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Text File | 2000-03-21 | 40.6 KB | 1,506 lines

=head1 NAME perlmodlib - constructing new Perl modules and finding existing ones =head1 DESCRIPTION =head1 THE PERL MODULE LIBRARY Many modules are included the Perl distribution. These are described below, and all end in F<.pm>. You may discover compiled library file (usually ending in F<.so>) or small pieces of modules to be autoloaded (ending in F<.al>); these were automatically generated by the installation process. You may also discover files in the library directory that end in either F<.pl> or F<.ph>. These are old libraries supplied so that old programs that use them still run. The F<.pl> files will all eventually be converted into standard modules, and the F<.ph> files made by B<h2ph> will probably end up as extension modules made by B<h2xs>. (Some F<.ph> values may already be available through the POSIX, Errno, or Fcntl modules.) The B<pl2pm> file in the distribution may help in your conversion, but it's just a mechanical process and therefore far from bulletproof. =head2 Pragmatic Modules They work somewhat like compiler directives (pragmata) in that they tend to affect the compilation of your program, and thus will usually work well only when used within a C<use>, or C<no>. Most of these are lexically scoped, so an inner BLOCK may countermand them by saying: no integer; no strict 'refs'; no warnings; which lasts until the end of that BLOCK. Some pragmas are lexically scoped--typically those that affect the C<$^H> hints variable. Others affect the current package instead, like C<use vars> and C<use subs>, which allow you to predeclare a variables or subroutines within a particular I<file> rather than just a block. Such declarations are effective for the entire file for which they were declared. You cannot rescind them with C<no vars> or C<no subs>. The following pragmas are defined (and have their own documentation). =over 12 =item attributes Get/set subroutine or variable attributes =item attrs Set/get attributes of a subroutine (deprecated) =item autouse Postpone load of modules until a function is used =item base Establish IS-A relationship with base class at compile time =item blib Use MakeMaker's uninstalled version of a package =item caller Inherit pragmatic attributes from caller's context =item charnames Define character names for C<\N{named}> string literal escape. =item constant Declare constants =item diagnostics Force verbose warning diagnostics =item fields Declare a class's attribute fields at compile-time =item filetest Control the filetest operators like C<-r>, C<-w> for AFS, etc. =item integer Compute arithmetic in integer instead of double =item less Request less of something from the compiler (unimplemented) =item lib Manipulate @INC at compile time =item locale Use or avoid POSIX locales for built-in operations =item ops Restrict unsafe operations when compiling =item overload Overload Perl operations =item re Alter regular expression behavior =item sigtrap Enable simple signal handling =item strict Restrict unsafe constructs =item subs Predeclare subroutine names =item utf8 Turn on UTF-8 and Unicode support =item vars Predeclare global variable names (obsoleted by our()) =item warnings Control optional warnings =back =head2 Standard Modules Standard, bundled modules are all expected to behave in a well-defined manner with respect to namespace pollution because they use the Exporter module. See their own documentation for details. =over 12 =item AnyDBM_File Provide framework for multiple DBM libraries =item AutoLoader Load subroutines only on demand =item AutoSplit Split a package for autoloading =item B Guts of the Perl code generator (aka compiler) =item B::Asmdata Autogenerated data about Perl ops, used to generate bytecode =item B::Assembler Assemble Perl bytecode =item B::Bblock Walk basic blocks =item B::Bytecode Perl compiler's bytecode backend =item B::C Perl compiler's C backend =item B::CC Perl compiler's optimized C translation backend =item B::Debug Walk Perl syntax tree, printing debug info about ops =item B::Deparse Perl compiler backend to produce Perl code =item B::Disassembler Disassemble Perl bytecode =item B::Lint Module to catch dubious constructs =item B::Showlex Show lexical variables used in functions or files =item B::Stackobj Helper module for CC backend B::Stash -- XXX NFI XXX =item B::Terse Walk Perl syntax tree, printing terse info about ops =item B::Xref Generates cross reference reports for Perl programs =item Benchmark Benchmark running times of code =item ByteLoader Load byte-compiled Perl code =item CGI Simple Common Gateway Interface class =item CGI::Apache Make things work with CGI.pm against Perl-Apache API =item CGI::Carp CGI routines for writing to the HTTPD (or other) error log =item CGI::Cookie Interface to Netscape Cookies =item CGI::Fast CGI Interface for Fast CGI =item CGI::Pretty Module to produce nicely formatted HTML code =item CGI::Push Simple Interface to Server Push =item CGI::Switch Try more than one constructors and return the first object available =item CPAN Query, download, and build Perl modules from CPAN sites =item CPAN::FirstTime Utility for CPAN::Config file initialization =item CPAN::Nox Wrapper around CPAN.pm without using any XS module =item Carp Act like warn/die from perspective of caller =item Carp::Heavy Carp guts =item Class::Struct Declare struct-like datatypes as Perl classes =item Config Access Perl configuration information =item Cwd Get pathname of current working directory =item DB Programmatic interface to the Perl debugging API (experimental) =item DB_File Perl5 access to Berkeley DB version 1.x =item Data::Dumper Serialize Perl data structures =item Devel::DProf A Perl execution profiler =item Devel::Peek A data debugging tool for the XS programmer =item Devel::SelfStubber Generate stubs for a SelfLoading module =item DirHandle Supply object methods for directory handles =item Dumpvalue Provide screen dump of Perl data =item DynaLoader Dynamically load C libraries into Perl code =item English Use English (or awk) names for ugly punctuation variables =item Env Access environment variables as regular ones =item Errno Load the libc errno.h defines =item Exporter Implement default import method for modules =item Exporter::Heavy Exporter guts =item ExtUtils::Command Utilities to replace common Unix commands in Makefiles etc. =item ExtUtils::Embed Utilities for embedding Perl in C/C++ programs =item ExtUtils::Install Install files from here to there =item ExtUtils::Installed Inventory management of installed modules =item ExtUtils::Liblist Determine libraries to use and how to use them =item ExtUtils::MM_Cygwin Methods to override Unix behavior in ExtUtils::MakeMaker =item ExtUtils::MM_OS2 Methods to override Unix behavior in ExtUtils::MakeMaker =item ExtUtils::MM_Unix Methods used by ExtUtils::MakeMaker =item ExtUtils::MM_VMS Methods to override Unix behavior in ExtUtils::MakeMaker =item ExtUtils::MM_Win32 Methods to override Unix behavior in ExtUtils::MakeMaker =item ExtUtils::MakeMaker Create an extension Makefile =item ExtUtils::Manifest Utilities to write and check a MANIFEST file ExtUtils::Miniperl, writemain - Write the C code for perlmain.c =item ExtUtils::Mkbootstrap Make a bootstrap file for use by DynaLoader =item ExtUtils::Mksymlists Write linker options files for dynamic extension =item ExtUtils::Packlist Manage .packlist files =item ExtUtils::testlib Add blib/* directories to @INC =item Fatal Replace functions with equivalents which succeed or die =item Fcntl Load the libc fcntl.h defines =item File::Basename Split a pathname into pieces =item File::CheckTree Run many filetest checks on a tree =item File::Compare Compare files or filehandles =item File::Copy Copy files or filehandles =item File::DosGlob DOS-like globbing and then some =item File::Find Traverse a file tree =item File::Glob Perl extension for BSD filename globbing =item File::Path Create or remove a series of directories =item File::Spec Portably perform operations on file names =item File::Spec::Functions Portably perform operations on file names =item File::Spec::Mac File::Spec for MacOS =item File::Spec::OS2 Methods for OS/2 file specs =item File::Spec::Unix Methods used by File::Spec =item File::Spec::VMS Methods for VMS file specs =item File::Spec::Win32 Methods for Win32 file specs =item File::stat By-name interface to Perl's built-in stat() functions =item FileCache Keep more files open than the system permits =item FileHandle Supply object methods for filehandles =item FindBin Locate installation directory of running Perl program =item GDBM_File Access to the gdbm library =item Getopt::Long Extended processing of command line options =item Getopt::Std Process single-character switches with switch clustering =item I18N::Collate Compare 8-bit scalar data according to current locale =item IO Front-end to load various IO modules =item IO::Dir Supply object methods for directory handles =item IO::File Supply object methods for filehandles =item IO::Handle Supply object methods for I/O handles =item IO::Pipe Supply object methods for pipes =item IO::Poll Object interface to system poll call =item IO::Seekable Supply seek based methods for I/O objects =item IO::Select OO interface to the select system call =item IO::Socket Object interface to socket communications =item IO::Socket::INET Object interface for AF_INET domain sockets =item IO::Socket::UNIX Object interface for AF_UNIX domain sockets =item IPC::Msg SysV Msg IPC object class =item IPC::Open2 Open a process for both reading and writing =item IPC::Open3 Open a process for reading, writing, and error handling =item IPC::Semaphore SysV Semaphore IPC object class =item IPC::SysV SysV IPC constants =item Math::BigFloat Arbitrary length float math package =item Math::BigInt Arbitrary size integer math package =item Math::Complex Complex numbers and associated mathematical functions =item Math::Trig Trigonometric functions =item Net::Ping Check a remote host for reachability =item Net::hostent By-name interface to Perl's built-in gethost*() functions =item Net::netent By-name interface to Perl's built-in getnet*() functions =item Net::protoent By-name interface to Perl's built-in getproto*() functions =item Net::servent By-name interface to Perl's built-in getserv*() functions =item O Generic interface to Perl Compiler backends =item Opcode Disable named opcodes when compiling Perl code =item POSIX Perl interface to IEEE Std 1003.1 =item Pod::Checker Check pod documents for syntax errors =item Pod::Html Module to convert pod files to HTML =item Pod::InputObjects Manage POD objects =item Pod::Man Convert POD data to formatted *roff input =item Pod::Parser Base class for creating POD filters and translators =item Pod::Select Extract selected sections of POD from input =item Pod::Text Convert POD data to formatted ASCII text =item Pod::Text::Color Convert POD data to formatted color ASCII text =item Pod::Usage Print a usage message from embedded pod documentation =item SDBM_File Tied access to sdbm files =item Safe Compile and execute code in restricted compartments =item Search::Dict Search for key in dictionary file =item SelectSaver Save and restore selected file handle =item SelfLoader Load functions only on demand =item Shell Run shell commands transparently within Perl =item Socket Load the libc socket.h defines and structure manipulators =item Symbol Manipulate Perl symbols and their names =item Sys::Hostname Try every conceivable way to get hostname =item Sys::Syslog Interface to the libc syslog(3) calls =item Term::Cap Termcap interface =item Term::Complete Word completion module =item Term::ReadLine Interface to various `readline' packages. =item Test Provides a simple framework for writing test scripts =item Test::Harness Run Perl standard test scripts with statistics =item Text::Abbrev Create an abbreviation table from a list =item Text::ParseWords Parse text into a list of tokens or array of arrays =item Text::Soundex Implementation of the Soundex Algorithm as described by Knuth Text::Tabs -- expand and unexpand tabs per expand(1) and unexpand(1) =item Text::Wrap Line wrapping to form simple paragraphs =item Tie::Array Base class for tied arrays =item Tie::Handle Base class definitions for tied handles =item Tie::Hash Base class definitions for tied hashes =item Tie::RefHash Use references as hash keys =item Tie::Scalar Base class definitions for tied scalars =item Tie::SubstrHash Fixed-table-size, fixed-key-length hashing =item Time::Local Efficiently compute time from local and GMT time =item Time::gmtime By-name interface to Perl's built-in gmtime() function =item Time::localtime By-name interface to Perl's built-in localtime() function =item Time::tm Internal object used by Time::gmtime and Time::localtime =item UNIVERSAL Base class for ALL classes (blessed references) =item User::grent By-name interface to Perl's built-in getgr*() functions =item User::pwent By-name interface to Perl's built-in getpw*() functions =back To find out I<all> modules installed on your system, including those without documentation or outside the standard release, just do this: % find `perl -e 'print "@INC"'` -name '*.pm' -print To get a log of all module distributions which have been installed since perl was installed, just do: % perldoc perllocal Modules should all have their own documentation installed and accessible via your system man(1) command, or via the C<perldoc> program. If you do not have a B<find> program, you can use the Perl B<find2perl> program instead, which generates Perl code as output you can run through perl. If you have a B<man> program but it doesn't find your modules, you'll have to fix your manpath. See L<perl> for details. =head2 Extension Modules Extension modules are written in C (or a mix of Perl and C). They are usually dynamically loaded into Perl if and when you need them, but may also be be linked in statically. Supported extension modules include Socket, Fcntl, and POSIX. Many popular C extension modules do not come bundled (at least, not completely) due to their sizes, volatility, or simply lack of time for adequate testing and configuration across the multitude of platforms on which Perl was beta-tested. You are encouraged to look for them on CPAN (described below), or using web search engines like Alta Vista or Deja News. =head1 CPAN CPAN stands for Comprehensive Perl Archive Network; it's a globally replicated trove of Perl materials, including documentation, style guides, tricks and trap, alternate ports to non-Unix systems and occasional binary distributions for these. Search engines for CPAN can be found at http://cpan.perl.com/ and at http://theory.uwinnipeg.ca/mod_perl/cpan-search.pl . Most importantly, CPAN includes around a thousand unbundled modules, some of which require a C compiler to build. Major categories of modules are: =over =item * Language Extensions and Documentation Tools =item * Development Support =item * Operating System Interfaces =item * Networking, Device Control (modems) and InterProcess Communication =item * Data Types and Data Type Utilities =item * Database Interfaces =item * User Interfaces =item * Interfaces to / Emulations of Other Programming Languages =item * File Names, File Systems and File Locking (see also File Handles) =item * String Processing, Language Text Processing, Parsing, and Searching =item * Option, Argument, Parameter, and Configuration File Processing =item * Internationalization and Locale =item * Authentication, Security, and Encryption =item * World Wide Web, HTML, HTTP, CGI, MIME =item * Server and Daemon Utilities =item * Archiving and Compression =item * Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing =item * Mail and Usenet News =item * Control Flow Utilities (callbacks and exceptions etc) =item * File Handle and Input/Output Stream Utilities =item * Miscellaneous Modules =back Registered CPAN sites as of this writing include the following. You should try to choose one close to you: =over =item Africa South Africa ftp://ftp.is.co.za/programming/perl/CPAN/ ftp://ftp.saix.net/pub/CPAN/ ftp://ftp.sun.ac.za/CPAN/ ftp://ftpza.co.za/pub/mirrors/cpan/ =item Asia China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/ Hong Kong ftp://ftp.pacific.net.hk/pub/mirror/CPAN/ Indonesia ftp://malone.piksi.itb.ac.id/pub/CPAN/ Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/ Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/ ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/ ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/ ftp://ftp.meisei-u.ac.jp/pub/CPAN/ ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/ ftp://mirror.nucba.ac.jp/mirror/Perl/ Saudi-Arabia ftp://ftp.isu.net.sa/pub/CPAN/ Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/ South Korea ftp://ftp.bora.net/pub/CPAN/ ftp://ftp.kornet.net/pub/CPAN/ ftp://ftp.nuri.net/pub/CPAN/ Taiwan ftp://coda.nctu.edu.tw/computer-languages/perl/CPAN/ ftp://ftp.ee.ncku.edu.tw/pub3/perl/CPAN/ ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/ Thailand ftp://ftp.nectec.or.th/pub/mirrors/CPAN/ =item Australasia Australia ftp://cpan.topend.com.au/pub/CPAN/ ftp://ftp.labyrinth.net.au/pub/perl-CPAN/ ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/ ftp://mirror.aarnet.edu.au/pub/perl/CPAN/ New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/ ftp://sunsite.net.nz/pub/languages/perl/CPAN/ =item Central America Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/ =item Europe Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/ Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/ Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/ Croatia ftp://ftp.linux.hr/pub/CPAN/ Czech Republic ftp://ftp.fi.muni.cz/pub/perl/ ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/ Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/ Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/ Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/ France ftp://ftp.grolier.fr/pub/perl/CPAN/ ftp://ftp.lip6.fr/pub/perl/CPAN/ ftp://ftp.oleane.net/pub/mirrors/CPAN/ ftp://ftp.pasteur.fr/pub/computing/CPAN/ ftp://ftp.uvsq.fr/pub/perl/CPAN/ German ftp://ftp.gigabell.net/pub/CPAN/ Germany ftp://ftp.archive.de.uu.net/pub/CPAN/ ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/ ftp://ftp.gmd.de/packages/CPAN/ ftp://ftp.gwdg.de/pub/languages/perl/CPAN/ ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/ ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/ ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/ ftp://ftp.uni-erlangen.de/pub/source/CPAN/ ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/ Germany ftp://ftp.archive.de.uu.net/pub/CPAN/ ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/ ftp://ftp.gmd.de/packages/CPAN/ ftp://ftp.gwdg.de/pub/languages/perl/CPAN/ ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/ ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/ ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/ ftp://ftp.uni-erlangen.de/pub/source/CPAN/ ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/ Greece ftp://ftp.ntua.gr/pub/lang/perl/ Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/ Iceland ftp://ftp.gm.is/pub/CPAN/ Ireland ftp://cpan.indigo.ie/pub/CPAN/ ftp://sunsite.compapp.dcu.ie/pub/perl/ Italy ftp://cis.uniRoma2.it/CPAN/ ftp://ftp.flashnet.it/pub/CPAN/ ftp://ftp.unina.it/pub/Other/CPAN/ ftp://ftp.unipi.it/pub/mirror/perl/CPAN/ Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/ ftp://ftp.nluug.nl/pub/languages/perl/CPAN/ Norway ftp://ftp.uit.no/pub/languages/perl/cpan/ ftp://sunsite.uio.no/pub/languages/perl/CPAN/ Poland ftp://ftp.man.torun.pl/pub/CPAN/ ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/ ftp://sunsite.icm.edu.pl/pub/CPAN/ Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/ ftp://ftp.ist.utl.pt/pub/CPAN/ ftp://ftp.ua.pt/pub/CPAN/ Romania ftp://ftp.dnttm.ro/pub/CPAN/ Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/ ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/ Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/ Slovenia ftp://ftp.arnes.si/software/perl/CPAN/ Spain ftp://ftp.etse.urv.es/pub/perl/ ftp://ftp.rediris.es/mirror/CPAN/ Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/ Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/ Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/ United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/ ftp://ftp.flirble.org/pub/languages/perl/CPAN/ ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/ ftp://ftp.plig.org/pub/CPAN/ ftp://sunsite.doc.ic.ac.uk/packages/CPAN/ =item North America Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/ California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/ ftp://cpan.valueclick.com/CPAN/ ftp://ftp.cdrom.com/pub/perl/CPAN/ http://download.sourceforge.net/mirrors/CPAN/ Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/ Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/ Georgia ftp://ftp.twoguys.org/CPAN/ Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/ Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/ ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/ Kentucky ftp://ftp.uky.edu/CPAN/ Manitoba ftp://theoryx5.uwinnipeg.ca/pub/CPAN/ Massachusetts ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/ ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/ Mexico ftp://ftp.msg.com.mx/pub/CPAN/ New York ftp://ftp.deao.net/pub/CPAN/ ftp://ftp.rge.com/pub/languages/perl/ North Carolina ftp://ftp.duke.edu/pub/perl/ Nova Scotia ftp://cpan.chebucto.ns.ca/pub/CPAN/ Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/ Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/ Oregon ftp://ftp.orst.edu/pub/packages/CPAN/ Pennsylvania ftp://ftp.epix.net/pub/languages/perl/ Tennessee ftp://ftp.sunsite.utk.edu/pub/CPAN/ Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/ ftp://jhcloos.com/pub/mirror/CPAN/ Utah ftp://mirror.xmission.com/CPAN/ Virginia ftp://ftp.perl.org/pub/perl/CPAN/ ftp://ruff.cs.jmu.edu/pub/CPAN/ Washington ftp://ftp-mirror.internap.com/pub/CPAN/ ftp://ftp.llarian.net/pub/CPAN/ ftp://ftp.spu.edu/pub/CPAN/ =item South America Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/ ftp://ftp.matrix.com.br/pub/perl/ Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/PERL/ =back For an up-to-date listing of CPAN sites, see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES . =head1 Modules: Creation, Use, and Abuse (The following section is borrowed directly from Tim Bunce's modules file, available at your nearest CPAN site.) Perl implements a class using a package, but the presence of a package doesn't imply the presence of a class. A package is just a namespace. A class is a package that provides subroutines that can be used as methods. A method is just a subroutine that expects, as its first argument, either the name of a package (for "static" methods), or a reference to something (for "virtual" methods). A module is a file that (by convention) provides a class of the same name (sans the .pm), plus an import method in that class that can be called to fetch exported symbols. This module may implement some of its methods by loading dynamic C or C++ objects, but that should be totally transparent to the user of the module. Likewise, the module might set up an AUTOLOAD function to slurp in subroutine definitions on demand, but this is also transparent. Only the F<.pm> file is required to exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about the AUTOLOAD mechanism. =head2 Guidelines for Module Creation =over 4 =item Do similar modules already exist in some form? If so, please try to reuse the existing modules either in whole or by inheriting useful features into a new class. If this is not practical try to get together with the module authors to work on extending or enhancing the functionality of the existing modules. A perfect example is the plethora of packages in perl4 for dealing with command line options. If you are writing a module to expand an already existing set of modules, please coordinate with the author of the package. It helps if you follow the same naming scheme and module interaction scheme as the original author. =item Try to design the new module to be easy to extend and reuse. Try to C<use warnings;> (or C<use warnings qw(...);>). Remember that you can add C<no warnings qw(...);> to individual blocks of code that need less warnings. Use blessed references. Use the two argument form of bless to bless into the class name given as the first parameter of the constructor, e.g.,: sub new { my $class = shift; return bless {}, $class; } or even this if you'd like it to be used as either a static or a virtual method. sub new { my $self = shift; my $class = ref($self) || $self; return bless {}, $class; } Pass arrays as references so more parameters can be added later (it's also faster). Convert functions into methods where appropriate. Split large methods into smaller more flexible ones. Inherit methods from other modules if appropriate. Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>. Generally you can delete the C<eq 'FOO'> part with no harm at all. Let the objects look after themselves! Generally, avoid hard-wired class names as far as possible. Avoid C<< $r->Class::func() >> where using C<@ISA=qw(... Class ...)> and C<< $r->func() >> would work (see L<perlbot> for more details). Use autosplit so little used or newly added functions won't be a burden to programs that don't use them. Add test functions to the module after __END__ either using AutoSplit or by saying: eval join('',<main::DATA>) || die $@ unless caller(); Does your module pass the 'empty subclass' test? If you say C<@SUBCLASS::ISA = qw(YOURCLASS);> your applications should be able to use SUBCLASS in exactly the same way as YOURCLASS. For example, does your application still work if you change: C<$obj = new YOURCLASS;> into: C<$obj = new SUBCLASS;> ? Avoid keeping any state information in your packages. It makes it difficult for multiple other packages to use yours. Keep state information in objects. Always use B<-w>. Try to C<use strict;> (or C<use strict qw(...);>). Remember that you can add C<no strict qw(...);> to individual blocks of code that need less strictness. Always use B<-w>. Follow the guidelines in the perlstyle(1) manual. Always use B<-w>. =item Some simple style guidelines The perlstyle manual supplied with Perl has many helpful points. Coding style is a matter of personal taste. Many people evolve their style over several years as they learn what helps them write and maintain good code. Here's one set of assorted suggestions that seem to be widely used by experienced developers: Use underscores to separate words. It is generally easier to read $var_names_like_this than $VarNamesLikeThis, especially for non-native speakers of English. It's also a simple rule that works consistently with VAR_NAMES_LIKE_THIS. Package/Module names are an exception to this rule. Perl informally reserves lowercase module names for 'pragma' modules like integer and strict. Other modules normally begin with a capital letter and use mixed case with no underscores (need to be short and portable). You may find it helpful to use letter case to indicate the scope or nature of a variable. For example: $ALL_CAPS_HERE constants only (beware clashes with Perl vars) $Some_Caps_Here package-wide global/static $no_caps_here function scope my() or local() variables Function and method names seem to work best as all lowercase. e.g., C<< $obj->as_string() >>. You can use a leading underscore to indicate that a variable or function should not be used outside the package that defined it. =item Select what to export. Do NOT export method names! Do NOT export anything else by default without a good reason! Exports pollute the namespace of the module user. If you must export try to use @EXPORT_OK in preference to @EXPORT and avoid short or common names to reduce the risk of name clashes. Generally anything not exported is still accessible from outside the module using the ModuleName::item_name (or C<< $blessed_ref->method >>) syntax. By convention you can use a leading underscore on names to indicate informally that they are 'internal' and not for public use. (It is actually possible to get private functions by saying: C<my $subref = sub { ... }; &$subref;>. But there's no way to call that directly as a method, because a method must have a name in the symbol table.) As a general rule, if the module is trying to be object oriented then export nothing. If it's just a collection of functions then @EXPORT_OK anything but use @EXPORT with caution. =item Select a name for the module. This name should be as descriptive, accurate, and complete as possible. Avoid any risk of ambiguity. Always try to use two or more whole words. Generally the name should reflect what is special about what the module does rather than how it does it. Please use nested module names to group informally or categorize a module. There should be a very good reason for a module not to have a nested name. Module names should begin with a capital letter. Having 57 modules all called Sort will not make life easy for anyone (though having 23 called Sort::Quick is only marginally better :-). Imagine someone trying to install your module alongside many others. If in any doubt ask for suggestions in comp.lang.perl.misc. If you are developing a suite of related modules/classes it's good practice to use nested classes with a common prefix as this will avoid namespace clashes. For example: Xyz::Control, Xyz::View, Xyz::Model etc. Use the modules in this list as a naming guide. If adding a new module to a set, follow the original author's standards for naming modules and the interface to methods in those modules. To be portable each component of a module name should be limited to 11 characters. If it might be used on MS-DOS then try to ensure each is unique in the first 8 characters. Nested modules make this easier. =item Have you got it right? How do you know that you've made the right decisions? Have you picked an interface design that will cause problems later? Have you picked the most appropriate name? Do you have any questions? The best way to know for sure, and pick up many helpful suggestions, is to ask someone who knows. Comp.lang.perl.misc is read by just about all the people who develop modules and it's the best place to ask. All you need to do is post a short summary of the module, its purpose and interfaces. A few lines on each of the main methods is probably enough. (If you post the whole module it might be ignored by busy people - generally the very people you want to read it!) Don't worry about posting if you can't say when the module will be ready - just say so in the message. It might be worth inviting others to help you, they may be able to complete it for you! =item README and other Additional Files. It's well known that software developers usually fully document the software they write. If, however, the world is in urgent need of your software and there is not enough time to write the full documentation please at least provide a README file containing: =over 10 =item * A description of the module/package/extension etc. =item * A copyright notice - see below. =item * Prerequisites - what else you may need to have. =item * How to build it - possible changes to Makefile.PL etc. =item * How to install it. =item * Recent changes in this release, especially incompatibilities =item * Changes / enhancements you plan to make in the future. =back If the README file seems to be getting too large you may wish to split out some of the sections into separate files: INSTALL, Copying, ToDo etc. =over 4 =item Adding a Copyright Notice. How you choose to license your work is a personal decision. The general mechanism is to assert your Copyright and then make a declaration of how others may copy/use/modify your work. Perl, for example, is supplied with two types of licence: The GNU GPL and The Artistic Licence (see the files README, Copying, and Artistic). Larry has good reasons for NOT just using the GNU GPL. My personal recommendation, out of respect for Larry, Perl, and the Perl community at large is to state something simply like: Copyright (c) 1995 Your Name. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. This statement should at least appear in the README file. You may also wish to include it in a Copying file and your source files. Remember to include the other words in addition to the Copyright. =item Give the module a version/issue/release number. To be fully compatible with the Exporter and MakeMaker modules you should store your module's version number in a non-my package variable called $VERSION. This should be a floating point number with at least two digits after the decimal (i.e., hundredths, e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version. See L<Exporter> for details. It may be handy to add a function or method to retrieve the number. Use the number in announcements and archive file names when releasing the module (ModuleName-1.02.tar.Z). See perldoc ExtUtils::MakeMaker.pm for details. =item How to release and distribute a module. It's good idea to post an announcement of the availability of your module (or the module itself if small) to the comp.lang.perl.announce Usenet newsgroup. This will at least ensure very wide once-off distribution. If possible, register the module with CPAN. You should include details of its location in your announcement. Some notes about ftp archives: Please use a long descriptive file name that includes the version number. Most incoming directories will not be readable/listable, i.e., you won't be able to see your file after uploading it. Remember to send your email notification message as soon as possible after uploading else your file may get deleted automatically. Allow time for the file to be processed and/or check the file has been processed before announcing its location. FTP Archives for Perl Modules: Follow the instructions and links on: http://www.perl.com/CPAN/modules/00modlist.long.html http://www.perl.com/CPAN/modules/04pause.html or upload to one of these sites: https://pause.kbx.de/pause/ http://pause.perl.org/pause/ and notify <modules@perl.org>. By using the WWW interface you can ask the Upload Server to mirror your modules from your ftp or WWW site into your own directory on CPAN! Please remember to send me an updated entry for the Module list! =item Take care when changing a released module. Always strive to remain compatible with previous released versions. Otherwise try to add a mechanism to revert to the old behavior if people rely on it. Document incompatible changes. =back =back =head2 Guidelines for Converting Perl 4 Library Scripts into Modules =over 4 =item There is no requirement to convert anything. If it ain't broke, don't fix it! Perl 4 library scripts should continue to work with no problems. You may need to make some minor changes (like escaping non-array @'s in double quoted strings) but there is no need to convert a .pl file into a Module for just that. =item Consider the implications. All Perl applications that make use of the script will need to be changed (slightly) if the script is converted into a module. Is it worth it unless you plan to make other changes at the same time? =item Make the most of the opportunity. If you are going to convert the script to a module you can use the opportunity to redesign the interface. The guidelines for module creation above include many of the issues you should consider. =item The pl2pm utility will get you started. This utility will read *.pl files (given as parameters) and write corresponding *.pm files. The pl2pm utilities does the following: =over 10 =item * Adds the standard Module prologue lines =item * Converts package specifiers from ' to :: =item * Converts die(...) to croak(...) =item * Several other minor changes =back Being a mechanical process pl2pm is not bullet proof. The converted code will need careful checking, especially any package statements. Don't delete the original .pl file till the new .pm one works! =back =head2 Guidelines for Reusing Application Code =over 4 =item Complete applications rarely belong in the Perl Module Library. =item Many applications contain some Perl code that could be reused. Help save the world! Share your code in a form that makes it easy to reuse. =item Break-out the reusable code into one or more separate module files. =item Take the opportunity to reconsider and redesign the interfaces. =item In some cases the 'application' can then be reduced to a small fragment of code built on top of the reusable modules. In these cases the application could invoked as: % perl -e 'use Module::Name; method(@ARGV)' ... or % perl -mModule::Name ... (in perl5.002 or higher) =back =head1 NOTE Perl does not enforce private and public parts of its modules as you may have been used to in other languages like C++, Ada, or Modula-17. Perl doesn't have an infatuation with enforced privacy. It would prefer that you stayed out of its living room because you weren't invited, not because it has a shotgun. The module and its user have a contract, part of which is common law, and part of which is "written". Part of the common law contract is that a module doesn't pollute any namespace it wasn't asked to. The written contract for the module (A.K.A. documentation) may make other provisions. But then you know when you C<use RedefineTheWorld> that you're redefining the world and willing to take the consequences.