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

Pragmatic Modules

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

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

which lasts until the end of that BLOCK.

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

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

attributes: Get/set subroutine or variable attributes
attrs: Set/get attributes of a subroutine (deprecated)
autouse: Postpone load of modules until a function is used
base: Establish 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: Force byte semantics rather than character semantics
charnames: Define character names for \N{named} string literal escapes
constant: Declare constants
diagnostics: Produce verbose warning diagnostics
encoding: Allows you to write your script in non-ascii or non-utf8
encoding::warnings: Warn on implicit encoding conversions
feature: Enable new syntactic 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 and avoid POSIX locales for built-in operations
mro: Method Resolution Order
open: Set default PerlIO layers for input and output
ops: Restrict unsafe operations when compiling
overload: Package for overloading Perl operations
re: Alter regular expression behaviour
sigtrap: Enable simple signal handling
sort: Control sort() behaviour
strict: Restrict unsafe constructs
subs: Predeclare sub names
threads: Perl 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 (obsolete)
version: Perl extension for Version Objects
vmsish: Control VMS-specific language features
warnings: Control optional warnings
warnings::register: Warnings import function

Standard Modules

Standard, bundled modules are all expected to behave in a well-defined manner with respect to namespace pollution because they use the Exporter module. See their own documentation for details.

It's possible that not all modules listed below are installed on your system. For example, the GDBM_File module will not be installed if you don't have the gdbm library.

AnyDBM_File: Provide framework for multiple DBMs
Archive::Extract: A generic archive extracting mechanism
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
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::Lint: Perl lint
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
CGI: Simple Common Gateway Interface Class
CGI::Apache: Backward compatibility module for CGI.pm
CGI::Carp: CGI routines for writing to the HTTPD (or other) error log
CGI::Cookie: Interface to Netscape Cookies
CGI::Fast: CGI Interface for Fast CGI
CGI::Pretty: Module to produce nicely formatted HTML code
CGI::Push: Simple Interface to Server Push
CGI::Switch: Backward compatibility module for defunct CGI::Switch
CGI::Util: Internal utilities used by CGI module
CORE: Pseudo-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::FirstTime: Utility for CPAN::Config file Initialization
CPAN::Kwalify: Interface between CPAN.pm and Kwalify.pm
CPAN::Nox: Wrapper around CPAN.pm without using any XS module
CPAN::Version: Utility functions to compare CPAN versions
CPANPLUS: API & CLI access to the CPAN mirrors
CPANPLUS::Dist::Base: Base class for custom distribution classes
CPANPLUS::Dist::Sample: Sample code to create your own Dist::* plugin
CPANPLUS::Shell::Classic: CPAN.pm emulation for CPANPLUS
CPANPLUS::Shell::Default::Plugins::HOWTO: Documentation on how to write your own plugins
Carp: Warn of errors (from perspective of caller)
Carp::Heavy: Heavy machinery, no user serviceable parts inside
Class::ISA: Report the search path for a class's ISA tree
Class::Struct: Declare struct-like datatypes as Perl classes
Compress::Raw::Zlib: Low-Level Interface to zlib compression library
Compress::Zlib: Interface to zlib compression library
Config: Access Perl configuration information
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::DProf: A Perl code profiler
Devel::InnerPackage: Find all the inner packages of a package
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: Supply object methods for directory handles
Dumpvalue: Provides screen dump of Perl data.
DynaLoader: Dynamically load C libraries into Perl code
Encode: Character encodings
Encode::Alias: Alias definitions to encodings
Encode::Byte: Single Byte Encodings
Encode::CJKConstants: Internally used by Encode::??::ISO_2022_*
Encode::CN: China-based Chinese Encodings
Encode::CN::HZ: Internally used by Encode::CN
Encode::Config: Internally used by Encode
Encode::EBCDIC: EBCDIC Encodings
Encode::Encoder: Object Oriented Encoder
Encode::Encoding: Encode Implementation Base Class
Encode::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 'B' and 'Q' header encoding
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: Base class for ExtUtils::Constant objects
ExtUtils::Embed: Utilities for embedding Perl in C/C++ applications
ExtUtils::Install: Install files from here to there
ExtUtils::Installed: Inventory management of installed modules
ExtUtils::Liblist: Determine libraries to use and how to use them
ExtUtils::MM: OS adjusted ExtUtils::MakeMaker subclass
ExtUtils::MM_AIX: AIX specific subclass of ExtUtils::MM_Unix
ExtUtils::MM_Any: Platform-agnostic MM methods
ExtUtils::MM_BeOS: Methods to override UN*X behaviour in ExtUtils::MakeMaker
ExtUtils::MM_Cygwin: Methods to override UN*X behaviour in ExtUtils::MakeMaker
ExtUtils::MM_DOS: DOS specific subclass of ExtUtils::MM_Unix
ExtUtils::MM_MacOS: Once produced Makefiles for MacOS Classic
ExtUtils::MM_NW5: Methods to override UN*X behaviour in ExtUtils::MakeMaker
ExtUtils::MM_OS2: Methods to override UN*X behaviour in ExtUtils::MakeMaker
ExtUtils::MM_QNX: QNX specific subclass of ExtUtils::MM_Unix
ExtUtils::MM_UWIN: U/WIN specific subclass of ExtUtils::MM_Unix
ExtUtils::MM_Unix: Methods used by ExtUtils::MakeMaker
ExtUtils::MM_VMS: Methods to override UN*X behaviour in ExtUtils::MakeMaker
ExtUtils::MM_VOS: VOS specific subclass of ExtUtils::MM_Unix
ExtUtils::MM_Win32: Methods to override UN*X behaviour in ExtUtils::MakeMaker
ExtUtils::MM_Win95: Method to customize MakeMaker for Win9X
ExtUtils::MY: ExtUtils::MakeMaker subclass for customization
ExtUtils::MakeMaker: Create a module Makefile
ExtUtils::MakeMaker::Config: Wrapper around Config.pm
ExtUtils::MakeMaker::FAQ: Frequently Asked Questions About MakeMaker
ExtUtils::MakeMaker::Tutorial: Writing a module with MakeMaker
ExtUtils::MakeMaker::bytes: Version-agnostic bytes.pm
ExtUtils::MakeMaker::vmsish: Platform-agnostic vmsish.pm
ExtUtils::Manifest: Utilities to write and check a MANIFEST file
ExtUtils::Mkbootstrap: Make a bootstrap file for use by DynaLoader
ExtUtils::Mksymlists: Write linker options files for dynamic extension