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 They should all have their own documentation installed and accessible
810 via your system man(1) command. If you do not have a B<find>
811 program, you can use the Perl B<find2perl> program instead, which
812 generates Perl code as output you can run through perl. If you
813 have a B<man> program but it doesn't find your modules, you'll have
814 to fix your manpath. See L<perl> for details. If you have no
815 system B<man> command, you might try the B<perldoc> program.
817 =head2 Extension Modules
819 Extension modules are written in C (or a mix of Perl and C). They
820 are usually dynamically loaded into Perl if and when you need them,
821 but may also be be linked in statically. Supported extension modules
822 include Socket, Fcntl, and POSIX.
824 Many popular C extension modules do not come bundled (at least, not
825 completely) due to their sizes, volatility, or simply lack of time
826 for adequate testing and configuration across the multitude of
827 platforms on which Perl was beta-tested. You are encouraged to
828 look for them on CPAN (described below), or using web search engines
829 like Alta Vista or Deja News.
833 CPAN stands for Comprehensive Perl Archive Network; it's a globally
834 replicated trove of Perl materials, including documentation, style
835 guides, tricks and trap, alternate ports to non-Unix systems and
836 occasional binary distributions for these. Search engines for
837 CPAN can be found at http://cpan.perl.com/ and at
838 http://theory.uwinnipeg.ca/mod_perl/cpan-search.pl .
840 Most importantly, CPAN includes around a thousand unbundled modules,
841 some of which require a C compiler to build. Major categories of
847 Language Extensions and Documentation Tools
853 Operating System Interfaces
856 Networking, Device Control (modems) and InterProcess Communication
859 Data Types and Data Type Utilities
868 Interfaces to / Emulations of Other Programming Languages
871 File Names, File Systems and File Locking (see also File Handles)
874 String Processing, Language Text Processing, Parsing, and Searching
877 Option, Argument, Parameter, and Configuration File Processing
880 Internationalization and Locale
883 Authentication, Security, and Encryption
886 World Wide Web, HTML, HTTP, CGI, MIME
889 Server and Daemon Utilities
892 Archiving and Compression
895 Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
901 Control Flow Utilities (callbacks and exceptions etc)
904 File Handle and Input/Output Stream Utilities
907 Miscellaneous Modules
911 Registered CPAN sites as of this writing include the following.
912 You should try to choose one close to you:
918 South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
919 ftp://ftpza.co.za/pub/mirrors/cpan/
923 China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
924 Hong Kong ftp://ftp.hkstar.com/pub/CPAN/
925 Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
926 Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
927 ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
928 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
929 ftp://ftp.meisei-u.ac.jp/pub/CPAN/
930 ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/
931 ftp://mirror.nucba.ac.jp/mirror/Perl/
932 Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
933 South Korea ftp://ftp.bora.net/pub/CPAN/
934 ftp://ftp.nuri.net/pub/CPAN/
935 Taiwan ftp://ftp.wownet.net/pub2/PERL/
936 ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
937 Thailand ftp://ftp.cs.riubon.ac.th/pub/mirrors/CPAN/
938 ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
942 Australia ftp://cpan.topend.com.au/pub/CPAN/
943 ftp://ftp.labyrinth.net.au/pub/perl/CPAN/
944 ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
945 ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
946 New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
947 ftp://sunsite.net.nz/pub/languages/perl/CPAN/
951 Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
955 Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
956 Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
957 Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
958 Croatia ftp://ftp.linux.hr/pub/CPAN/
959 Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
960 ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
961 Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
962 Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
963 Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
964 France ftp://ftp.lip6.fr/pub/perl/CPAN/
965 ftp://ftp.oleane.net/pub/mirrors/CPAN/
966 ftp://ftp.pasteur.fr/pub/computing/CPAN/
967 Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
968 ftp://ftp.gmd.de/packages/CPAN/
969 ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
970 ftp://ftp.leo.org/pub/comp/programming/languages/script/perl/CPAN/
971 ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
972 ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
973 ftp://ftp.uni-erlangen.de/pub/source/CPAN/
974 ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
975 Greece ftp://ftp.ntua.gr/pub/lang/perl/
976 Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
977 Ireland ftp://sunsite.compapp.dcu.ie/pub/perl/
978 Italy ftp://cis.uniRoma2.it/CPAN/
979 ftp://ftp.flashnet.it/pub/CPAN/
980 ftp://ftp.unina.it/pub/Other/CPAN/
981 ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
982 Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
983 ftp://ftp.EU.net/packages/cpan/
984 ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
985 Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
986 ftp://sunsite.uio.no/pub/languages/perl/CPAN/
987 Poland ftp://ftp.man.szczecin.pl/pub/perl/CPAN/
988 ftp://ftp.man.torun.pl/pub/doc/CPAN/
989 ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
990 ftp://sunsite.icm.edu.pl/pub/CPAN/
991 Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
992 ftp://ftp.ist.utl.pt/pub/CPAN/
993 ftp://ftp.ua.pt/pub/CPAN/
994 Romania ftp://ftp.dntis.ro/pub/mirrors/perl-cpan/
995 ftp://ftp.dnttm.ro/pub/CPAN/
996 Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/
997 ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
998 Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
999 Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
1000 Spain ftp://ftp.etse.urv.es/pub/perl/
1001 ftp://ftp.rediris.es/mirror/CPAN/
1002 Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
1003 Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
1004 Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
1005 United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
1006 ftp://ftp.flirble.org/pub/languages/perl/CPAN/
1007 ftp://ftp.plig.org/pub/CPAN/
1008 ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
1009 ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/
1013 Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
1014 California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
1015 ftp://ftp.cdrom.com/pub/perl/CPAN/
1016 ftp://ftp.digital.com/pub/plan/perl/CPAN/
1017 Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
1018 Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
1019 Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
1020 Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
1021 ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
1022 Manitoba ftp://theory.uwinnipeg.ca/pub/CPAN/
1023 Massachusetts ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
1024 ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
1025 Mexico ftp://ftp.msg.com.mx/pub/CPAN/
1026 Minnesota ftp://ftp.midearthbbs.com/CPAN/
1027 New York ftp://ftp.rge.com/pub/languages/perl/
1028 North Carolina ftp://ftp.duke.edu/pub/perl/
1029 Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
1030 Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/
1031 Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
1032 Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
1033 Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
1034 Utah ftp://mirror.xmission.com/CPAN/
1035 Virginia ftp://ftp.perl.org/pub/perl/CPAN/
1036 ftp://ruff.cs.jmu.edu/pub/CPAN/
1037 Washington ftp://ftp-mirror.internap.com/pub/CPAN/
1038 ftp://ftp.spu.edu/pub/CPAN/
1042 Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
1043 Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/
1047 For an up-to-date listing of CPAN sites,
1048 see http://www.perl.com/perl/CPAN or ftp://www.perl.com/perl/ .
1050 =head1 Modules: Creation, Use, and Abuse
1052 (The following section is borrowed directly from Tim Bunce's modules
1053 file, available at your nearest CPAN site.)
1055 Perl implements a class using a package, but the presence of a
1056 package doesn't imply the presence of a class. A package is just a
1057 namespace. A class is a package that provides subroutines that can be
1058 used as methods. A method is just a subroutine that expects, as its
1059 first argument, either the name of a package (for "static" methods),
1060 or a reference to something (for "virtual" methods).
1062 A module is a file that (by convention) provides a class of the same
1063 name (sans the .pm), plus an import method in that class that can be
1064 called to fetch exported symbols. This module may implement some of
1065 its methods by loading dynamic C or C++ objects, but that should be
1066 totally transparent to the user of the module. Likewise, the module
1067 might set up an AUTOLOAD function to slurp in subroutine definitions on
1068 demand, but this is also transparent. Only the F<.pm> file is required to
1069 exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
1070 the AUTOLOAD mechanism.
1072 =head2 Guidelines for Module Creation
1076 =item Do similar modules already exist in some form?
1078 If so, please try to reuse the existing modules either in whole or
1079 by inheriting useful features into a new class. If this is not
1080 practical try to get together with the module authors to work on
1081 extending or enhancing the functionality of the existing modules.
1082 A perfect example is the plethora of packages in perl4 for dealing
1083 with command line options.
1085 If you are writing a module to expand an already existing set of
1086 modules, please coordinate with the author of the package. It
1087 helps if you follow the same naming scheme and module interaction
1088 scheme as the original author.
1090 =item Try to design the new module to be easy to extend and reuse.
1094 Use blessed references. Use the two argument form of bless to bless
1095 into the class name given as the first parameter of the constructor,
1100 return bless {}, $class;
1103 or even this if you'd like it to be used as either a static
1104 or a virtual method.
1108 my $class = ref($self) || $self;
1109 return bless {}, $class;
1112 Pass arrays as references so more parameters can be added later
1113 (it's also faster). Convert functions into methods where
1114 appropriate. Split large methods into smaller more flexible ones.
1115 Inherit methods from other modules if appropriate.
1117 Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>.
1118 Generally you can delete the C<eq 'FOO'> part with no harm at all.
1119 Let the objects look after themselves! Generally, avoid hard-wired
1120 class names as far as possible.
1122 Avoid C<$r-E<gt>Class::func()> where using C<@ISA=qw(... Class ...)> and
1123 C<$r-E<gt>func()> would work (see L<perlbot> for more details).
1125 Use autosplit so little used or newly added functions won't be a
1126 burden to programs that don't use them. Add test functions to
1127 the module after __END__ either using AutoSplit or by saying:
1129 eval join('',<main::DATA>) || die $@ unless caller();
1131 Does your module pass the 'empty subclass' test? If you say
1132 C<@SUBCLASS::ISA = qw(YOURCLASS);> your applications should be able
1133 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
1134 does your application still work if you change: C<$obj = new YOURCLASS;>
1135 into: C<$obj = new SUBCLASS;> ?
1137 Avoid keeping any state information in your packages. It makes it
1138 difficult for multiple other packages to use yours. Keep state
1139 information in objects.
1143 Try to C<use strict;> (or C<use strict qw(...);>).
1144 Remember that you can add C<no strict qw(...);> to individual blocks
1145 of code that need less strictness.
1149 Follow the guidelines in the perlstyle(1) manual.
1153 =item Some simple style guidelines
1155 The perlstyle manual supplied with Perl has many helpful points.
1157 Coding style is a matter of personal taste. Many people evolve their
1158 style over several years as they learn what helps them write and
1159 maintain good code. Here's one set of assorted suggestions that
1160 seem to be widely used by experienced developers:
1162 Use underscores to separate words. It is generally easier to read
1163 $var_names_like_this than $VarNamesLikeThis, especially for
1164 non-native speakers of English. It's also a simple rule that works
1165 consistently with VAR_NAMES_LIKE_THIS.
1167 Package/Module names are an exception to this rule. Perl informally
1168 reserves lowercase module names for 'pragma' modules like integer
1169 and strict. Other modules normally begin with a capital letter and
1170 use mixed case with no underscores (need to be short and portable).
1172 You may find it helpful to use letter case to indicate the scope
1173 or nature of a variable. For example:
1175 $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
1176 $Some_Caps_Here package-wide global/static
1177 $no_caps_here function scope my() or local() variables
1179 Function and method names seem to work best as all lowercase.
1180 e.g., C<$obj-E<gt>as_string()>.
1182 You can use a leading underscore to indicate that a variable or
1183 function should not be used outside the package that defined it.
1185 =item Select what to export.
1187 Do NOT export method names!
1189 Do NOT export anything else by default without a good reason!
1191 Exports pollute the namespace of the module user. If you must
1192 export try to use @EXPORT_OK in preference to @EXPORT and avoid
1193 short or common names to reduce the risk of name clashes.
1195 Generally anything not exported is still accessible from outside the
1196 module using the ModuleName::item_name (or C<$blessed_ref-E<gt>method>)
1197 syntax. By convention you can use a leading underscore on names to
1198 indicate informally that they are 'internal' and not for public use.
1200 (It is actually possible to get private functions by saying:
1201 C<my $subref = sub { ... }; &$subref;>. But there's no way to call that
1202 directly as a method, because a method must have a name in the symbol
1205 As a general rule, if the module is trying to be object oriented
1206 then export nothing. If it's just a collection of functions then
1207 @EXPORT_OK anything but use @EXPORT with caution.
1209 =item Select a name for the module.
1211 This name should be as descriptive, accurate, and complete as
1212 possible. Avoid any risk of ambiguity. Always try to use two or
1213 more whole words. Generally the name should reflect what is special
1214 about what the module does rather than how it does it. Please use
1215 nested module names to group informally or categorize a module.
1216 There should be a very good reason for a module not to have a nested name.
1217 Module names should begin with a capital letter.
1219 Having 57 modules all called Sort will not make life easy for anyone
1220 (though having 23 called Sort::Quick is only marginally better :-).
1221 Imagine someone trying to install your module alongside many others.
1222 If in any doubt ask for suggestions in comp.lang.perl.misc.
1224 If you are developing a suite of related modules/classes it's good
1225 practice to use nested classes with a common prefix as this will
1226 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
1227 Xyz::Model etc. Use the modules in this list as a naming guide.
1229 If adding a new module to a set, follow the original author's
1230 standards for naming modules and the interface to methods in
1233 To be portable each component of a module name should be limited to
1234 11 characters. If it might be used on MS-DOS then try to ensure each is
1235 unique in the first 8 characters. Nested modules make this easier.
1237 =item Have you got it right?
1239 How do you know that you've made the right decisions? Have you
1240 picked an interface design that will cause problems later? Have
1241 you picked the most appropriate name? Do you have any questions?
1243 The best way to know for sure, and pick up many helpful suggestions,
1244 is to ask someone who knows. Comp.lang.perl.misc is read by just about
1245 all the people who develop modules and it's the best place to ask.
1247 All you need to do is post a short summary of the module, its
1248 purpose and interfaces. A few lines on each of the main methods is
1249 probably enough. (If you post the whole module it might be ignored
1250 by busy people - generally the very people you want to read it!)
1252 Don't worry about posting if you can't say when the module will be
1253 ready - just say so in the message. It might be worth inviting
1254 others to help you, they may be able to complete it for you!
1256 =item README and other Additional Files.
1258 It's well known that software developers usually fully document the
1259 software they write. If, however, the world is in urgent need of
1260 your software and there is not enough time to write the full
1261 documentation please at least provide a README file containing:
1266 A description of the module/package/extension etc.
1269 A copyright notice - see below.
1272 Prerequisites - what else you may need to have.
1275 How to build it - possible changes to Makefile.PL etc.
1281 Recent changes in this release, especially incompatibilities
1284 Changes / enhancements you plan to make in the future.
1288 If the README file seems to be getting too large you may wish to
1289 split out some of the sections into separate files: INSTALL,
1294 =item Adding a Copyright Notice.
1296 How you choose to license your work is a personal decision.
1297 The general mechanism is to assert your Copyright and then make
1298 a declaration of how others may copy/use/modify your work.
1300 Perl, for example, is supplied with two types of licence: The GNU
1301 GPL and The Artistic Licence (see the files README, Copying, and
1302 Artistic). Larry has good reasons for NOT just using the GNU GPL.
1304 My personal recommendation, out of respect for Larry, Perl, and the
1305 Perl community at large is to state something simply like:
1307 Copyright (c) 1995 Your Name. All rights reserved.
1308 This program is free software; you can redistribute it and/or
1309 modify it under the same terms as Perl itself.
1311 This statement should at least appear in the README file. You may
1312 also wish to include it in a Copying file and your source files.
1313 Remember to include the other words in addition to the Copyright.
1315 =item Give the module a version/issue/release number.
1317 To be fully compatible with the Exporter and MakeMaker modules you
1318 should store your module's version number in a non-my package
1319 variable called $VERSION. This should be a floating point
1320 number with at least two digits after the decimal (i.e., hundredths,
1321 e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
1322 See L<Exporter> for details.
1324 It may be handy to add a function or method to retrieve the number.
1325 Use the number in announcements and archive file names when
1326 releasing the module (ModuleName-1.02.tar.Z).
1327 See perldoc ExtUtils::MakeMaker.pm for details.
1329 =item How to release and distribute a module.
1331 It's good idea to post an announcement of the availability of your
1332 module (or the module itself if small) to the comp.lang.perl.announce
1333 Usenet newsgroup. This will at least ensure very wide once-off
1336 If possible, register the module with CPAN. You should
1337 include details of its location in your announcement.
1339 Some notes about ftp archives: Please use a long descriptive file
1340 name that includes the version number. Most incoming directories
1341 will not be readable/listable, i.e., you won't be able to see your
1342 file after uploading it. Remember to send your email notification
1343 message as soon as possible after uploading else your file may get
1344 deleted automatically. Allow time for the file to be processed
1345 and/or check the file has been processed before announcing its
1348 FTP Archives for Perl Modules:
1350 Follow the instructions and links on
1352 http://franz.ww.tu-berlin.de/modulelist
1354 or upload to one of these sites:
1356 ftp://franz.ww.tu-berlin.de/incoming
1357 ftp://ftp.cis.ufl.edu/incoming
1359 and notify <F<upload@franz.ww.tu-berlin.de>>.
1361 By using the WWW interface you can ask the Upload Server to mirror
1362 your modules from your ftp or WWW site into your own directory on
1365 Please remember to send me an updated entry for the Module list!
1367 =item Take care when changing a released module.
1369 Always strive to remain compatible with previous released versions.
1370 Otherwise try to add a mechanism to revert to the
1371 old behavior if people rely on it. Document incompatible changes.
1377 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
1381 =item There is no requirement to convert anything.
1383 If it ain't broke, don't fix it! Perl 4 library scripts should
1384 continue to work with no problems. You may need to make some minor
1385 changes (like escaping non-array @'s in double quoted strings) but
1386 there is no need to convert a .pl file into a Module for just that.
1388 =item Consider the implications.
1390 All Perl applications that make use of the script will need to
1391 be changed (slightly) if the script is converted into a module. Is
1392 it worth it unless you plan to make other changes at the same time?
1394 =item Make the most of the opportunity.
1396 If you are going to convert the script to a module you can use the
1397 opportunity to redesign the interface. The guidelines for module
1398 creation above include many of the issues you should consider.
1400 =item The pl2pm utility will get you started.
1402 This utility will read *.pl files (given as parameters) and write
1403 corresponding *.pm files. The pl2pm utilities does the following:
1408 Adds the standard Module prologue lines
1411 Converts package specifiers from ' to ::
1414 Converts die(...) to croak(...)
1417 Several other minor changes
1421 Being a mechanical process pl2pm is not bullet proof. The converted
1422 code will need careful checking, especially any package statements.
1423 Don't delete the original .pl file till the new .pm one works!
1427 =head2 Guidelines for Reusing Application Code
1431 =item Complete applications rarely belong in the Perl Module Library.
1433 =item Many applications contain some Perl code that could be reused.
1435 Help save the world! Share your code in a form that makes it easy
1438 =item Break-out the reusable code into one or more separate module files.
1440 =item Take the opportunity to reconsider and redesign the interfaces.
1442 =item In some cases the 'application' can then be reduced to a small
1444 fragment of code built on top of the reusable modules. In these cases
1445 the application could invoked as:
1447 % perl -e 'use Module::Name; method(@ARGV)' ...
1449 % perl -mModule::Name ... (in perl5.002 or higher)
1455 Perl does not enforce private and public parts of its modules as you may
1456 have been used to in other languages like C++, Ada, or Modula-17. Perl
1457 doesn't have an infatuation with enforced privacy. It would prefer
1458 that you stayed out of its living room because you weren't invited, not
1459 because it has a shotgun.
1461 The module and its user have a contract, part of which is common law,
1462 and part of which is "written". Part of the common law contract is
1463 that a module doesn't pollute any namespace it wasn't asked to. The
1464 written contract for the module (A.K.A. documentation) may make other
1465 provisions. But then you know when you C<use RedefineTheWorld> that
1466 you're redefining the world and willing to take the consequences.