Perl 5 version 28.3 documentation



perlmodlib - constructing new Perl modules and finding existing ones


Many modules are included in the Perl distribution. These are described below, and all end in .pm. You may discover compiled library files (usually ending in .so) or small pieces of modules to be autoloaded (ending in .al); these were automatically generated by the installation process. You may also discover files in the library directory that end in either .pl or .ph. These are old libraries 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:

  1. no integer;
  2. no strict 'refs';
  3. 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).

  • arybase

    Set indexing base via $[

  • attributes

    Get/set subroutine or variable attributes

  • autodie

    Replace functions with ones that succeed or die with lexical scope

  • autodie::exception

    Exceptions from autodying functions.

  • autodie::exception::system

    Exceptions from autodying system().

  • autodie::hints

    Provide hints about user subroutines to autodie

  • autodie::skip

    Skip a package when throwing autodie exceptions

  • autouse

    Postpone load of modules until a function is used

  • base

    Establish an ISA 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

    Expose the individual bytes of characters

  • charnames

    Access to Unicode character names and named character sequences; also define character names

  • constant

    Declare constants

  • deprecate

    Perl pragma for deprecating the core version of a module

  • diagnostics

    Produce verbose warning diagnostics

  • encoding

    Allows you to write your script in non-ASCII and non-UTF-8

  • encoding::warnings

    Warn on implicit encoding conversions

  • experimental

    Experimental features made easy

  • feature

    Enable new features

  • 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

  • lib

    Manipulate @INC at compile time

  • locale

    Use or avoid POSIX locales for built-in operations

  • mro

    Method Resolution Order

  • ok

    Alternative to Test::More::use_ok

  • open

    Set default PerlIO layers for input and output

  • ops

    Restrict unsafe operations when compiling

  • overload

    Package for overloading Perl operations

  • overloading

    Lexically control overloading

  • parent

    Establish an ISA relationship with base classes at compile time

  • re

    Alter regular expression behaviour

  • sigtrap

    Enable simple signal handling

  • sort

    Control sort() behaviour

  • strict

    Restrict unsafe constructs

  • subs

    Predeclare subroutine names

  • threads

    Perl interpreter-based threads

  • 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

  • version

    Perl extension for Version Objects

  • vmsish

    Control VMS-specific language features

  • 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.

  • Amiga::ARexx

    Perl extension for ARexx support

  • Amiga::Exec

    Perl extension for low level amiga support

  • AnyDBM_File

    Provide framework for multiple DBMs

  • App::Cpan

    Easily interact with CPAN from the command line

  • App::Prove

    Implements the prove command.

  • App::Prove::State

    State storage for the prove command.

  • App::Prove::State::Result

    Individual test suite results.

  • App::Prove::State::Result::Test

    Individual test results.

  • Archive::Tar

    Module for manipulations of tar archives

  • Archive::Tar::File

    A subclass for in-memory extracted file from Archive::Tar

  • Attribute::Handlers

    Simpler definition of attribute handlers

  • AutoLoader

    Load subroutines only on demand

  • AutoSplit

    Split a package for autoloading

  • B

    The Perl Compiler 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::Op_private
    1. OP op_private flag definitions
  • B::Showlex

    Show lexical variables used in functions or files

  • 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

  • IO::Socket::IP

    Family-neutral IP socket supporting both IPv4 and IPv6

  • Socket

    Networking constants and support functions

  • CORE

    Namespace for Perl's core routines

  • CPAN

    Query, download and build perl modules from CPAN sites


    A recipe book for programming with

  • CPAN::Debug

    Internal debugging for

  • CPAN::Distroprefs

    Read and match distroprefs

  • CPAN::FirstTime

    Utility for CPAN::Config file Initialization

  • CPAN::HandleConfig

    Internal configuration handling for

  • CPAN::Kwalify

    Interface between and

  • CPAN::Meta

    The distribution metadata for a CPAN dist

  • CPAN::Meta::Converter

    Convert CPAN distribution metadata structures

  • CPAN::Meta::Feature

    An optional feature provided by a CPAN distribution

  • CPAN::Meta::History

    History of CPAN Meta Spec changes

  • CPAN::Meta::History::Meta_1_0

    Version 1.0 metadata specification for META.yml

  • CPAN::Meta::History::Meta_1_1

    Version 1.1 metadata specification for META.yml

  • CPAN::Meta::History::Meta_1_2

    Version 1.2 metadata specification for META.yml

  • CPAN::Meta::History::Meta_1_3

    Version 1.3 metadata specification for META.yml

  • CPAN::Meta::History::Meta_1_4

    Version 1.4 metadata specification for META.yml

  • CPAN::Meta::Merge

    Merging CPAN Meta fragments

  • CPAN::Meta::Prereqs

    A set of distribution prerequisites by phase and type

  • CPAN::Meta::Requirements

    A set of version requirements for a CPAN dist

  • CPAN::Meta::Spec

    Specification for CPAN distribution metadata

  • CPAN::Meta::Validator

    Validate CPAN distribution metadata structures

  • CPAN::Meta::YAML

    Read and write a subset of YAML for CPAN Meta files

  • CPAN::Nox

    Wrapper around without using any XS module

  • CPAN::Plugin

    Base class for CPAN shell extensions

  • CPAN::Plugin::Specfile

    Proof of concept implementation of a trivial CPAN::Plugin

  • CPAN::Queue

    Internal queue support for

  • CPAN::Tarzip

    Internal handling of tar archives for

  • CPAN::Version

    Utility functions to compare CPAN versions

  • Carp

    Alternative warn and die for modules

  • Class::Struct

    Declare struct-like datatypes as Perl classes

  • Compress::Raw::Bzip2

    Low-Level Interface to bzip2 compression library

  • Compress::Raw::Zlib

    Low-Level Interface to zlib compression library

  • Compress::Zlib

    Interface to zlib compression library

  • Config

    Access Perl configuration information

  • Config::Perl::V

    Structured data retrieval of perl -V output

  • Cwd

    Get pathname of current working directory

  • DB

    Programmatic interface to the Perl debugging API

  • DBM_Filter

    Filter DBM keys/values

  • DBM_Filter::compress

    Filter for DBM_Filter

  • DBM_Filter::encode

    Filter for DBM_Filter

  • DBM_Filter::int32

    Filter for DBM_Filter

  • DBM_Filter::null

    Filter for DBM_Filter

  • DBM_Filter::utf8

    Filter for DBM_Filter

  • DB_File

    Perl5 access to Berkeley DB version 1.x

  • Data::Dumper

    Stringified perl data structures, suitable for both printing and eval

  • Devel::PPPort


  • 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::SHA

    Perl extension for SHA-1/224/256/384/512

  • Digest::base

    Digest base class

  • Digest::file

    Calculate digests of files

  • DirHandle

    (obsolete) supply object methods for directory handles

  • Dumpvalue

    Provides screen dump of Perl data.

  • DynaLoader

    Dynamically load C libraries into Perl code

  • Encode

    Character encodings in Perl

  • 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::GSM0338

    ESTI GSM 03.38 Encoding

  • 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 encoding for an unstructured email header

  • Encode::MIME::Name

    Internally used by Encode

  • 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::CBuilder

    Compile and link C code for Perl modules

  • ExtUtils::CBuilder::Platform::Windows

    Builder class for Windows platforms

  • 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

    Generate C code for XS modules' constants.

  • ExtUtils::Embed

    Utilities for embedding Perl in C/C++ applications

  • ExtUtils::Install

    Install files from here to there

  • ExtUtils::Installed

    Inventory management of installed modules

  • ExtUtils::Liblist

    Determine libraries to use and how to use them

  • ExtUtils::MM

    OS adjusted ExtUtils::MakeMaker subclass

  • ExtUtils::MM_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_Darwin

    Special behaviors for OS X

  • 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

  • ExtUtils::MakeMaker::FAQ

    Frequently Asked Questions About MakeMaker

  • ExtUtils::MakeMaker::Locale

    Bundled Encode::Locale

  • ExtUtils::MakeMaker::Tutorial

    Writing a module with MakeMaker

  • ExtUtils::Manifest

    Utilities to write and check a MANIFEST file

  • ExtUtils::Miniperl

    Write the C code for miniperlmain.c and perlmain.c

  • ExtUtils::Mkbootstrap

    Make a bootstrap file for use by DynaLoader

  • ExtUtils::Mksymlists

    Write linker options files for dynamic extension

  • ExtUtils::Packlist

    Manage .packlist files

  • ExtUtils::ParseXS

    Converts Perl XS code into C code

  • ExtUtils::ParseXS::Constants

    Initialization values for some globals

  • ExtUtils::ParseXS::Eval

    Clean package to evaluate code in

  • ExtUtils::ParseXS::Utilities

    Subroutines used with ExtUtils::ParseXS

  • ExtUtils::Typemaps

    Read/Write/Modify Perl/XS typemap files

  • ExtUtils::Typemaps::Cmd

    Quick commands for handling typemaps

  • ExtUtils::Typemaps::InputMap

    Entry in the INPUT section of a typemap

  • ExtUtils::Typemaps::OutputMap

    Entry in the OUTPUT section of a typemap

  • ExtUtils::Typemaps::Type

    Entry in the TYPEMAP section of a typemap

  • ExtUtils::XSSymSet

    Keep sets of symbol names palatable to the VMS linker

  • 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::Compare

    Compare files or filehandles

  • File::Copy

    Copy files or filehandles

  • File::DosGlob

    DOS like globbing and then some

  • File::Fetch

    A generic file fetching mechanism

  • File::Find

    Traverse a directory tree.

  • File::Glob

    Perl extension for BSD glob routine

  • File::GlobMapper

    Extend File Glob to Allow Input and Output Files

  • File::Path

    Create or remove directory trees

  • File::Spec

    Portably perform operations on file names

  • File::Spec::AmigaOS

    File::Spec for AmigaOS

  • 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

  • HTTP::Tiny

    A small, simple, correct HTTP/1.1 client

  • Hash::Util

    A selection of general-utility hash subroutines

  • Hash::Util::FieldHash

    Support for Inside-Out Classes

  • 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::Compress::Base

    Base Class for IO::Compress modules

  • IO::Compress::Bzip2

    Write bzip2 files/buffers

  • IO::Compress::Deflate

    Write RFC 1950 files/buffers

  • IO::Compress::FAQ

    Frequently Asked Questions about IO::Compress

  • IO::Compress::Gzip

    Write RFC 1952 files/buffers

  • IO::Compress::RawDeflate

    Write RFC 1951 files/buffers

  • IO::Compress::Zip

    Write zip files/buffers

  • 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

  • IO::Uncompress::AnyInflate

    Uncompress zlib-based (zip, gzip) file/buffer

  • IO::Uncompress::AnyUncompress

    Uncompress gzip, zip, bzip2 or lzop file/buffer

  • IO::Uncompress::Base

    Base Class for IO::Uncompress modules

  • IO::Uncompress::Bunzip2

    Read bzip2 files/buffers

  • IO::Uncompress::Gunzip

    Read RFC 1952 files/buffers

  • IO::Uncompress::Inflate

    Read RFC 1950 files/buffers

  • IO::Uncompress::RawInflate

    Read RFC 1951 files/buffers

  • IO::Uncompress::Unzip

    Read zip files/buffers

  • IO::Zlib

    IO:: style interface to Compress::Zlib

  • IPC::Cmd

    Finding and running system commands made easy

  • IPC::Msg

    SysV Msg IPC object class

  • IPC::Open2

    Open a process for both reading and writing using open2()

  • IPC::Open3

    Open a process for reading, writing, and error handling using open3()

  • IPC::Semaphore

    SysV Semaphore IPC object class

  • IPC::SharedMem

    SysV Shared Memory IPC object class

  • IPC::SysV

    System V IPC constants and system calls

  • Internals

    Reserved special namespace for internals related functions

  • JSON::PP

    JSON::XS compatible pure-Perl module.

  • JSON::PP::Boolean

    Dummy module providing JSON::PP::Boolean

  • List::Util

    A selection of general-utility list subroutines

  • List::Util::XS

    Indicate if List::Util was compiled with a C compiler

  • Locale::Codes

    A distribution of modules to handle locale codes

  • Locale::Codes::Changes

    Details changes to Locale::Codes

  • Locale::Codes::Country

    Module for dealing with country code sets

  • Locale::Codes::Currency

    Module for dealing with currency code sets

  • Locale::Codes::LangExt

    Module for dealing with langext code sets

  • Locale::Codes::LangFam

    Module for dealing with langfam code sets

  • Locale::Codes::LangVar

    Module for dealing with langvar code sets

  • Locale::Codes::Language

    Module for dealing with language code sets

  • Locale::Codes::Script

    Module for dealing with script code sets

  • Locale::Codes::Types

    Types of data sets supported

  • Locale::Country

    Module for dealing with country code sets

  • Locale::Currency

    Module for dealing with currency code sets

  • Locale::Language

    Module for dealing with language code sets

  • Locale::Maketext

    Framework for localization

  • Locale::Maketext::Cookbook

    Recipes for using Locale::Maketext

  • Locale::Maketext::Guts

    Deprecated module to load Locale::Maketext utf8 code

  • Locale::Maketext::GutsLoader

    Deprecated module to load Locale::Maketext utf8 code

  • Locale::Maketext::Simple

    Simple interface to Locale::Maketext::Lexicon

  • Locale::Maketext::TPJ13

    Article about software localization

  • Locale::Script

    Module for dealing with script code sets

  • MIME::Base64

    Encoding and decoding of base64 strings

  • MIME::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::BigInt::FastCalc

    Math::BigInt::Calc with some XS for more speed

  • Math::BigInt::Lib

    Virtual parent class for Math::BigInt libraries

  • 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

  • Module::CoreList

    What modules shipped with versions of perl

  • Module::CoreList::Utils

    What utilities shipped with versions of perl

  • Module::Load

    Runtime require of both modules and files

  • Module::Load::Conditional

    Looking up module information / loading at runtime

  • Module::Loaded

    Mark modules as loaded or unloaded

  • Module::Metadata

    Gather package and POD information from perl module files

  • 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::FTP::dataconn

    FTP Client data connection 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


    Perl interface to IEEE Std 1003.1

  • Params::Check

    A generic input parsing/checking mechanism.

  • Parse::CPAN::Meta

    Parse META.yml and META.json CPAN metadata files

  • Perl::OSType

    Map Perl operating system names to generic types

  • PerlIO

    On demand loader for PerlIO layers and root of PerlIO::* name space

  • PerlIO::encoding

    Encoding layer

  • PerlIO::mmap

    Memory mapped IO

  • 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::Escapes

    For resolving Pod E<...> sequences

  • 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::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

    Look up Perl documentation in Pod format.

  • Pod::Perldoc::BaseTo

    Base for Pod::Perldoc formatters

  • Pod::Perldoc::GetOptsOO

    Customized option parser for Pod::Perldoc

  • Pod::Perldoc::ToANSI

    Render Pod with ANSI color escapes

  • 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::ToTerm

    Render Pod with terminal escapes

  • 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::Select

    Extract selected sections of POD from input

  • Pod::Simple

    Framework for parsing Pod

  • Pod::Simple::Checker

    Check the Pod syntax of a document

  • Pod::Simple::Debug

    Put Pod::Simple into trace/debug mode

  • Pod::Simple::DumpAsText

    Dump Pod-parsing events as text

  • Pod::Simple::DumpAsXML

    Turn Pod into XML

  • Pod::Simple::HTML

    Convert Pod to HTML

  • Pod::Simple::HTMLBatch

    Convert several Pod files to several HTML files

  • Pod::Simple::LinkSection

    Represent "section" attributes of L codes

  • Pod::Simple::Methody

    Turn Pod::Simple events into method calls

  • Pod::Simple::PullParser

    A pull-parser interface to parsing Pod

  • Pod::Simple::PullParserEndToken

    End-tokens from Pod::Simple::PullParser

  • Pod::Simple::PullParserStartToken

    Start-tokens from Pod::Simple::PullParser

  • Pod::Simple::PullParserTextToken

    Text-tokens from Pod::Simple::PullParser

  • Pod::Simple::PullParserToken

    Tokens from Pod::Simple::PullParser

  • Pod::Simple::RTF

    Format Pod as RTF

  • Pod::Simple::Search

    Find POD documents in directory trees

  • Pod::Simple::SimpleTree

    Parse Pod into a simple parse tree

  • Pod::Simple::Subclassing

    Write a formatter as a Pod::Simple subclass

  • Pod::Simple::Text

    Format Pod as plaintext

  • Pod::Simple::TextContent

    Get the text content of Pod

  • Pod::Simple::XHTML

    Format Pod as validating XHTML

  • Pod::Simple::XMLOutStream

    Turn Pod into XML

  • Pod::Text

    Convert POD data to formatted text

  • Pod::Text::Color

    Convert POD data to formatted color ASCII 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

    Look - search for key in dictionary file

  • SelectSaver

    Save and restore selected file handle

  • SelfLoader

    Load functions only on demand

  • Storable

    Persistence for Perl data structures

  • Sub::Util

    A selection of utility subroutines for subs and CODE references

  • 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

  • Sys::Syslog::Win32

    Win32 support for Sys::Syslog

  • TAP::Base

    Base class that provides common functionality to TAP::Parser

  • TAP::Formatter::Base

    Base class for harness output delegates

  • TAP::Formatter::Color

    Run Perl test scripts with color

  • TAP::Formatter::Console

    Harness output delegate for default console output

  • TAP::Formatter::Console::ParallelSession

    Harness output delegate for parallel console output

  • TAP::Formatter::Console::Session

    Harness output delegate for default console output

  • TAP::Formatter::File

    Harness output delegate for file output

  • TAP::Formatter::File::Session

    Harness output delegate for file output

  • TAP::Formatter::Session

    Abstract base class for harness output delegate

  • TAP::Harness

    Run test scripts with statistics

  • TAP::Harness::Env

    Parsing harness related environmental variables where appropriate

  • TAP::Object

    Base class that provides common functionality to all TAP::* modules

  • TAP::Parser

    Parse TAP output

  • TAP::Parser::Aggregator

    Aggregate TAP::Parser results

  • TAP::Parser::Grammar

    A grammar for the Test Anything Protocol.

  • TAP::Parser::Iterator

    Base class for TAP source iterators

  • TAP::Parser::Iterator::Array

    Iterator for array-based TAP sources

  • TAP::Parser::Iterator::Process

    Iterator for process-based TAP sources

  • TAP::Parser::Iterator::Stream

    Iterator for filehandle-based TAP sources

  • TAP::Parser::IteratorFactory

    Figures out which SourceHandler objects to use for a given Source

  • TAP::Parser::Multiplexer

    Multiplex multiple TAP::Parsers

  • TAP::Parser::Result

    Base class for TAP::Parser output objects

  • TAP::Parser::Result::Bailout

    Bailout result token.

  • TAP::Parser::Result::Comment

    Comment result token.

  • TAP::Parser::Result::Plan

    Plan result token.

  • TAP::Parser::Result::Pragma

    TAP pragma token.

  • TAP::Parser::Result::Test

    Test result token.

  • TAP::Parser::Result::Unknown

    Unknown result token.

  • TAP::Parser::Result::Version

    TAP syntax version token.

  • TAP::Parser::Result::YAML

    YAML result token.

  • TAP::Parser::ResultFactory

    Factory for creating TAP::Parser output objects

  • TAP::Parser::Scheduler

    Schedule tests during parallel testing

  • TAP::Parser::Scheduler::Job

    A single testing job.

  • TAP::Parser::Scheduler::Spinner

    A no-op job.

  • TAP::Parser::Source

    A TAP source & meta data about it

  • TAP::Parser::SourceHandler

    Base class for different TAP source handlers

  • TAP::Parser::SourceHandler::Executable

    Stream output from an executable TAP source

  • TAP::Parser::SourceHandler::File

    Stream TAP from a text file.

  • TAP::Parser::SourceHandler::Handle

    Stream TAP from an IO::Handle or a GLOB.

  • TAP::Parser::SourceHandler::Perl

    Stream TAP from a Perl executable

  • TAP::Parser::SourceHandler::RawTAP

    Stream output from raw TAP in a scalar/array ref.

  • TAP::Parser::YAMLish::Reader

    Read YAMLish data from iterator

  • TAP::Parser::YAMLish::Writer

    Write YAMLish data

  • 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

  • Test2

    Framework for writing test tools that all work together.

  • Test2::API

    Primary interface for writing Test2 based testing tools.

  • Test2::API::Breakage

    What breaks at what version

  • Test2::API::Context

    Object to represent a testing context.

  • Test2::API::Instance

    Object used by Test2::API under the hood

  • Test2::API::Stack

    Object to manage a stack of Test2::Hub

  • Test2::Event

    Base class for events

  • Test2::Event::Bail


  • Test2::Event::Diag

    Diag event type

  • Test2::Event::Encoding

    Set the encoding for the output stream

  • Test2::Event::Exception

    Exception event

  • Test2::Event::Fail

    Event for a simple failed assertion

  • Test2::Event::Generic

    Generic event type.

  • Test2::Event::Note

    Note event type

  • Test2::Event::Ok

    Ok event type

  • Test2::Event::Pass

    Event for a simple passing assertion

  • Test2::Event::Plan

    The event of a plan

  • Test2::Event::Skip

    Skip event type

  • Test2::Event::Subtest

    Event for subtest types

  • Test2::Event::TAP::Version

    Event for TAP version.

  • Test2::Event::V2

    Second generation event.

  • Test2::Event::Waiting

    Tell all procs/threads it is time to be done

  • Test2::EventFacet

    Base class for all event facets.

  • Test2::EventFacet::About

    Facet with event details.

  • Test2::EventFacet::Amnesty

    Facet for assertion amnesty.

  • Test2::EventFacet::Assert

    Facet representing an assertion.

  • Test2::EventFacet::Control

    Facet for hub actions and behaviors.

  • Test2::EventFacet::Error

    Facet for errors that need to be shown.

  • Test2::EventFacet::Info

    Facet for information a developer might care about.

  • Test2::EventFacet::Meta

    Facet for meta-data

  • Test2::EventFacet::Parent

    Base class for all event facets.

  • Test2::EventFacet::Plan

    Facet for setting the plan

  • Test2::EventFacet::Render

    Facet that dictates how to render an event.

  • Test2::EventFacet::Trace

    Debug information for events

  • Test2::Formatter

    Namespace for formatters.

  • Test2::Formatter::TAP

    Standard TAP formatter

  • Test2::Hub

    The conduit through which all events flow.

  • Test2::Hub::Interceptor

    Hub used by interceptor to grab results.

  • Test2::Hub::Interceptor::Terminator

    Exception class used by

  • Test2::Hub::Subtest

    Hub used by subtests

  • Test2::IPC

    Turn on IPC for threading or forking support.

  • Test2::IPC::Driver

    Base class for Test2 IPC drivers.

  • Test2::IPC::Driver::Files

    Temp dir + Files concurrency model.

  • Test2::Tools::Tiny

    Tiny set of tools for unfortunate souls who cannot use

  • Test2::Transition

    Transition notes when upgrading to Test2

  • Test2::Util

    Tools used by Test2 and friends.

  • Test2::Util::ExternalMeta

    Allow third party tools to safely attach meta-data

  • Test2::Util::Facets2Legacy

    Convert facet data to the legacy event API.

  • Test2::Util::HashBase

    Build hash based classes.

  • Test2::Util::Trace

    Legacy wrapper fro Test2::EventFacet::Trace.

  • Test::Builder

    Backend for building test libraries

  • Test::Builder::Formatter

    Test::Builder subclass of Test2::Formatter::TAP

  • Test::Builder::IO::Scalar

    A copy of IO::Scalar for Test::Builder

  • 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::Builder::TodoDiag

    Test::Builder subclass of Test2::Event::Diag

  • Test::Harness

    Run Perl standard test scripts with statistics

  • Test::Harness::Beyond

    Beyond make test

  • Test::More

    Yet another framework for writing test scripts

  • Test::Simple

    Basic utilities for writing tests.

  • Test::Tester

    Ease testing test modules built with Test::Builder

  • Test::Tester::Capture

    Help testing test modules built with Test::Builder

  • Test::Tester::CaptureRunner

    Help testing test modules built with Test::Builder

  • Test::Tutorial

    A tutorial about writing really basic tests

  • Test::use::ok

    Alternative to Test::More::use_ok

  • Text::Abbrev

    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::Tabs

    Expand and unexpand tabs like 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

  • 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::Hash::NamedCapture

    Named regexp capture buffers

  • Tie::Memoize

    Add data to hash when needed

  • Tie::RefHash

    Use references as hash keys

  • Tie::Scalar

    Base class definitions for tied scalars

  • Tie::StdHandle

    Base class definitions for tied handles

  • 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::Piece

    Object Oriented time objects

  • Time::Seconds

    A simple API to convert seconds to other date values

  • 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


    Base class for ALL classes (blessed references)

  • Unicode::Collate

    Unicode Collation Algorithm

  • Unicode::Collate::CJK::Big5

    Weighting CJK Unified Ideographs

  • Unicode::Collate::CJK::GB2312

    Weighting CJK Unified Ideographs

  • Unicode::Collate::CJK::JISX0208

    Weighting JIS KANJI for Unicode::Collate

  • Unicode::Collate::CJK::Korean

    Weighting CJK Unified Ideographs

  • Unicode::Collate::CJK::Pinyin

    Weighting CJK Unified Ideographs

  • Unicode::Collate::CJK::Stroke

    Weighting CJK Unified Ideographs

  • Unicode::Collate::CJK::Zhuyin

    Weighting CJK Unified Ideographs

  • Unicode::Collate::Locale

    Linguistic tailoring for DUCET via Unicode::Collate

  • 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

  • VMS::DCLsym

    Perl extension to manipulate DCL symbols

  • VMS::Filespec

    Convert between VMS and Unix file specification syntax

  • VMS::Stdio

    Standard I/O functions via VMS extensions

  • Win32

    Interfaces to some Win32 API Functions

  • Win32API::File

    Low-level access to Win32 system API calls for files/dirs.

  • Win32CORE

    Win32 CORE function stubs

  • 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

  • autodie::Scope::Guard

    Wrapper class for calling subs at end of scope

  • autodie::Scope::GuardStack
    1. Hook stack for managing scopes via %^H
  • autodie::Util

    Internal Utility subroutines for autodie and Fatal

  • version::Internals

    Perl extension for Version Objects

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).

  1. % perl -MFile::Find=find -MFile::Spec::Functions -Tlwe \
  2. 'find { wanted => sub { print canonpath $_ if /\.pm\z/ },
  3. 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 stands for Comprehensive Perl Archive Network; it's a globally replicated trove of Perl materials, including documentation, style guides, tricks and traps, alternate ports to non-Unix systems and occasional binary distributions for these. Search engines for CPAN can be found at

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

Registered CPAN sites


  • South Africa
  • Uganda
  • Zimbabwe


  • Bangladesh
  • China
  • India
  • Indonesia
  • Iran
  • Israel
  • Japan
  • Kazakhstan
  • Philippines
  • Qatar
  • Republic of Korea
  • Singapore
  • Taiwan
  • Turkey
  • Viet Nam


  • Austria
  • Belarus
  • Belgium
  • Bosnia and Herzegovina
  • Bulgaria
  • Croatia
  • Czech Republic
  • Denmark
  • Finland
  • France
  • Germany
  • Greece
  • Hungary
  • Ireland
  • Italy
  • Latvia
  • Lithuania
  • Moldova
  • Netherlands
  • Norway
  • Poland
  • Portugal
  • Romania
  • Russian Federation
  • Serbia
  • Slovakia
  • Slovenia
  • Spain
  • Sweden
  • Switzerland
  • Ukraine
  • United Kingdom

North America

  • Canada
  • Costa Rica
  • Mexico
  • United States
    • Alabama
    • Arizona
    • California
    • Idaho
    • Illinois
    • Indiana
    • Kansas
    • Massachusetts
    • Michigan
    • New Hampshire
    • New Jersey
    • New York
    • North Carolina
    • Oregon
    • Pennsylvania
    • South Carolina
    • Texas
    • Utah
    • Virginia
    • Washington
    • Wisconsin


  • Australia
  • New Caledonia
  • New Zealand

South America

  • Argentina
  • Brazil
  • Chile

RSYNC Mirrors

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For an up-to-date listing of CPAN sites, see or

Modules: Creation, Use, and Abuse

(The following section is borrowed directly from Tim Bunce's modules file, available at your nearest CPAN site.)

Perl implements a class using a package, but the presence of a package doesn't imply the presence of a class. A package is just a 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, perlobj, 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.,:

    1. sub new {
    2. my $class = shift;
    3. return bless {}, $class;
    4. }

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

    1. sub new {
    2. my $self = shift;
    3. my $class = ref($self) || $self;
    4. return bless {}, $class;
    5. }

    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.

    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:

    1. 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 = YOURCLASS->new(); into: $obj = SUBCLASS->new(); ?

    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 perlstyle.

    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:

    1. $ALL_CAPS_HERE constants only (beware clashes with Perl vars)
    2. $Some_Caps_Here package-wide global/static
    3. $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 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.

    For additional guidance on the naming of modules, please consult:


    or send mail to the <> mailing list.

  • 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. The <> mailing list is useful for this purpose; it's also accessible via news interface as perl.module-authors at

    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:

      1. Copyright (c) 1995 Your Name. All rights reserved.
      2. This program is free software; you can redistribute it and/or
      3. 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 positive floating point number with at least two digits after the decimal (i.e., hundredths, e.g, $VERSION = "0.01" ). Don't use a "1.3.2" style version. See Exporter for details.

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

    • How to release and distribute a module.

      If possible, register the module with CPAN. Follow the instructions and links on:


      and upload to:


      and notify <>. This will allow anyone to install your module using the cpan tool distributed with Perl.

      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!

    • 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:

    1. % perl -e 'use Module::Name; method(@ARGV)' ...
    2. or
    3. % perl -mModule::Name ... (in perl5.002 or higher)


Perl does not enforce private and public parts of its modules as you may have been used to in other languages like C++, Ada, or Modula-17. Perl doesn't have an infatuation with enforced privacy. It would prefer that you stayed out of its living room because you weren't invited, not because it has a shotgun.

The module and its user have a contract, part of which is common law, and part of which is "written". Part of the common law contract is that a module doesn't pollute any namespace it wasn't asked to. The written contract for the module (A.K.A. documentation) may make other provisions. But then you know when you use RedefineTheWorld that you're redefining the world and willing to take the consequences.