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perlmodlib - constructing new Perl modules and finding existing onesDESCRIPTION
THE PERL MODULE LIBRARY
Many modules are included the Perl distribution. These are described below, and all end in .pm. You may discover compiled library file (usually ending in .so) or small pieces of modules to be autoloaded (ending in .al); these were automatically generated by the installation process. You may also discover files in the library directory that end in either .pl or .ph. These are old libraries supplied so that old programs that use them still run. The .pl files will all eventually be converted into standard modules, and the .ph files made by h2ph will probably end up as extension modules made by h2xs. (Some .ph values may already be available through the POSIX, Errno, or Fcntl modules.) The pl2pm file in the distribution may help in your conversion, but it's just a mechanical process and therefore far from bulletproof. 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 `use', or `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 `$^H' hints variable. Others affect the current package instead, like `use vars' and `use subs', which allow you to predeclare a variables or subroutines within a particular file rather than just a block. Such declarations are effective for the entire file for which they were declared. You cannot rescind them with `no vars' or `no subs'. The following pragmas are defined (and have their own documentation). attributes Get/set subroutine or variable attributes attrs Set/get attributes of a subroutine (deprecated) autouse Postpone load of modules until a function is used base Establish IS-A relationship with base class at compile time blib Use MakeMaker's uninstalled version of a package caller Inherit pragmatic attributes from caller's context charnames Define character names for `\N{named}' string literal escape. constant Declare constants diagnostics Force verbose warning diagnostics fields Declare a class's attribute fields at compile- time filetest Control the filetest operators like `-r', `-w' for AFS, etc. integer Compute arithmetic in integer instead of double less Request less of something from the compiler (unimplemented) lib Manipulate @INC at compile time locale Use or avoid POSIX locales for built-in operations ops Restrict unsafe operations when compiling overload Overload Perl operations re Alter regular expression behavior sigtrap Enable simple signal handling strict Restrict unsafe constructs subs Predeclare subroutine names utf8 Turn on UTF-8 and Unicode support vars Predeclare global variable names (obsoleted by our()) warnings Control optional warnings 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. AnyDBM_File Provide framework for multiple DBM libraries AutoLoader Load subroutines only on demand AutoSplit Split a package for autoloading B Guts of the Perl code generator (aka compiler) B::Asmdata Autogenerated data about Perl ops, used to generate bytecode B::Assembler Assemble Perl bytecode B::Bblock Walk basic blocks B::Bytecode Perl compiler's bytecode backend B::C Perl compiler's C backend B::CC Perl compiler's optimized C translation backend B::Debug Walk Perl syntax tree, printing debug info about ops B::Deparse Perl compiler backend to produce Perl code B::Disassembler Disassemble Perl bytecode B::Lint Module to catch dubious constructs B::Showlex Show lexical variables used in functions or files B::Stackobj Helper module for CC backend B::Stash -- XXX NFI XXX B::Terse Walk Perl syntax tree, printing terse info about ops B::Xref Generates cross reference reports for Perl programs Benchmark Benchmark running times of code ByteLoader Load byte-compiled Perl code CGI Simple Common Gateway Interface class CGI::Apache Make things work with CGI.pm against Perl-Apache API CGI::Carp CGI routines for writing to the HTTPD (or other) error log CGI::Cookie Interface to Netscape Cookies CGI::Fast CGI Interface for Fast CGI CGI::Pretty Module to produce nicely formatted HTML code CGI::Push Simple Interface to Server Push CGI::Switch Try more than one constructors and return the first object available CPAN Query, download, and build Perl modules from CPAN sites CPAN::FirstTime Utility for CPAN::Config file initialization CPAN::Nox Wrapper around CPAN.pm without using any XS module Carp Act like warn/die from perspective of caller Carp::Heavy Carp guts Class::Struct Declare struct-like datatypes as Perl classes Config Access Perl configuration information Cwd Get pathname of current working directory DB Programmatic interface to the Perl debugging API (experimental) DB_File Perl5 access to Berkeley DB version 1.x Data::Dumper Serialize Perl data structures Devel::DProf A Perl execution profiler Devel::Peek A data debugging tool for the XS programmer Devel::SelfStubber Generate stubs for a SelfLoading module DirHandle Supply object methods for directory handles Dumpvalue Provide screen dump of Perl data DynaLoader Dynamically load C libraries into Perl code English Use English (or awk) names for ugly punctuation variables Env Access environment variables as regular ones Errno Load the libc errno.h defines Exporter Implement default import method for modules Exporter::Heavy Exporter guts ExtUtils::Command Utilities to replace common Unix commands in Makefiles etc. ExtUtils::Embed Utilities for embedding Perl in C/C++ programs ExtUtils::Install Install files from here to there ExtUtils::Installed Inventory management of installed modules ExtUtils::Liblist Determine libraries to use and how to use them ExtUtils::MM_Cygwin Methods to override Unix behavior in ExtUtils::MakeMaker ExtUtils::MM_OS2 Methods to override Unix behavior in ExtUtils::MakeMaker ExtUtils::MM_Unix Methods used by ExtUtils::MakeMaker ExtUtils::MM_VMS Methods to override Unix behavior in ExtUtils::MakeMaker ExtUtils::MM_Win32 Methods to override Unix behavior in ExtUtils::MakeMaker ExtUtils::MakeMaker Create an extension Makefile ExtUtils::Manifest Utilities to write and check a MANIFEST file ExtUtils::Miniperl, writemain - Write the C code for perlmain.c ExtUtils::Mkbootstrap Make a bootstrap file for use by DynaLoader ExtUtils::Mksymlists Write linker options files for dynamic extension ExtUtils::Packlist Manage .packlist files ExtUtils::testlib Add blib/* directories to @INC Fatal Replace functions with equivalents which succeed or die Fcntl Load the libc fcntl.h defines File::Basename Split a pathname into pieces File::CheckTree Run many filetest checks on a tree File::Compare Compare files or filehandles File::Copy Copy files or filehandles File::DosGlob DOS-like globbing and then some File::Find Traverse a file tree File::Glob Perl extension for BSD filename globbing File::Path Create or remove a series of directories File::Spec Portably perform operations on file names File::Spec::Functions Portably perform operations on file names File::Spec::Mac File::Spec for MacOS File::Spec::OS2 Methods for OS/2 file specs File::Spec::Unix Methods used by File::Spec File::Spec::VMS Methods for VMS file specs File::Spec::Win32 Methods for Win32 file specs File::stat By-name interface to Perl's built-in stat() functions FileCache Keep more files open than the system permits FileHandle Supply object methods for filehandles FindBin Locate installation directory of running Perl program GDBM_File Access to the gdbm library Getopt::Long Extended processing of command line options Getopt::Std Process single-character switches with switch clustering I18N::Collate Compare 8-bit scalar data according to current locale IO Front-end to load various IO modules IO::Dir Supply object methods for directory handles IO::File Supply object methods for filehandles IO::Handle Supply object methods for I/O handles IO::Pipe Supply object methods for pipes IO::Poll Object interface to system poll call IO::Seekable Supply seek based methods for I/O objects IO::Select OO interface to the select system call IO::Socket Object interface to socket communications IO::Socket::INET Object interface for AF_INET domain sockets IO::Socket::UNIX Object interface for AF_UNIX domain sockets IPC::Msg SysV Msg IPC object class IPC::Open2 Open a process for both reading and writing IPC::Open3 Open a process for reading, writing, and error handling IPC::Semaphore SysV Semaphore IPC object class IPC::SysV SysV IPC constants Math::BigFloat Arbitrary length float math package Math::BigInt Arbitrary size integer math package Math::Complex Complex numbers and associated mathematical functions Math::Trig Trigonometric functions Net::Ping Check a remote host for reachability Net::hostent By-name interface to Perl's built-in gethost*() functions Net::netent By-name interface to Perl's built-in getnet*() functions Net::protoent By-name interface to Perl's built-in getproto*() functions Net::servent By-name interface to Perl's built-in getserv*() functions O Generic interface to Perl Compiler backends Opcode Disable named opcodes when compiling Perl code POSIX Perl interface to IEEE Std 1003.1 Pod::Checker Check pod documents for syntax errors Pod::Html Module to convert pod files to HTML Pod::InputObjects Manage POD objects Pod::Man Convert POD data to formatted *roff input Pod::Parser Base class for creating POD filters and translators Pod::Select Extract selected sections of POD from input Pod::Text Convert POD data to formatted ASCII text Pod::Text::Color Convert POD data to formatted color ASCII text Pod::Usage Print a usage message from embedded pod documentation SDBM_File Tied access to sdbm files Safe Compile and execute code in restricted compartments Search::Dict Search for key in dictionary file SelectSaver Save and restore selected file handle SelfLoader Load functions only on demand Shell Run shell commands transparently within Perl Socket Load the libc socket.h defines and structure manipulators Symbol Manipulate Perl symbols and their names Sys::Hostname Try every conceivable way to get hostname Sys::Syslog Interface to the libc syslog(3) calls Term::Cap Termcap interface Term::Complete Word completion module Term::ReadLine Interface to various `readline' packages. Test Provides a simple framework for writing test scripts Test::Harness Run Perl standard test scripts with statistics Text::Abbrev Create an abbreviation table from a list Text::ParseWords Parse text into a list of tokens or array of arrays Text::Soundex Implementation of the Soundex Algorithm as described by Knuth Text::Tabs -- expand and unexpand tabs per expand(1) and unexpand(1) Text::Wrap Line wrapping to form simple paragraphs Tie::Array Base class for tied arrays Tie::Handle Base class definitions for tied handles Tie::Hash Base class definitions for tied hashes Tie::RefHash Use references as hash keys Tie::Scalar Base class definitions for tied scalars Tie::SubstrHash Fixed-table-size, fixed-key-length hashing Time::Local Efficiently compute time from local and GMT time Time::gmtime By-name interface to Perl's built-in gmtime() function Time::localtime By-name interface to Perl's built-in localtime() function Time::tm Internal object used by Time::gmtime and Time::localtime UNIVERSAL Base class for ALL classes (blessed references) User::grent By-name interface to Perl's built-in getgr*() functions User::pwent By-name interface to Perl's built-in getpw*() functions To find out 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 `perldoc' program. If you do not have a find program, you can use the Perl find2perl program instead, which generates Perl code as output you can run through perl. If you have a man program but it doesn't find your modules, you'll have to fix your manpath. See the perl manpage for details. 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.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: o Language Extensions and Documentation Tools o Development Support o Operating System Interfaces Communication o Networking, Device Control (modems) and InterProcess o Data Types and Data Type Utilities o Database Interfaces o User Interfaces o Interfaces to / Emulations of Other Programming Languages Handles) o File Names, File Systems and File Locking (see also File Searching o String Processing, Language Text Processing, Parsing, and o Option, Argument, Parameter, and Configuration File Processing o Internationalization and Locale o Authentication, Security, and Encryption o World Wide Web, HTML, HTTP, CGI, MIME o Server and Daemon Utilities o Archiving and Compression o Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing o Mail and Usenet News o Control Flow Utilities (callbacks and exceptions etc) o File Handle and Input/Output Stream Utilities o Miscellaneous Modules Registered CPAN sites as of this writing include the following. You should try to choose one close to you: 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/ 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/ 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/ Central America Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/ 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/ 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/ 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/ For an up-to-date listing of CPAN sites, see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES .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 .pm file is required to exist. See the perlsub manpage, the perltoot manpage, and the AutoLoader manpage for details about the AUTOLOAD mechanism. Guidelines for Module Creation 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. Try to design the new module to be easy to extend and reuse. Try to `use warnings;' (or `use warnings qw(...);'). Remember that you can add `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: `die "Invalid" unless ref $ref eq 'FOO''. Generally you can delete the `eq 'FOO'' part with no harm at all. Let the objects look after themselves! Generally, avoid hard-wired class names as far as possible. Avoid `$r->Class::func()' where using `@ISA=qw(... Class ...)' and `$r->func()' would work (see the perlbot manpage 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 $@ unless caller(); Does your module pass the 'empty subclass' test? If you say `@SUBCLASS::ISA = qw(YOURCLASS);' your applications should be able to use SUBCLASS in exactly the same way as YOURCLASS. For example, does your application still work if you change: `$obj = new YOURCLASS;' into: `$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 -w. Try to `use strict;' (or `use strict qw(...);'). Remember that you can add `no strict qw(...);' to individual blocks of code that need less strictness. Always use -w. Follow the guidelines in the perlstyle(1) manual. Always use -w. 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 $no_caps_here function scope my() or local() variables Function and method names seem to work best as all lowercase. e.g., `$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. 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 `$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: `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. 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. 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! 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: o A description of the module/package/extension etc. o A copyright notice - see below. o Prerequisites - what else you may need to have. o How to build it - possible changes to Makefile.PL etc. o How to install it. incompatibilities o Recent changes in this release, especially o Changes / enhancements you plan to make in the future. 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. 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. 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 $VERSION. This should be a floating point number with at least two digits after the decimal (i.e., hundredths, e.g, `$VERSION = "0.01"'). Don't use a "1.3.2" style version. See the Exporter manpage 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. 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 <[email protected]>. 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! 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. Guidelines for Converting Perl 4 Library Scripts into Modules 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. 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? 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. 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: o Adds the standard Module prologue lines o Converts package specifiers from ' to :: o Converts die(...) to croak(...) o Several other minor changes 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! Guidelines for Reusing Application Code Complete applications rarely belong in the Perl Module Library. 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. files. Break-out the reusable code into one or more separate module Take the opportunity to reconsider and redesign the interfaces. 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)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 `use RedefineTheWorld' that you're redefining the world and willing to take the consequences.
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