perlmodlib - constructing new Perl modules and finding existing ones

- NAME
- THE PERL MODULE LIBRARY

- Pragmatic Modules
- Standard Modules
- Extension Modules

- CPAN

- Africa
- Asia
- Central America
- Europe
- North America
- Oceania
- South America
- RSYNC Mirrors

- Modules: Creation, Use, and Abuse

- Guidelines for Module Creation
- Guidelines for Converting Perl 4 Library Scripts into Modules
- Guidelines for Reusing Application Code

- NOTE

# 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 the perl manpage 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 the perlsub manpage, the perltoot manpage, and the AutoLoader manpage for details about the AUTOLOAD mechanism.

## Guidelines for Module Creation

- Do similar modules already exist in some form?

  If so, please try to reuse the existing modules either in whole or by inheriting useful features into a new class. If this is not practical try to get together with the module authors to work on extending or enhancing the functionality of the existing modules. A perfect example is the plethora of packages in perl4 for dealing with command line options.

  If you are writing a module to expand an already existing set of modules, please coordinate with the author of the package. It helps if you follow the same naming scheme and module interaction scheme as the original author.

- Try to design the new module to be easy to extend and reuse.

  Try to `use warnings;` (or `use warnings qw(...);`). Remember that you can add `no warnings qw(...);` to individual blocks of code that need less warnings.

  Use blessed references. Use the two argument form of bless to bless into the class name given as the first parameter of the constructor, e.g.,:

       sub new {
           my $class = shift;
           return bless {}, $class;
       }

  or even this if you'd like it to be used as either a static or a virtual method.

       sub new {
           my $self  = shift;
           my $class = ref($self) || $self;
           return bless {}, $class;
       }

  Pass arrays as references so more parameters can be added later (it's also faster). Convert functions into methods where appropriate. Split large methods into smaller more flexible ones. Inherit methods from other modules if appropriate.

  Avoid class name tests like: `die "Invalid" unless ref $ref eq 'FOO'`. Generally you can delete the `eq 'FOO'` part with no harm at all. Let the objects look after themselves! Generally, avoid hard-wired class names as far as possible.

  Avoid `$r->Class::func()` where using `@ISA=qw(... Class ...)` and `$r->func()` would work (see the perlbot manpage for more details).

  Use autosplit so little used or newly added functions won't be a burden to programs that don't use them. Add test functions to the module after __END__ either using AutoSplit or by saying:

       eval join('',<main::DATA>) || die $@ unless caller();

  Does your module pass the 'empty subclass' test? If you say `@SUBCLASS::ISA = qw(YOURCLASS);` your applications should be able to use SUBCLASS in exactly the same way as YOURCLASS. For example, does your application still work if you change: `$obj = new YOURCLASS;` into: `$obj = new SUBCLASS;` ?

  Avoid keeping any state information in your packages. It makes it difficult for multiple other packages to use yours. Keep state information in objects.

  Always use -w.

  Try to `use strict;` (or `use strict qw(...);`). Remember that you can add `no strict qw(...);` to individual blocks of code that need less strictness.

  Always use -w.

  Follow the guidelines in the `perlstyle(1)` manual.

  Always use -w.

- Some simple style guidelines

  The perlstyle manual supplied with Perl has many helpful points.

  Coding style is a matter of personal taste. Many people evolve their style over several years as they learn what helps them write and maintain good code. Here's one set of assorted suggestions that seem to be widely used by experienced developers:

  Use underscores to separate words. It is generally easier to read $var_names_like_this than $VarNamesLikeThis, especially for non-native speakers of English. It's also a simple rule that works consistently with VAR_NAMES_LIKE_THIS.

  Package/Module names are an exception to this rule. Perl informally reserves lowercase module names for 'pragma' modules like integer and strict. Other modules normally begin with a capital letter and use mixed case with no underscores (need to be short and portable).

  You may find it helpful to use letter case to indicate the scope or nature of a variable. For example:

       $ALL_CAPS_HERE   constants only (beware clashes with Perl vars)
       $Some_Caps_Here  package-wide global/static
       $no_caps_here    function scope my() or local() variables

  Function and method names seem to work best as all lowercase. e.g., `$obj->as_string()`.

  You can use a leading underscore to indicate that a variable or function should not be used outside the package that defined it.

- Select what to export.

  Do NOT export method names!

  Do NOT export anything else by default without a good reason!

  Exports pollute the namespace of the module user. If you must export try to use @EXPORT_OK in preference to @EXPORT and avoid short or common names to reduce the risk of name clashes.

  Generally anything not exported is still accessible from outside the module using the ModuleName::item_name (or `$blessed_ref->method`) syntax. By convention you can use a leading underscore on names to indicate informally that they are 'internal' and not for public use.

  (It is actually possible to get private functions by saying: `my $subref = sub { ... }; &$subref;`. But there's no way to call that directly as a method, because a method must have a name in the symbol table.)

  As a general rule, if the module is trying to be object oriented then export nothing. If it's just a collection of functions then @EXPORT_OK anything but use @EXPORT with caution.

- Select a name for the module.

  This name should be as descriptive, accurate, and complete as possible. Avoid any risk of ambiguity. Always try to use two or more whole words. Generally the name should reflect what is special about what the module does rather than how it does it. Please use nested module names to group informally or categorize a module. There should be a very good reason for a module not to have a nested name. Module names should begin with a capital letter.

  Having 57 modules all called Sort will not make life easy for anyone (though having 23 called Sort::Quick is only marginally better :-). Imagine someone trying to install your module alongside many others. If in any doubt ask for suggestions in comp.lang.perl.misc.

  If you are developing a suite of related modules/classes it's good practice to use nested classes with a common prefix as this will avoid namespace clashes. For example: Xyz::Control, Xyz::View, Xyz::Model etc. Use the modules in this list as a naming guide.

  If adding a new module to a set, follow the original author's standards for naming modules and the interface to methods in those modules.

  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 the perlgpl manpage and the perlartistic manpage). Larry has good reasons for NOT just using the GNU GPL.

    My personal recommendation, out of respect for Larry, Perl, and the Perl community at large is to state something simply like:

         Copyright (c) 1995 Your Name. All rights reserved.
         This program is free software; you can redistribute it and/or
         modify it under the same terms as Perl itself.

    This statement should at least appear in the README file. You may also wish to include it in a Copying file and your source files. Remember to include the other words in addition to the Copyright.

  - Give the module a version/issue/release number.

    To be fully compatible with the Exporter and MakeMaker modules you should store your module's version number in a non-my package variable called $VERSION. This should be a floating point number with at least two digits after the decimal (i.e., hundredths, e.g, `$VERSION = "0.01"`). Don't use a ``1.3.2'' style version. See the Exporter manpage for details.

    It may be handy to add a function or method to retrieve the number. Use the number in announcements and archive file names when releasing the module (ModuleName-1.02.tar.Z). See perldoc ExtUtils::MakeMaker.pm for details.

  - How to release and distribute a module.

    It's good idea to post an announcement of the availability of your module (or the module itself if small) to the comp.lang.perl.announce Usenet newsgroup. This will at least ensure very wide once-off distribution.

    If possible, register the module with CPAN. You should include details of its location in your announcement.

    Some notes about ftp archives: Please use a long descriptive file name that includes the version number. Most incoming directories will not be readable/listable, i.e., you won't be able to see your file after uploading it. Remember to send your email notification message as soon as possible after uploading else your file may get deleted automatically. Allow time for the file to be processed and/or check the file has been processed before announcing its location.

    FTP Archives for Perl Modules:

    Follow the instructions and links on:

           http://www.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.

perlmodlib - constructing new Perl modules and finding existing ones