/
1003 Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
1004 Iceland ftp://ftp.gm.is/pub/CPAN/
1005 Ireland ftp://cpan.indigo.ie/pub/CPAN/
1006 ftp://sunsite.compapp.dcu.ie/pub/perl/
1007 Italy ftp://cis.uniRoma2.it/CPAN/
1008 ftp://ftp.flashnet.it/pub/CPAN/
1009 ftp://ftp.unina.it/pub/Other/CPAN/
1010 ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
1011 Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
1012 ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
1013 Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
1014 ftp://sunsite.uio.no/pub/languages/perl/CPAN/
1015 Poland ftp://ftp.man.torun.pl/pub/CPAN/
1016 ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
1017 ftp://sunsite.icm.edu.pl/pub/CPAN/
1018 Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
1019 ftp://ftp.ist.utl.pt/pub/CPAN/
1020 ftp://ftp.ua.pt/pub/CPAN/
1021 Romania ftp://ftp.dnttm.ro/pub/CPAN/
1022 Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/
1023 ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
1024 Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
1025 Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
1026 Spain ftp://ftp.etse.urv.es/pub/perl/
1027 ftp://ftp.rediris.es/mirror/CPAN/
1028 Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
1029 Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
1030 Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
1031 United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
1032 ftp://ftp.flirble.org/pub/languages/perl/CPAN/
1033 ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/
1034 ftp://ftp.plig.org/pub/CPAN/
1035 ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
1040 Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
1041 California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
1042 ftp://cpan.valueclick.com/CPAN/
1043 ftp://ftp.cdrom.com/pub/perl/CPAN/
1044 http://download.sourceforge.net/mirrors/CPAN/
1045 Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
1046 Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
1047 Georgia ftp://ftp.twoguys.org/CPAN/
1048 Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
1049 Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
1050 ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
1051 Kentucky ftp://ftp.uky.edu/CPAN/
1052 Manitoba ftp://theoryx5.uwinnipeg.ca/pub/CPAN/
1053 Massachusetts ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
1054 ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
1055 Mexico ftp://ftp.msg.com.mx/pub/CPAN/
1056 New York ftp://ftp.deao.net/pub/CPAN/
1057 ftp://ftp.rge.com/pub/languages/perl/
1058 North Carolina ftp://ftp.duke.edu/pub/perl/
1059 Nova Scotia ftp://cpan.chebucto.ns.ca/pub/CPAN/
1060 Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
1061 Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/
1062 Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
1063 Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
1064 Tennessee ftp://ftp.sunsite.utk.edu/pub/CPAN/
1065 Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
1066 ftp://jhcloos.com/pub/mirror/CPAN/
1067 Utah ftp://mirror.xmission.com/CPAN/
1068 Virginia ftp://ftp.perl.org/pub/perl/CPAN/
1069 ftp://ruff.cs.jmu.edu/pub/CPAN/
1070 Washington ftp://ftp-mirror.internap.com/pub/CPAN/
1071 ftp://ftp.llarian.net/pub/CPAN/
1072 ftp://ftp.spu.edu/pub/CPAN/
1077 Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
1078 ftp://ftp.matrix.com.br/pub/perl/
1079 Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/PERL/
1083 For an up-to-date listing of CPAN sites,
1084 see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES .
1086 =head1 Modules: Creation, Use, and Abuse
1088 (The following section is borrowed directly from Tim Bunce's modules
1089 file, available at your nearest CPAN site.)
1091 Perl implements a class using a package, but the presence of a
1092 package doesn't imply the presence of a class. A package is just a
1093 namespace. A class is a package that provides subroutines that can be
1094 used as methods. A method is just a subroutine that expects, as its
1095 first argument, either the name of a package (for "static" methods),
1096 or a reference to something (for "virtual" methods).
1098 A module is a file that (by convention) provides a class of the same
1099 name (sans the .pm), plus an import method in that class that can be
1100 called to fetch exported symbols. This module may implement some of
1101 its methods by loading dynamic C or C++ objects, but that should be
1102 totally transparent to the user of the module. Likewise, the module
1103 might set up an AUTOLOAD function to slurp in subroutine definitions on
1104 demand, but this is also transparent. Only the F<.pm> file is required to
1105 exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
1106 the AUTOLOAD mechanism.
1108 =head2 Guidelines for Module Creation
1112 =item Do similar modules already exist in some form?
1114 If so, please try to reuse the existing modules either in whole or
1115 by inheriting useful features into a new class. If this is not
1116 practical try to get together with the module authors to work on
1117 extending or enhancing the functionality of the existing modules.
1118 A perfect example is the plethora of packages in perl4 for dealing
1119 with command line options.
1121 If you are writing a module to expand an already existing set of
1122 modules, please coordinate with the author of the package. It
1123 helps if you follow the same naming scheme and module interaction
1124 scheme as the original author.
1126 =item Try to design the new module to be easy to extend and reuse.
1128 Try to C<use warnings;> (or C<use warnings qw(...);>).
1129 Remember that you can add C<no warnings qw(...);> to individual blocks
1130 of code that need less warnings.
1132 Use blessed references. Use the two argument form of bless to bless
1133 into the class name given as the first parameter of the constructor,
1138 return bless {}, $class;
1141 or even this if you'd like it to be used as either a static
1142 or a virtual method.
1146 my $class = ref($self) || $self;
1147 return bless {}, $class;
1150 Pass arrays as references so more parameters can be added later
1151 (it's also faster). Convert functions into methods where
1152 appropriate. Split large methods into smaller more flexible ones.
1153 Inherit methods from other modules if appropriate.
1155 Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>.
1156 Generally you can delete the C<eq 'FOO'> part with no harm at all.
1157 Let the objects look after themselves! Generally, avoid hard-wired
1158 class names as far as possible.
1160 Avoid C<< $r->Class::func() >> where using C<@ISA=qw(... Class ...)> and
1161 C<< $r->func() >> would work (see L<perlbot> for more details).
1163 Use autosplit so little used or newly added functions won't be a
1164 burden to programs that don't use them. Add test functions to
1165 the module after __END__ either using AutoSplit or by saying:
1167 eval join('',<main::DATA>) || die $@ unless caller();
1169 Does your module pass the 'empty subclass' test? If you say
1170 C<@SUBCLASS::ISA = qw(YOURCLASS);> your applications should be able
1171 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
1172 does your application still work if you change: C<$obj = new YOURCLASS;>
1173 into: C<$obj = new SUBCLASS;> ?
1175 Avoid keeping any state information in your packages. It makes it
1176 difficult for multiple other packages to use yours. Keep state
1177 information in objects.
1181 Try to C<use strict;> (or C<use strict qw(...);>).
1182 Remember that you can add C<no strict qw(...);> to individual blocks
1183 of code that need less strictness.
1187 Follow the guidelines in the perlstyle(1) manual.
1191 =item Some simple style guidelines
1193 The perlstyle manual supplied with Perl has many helpful points.
1195 Coding style is a matter of personal taste. Many people evolve their
1196 style over several years as they learn what helps them write and
1197 maintain good code. Here's one set of assorted suggestions that
1198 seem to be widely used by experienced developers:
1200 Use underscores to separate words. It is generally easier to read
1201 $var_names_like_this than $VarNamesLikeThis, especially for
1202 non-native speakers of English. It's also a simple rule that works
1203 consistently with VAR_NAMES_LIKE_THIS.
1205 Package/Module names are an exception to this rule. Perl informally
1206 reserves lowercase module names for 'pragma' modules like integer
1207 and strict. Other modules normally begin with a capital letter and
1208 use mixed case with no underscores (need to be short and portable).
1210 You may find it helpful to use letter case to indicate the scope
1211 or nature of a variable. For example:
1213 $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
1214 $Some_Caps_Here package-wide global/static
1215 $no_caps_here function scope my() or local() variables
1217 Function and method names seem to work best as all lowercase.
1218 e.g., C<< $obj->as_string() >>.
1220 You can use a leading underscore to indicate that a variable or
1221 function should not be used outside the package that defined it.
1223 =item Select what to export.
1225 Do NOT export method names!
1227 Do NOT export anything else by default without a good reason!
1229 Exports pollute the namespace of the module user. If you must
1230 export try to use @EXPORT_OK in preference to @EXPORT and avoid
1231 short or common names to reduce the risk of name clashes.
1233 Generally anything not exported is still accessible from outside the
1234 module using the ModuleName::item_name (or C<< $blessed_ref->method >>)
1235 syntax. By convention you can use a leading underscore on names to
1236 indicate informally that they are 'internal' and not for public use.
1238 (It is actually possible to get private functions by saying:
1239 C<my $subref = sub { ... }; &$subref;>. But there's no way to call that
1240 directly as a method, because a method must have a name in the symbol
1243 As a general rule, if the module is trying to be object oriented
1244 then export nothing. If it's just a collection of functions then
1245 @EXPORT_OK anything but use @EXPORT with caution.
1247 =item Select a name for the module.
1249 This name should be as descriptive, accurate, and complete as
1250 possible. Avoid any risk of ambiguity. Always try to use two or
1251 more whole words. Generally the name should reflect what is special
1252 about what the module does rather than how it does it. Please use
1253 nested module names to group informally or categorize a module.
1254 There should be a very good reason for a module not to have a nested name.
1255 Module names should begin with a capital letter.
1257 Having 57 modules all called Sort will not make life easy for anyone
1258 (though having 23 called Sort::Quick is only marginally better :-).
1259 Imagine someone trying to install your module alongside many others.
1260 If in any doubt ask for suggestions in comp.lang.perl.misc.
1262 If you are developing a suite of related modules/classes it's good
1263 practice to use nested classes with a common prefix as this will
1264 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
1265 Xyz::Model etc. Use the modules in this list as a naming guide.
1267 If adding a new module to a set, follow the original author's
1268 standards for naming modules and the interface to methods in
1271 To be portable each component of a module name should be limited to
1272 11 characters. If it might be used on MS-DOS then try to ensure each is
1273 unique in the first 8 characters. Nested modules make this easier.
1275 =item Have you got it right?
1277 How do you know that you've made the right decisions? Have you
1278 picked an interface design that will cause problems later? Have
1279 you picked the most appropriate name? Do you have any questions?
1281 The best way to know for sure, and pick up many helpful suggestions,
1282 is to ask someone who knows. Comp.lang.perl.misc is read by just about
1283 all the people who develop modules and it's the best place to ask.
1285 All you need to do is post a short summary of the module, its
1286 purpose and interfaces. A few lines on each of the main methods is
1287 probably enough. (If you post the whole module it might be ignored
1288 by busy people - generally the very people you want to read it!)
1290 Don't worry about posting if you can't say when the module will be
1291 ready - just say so in the message. It might be worth inviting
1292 others to help you, they may be able to complete it for you!
1294 =item README and other Additional Files.
1296 It's well known that software developers usually fully document the
1297 software they write. If, however, the world is in urgent need of
1298 your software and there is not enough time to write the full
1299 documentation please at least provide a README file containing:
1304 A description of the module/package/extension etc.
1307 A copyright notice - see below.
1310 Prerequisites - what else you may need to have.
1313 How to build it - possible changes to Makefile.PL etc.
1319 Recent changes in this release, especially incompatibilities
1322 Changes / enhancements you plan to make in the future.
1326 If the README file seems to be getting too large you may wish to
1327 split out some of the sections into separate files: INSTALL,
1332 =item Adding a Copyright Notice.
1334 How you choose to license your work is a personal decision.
1335 The general mechanism is to assert your Copyright and then make
1336 a declaration of how others may copy/use/modify your work.
1338 Perl, for example, is supplied with two types of licence: The GNU
1339 GPL and The Artistic Licence (see the files README, Copying, and
1340 Artistic). Larry has good reasons for NOT just using the GNU GPL.
1342 My personal recommendation, out of respect for Larry, Perl, and the
1343 Perl community at large is to state something simply like:
1345 Copyright (c) 1995 Your Name. All rights reserved.
1346 This program is free software; you can redistribute it and/or
1347 modify it under the same terms as Perl itself.
1349 This statement should at least appear in the README file. You may
1350 also wish to include it in a Copying file and your source files.
1351 Remember to include the other words in addition to the Copyright.
1353 =item Give the module a version/issue/release number.
1355 To be fully compatible with the Exporter and MakeMaker modules you
1356 should store your module's version number in a non-my package
1357 variable called $VERSION. This should be a floating point
1358 number with at least two digits after the decimal (i.e., hundredths,
1359 e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
1360 See L<Exporter> for details.
1362 It may be handy to add a function or method to retrieve the number.
1363 Use the number in announcements and archive file names when
1364 releasing the module (ModuleName-1.02.tar.Z).
1365 See perldoc ExtUtils::MakeMaker.pm for details.
1367 =item How to release and distribute a module.
1369 It's good idea to post an announcement of the availability of your
1370 module (or the module itself if small) to the comp.lang.perl.announce
1371 Usenet newsgroup. This will at least ensure very wide once-off
1374 If possible, register the module with CPAN. You should
1375 include details of its location in your announcement.
1377 Some notes about ftp archives: Please use a long descriptive file
1378 name that includes the version number. Most incoming directories
1379 will not be readable/listable, i.e., you won't be able to see your
1380 file after uploading it. Remember to send your email notification
1381 message as soon as possible after uploading else your file may get
1382 deleted automatically. Allow time for the file to be processed
1383 and/or check the file has been processed before announcing its
1386 FTP Archives for Perl Modules:
1388 Follow the instructions and links on:
1390 http://www.perl.com/CPAN/modules/00modlist.long.html
1391 http://www.perl.com/CPAN/modules/04pause.html
1393 or upload to one of these sites:
1395 https://pause.kbx.de/pause/
1396 http://pause.perl.org/pause/
1398 and notify <modules@perl.org>.
1400 By using the WWW interface you can ask the Upload Server to mirror
1401 your modules from your ftp or WWW site into your own directory on
1404 Please remember to send me an updated entry for the Module list!
1406 =item Take care when changing a released module.
1408 Always strive to remain compatible with previous released versions.
1409 Otherwise try to add a mechanism to revert to the
1410 old behavior if people rely on it. Document incompatible changes.
1416 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
1420 =item There is no requirement to convert anything.
1422 If it ain't broke, don't fix it! Perl 4 library scripts should
1423 continue to work with no problems. You may need to make some minor
1424 changes (like escaping non-array @'s in double quoted strings) but
1425 there is no need to convert a .pl file into a Module for just that.
1427 =item Consider the implications.
1429 All Perl applications that make use of the script will need to
1430 be changed (slightly) if the script is converted into a module. Is
1431 it worth it unless you plan to make other changes at the same time?
1433 =item Make the most of the opportunity.
1435 If you are going to convert the script to a module you can use the
1436 opportunity to redesign the interface. The guidelines for module
1437 creation above include many of the issues you should consider.
1439 =item The pl2pm utility will get you started.
1441 This utility will read *.pl files (given as parameters) and write
1442 corresponding *.pm files. The pl2pm utilities does the following:
1447 Adds the standard Module prologue lines
1450 Converts package specifiers from ' to ::
1453 Converts die(...) to croak(...)
1456 Several other minor changes
1460 Being a mechanical process pl2pm is not bullet proof. The converted
1461 code will need careful checking, especially any package statements.
1462 Don't delete the original .pl file till the new .pm one works!
1466 =head2 Guidelines for Reusing Application Code
1470 =item Complete applications rarely belong in the Perl Module Library.
1472 =item Many applications contain some Perl code that could be reused.
1474 Help save the world! Share your code in a form that makes it easy
1477 =item Break-out the reusable code into one or more separate module files.
1479 =item Take the opportunity to reconsider and redesign the interfaces.
1481 =item In some cases the 'application' can then be reduced to a small
1483 fragment of code built on top of the reusable modules. In these cases
1484 the application could invoked as:
1486 % perl -e 'use Module::Name; method(@ARGV)' ...
1488 % perl -mModule::Name ... (in perl5.002 or higher)
1494 Perl does not enforce private and public parts of its modules as you may
1495 have been used to in other languages like C++, Ada, or Modula-17. Perl
1496 doesn't have an infatuation with enforced privacy. It would prefer
1497 that you stayed out of its living room because you weren't invited, not
1498 because it has a shotgun.
1500 The module and its user have a contract, part of which is common law,
1501 and part of which is "written". Part of the common law contract is
1502 that a module doesn't pollute any namespace it wasn't asked to. The
1503 written contract for the module (A.K.A. documentation) may make other
1504 provisions. But then you know when you C<use RedefineTheWorld> that
1505 you're redefining the world and willing to take the consequences.