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

# NAME

perlmodlib - constructing new Perl modules and finding existing ones

# THE PERL MODULE LIBRARY

Many modules are included in the Perl distribution. These are described below, and all end in .pm. You may discover compiled library files (usually ending in .so) or small pieces of modules to be autoloaded (ending in .al); these were automatically generated by the installation process. You may also discover files in the library directory that end in either .pl or .ph. These are old libraries supplied so that old programs that use them still run. The .pl files will all eventually be converted into standard modules, and the .ph files made by h2ph will probably end up as extension modules made by h2xs. (Some .ph values may already be available through the POSIX, Errno, or Fcntl modules.) The pl2pm file in the distribution may help in your conversion, but it's just a mechanical process and therefore far from bulletproof.

## Pragmatic Modules

They work somewhat like compiler directives (pragmata) in that they tend to affect the compilation of your program, and thus will usually work well only when used within a "use", or "no". Most of these are lexically scoped, so an inner BLOCK may countermand them by saying:

        no integer;
        no strict 'refs';
        no warnings;

which lasts until the end of that BLOCK.

Some pragmas are lexically scoped--typically those that affect the $^H hints variable. Others affect the current package instead, like "use vars" and "use subs", which allow you to predeclare a variables or subroutines within a particular file rather than just a block. Such declarations are effective for the entire file for which they were declared. You cannot rescind them with "no vars" or "no subs".

The following pragmas are defined (and have their own documentation).

attributes
  Get/set subroutine or variable attributes
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
bigfloat
  Transparent big floating point number support for Perl
bigint
  Transparent big integer support for Perl
bignum
  Transparent big number support for Perl
bigrat
  Transparent big rational number support for Perl
blib
  Use MakeMaker's uninstalled version of a package
builtin
  Import built-in utility functions
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 inclusion of a module in core
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
stable
  Experimental features made easy, once we know they're stable
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
  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.

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::Deparse
  Perl compiler backend to produce perl code
B::Op_private
  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
"Test2::Tools::Refcount"
  Assert reference counts on objects
CORE
  Namespace for Perl's core routines
CPAN
  Query, download and build perl modules from CPAN sites
CPAN::API::HOWTO
  A recipe book for programming with CPAN.pm
CPAN::Debug
  Internal debugging for CPAN.pm
CPAN::Distroprefs
  Read and match distroprefs
CPAN::FirstTime
  Utility for CPAN::Config file Initialization
CPAN::HandleConfig
  Internal configuration handling for CPAN.pm
CPAN::Kwalify
  Interface between CPAN.pm and Kwalify.pm
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::Requirements::Range
  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 CPAN.pm 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.pm
CPAN::Tarzip
  Internal handling of tar archives for CPAN.pm
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 or zlib-ng compression library
Compress::Zlib
  Interface to zlib compression library
Config
  Access Perl configuration information
Config::Extensions
  Hash lookup of which core extensions were built.
Config::Perl::V
  Structured data retrieval of perl -V output
Configure
  Provide auto-configuration utilities
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
  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::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
  ETSI 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_OS390
  OS390 specific subclass of ExtUtils::MM_Unix
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::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::PL2Bat
  Batch file creation to run perl scripts on Windows
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
  Various flag constants and helper functions from C's fcntl.h
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::Long::Parser
  Getopt::Long object oriented interface
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, zstd, xz, lzma, lzip, lzf 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::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
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 math package
Math::BigInt::Calc
  Pure Perl module to support Math::BigInt
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 size rational number math package
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::NDBM_File
  Glue to provide EXISTS for NDBM_File for Storable use
Memoize::SDBM_File
  DEPRECATED compability shim
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
OpenBSD::Pledge
  Perl interface to OpenBSD pledge(2)
OpenBSD::Unveil
  Perl interface to OpenBSD unveil(2)
POSIX
  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::Functions
  Group Perl's functions a la perlfunc.pod
Pod::Html
  Module to convert pod files to HTML
Pod::Html::Util
  Helper functions for Pod-Html
Pod::Man
  Convert POD data to formatted *roff input
Pod::ParseLink
  Parse an L<> formatting code in POD text
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::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::JustPod
  Just the Pod, the whole Pod, and nothing but the Pod
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::Overstrike
  Convert POD data to formatted overstrike text
Pod::Text::Termcap
  Convert POD data to ASCII text with format escapes
Pod::Usage
  Extracts POD documentation and shows usage information
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::ReadKey
  A perl module for simple terminal control
Term::ReadLine
  Perl interface to various "readline" packages.
Term::Table
  Format a header and rows into a table
Term::Table::Cell
  Representation of a cell in a table.
Term::Table::CellStack
  Combine several cells into one (vertical)
Term::Table::HashBase
  Build hash based classes.
Term::Table::LineBreak
  Break up lines for use in tables.
Term::Table::Util
  Utilities for Term::Table.
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::InterceptResult
  Representation of a list of events.
Test2::API::InterceptResult::Event
  Representation of an event for use in
Test2::API::InterceptResult::Hub
  Hub used by InterceptResult.
Test2::API::InterceptResult::Squasher
  Encapsulation of the algorithm that
Test2::API::Stack
  Object to manage a stack of Test2::Hub
Test2::AsyncSubtest
  Object representing an async subtest.
Test2::AsyncSubtest::Event::Attach
  Event to attach a subtest to the parent.
Test2::AsyncSubtest::Event::Detach
  Event to detach a subtest from the parent.
Test2::AsyncSubtest::Hub
  Hub used by async subtests.
Test2::Bundle
  Documentation for bundles.
Test2::Bundle::Extended
  Old name for Test2::V0
Test2::Bundle::More
  ALMOST a drop-in replacement for Test::More.
Test2::Bundle::Simple
  ALMOST a drop-in replacement for Test::Simple.
Test2::Compare
  Test2 extension for writing deep comparison tools.
Test2::Compare::Array
  Internal representation of an array comparison.
Test2::Compare::Bag
  Internal representation of a bag comparison.
Test2::Compare::Base
  Base class for comparison classes.
Test2::Compare::Bool
  Compare two values as booleans
Test2::Compare::Custom
  Custom field check for comparisons.
Test2::Compare::DeepRef
  Ref comparison
Test2::Compare::Delta
  Representation of differences between nested data
Test2::Compare::Event
  Event specific Object subclass.
Test2::Compare::EventMeta
  Meta class for events in deep comparisons
Test2::Compare::Float
  Compare two values as numbers with tolerance.
Test2::Compare::Hash
  Representation of a hash in a deep comparison.
Test2::Compare::Isa
  Check if the value is an instance of the class.
Test2::Compare::Meta
  Check library for meta-checks
Test2::Compare::Negatable
  Poor mans 'role' for compare objects that can be negated.
Test2::Compare::Number
  Compare two values as numbers
Test2::Compare::Object
  Representation of an object during deep
Test2::Compare::OrderedSubset
  Internal representation of an ordered subset.
Test2::Compare::Pattern
  Use a pattern to validate values in a deep
Test2::Compare::Ref
  Ref comparison
Test2::Compare::Regex
  Regex direct comparison
Test2::Compare::Scalar
  Representation of a Scalar Ref in deep
Test2::Compare::Set
  Allows a field to be matched against a set of
Test2::Compare::String
  Compare two values as strings
Test2::Compare::Undef
  Check that something is undefined
Test2::Compare::Wildcard
  Placeholder check.
Test2::Event
  Base class for events
Test2::Event::Bail
  Bailout!
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::Hub
  Facet for the hubs an event passes through.
Test2::EventFacet::Info
  Facet for information a developer might care about.
Test2::EventFacet::Info::Table
  Intermediary representation of a table.
Test2::EventFacet::Meta
  Facet for meta-data
Test2::EventFacet::Parent
  Facet for events contains other events
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::Manual
  Documentation hub for Test2 and Test2-Suite.
Test2::Manual::Anatomy
  The hub for documentation of the inner workings of
Test2::Manual::Anatomy::API
  Internals documentation for the API.
Test2::Manual::Anatomy::Context
  Internals documentation for the Context
Test2::Manual::Anatomy::Event
  The internals of events
Test2::Manual::Anatomy::Hubs
  Internals documentation for the hub stack, and
Test2::Manual::Anatomy::IPC
  Manual for the IPC system.
Test2::Manual::Anatomy::Utilities
  Overview of utilities for Test2.
Test2::Manual::Concurrency
  Documentation for Concurrency support.
Test2::Manual::Contributing
  How to contribute to the Test2 project.
Test2::Manual::EndToEnd
  Overview of Test2 from load to finish.
Test2::Manual::Testing
  Hub for documentation about writing tests with Test2.
Test2::Manual::Testing::Introduction
  Introduction to testing with Test2.
Test2::Manual::Testing::Migrating
  How to migrate existing tests from
Test2::Manual::Testing::Planning
  The many ways to set a plan.
Test2::Manual::Testing::Todo
  Tutorial for marking tests as TODO.
Test2::Manual::Tooling
  Manual page for tool authors.
Test2::Manual::Tooling::FirstTool
  Write your first tool with Test2.
Test2::Manual::Tooling::Formatter
  How to write a custom formatter, in our
Test2::Manual::Tooling::Nesting
  Tutorial for using other tools within your
Test2::Manual::Tooling::Plugin::TestExit
  How to safely add pre-exit
Test2::Manual::Tooling::Plugin::TestingDone
  Run code when the test file is
Test2::Manual::Tooling::Plugin::ToolCompletes
  How to add behaviors that occur
Test2::Manual::Tooling::Plugin::ToolStarts
  How to add behaviors that occur
Test2::Manual::Tooling::Subtest
  How to implement a tool that makes use of
Test2::Manual::Tooling::TestBuilder
  This section maps Test::Builder methods
Test2::Manual::Tooling::Testing
  Tutorial on how to test your testing tools.
Test2::Mock
  Module for managing mocked classes and instances.
Test2::Plugin
  Documentation for plugins
Test2::Plugin::BailOnFail
  Automatically bail out of testing on the first test
Test2::Plugin::DieOnFail
  Automatically die on the first test failure.
Test2::Plugin::ExitSummary
  Add extra diagnostics on failure at the end of the
Test2::Plugin::SRand
  Control the random seed for more controlled test
Test2::Plugin::Times
  Output timing data at the end of the test.
Test2::Plugin::UTF8
  Test2 plugin to test with utf8.
Test2::Require
  Base class and documentation for skip-unless type test
Test2::Require::AuthorTesting
  Only run a test when the AUTHOR_TESTING
Test2::Require::AutomatedTesting
  Only run a test when the AUTOMATED_TESTING
Test2::Require::EnvVar
  Only run a test when a specific environment variable
Test2::Require::ExtendedTesting
  Only run a test when the EXTENDED_TESTING
Test2::Require::Fork
  Skip a test file unless the system supports forking
Test2::Require::Module
  Skip tests if certain packages are not installed, or
Test2::Require::NonInteractiveTesting
  Only run a test when the NONINTERACTIVE_TESTING
Test2::Require::Perl
  Skip the test unless the necessary version of Perl is
Test2::Require::RealFork
  Skip a test file unless the system supports true
Test2::Require::ReleaseTesting
  Only run a test when the RELEASE_TESTING
Test2::Require::Threads
  Skip a test file unless the system supports threading
Test2::Suite
  Distribution with a rich set of tools built upon the Test2
Test2::Todo
  TODO extension for Test2.
Test2::Tools
  Documentation for Tools.
Test2::Tools::AsyncSubtest
  Tools for writing async subtests.
Test2::Tools::Basic
  Test2 implementation of the basic testing tools.
Test2::Tools::Class
  Test2 implementation of the tools for testing classes.
Test2::Tools::ClassicCompare
  Classic (Test::More style) comparison tools.
Test2::Tools::Compare
  Tools for comparing deep data structures.
Test2::Tools::Defer
  Write tests that get executed at a later time
Test2::Tools::Encoding
  Tools for managing the encoding of Test2 based
Test2::Tools::Event
  Tools for generating test events.
Test2::Tools::Exception
  Test2 based tools for checking exceptions
Test2::Tools::Exports
  Tools for validating exporters.
Test2::Tools::GenTemp
  Tool for generating a populated temp directory.
Test2::Tools::Grab
  Temporarily intercept all events without adding a scope
Test2::Tools::Mock
  Class/Instance mocking for Test2.
Test2::Tools::Ref
  Tools for validating references.
Test2::Tools::Spec
  RSPEC implementation on top of Test2::Workflow
Test2::Tools::Subtest
  Tools for writing subtests
Test2::Tools::Target
  Alias the testing target package.
Test2::Tools::Tester
  Tools to help you test other testing tools.
Test2::Tools::Tiny
  Tiny set of tools for unfortunate souls who cannot use
Test2::Tools::Warnings
  Tools to verify warnings.
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::Grabber
  Object used to temporarily intercept all events.
Test2::Util::Guard
  Inline copy of Scope::Guard
Test2::Util::HashBase
  Build hash based classes.
Test2::Util::Importer
  Inline copy of Importer.
Test2::Util::Ref
  Tools for inspecting or manipulating references.
Test2::Util::Stash
  Utilities for manipulating stashes and globs.
Test2::Util::Sub
  Tools for inspecting and manipulating subs.
Test2::Util::Table
  Format a header and rows into a table
Test2::Util::Table::LineBreak
  Break up lines for use in tables.
Test2::Util::Times
  Format timing/benchmark information.
Test2::Util::Trace
  Legacy wrapper fro Test2::EventFacet::Trace.
Test2::V0
  0Th edition of the Test2 recommended bundle.
Test2::Workflow
  A test workflow is a way of structuring tests using
Test2::Workflow::BlockBase
  Base class for all workflow blocks.
Test2::Workflow::Build
  Represents a build in progress.
Test2::Workflow::Runner
  Runs the workflows.
Test2::Workflow::Task
  Encapsulation of a Task
Test2::Workflow::Task::Action
  Encapsulation of an action.
Test2::Workflow::Task::Group
  Encapsulation of a group (describe).
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
UNIVERSAL
  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
  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).

        % 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 @INC from being populated by "PERL5LIB", "PERLLIB", and "PERL_USE_UNSAFE_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 Google or DuckDuckGo.

# 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 https://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

You can find the CPAN online at <https://www.cpan.org/>

# 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.,:

       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.

  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: "$obj = YOURCLASS->new();" into: "$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:

       $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 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:

          https://pause.perl.org/pause/query?ACTION=pause_namingmodules

  or send mail to the <module-authors@perl.org> 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 <module-authors@perl.org> mailing list is useful for this purpose; it's also accessible via news interface as perl.module-authors at nntp.perl.org.

  All you need to do is post a short summary of the module, its purpose and interfaces. A few lines on each of the main methods is probably enough. (If you post the whole module it might be ignored by busy people - generally the very people you want to read it!)

  Don't worry about posting if you can't say when the module will be ready - just say so in the message. It might be worth inviting others to help you, they may be able to complete it for you!

- README and other Additional Files.

  It's well known that software developers usually fully document the software they write. If, however, the world is in urgent need of your software and there is not enough time to write the full documentation please at least provide a README file containing:

- A description of the module/package/extension etc.
- A copyright notice - see below.
- Prerequisites - what else you may need to have.
- How to build it - possible changes to Makefile.PL etc.
- How to install it.
- Recent changes in this release, especially incompatibilities
- Changes / enhancements you plan to make in the future.

If the README file seems to be getting too large you may wish to split out some of the sections into separate files: INSTALL, Copying, ToDo etc.

- Adding a Copyright Notice.

  How you choose to license your work is a personal decision. The general mechanism is to assert your Copyright and then make a declaration of how others may copy/use/modify your work.

  Perl, for example, is supplied with two types of licence: The GNU GPL and The Artistic Licence (see the files README, Copying, and Artistic, or perlgpl and perlartistic). Larry has good reasons for NOT just using the GNU GPL.

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

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

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

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

  To be fully compatible with the Exporter and MakeMaker modules you should store your module's version number in a non-my package variable called $VERSION. This should be a positive floating point number with at least two digits after the decimal (i.e., hundredths, e.g, "$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 ExtUtils::MakeMaker.pm for details.

- How to release and distribute a module.

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

         https://www.cpan.org/modules/04pause.html

  and upload to:

         https://pause.perl.org/

  and notify <modules@perl.org>. 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:

           % 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.

2025-10-12 | perl v5.40.1