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RedHat 9 (Linux i386) - man page for perlmodlib (redhat section 1)

PERLMODLIB(1)						 Perl Programmers Reference Guide					     PERLMODLIB(1)

perlmodlib - constructing new Perl modules and finding existing ones
Many modules are included in the Perl distribution. These are described below, and all end in .pm. You may discover compiled library files (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 sup- plied 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 bigint Transparent BigInteger support for Perl bignum Transparent BigNumber support for Perl bigrat Transparent BigNumber/BigRationale support for Perl blib Use MakeMaker's uninstalled version of a package bytes Force byte semantics rather than character semantics charnames Define character names for "\N{named}" string literal escapes constant Declare constants diagnostics Perl compiler pragma to force verbose warning diagnostics encoding Allows you to write your script in non-ascii or non-utf8 fields Compile-time class fields filetest Control the filetest permission operators if "use" a Perl module if a condition holds integer Use integer arithmetic instead of floating point less Request less of something from the compiler lib Manipulate @INC at compile time locale Use and avoid POSIX locales for built-in operations open Set default PerlIO layers for input and output ops Restrict unsafe operations when compiling overload Package for overloading perl operations re Alter regular expression behaviour sigtrap Enable simple signal handling sort Control sort() behaviour strict Restrict unsafe constructs subs Predeclare sub names threads Perl extension allowing use of interpreter based threads from perl threads::shared Perl extension for sharing data structures between threads utf8 Enable/disable UTF-8 (or UTF-EBCDIC) in source code vars Predeclare global variable names (obsolete) version Perl extension for Version Objects vmsish Control VMS-specific language features warnings Control optional warnings warnings::register Warnings import function 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. It's possible that not all modules listed below are installed on your system. For example, the GDBM_File module will not be installed if you don't have the gdbm library. AnyDBM_File Provide framework for multiple DBMs Attribute::Handlers Simpler definition of attribute handlers AutoLoader Load subroutines only on demand AutoSplit Split a package for autoloading B The Perl 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::Concise Walk Perl syntax tree, printing concise info about ops 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 Perl lint B::Showlex Show lexical variables used in functions or files B::Stackobj Helper module for CC backend B::Stash Show what stashes are loaded 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 Perl code ByteLoader Load byte compiled perl code CGI Simple Common Gateway Interface Class CGI::Apache Backward compatibility module for 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 Backward compatibility module for defunct CGI::Switch CGI::Util Internal utilities used by CGI module CPAN Query, download and build perl modules from CPAN sites CPAN::FirstTime Utility for CPAN::Config file Initialization CPAN::Nox Wrapper around without using any XS module Carp Warn of errors (from perspective of caller) Carp::Heavy No user serviceable parts inside Class::ISA Report the search path for a class's ISA tree 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 (draft, subject to DB_File Perl5 access to Berkeley DB version 1.x Data::Dumper Stringified perl data structures, suitable for both printing and "eval" Devel::DProf A Perl code profiler Devel::Peek A data debugging tool for the XS programmer Devel::SelfStubber Generate stubs for a SelfLoading module Digest Modules that calculate message digests Digest::MD5 Perl interface to the MD5 Algorithm DirHandle Supply object methods for directory handles Dumpvalue Provides screen dump of Perl data. DynaLoader Dynamically load C libraries into Perl code Encode Character encodings Encode::Alias Alias definitions to encodings Encode::Byte Single Byte Encodings Encode::CJKConstants Internally used by Encode::??::ISO_2022_* Encode::CN China-based Chinese Encodings Encode::CN::HZ Internally used by Encode::CN Encode::Config Internally used by Encode Encode::EBCDIC EBCDIC Encodings Encode::Encoder Object Oriented Encoder Encode::Encoding Encode Implementation Base Class Encode::Guess Guesses encoding from data Encode::JP Japanese Encodings Encode::JP::H2Z Internally used by Encode::JP::2022_JP* Encode::JP::JIS7 Internally used by Encode::JP Encode::KR Korean Encodings Encode::KR::2022_KR Internally used by Encode::KR Encode::MIME::Header MIME 'B' and 'Q' header encoding Encode::PerlIO A detailed document on Encode and PerlIO Encode::Supported Encodings supported by Encode Encode::Symbol Symbol Encodings Encode::TW Taiwan-based Chinese Encodings Encode::Unicode Various Unicode Transformation Formats English Use nice English (or awk) names for ugly punctuation variables Env Perl module that imports environment variables as scalars or arrays Errno System errno constants Exporter Implements default import method for modules Exporter::Heavy Exporter guts ExtUtils::Command Utilities to replace common UNIX commands in Makefiles etc. ExtUtils::Command::MM Commands for the MM's to use in Makefiles ExtUtils::Constant Generate XS code to import C header constants ExtUtils::Embed Utilities for embedding Perl in C/C++ applications 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 OS adjusted ExtUtils::MakeMaker subclass ExtUtils::MM_Any Platform agnostic MM methods ExtUtils::MM_BeOS Methods to override UN*X behaviour in ExtUtils::MakeMaker ExtUtils::MM_Cygwin Methods to override UN*X behaviour in ExtUtils::MakeMaker ExtUtils::MM_DOS DOS specific subclass of ExtUtils::MM_Unix ExtUtils::MM_MacOS Methods to override UN*X behaviour in ExtUtils::MakeMaker ExtUtils::MM_NW5 Methods to override UN*X behaviour in ExtUtils::MakeMaker ExtUtils::MM_OS2 Methods to override UN*X behaviour in ExtUtils::MakeMaker ExtUtils::MM_UWIN U/WIN specific subclass of ExtUtils::MM_Unix ExtUtils::MM_Unix Methods used by ExtUtils::MakeMaker ExtUtils::MM_VMS Methods to override UN*X behaviour in ExtUtils::MakeMaker ExtUtils::MM_Win32 Methods to override UN*X behaviour in ExtUtils::MakeMaker ExtUtils::MM_Win95 Method to customize MakeMaker for Win9X ExtUtils::MY ExtUtils::MakeMaker subclass for customization ExtUtils::MakeMaker Create an extension Makefile ExtUtils::Manifest Utilities to write and check a MANIFEST file 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 C 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 directory tree. File::Glob Perl extension for BSD glob routine File::Path Create or remove directory trees File::Spec Portably perform operations on file names File::Spec::Cygwin Methods for Cygwin file specs File::Spec::Epoc Methods for Epoc file specs File::Spec::Functions Portably perform operations on file names File::Spec::Mac File::Spec for Mac OS (Classic) File::Spec::OS2 Methods for OS/2 file specs File::Spec::Unix File::Spec for Unix, base for other File::Spec modules File::Spec::VMS Methods for VMS file specs File::Spec::Win32 Methods for Win32 file specs File::Temp Return name and handle of a temporary file safely 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 Filter::Simple Simplified source filtering Filter::Util::Call Perl Source Filter Utility Module FindBin Locate directory of original perl script GDBM_File Perl5 access to the gdbm library. Getopt::Long Extended processing of command line options Getopt::Std Process single-character switches with switch clustering Hash::Util A selection of general-utility hash subroutines I18N::Collate Compare 8-bit scalar data according to the current locale I18N::LangTags Functions for dealing with RFC3066-style language tags I18N::LangTags::List Tags and names for human languages I18N::Langinfo Query locale information IO 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::Open2 Open a process for both reading and writing IPC::Open3 Open a process for reading, writing, and error handling IPC::SysV SysV IPC constants IPC::SysV::Msg SysV Msg IPC object class IPC::SysV::Semaphore SysV Semaphore IPC object class List::Util A selection of general-utility list subroutines Locale::Constants Constants for Locale codes Locale::Country ISO codes for country identification (ISO 3166) Locale::Currency ISO three letter codes for currency identification (ISO 4217) Locale::Language ISO two letter codes for language identification (ISO 639) Locale::Maketext Framework for localization Locale::Maketext::TPJ13 Article about software localization Locale::Script ISO codes for script identification (ISO 15924) MIME::Base64 Encoding and decoding of base64 strings MIME::Base64::QuotedPrint Encoding and decoding of quoted-printable strings Math::BigFloat Arbitrary size floating point math package Math::BigInt Arbitrary size integer math package Math::BigInt::Calc Pure Perl module to support Math::BigInt Math::BigInt::Scalar Pure Perl module to test Math::BigInt with scalars Math::BigRat Arbitrarily big rationales Math::Complex Complex numbers and associated mathematical functions Math::Trig Trigonometric functions Memoize Make functions faster by trading space for time Memoize::AnyDBM_File Glue to provide EXISTS for AnyDBM_File for Storable use Memoize::Expire Plug-in module for automatic expiration of memoized values Memoize::ExpireFile Test for Memoize expiration semantics Memoize::ExpireTest Test for Memoize expiration semantics Memoize::NDBM_File Glue to provide EXISTS for NDBM_File for Storable use Memoize::SDBM_File Glue to provide EXISTS for SDBM_File for Storable use Memoize::Storable Store Memoized data in Storable database NDBM_File Tied access to ndbm files NEXT Provide a pseudo-class NEXT that allows method redispatch Net::Cmd Network Command class (as used by FTP, SMTP etc) Net::Config Local configuration data for libnet Net::Domain Attempt to evaluate the current host's internet name and domain Net::FTP FTP Client class Net::NNTP NNTP Client class Net::Netrc OO interface to users netrc file Net::POP3 Post Office Protocol 3 Client class (RFC1939) Net::Ping Check a remote host for reachability Net::SMTP Simple Mail Transfer Protocol Client Net::Time Time and daytime network client interface Net::hostent By-name interface to Perl's built-in gethost*() functions Net::libnetFAQ Libnet Frequently Asked Questions 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 ODBM_File Tied access to odbm files Opcode Disable named opcodes when compiling perl code POSIX Perl interface to IEEE Std 1003.1 PerlIO On demand loader for PerlIO layers and root of PerlIO::* name space PerlIO::encoding Encoding layer PerlIO::scalar Support module for in-memory IO. PerlIO::via Helper class for PerlIO layers implemented in perl PerlIO::via::QuotedPrint PerlIO layer for quoted-printable strings Pod::Checker Check pod documents for syntax errors Pod::Find Find POD documents in directory trees Pod::Functions Group Perl's functions a la perlfunc.pod Pod::Html Module to convert pod files to HTML Pod::InputObjects Objects representing POD input paragraphs, commands, etc. Pod::LaTeX Convert Pod data to formatted Latex Pod::Man Convert POD data to formatted *roff input Pod::ParseLink Parse an L<> formatting code in POD text Pod::ParseUtils Helpers for POD parsing and conversion Pod::Parser Base class for creating POD filters and translators Pod::Plainer Perl extension for converting Pod to old style Pod. 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::Text::Overstrike Convert POD data to formatted overstrike text Pod::Text::Termcap Convert POD data to ASCII text with format escapes 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 Scalar::Util A selection of general-utility scalar subroutines 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 C socket.h defines and structure manipulators Storable Persistence for Perl data structures Switch A switch statement for Perl Symbol Manipulate Perl symbols and their names Sys::Hostname Try every conceivable way to get hostname Sys::Syslog Perl interface to the UNIX syslog(3) calls Term::ANSIColor Color screen output using ANSI escape sequences Term::Cap Perl termcap interface Term::Complete Perl word completion module Term::ReadLine Perl interface to various "readline" packages. Test Provides a simple framework for writing test scripts Test::Builder Backend for building test libraries Test::Harness Run perl standard test scripts with statistics Test::Harness::Assert Simple assert Test::Harness::Iterator Internal Test::Harness Iterator Test::Harness::Straps Detailed analysis of test results Test::More Yet another framework for writing test scripts Test::Simple Basic utilities for writing tests. Test::Tutorial A tutorial about writing really basic tests Text::Abbrev Create an abbreviation table from a list Text::Balanced Extract delimited text sequences from strings. Text::ParseWords Parse text into an array of tokens or array of arrays Text::Soundex Implementation of the Soundex Algorithm as Described by Knuth Text::Tabs Expand and unexpand tabs per the unix expand(1) and unexpand(1) Text::Wrap Line wrapping to form simple paragraphs Thread Manipulate threads in Perl (for old code only) Thread::Queue Thread-safe queues Thread::Semaphore Thread-safe semaphores Thread::Signal Start a thread which runs signal handlers reliably (for old code) Thread::Specific Thread-specific keys Tie::Array Base class for tied arrays Tie::File Access the lines of a disk file via a Perl array Tie::Handle Base class definitions for tied handles Tie::Hash Base class definitions for tied hashes Tie::Memoize Add data to hash when needed 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::HiRes High resolution alarm, sleep, gettimeofday, interval timers 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) Unicode::Collate Unicode Collation Algorithm Unicode::Normalize Unicode Normalization Forms Unicode::UCD Unicode character database User::grent By-name interface to Perl's built-in getgr*() functions User::pwent By-name interface to Perl's built-in getpw*() functions Win32 Interfaces to some Win32 API Functions XS::APItest Test the perl C API XS::Typemap Module to test the XS typemaps distributed with perl XSLoader Dynamically load C libraries into Perl code To find out all modules installed on your system, including those without documentation or outside the standard release, just do this: % find `perl -Te 'print "@INC"'` -name '*.pm' -print (The -T is here to prevent '.' from being listed in @INC.) They should all have their own documentation installed and accessible via your system man(1) command. 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 perl for details. If you have no system man command, you might try the perldoc program. Note also that the command "perldoc perllocal" gives you a (possibly incomplete) list of the modules that have been further installed on your system. (The perllocal.pod file is updated by the standard MakeMaker install process.) 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 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 Google.
CPAN stands for Comprehensive Perl Archive Network; it's a globally replicated trove of Perl materials, including documentation, style guides, tricks and traps, alternate ports to non-Unix systems and occasional binary distributions for these. Search engines for CPAN can be found at Most importantly, CPAN includes around a thousand unbundled modules, some of which require a C compiler to build. Major categories of mod- ules are: o Language Extensions and Documentation Tools o Development Support o Operating System Interfaces o Networking, Device Control (modems) and InterProcess Communication o Data Types and Data Type Utilities o Database Interfaces o User Interfaces o Interfaces to / Emulations of Other Programming Languages o File Names, File Systems and File Locking (see also File Handles) o String Processing, Language Text Processing, Parsing, and Searching 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 The list of the registered CPAN sites as of this writing follows. Please note that the sorting order is alphabetical on fields: Continent | |-->Country | |-->[state/province] | |-->ftp | |-->[http] and thus the North American servers happen to be listed between the European and the South American sites. You should try to choose one close to you. Africa South Africa Asia China India Indonesia Israel Japan Korea Philippines Russian Federation Saudi Arabia Singapore South Korea Taiwan Thailand Central America Costa Rica Europe Austria Belgium Bulgaria Croatia Czech Republic Denmark Estonia Finland France Germany Greece Hungary Iceland Ireland Italy Latvia Lithuania Netherlands Norway Poland Portugal Romania Russia Slovakia Slovenia Spain Sweden Switzerland Turkey Ukraine United Kingdom North America Alberta Manitoba Nova Scotia Ontario Quebec Mexico United States Alabama California Colorado Delaware District of Columbia Florida Illinois Indiana Kentucky Massachusetts Michigan New Jersey New York North Carolina Ohio Oklahoma Oregon Pennsylvania Tennessee Texas Utah Virginia ashington Wisconsin Oceania Australia New Zealand South America Argentina Brazil Chile RSYNC Mirrors For an up-to-date listing of CPAN sites, see or . 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 names- pace. 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 perlsub, perltoot, and AutoLoader for details about the AUTOLOAD mechanism. Guidelines for Module Creation o 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. o 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 construc- tor, 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 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 mod- ule 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 infor- mation 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. o 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. o 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. o 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 mod- ules. If developing modules for private internal or project specific use, that will never be released to the public, then you should ensure that their names will not clash with any future public module. You can do this either by using the reserved Local::* category or by using a category name that includes an underscore like Foo_Corp::*. 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. o 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 proba- bly 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 oth- ers to help you, they may be able to complete it for you! o 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. o Recent changes in this release, especially incompatibilities 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. o 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 dec- laration 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. o 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 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 for details. o 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 notifica- tion message as soon as possible after uploading else your file may get deleted automatically. Allow time for the file to be pro- cessed and/or check the file has been processed before announcing its location. FTP Archives for Perl Modules: Follow the instructions and links on: or upload to one of these sites: and notify <>. 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! o 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 o 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. o 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? o 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. o 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 o Complete applications rarely belong in the Perl Module Library. o 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. o Break-out the reusable code into one or more separate module files. o Take the opportunity to reconsider and redesign the interfaces. o 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)
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. perl v5.8.0 2003-02-18 PERLMODLIB(1)