PERLMODLIB(1)

NAME
perlmodlib - constructing new Perl modules and finding existing ones

THE PERL MODULE LIBRARY
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 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 classes at compile time

bigint
    Transparent BigInteger support for Perl

bignum
    Transparent BigNumber support for Perl

bigrat
    Transparent BigNumber/BigRational 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
    Produce 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)

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.pm

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 CPAN.pm without using any XS module

CPAN::Version
    Utility functions to compare CPAN versions

Carp
    Warn of errors (from perspective of caller)

Carp::Heavy
    Heavy machinery, 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

DBM_Filter
    Filter DBM keys/values

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::PPPort
    Perl/Pollution/Portability

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

Digest::base
    Digest base class

Digest::file
    Calculate digests of files

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

Encode::Unicode::UTF7
    UTF-7 encoding

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::Constant::Base
    Base class for ExtUtils::Constant objects

ExtUtils::Constant::Utils
    Helper functions for ExtUtils::Constant

ExtUtils::Constant::XS
    Base class for ExtUtils::Constant objects

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_AIX
    AIX specific subclass of ExtUtils::MM_Unix

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
    Once produced Makefiles for MacOS Classic

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_QNX
    QNX specific subclass of ExtUtils::MM_Unix

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_VOS
    VOS specific subclass of ExtUtils::MM_Unix

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 a module Makefile

ExtUtils::MakeMaker::Config
    Wrapper around Config.pm

ExtUtils::MakeMaker::FAQ
    Frequently Asked Questions About MakeMaker

ExtUtils::MakeMaker::Tutorial
    Writing a module with MakeMaker

ExtUtils::MakeMaker::bytes
    Version-agnostic bytes.pm

ExtUtils::MakeMaker::vmsish
    Platform-agnostic vmsish.pm

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
    Parse file paths into directory, filename and suffix.

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::Detect
    Detect the user's language preferences

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/float math package

Math::BigInt::Calc
    Pure Perl module to support Math::BigInt

Math::BigInt::CalcEmu
    Emulate low-level math with BigInt code

Math::BigRat
    Arbitrary big rational numbers

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 (et al) 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
    In-memory IO, scalar 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::Perldoc::ToChecker
    Let Perldoc check Pod for errors

Pod::Perldoc::ToMan
    Let Perldoc render Pod as man pages

Pod::Perldoc::ToNroff
    Let Perldoc convert Pod to nroff

Pod::Perldoc::ToPod
    Let Perldoc render Pod as ... Pod!

Pod::Perldoc::ToRtf
    Let Perldoc render Pod as RTF

Pod::Perldoc::ToText
    Let Perldoc render Pod as plaintext

Pod::Perldoc::ToTk
    Let Perldoc use Tk::Pod to render Pod

Pod::Perldoc::ToXml
    Let Perldoc render Pod as XML

Pod::PlainText
    Convert POD data to formatted ASCII text

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::Builder::Module
    Base class for test modules

Test::Builder::Tester
    Test testsuites that have been built with

Test::Builder::Tester::Color
    Turn on colour in Test::Builder::Tester

Test::Harness
    Run Perl standard test scripts with statistics

Test::Harness::Assert
    Simple assert

Test::Harness::Iterator
    Internal Test::Harness Iterator

Test::Harness::Point
    Object for tracking a single test point

Test::Harness::Straps
    Detailed analysis of test results

Test::Harness::TAP
    Documentation for the TAP format

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

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 use the following command (under the default win32 shell, double quotes should be used instead of single quotes).

    % perl -MFile::Find=find -MFile::Spec::Functions -Tlwe \
      'find { wanted => sub { print canonpath $_ if /\.pm\z/ },
      no_chdir => 1 }, @INC'

(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
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 http://www.cpan.org/

Most importantly, CPAN includes around a thousand unbundled modules, some of which require a C compiler to build. Major categories of modules are:

•   Language Extensions and Documentation Tools

•   Development Support

•   Operating System Interfaces

•   Networking, Device Control (modems) and InterProcess Communication

•   Data Types and Data Type Utilities

•   Database Interfaces

•   User Interfaces

•   Interfaces to / Emulations of Other Programming Languages

•   File Names, File Systems and File Locking (see also File Handles)

•   String Processing, Language Text Processing, Parsing, and Searching

•   Option, Argument, Parameter, and Configuration File Processing

•   Internationalization and Locale

•   Authentication, Security, and Encryption

•   World Wide Web, HTML, HTTP, CGI, MIME

•   Server and Daemon Utilities

•   Archiving and Compression

•   Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing

•   Mail and Usenet News

•   Control Flow Utilities (callbacks and exceptions etc)

•   File Handle and Input/Output Stream Utilities

•   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
                          http://ftp.rucus.ru.ac.za/pub/perl/CPAN/
                          ftp://ftp.rucus.ru.ac.za/pub/perl/CPAN/
                          ftp://ftp.is.co.za/programming/perl/CPAN/
                          ftp://ftp.saix.net/pub/CPAN/
                          ftp://ftp.sun.ac.za/CPAN/CPAN/

  Asia

China
                          http://cpan.linuxforum.net/
                          http://cpan.shellhung.org/
                          ftp://ftp.shellhung.org/pub/CPAN
                          ftp://mirrors.hknet.com/CPAN

Indonesia
                          http://mirrors.tf.itb.ac.id/cpan/
                          http://cpan.cbn.net.id/
                          ftp://ftp.cbn.net.id/mirror/CPAN

Israel
                          ftp://ftp.iglu.org.il/pub/CPAN/
                          http://cpan.lerner.co.il/
                          http://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
                          ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/

Japan
                          ftp://ftp.u-aizu.ac.jp/pub/CPAN
                          ftp://ftp.kddlabs.co.jp/CPAN/
                          ftp://ftp.ayamura.org/pub/CPAN/
                          ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
                          http://ftp.cpan.jp/
                          ftp://ftp.cpan.jp/CPAN/
                          ftp://ftp.dti.ad.jp/pub/lang/CPAN/
                          ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/

Malaysia
                          http://cpan.MyBSD.org.my
                          http://mirror.leafbug.org/pub/CPAN
                          http://ossig.mncc.com.my/mirror/pub/CPAN

Russian Federation
                          http://cpan.tomsk.ru
                          ftp://cpan.tomsk.ru/

Saudi Arabia
                          ftp://ftp.isu.net.sa/pub/CPAN/

Singapore
                          http://CPAN.en.com.sg/
                          ftp://cpan.en.com.sg/
                          http://mirror.averse.net/pub/CPAN
                          ftp://mirror.averse.net/pub/CPAN
                          http://cpan.oss.eznetsols.org
                          ftp://ftp.oss.eznetsols.org/cpan

South Korea
                          http://CPAN.bora.net/
                          ftp://ftp.bora.net/pub/CPAN/
                          http://mirror.kr.FreeBSD.org/CPAN
                          ftp://ftp.kr.FreeBSD.org/pub/CPAN

Taiwan
                          ftp://ftp.nctu.edu.tw/UNIX/perl/CPAN
                          http://cpan.cdpa.nsysu.edu.tw/
                          ftp://cpan.cdpa.nsysu.edu.tw/pub/CPAN
                          http://ftp.isu.edu.tw/pub/CPAN
                          ftp://ftp.isu.edu.tw/pub/CPAN
                          ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
                          http://ftp.tku.edu.tw/pub/CPAN/
                          ftp://ftp.tku.edu.tw/pub/CPAN/

Thailand
                          ftp://ftp.loxinfo.co.th/pub/cpan/
                          ftp://ftp.cs.riubon.ac.th/pub/mirrors/CPAN/

  Central America

Costa Rica
                          http://ftp.ucr.ac.cr/Unix/CPAN/
                          ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/

  Europe

Austria
                          http://cpan.inode.at/
                          ftp://cpan.inode.at
                          ftp://ftp.tuwien.ac.at/pub/CPAN/

Belgium
                          http://ftp.easynet.be/pub/CPAN/
                          ftp://ftp.easynet.be/pub/CPAN/
                          http://cpan.skynet.be
                          ftp://ftp.cpan.skynet.be/pub/CPAN
                          ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/

Bosnia and Herzegovina
                          http://cpan.blic.net/

Bulgaria
                          http://cpan.online.bg
                          ftp://cpan.online.bg/cpan
                          http://cpan.zadnik.org
                          ftp://ftp.zadnik.org/mirrors/CPAN/
                          http://cpan.lirex.net/
                          ftp://ftp.lirex.net/pub/mirrors/CPAN

Croatia
                          http://ftp.linux.hr/pub/CPAN/
                          ftp://ftp.linux.hr/pub/CPAN/

Czech Republic
                          ftp://ftp.fi.muni.cz/pub/CPAN/
                          ftp://sunsite.mff.cuni.cz/MIRRORS/ftp.funet.fi/pub/languages/perl/CPAN/

Denmark
                          http://mirrors.sunsite.dk/cpan/
                          ftp://sunsite.dk/mirrors/cpan/
                          http://cpan.cybercity.dk
                          http://www.cpan.dk/CPAN/
                          ftp://www.cpan.dk/ftp.cpan.org/CPAN/

Estonia
                          ftp://ftp.ut.ee/pub/languages/perl/CPAN/

Finland
                          ftp://ftp.funet.fi/pub/languages/perl/CPAN/
                          http://mirror.eunet.fi/CPAN

France
                          http://www.enstimac.fr/Perl/CPAN
                          http://ftp.u-paris10.fr/perl/CPAN
                          ftp://ftp.u-paris10.fr/perl/CPAN
                          http://cpan.mirrors.easynet.fr/
                          ftp://cpan.mirrors.easynet.fr/pub/ftp.cpan.org/
                          ftp://ftp.club-internet.fr/pub/perl/CPAN/
                          http://fr.cpan.org/
                          ftp://ftp.lip6.fr/pub/perl/CPAN/
                          ftp://ftp.oleane.net/pub/mirrors/CPAN/
                          ftp://ftp.pasteur.fr/pub/computing/CPAN/
                          http://mir2.ovh.net/ftp.cpan.org
                          ftp://mir1.ovh.net/ftp.cpan.org
                          http://ftp.crihan.fr/mirrors/ftp.cpan.org/
                          ftp://ftp.crihan.fr/mirrors/ftp.cpan.org/
                          http://ftp.u-strasbg.fr/CPAN
                          ftp://ftp.u-strasbg.fr/CPAN
                          ftp://cpan.cict.fr/pub/CPAN/
                          ftp://ftp.uvsq.fr/pub/perl/CPAN/

Germany
                          ftp://ftp.rub.de/pub/CPAN/
                          ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/CPAN/
                          ftp://ftp.uni-erlangen.de/pub/source/CPAN/
                          ftp://ftp-stud.fht-esslingen.de/pub/Mirrors/CPAN
                          http://pandemonium.tiscali.de/pub/CPAN/
                          ftp://pandemonium.tiscali.de/pub/CPAN/
                          http://ftp.gwdg.de/pub/languages/perl/CPAN/
                          ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
                          ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
                          ftp://ftp.leo.org/pub/CPAN/
                          http://cpan.noris.de/
                          ftp://cpan.noris.de/pub/CPAN/
                          ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
                          ftp://ftp.gmd.de/mirrors/CPAN/

Greece
                          ftp://ftp.acn.gr/pub/lang/perl
                          ftp://ftp.forthnet.gr/pub/languages/perl/CPAN
                          ftp://ftp.ntua.gr/pub/lang/perl/

Hungary
                          http://ftp.kfki.hu/packages/perl/CPAN/
                          ftp://ftp.kfki.hu/pub/packages/perl/CPAN/

Iceland
                          http://ftp.rhnet.is/pub/CPAN/
                          ftp://ftp.rhnet.is/pub/CPAN/

Ireland
                          http://cpan.indigo.ie/
                          ftp://cpan.indigo.ie/pub/CPAN/
                          http://ftp.heanet.ie/mirrors/ftp.perl.org/pub/CPAN
                          ftp://ftp.heanet.ie/mirrors/ftp.perl.org/pub/CPAN
                          http://sunsite.compapp.dcu.ie/pub/perl/
                          ftp://sunsite.compapp.dcu.ie/pub/perl/

Italy
                          http://cpan.nettuno.it/
                          http://gusp.dyndns.org/CPAN/
                          ftp://gusp.dyndns.org/pub/CPAN
                          http://softcity.iol.it/cpan
                          ftp://softcity.iol.it/pub/cpan
                          ftp://ftp.unina.it/pub/Other/CPAN/CPAN/
                          ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
                          ftp://cis.uniRoma2.it/CPAN/
                          ftp://ftp.edisontel.it/pub/CPAN_Mirror/
                          http://cpan.flashnet.it/
                          ftp://ftp.flashnet.it/pub/CPAN/

Latvia
                          http://kvin.lv/pub/CPAN/

Lithuania
                          ftp://ftp.unix.lt/pub/CPAN/

Netherlands
                          ftp://download.xs4all.nl/pub/mirror/CPAN/
                          ftp://ftp.nl.uu.net/pub/CPAN/
                          ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
                          http://cpan.cybercomm.nl/
                          ftp://mirror.cybercomm.nl/pub/CPAN
                          ftp://mirror.vuurwerk.nl/pub/CPAN/
                          ftp://ftp.cpan.nl/pub/CPAN/
                          http://ftp.easynet.nl/mirror/CPAN
                          ftp://ftp.easynet.nl/mirror/CPAN
                          http://archive.cs.uu.nl/mirror/CPAN/
                          ftp://ftp.cs.uu.nl/mirror/CPAN/

Norway
                          ftp://ftp.uninett.no/pub/languages/perl/CPAN
                          ftp://ftp.uit.no/pub/languages/perl/cpan/

Poland
                          ftp://ftp.mega.net.pl/CPAN
                          ftp://ftp.man.torun.pl/pub/doc/CPAN/
                          ftp://sunsite.icm.edu.pl/pub/CPAN/

Portugal
                          ftp://ftp.ua.pt/pub/CPAN/
                          ftp://perl.di.uminho.pt/pub/CPAN/
                          http://cpan.dei.uc.pt/
                          ftp://ftp.dei.uc.pt/pub/CPAN
                          ftp://ftp.nfsi.pt/pub/CPAN
                          http://ftp.linux.pt/pub/mirrors/CPAN
                          ftp://ftp.linux.pt/pub/mirrors/CPAN
                          http://cpan.ip.pt/
                          ftp://cpan.ip.pt/pub/cpan/
                          http://cpan.telepac.pt/
                          ftp://ftp.telepac.pt/pub/cpan/

Romania
                          ftp://ftp.bio-net.ro/pub/CPAN
                          ftp://ftp.kappa.ro/pub/mirrors/ftp.perl.org/pub/CPAN/
                          ftp://ftp.lug.ro/CPAN
                          ftp://ftp.roedu.net/pub/CPAN/
                          ftp://ftp.dntis.ro/pub/cpan/
                          ftp://ftp.iasi.roedu.net/pub/mirrors/ftp.cpan.org/
                          http://cpan.ambra.ro/
                          ftp://ftp.ambra.ro/pub/CPAN
                          ftp://ftp.dnttm.ro/pub/CPAN/
                          ftp://ftp.lasting.ro/pub/CPAN
                          ftp://ftp.timisoara.roedu.net/mirrors/CPAN/

Russia
                          ftp://ftp.chg.ru/pub/lang/perl/CPAN/
                          http://cpan.rinet.ru/
                          ftp://cpan.rinet.ru/pub/mirror/CPAN/
                          ftp://ftp.aha.ru/pub/CPAN/
                          ftp://ftp.corbina.ru/pub/CPAN/
                          http://cpan.sai.msu.ru/
                          ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/

Slovakia
                          ftp://ftp.cvt.stuba.sk/pub/CPAN/

Slovenia
                          ftp://ftp.arnes.si/software/perl/CPAN/

Spain
                          http://cpan.imasd.elmundo.es/
                          ftp://ftp.rediris.es/mirror/CPAN/
                          ftp://ftp.ri.telefonica-data.net/CPAN
                          ftp://ftp.etse.urv.es/pub/perl/

Sweden
                          http://ftp.du.se/CPAN/
                          ftp://ftp.du.se/pub/CPAN/
                          http://mirror.dataphone.se/CPAN
                          ftp://mirror.dataphone.se/pub/CPAN
                          ftp://ftp.sunet.se/pub/lang/perl/CPAN/

Switzerland
                          http://cpan.mirror.solnet.ch/
                          ftp://ftp.solnet.ch/mirror/CPAN/
                          ftp://ftp.danyk.ch/CPAN/
                          ftp://sunsite.cnlab-switch.ch/mirror/CPAN/

Turkey
                          http://ftp.ulak.net.tr/perl/CPAN/
                          ftp://ftp.ulak.net.tr/perl/CPAN
                          ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/

Ukraine
                          http://cpan.org.ua/
                          ftp://cpan.org.ua/
                          ftp://ftp.perl.org.ua/pub/CPAN/
                          http://no-more.kiev.ua/CPAN/
                          ftp://no-more.kiev.ua/pub/CPAN/

United Kingdom
                          http://www.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN
                          ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/
                          http://cpan.teleglobe.net/
                          ftp://cpan.teleglobe.net/pub/CPAN
                          http://cpan.mirror.anlx.net/
                          ftp://ftp.mirror.anlx.net/CPAN/
                          http://cpan.etla.org/
                          ftp://cpan.etla.org/pub/CPAN
                          ftp://ftp.demon.co.uk/pub/CPAN/
                          http://cpan.m.flirble.org/
                          ftp://ftp.flirble.org/pub/languages/perl/CPAN/
                          ftp://ftp.plig.org/pub/CPAN/
                          http://cpan.hambule.co.uk/
                          http://cpan.mirrors.clockerz.net/
                          ftp://ftp.clockerz.net/pub/CPAN/
                          ftp://usit.shef.ac.uk/pub/packages/CPAN/

  North America

Canada
    Alberta
                              http://cpan.sunsite.ualberta.ca/
                              ftp://cpan.sunsite.ualberta.ca/pub/CPAN/

    Manitoba
                              http://theoryx5.uwinnipeg.ca/pub/CPAN/
                              ftp://theoryx5.uwinnipeg.ca/pub/CPAN/

    Nova Scotia
                              ftp://cpan.chebucto.ns.ca/pub/CPAN/

    Ontario
                              ftp://ftp.nrc.ca/pub/CPAN/

Mexico
                          http://cpan.azc.uam.mx
                          ftp://cpan.azc.uam.mx/mirrors/CPAN
                          http://www.cpan.unam.mx/
                          ftp://ftp.unam.mx/pub/CPAN
                          http://www.msg.com.mx/CPAN/
                          ftp://ftp.msg.com.mx/pub/CPAN/

United States
    Alabama
                              http://mirror.hiwaay.net/CPAN/
                              ftp://mirror.hiwaay.net/CPAN/

    California
                              http://cpan.develooper.com/
                              http://www.cpan.org/
                              ftp://cpan.valueclick.com/pub/CPAN/
                              http://www.mednor.net/ftp/pub/mirrors/CPAN/
                              ftp://ftp.mednor.net/pub/mirrors/CPAN/
                              http://mirrors.gossamer-threads.com/CPAN
                              ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
                              http://mirrors.kernel.org/cpan/
                              ftp://mirrors.kernel.org/pub/CPAN
                              http://cpan-sj.viaverio.com/
                              ftp://cpan-sj.viaverio.com/pub/CPAN/
                              http://cpan.digisle.net/
                              ftp://cpan.digisle.net/pub/CPAN
                              http://www.perl.com/CPAN/
                              http://www.uberlan.net/CPAN

    Colorado
                              ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
                              http://cpan.four10.com

    Delaware
                              http://ftp.lug.udel.edu/pub/CPAN
                              ftp://ftp.lug.udel.edu/pub/CPAN

    District of Columbia
                              ftp://ftp.dc.aleron.net/pub/CPAN/

    Florida
                              ftp://ftp.cise.ufl.edu/pub/mirrors/CPAN/
                              http://mirror.csit.fsu.edu/pub/CPAN/
                              ftp://mirror.csit.fsu.edu/pub/CPAN/
                              http://cpan.mirrors.nks.net/

    Indiana
                              ftp://ftp.uwsg.iu.edu/pub/perl/CPAN/
                              http://cpan.netnitco.net/
                              ftp://cpan.netnitco.net/pub/mirrors/CPAN/
                              http://archive.progeny.com/CPAN/
                              ftp://archive.progeny.com/CPAN/
                              http://fx.saintjoe.edu/pub/CPAN
                              ftp://ftp.saintjoe.edu/pub/CPAN
                              http://csociety-ftp.ecn.purdue.edu/pub/CPAN
                              ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN

    Kentucky
                              http://cpan.uky.edu/
                              ftp://cpan.uky.edu/pub/CPAN/
                              http://slugsite.louisville.edu/cpan
                              ftp://slugsite.louisville.edu/CPAN

    Massachusetts
                              http://mirrors.towardex.com/CPAN
                              ftp://mirrors.towardex.com/pub/CPAN
                              ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/

    Michigan
                              ftp://cpan.cse.msu.edu/
                              http://cpan.calvin.edu/pub/CPAN
                              ftp://cpan.calvin.edu/pub/CPAN

    Nevada
                              http://www.oss.redundant.com/pub/CPAN
                              ftp://www.oss.redundant.com/pub/CPAN

    New Jersey
                              http://ftp.cpanel.net/pub/CPAN/
                              ftp://ftp.cpanel.net/pub/CPAN/
                              http://cpan.teleglobe.net/
                              ftp://cpan.teleglobe.net/pub/CPAN

    New York
                              http://cpan.belfry.net/
                              http://cpan.erlbaum.net/
                              ftp://cpan.erlbaum.net/
                              http://cpan.thepirtgroup.com/
                              ftp://cpan.thepirtgroup.com/
                              ftp://ftp.stealth.net/pub/CPAN/
                              http://www.rge.com/pub/languages/perl/
                              ftp://ftp.rge.com/pub/languages/perl/

    North Carolina
                              http://www.ibiblio.org/pub/languages/perl/CPAN
                              ftp://ftp.ibiblio.org/pub/languages/perl/CPAN
                              ftp://ftp.duke.edu/pub/perl/
                              ftp://ftp.ncsu.edu/pub/mirror/CPAN/

    Oklahoma
                              ftp://ftp.ou.edu/mirrors/CPAN/

    Oregon
                              ftp://ftp.orst.edu/pub/CPAN

    Pennsylvania
                              http://ftp.epix.net/CPAN/
                              ftp://ftp.epix.net/pub/languages/perl/
                              http://mirrors.phenominet.com/pub/CPAN/
                              ftp://mirrors.phenominet.com/pub/CPAN/
                              http://cpan.pair.com/
                              ftp://cpan.pair.com/pub/CPAN/
                              ftp://carroll.cac.psu.edu/pub/CPAN/

    Tennessee
                              ftp://ftp.sunsite.utk.edu/pub/CPAN/

    Texas
                              http://ftp.sedl.org/pub/mirrors/CPAN/
                              http://www.binarycode.org/cpan
                              ftp://mirror.telentente.com/pub/CPAN
                              http://mirrors.theonlinerecordstore.com/CPAN

    Utah
                              ftp://mirror.xmission.com/CPAN/

    Virginia
                              http://cpan-du.viaverio.com/
                              ftp://cpan-du.viaverio.com/pub/CPAN/
                              http://mirrors.rcn.net/pub/lang/CPAN/
                              ftp://mirrors.rcn.net/pub/lang/CPAN/
                              http://perl.secsup.org/
                              ftp://perl.secsup.org/pub/perl/
                              http://noc.cvaix.com/mirrors/CPAN/

    Washington
                              http://cpan.llarian.net/
                              ftp://cpan.llarian.net/pub/CPAN/
                              http://cpan.mirrorcentral.com/
                              ftp://ftp.mirrorcentral.com/pub/CPAN/
                              ftp://ftp-mirror.internap.com/pub/CPAN/

    Wisconsin
                              http://mirror.sit.wisc.edu/pub/CPAN/
                              ftp://mirror.sit.wisc.edu/pub/CPAN/
                              http://mirror.aphix.com/CPAN
                              ftp://mirror.aphix.com/pub/CPAN

  Oceania

Australia
                          http://ftp.planetmirror.com/pub/CPAN/
                          ftp://ftp.planetmirror.com/pub/CPAN/
                          ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
                          ftp://cpan.topend.com.au/pub/CPAN/
                          http://cpan.mirrors.ilisys.com.au

New Zealand
                          ftp://ftp.auckland.ac.nz/pub/perl/CPAN/

United States
                          http://aniani.ifa.hawaii.edu/CPAN/
                          ftp://aniani.ifa.hawaii.edu/CPAN/

  South America

Argentina
                          ftp://mirrors.bannerlandia.com.ar/mirrors/CPAN/
                          http://www.linux.org.ar/mirrors/cpan
                          ftp://ftp.linux.org.ar/mirrors/cpan

Brazil
                          ftp://cpan.pop-mg.com.br/pub/CPAN/
                          ftp://ftp.matrix.com.br/pub/perl/CPAN/
                          http://cpan.hostsul.com.br/
                          ftp://cpan.hostsul.com.br/

Chile
                          http://cpan.netglobalis.net/
                          ftp://cpan.netglobalis.net/pub/CPAN/

  RSYNC Mirrors
                      www.linux.org.ar::cpan
                      theoryx5.uwinnipeg.ca::CPAN
                      ftp.shellhung.org::CPAN
                      rsync.nic.funet.fi::CPAN
                      ftp.u-paris10.fr::CPAN
                      mir1.ovh.net::CPAN
                      rsync://ftp.crihan.fr::CPAN
                      ftp.gwdg.de::FTP/languages/perl/CPAN/
                      ftp.leo.org::CPAN
                      ftp.cbn.net.id::CPAN
                      rsync://ftp.heanet.ie/mirrors/ftp.perl.org/pub/CPAN
                      ftp.iglu.org.il::CPAN
                      gusp.dyndns.org::cpan
                      ftp.kddlabs.co.jp::cpan
                      ftp.ayamura.org::pub/CPAN/
                      mirror.leafbug.org::CPAN
                      rsync.en.com.sg::CPAN
                      mirror.averse.net::cpan
                      rsync.oss.eznetsols.org
                      ftp.kr.FreeBSD.org::CPAN
                      ftp.solnet.ch::CPAN
                      cpan.cdpa.nsysu.edu.tw::CPAN
                      cpan.teleglobe.net::CPAN
                      rsync://rsync.mirror.anlx.net::CPAN
                      ftp.sedl.org::cpan
                      ibiblio.org::CPAN
                      cpan-du.viaverio.com::CPAN
                      aniani.ifa.hawaii.edu::CPAN
                      archive.progeny.com::CPAN
                      rsync://slugsite.louisville.edu::CPAN
                      mirror.aphix.com::CPAN
                      cpan.teleglobe.net::CPAN
                      ftp.lug.udel.edu::cpan
                      mirrors.kernel.org::mirrors/CPAN
                      mirrors.phenominet.com::CPAN
                      cpan.pair.com::CPAN
                      cpan-sj.viaverio.com::CPAN
                      mirror.csit.fsu.edu::CPAN
                      csociety-ftp.ecn.purdue.edu::CPAN

For an up-to-date listing of CPAN sites, see http://www.cpan.org/SITES or ftp://www.cpan.org/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 perlsub, perltoot, and AutoLoader 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 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 "@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.

    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.

•   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:

    •   A description of the module/package/extension etc.

    •   A copyright notice - see below.

    •   Prerequisites - what else you may need to have.

    •   How to build it - possible changes to Makefile.PL etc.

    •   How to install it.

    •   Recent changes in this release, especially incompatibilities

    •   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, or perlgpl and perlartistic). 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 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.

    •   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.cpan.org/modules/00modlist.long.html
           http://www.cpan.org/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!

    •   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:

    •   Adds the standard Module prologue lines

    •   Converts package specifiers from ' to ::

    •   Converts die(...) to croak(...)

    •   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.

•   Break-out the reusable code into one or more separate module files.

•   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.