Man1 - perlmodlib.1perl

NAME
THE PERL MODULE LIBRARY
CPAN
- Africa
- Asia
- Europe
- North America
- Oceania
- South America
- RSYNC Mirrors
Modules: Creation, Use, and Abuse
NOTE

NAME

perlmodlib - constructing new Perl modules and finding existing ones

THE PERL MODULE LIBRARY

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

Pragmatic Modules

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

no integer; no strict refs; no warnings;

which lasts until the end of that BLOCK.

Some pragmas are lexically scopedΩ-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
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 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
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
(no term): 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
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::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 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
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: Load the C Fcntl.h defines
:Basename: Parse file paths into directory, filename and suffix.
:Compare: Compare files or filehandles
:Copy: Copy files or filehandles
:DosGlob: DOS like globbing and then some
:Fetch: A generic file fetching mechanism
:Find: Traverse a directory tree.
:Glob: Perl extension for BSD glob routine
:GlobMapper: Extend File Glob to Allow Input and Output Files
:Path: Create or remove directory trees
:Spec: Portably perform operations on file names
: :Spec for AmigaOS
: Methods for Cygwin file specs
: Methods for Epoc file specs
: Portably perform operations on file names
: :Spec for Mac OS (Classic)
: Methods for OS/2 file specs
: :Spec for Unix, base for other :Spec modules
: Methods for VMS file specs
: Methods for Win32 file specs
:Temp: Return name and handle of a temporary file safely
: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
: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/float 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 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:::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
(no term): Generic interface to Perl Compiler backends
ODBM_File: Tied access to odbm files
Opcode: Disable named opcodes when compiling perl code
POSIX: Perl interface to IEEE Std 1003.1
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::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:::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::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::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::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
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 ’.’ 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 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

The list of the registered CPAN sites follows. Please note that the sorting order is alphabetical on fields:

and thus the North American servers happen to be listed between the European and the South American sites.

Registered CPAN sites

North America

Canada

http://cpan.mirror.rafal.ca/ ftp://cpan.mirror.rafal.ca/pub/CPAN/ http://mirror.csclub.uwaterloo.ca/CPAN/ ftp://mirror.csclub.uwaterloo.ca/CPAN/ http://mirrors.gossamer-threads.com/CPAN/ http://mirror.its.dal.ca/cpan/ ftp://mirror.its.dal.ca/cpan/ ftp://ftp.ottix.net/pub/CPAN/

Costa Rica

http://mirrors.ucr.ac.cr/CPAN/

Mexico

http://www.msg.com.mx/CPAN/ ftp://ftp.msg.com.mx/pub/CPAN/

United States

Alabama

http://mirror.teklinks.com/CPAN/

Arizona: http://mirror.n5tech.com/CPAN/ http://mirrors.namecheap.com/CPAN/ ftp://mirrors.namecheap.com/CPAN/
California: http://cpan.develooper.com/ http://httpupdate127.cpanel.net/CPAN/ http://mirrors.sonic.net/cpan/ ftp://mirrors.sonic.net/cpan/ http://www.perl.com/CPAN/ http://cpan.yimg.com/
Idaho: http://mirrors.syringanetworks.net/CPAN/ ftp://mirrors.syringanetworks.net/CPAN/
Illinois: http://cpan.mirrors.hoobly.com/ http://mirror.team-cymru.org/CPAN/ ftp://mirror.team-cymru.org/CPAN/
Indiana: http://cpan.netnitco.net/ ftp://cpan.netnitco.net/pub/mirrors/CPAN/ ftp://ftp.uwsg.iu.edu/pub/perl/CPAN/
Kansas: http://mirrors.concertpass.com/cpan/
Massachusetts: http://mirrors.ccs.neu.edu/CPAN/
Michigan: http://cpan.cse.msu.edu/ ftp://cpan.cse.msu.edu/ http://httpupdate118.cpanel.net/CPAN/ http://mirrors-usa.go-parts.com/cpan/ http://ftp.wayne.edu/CPAN/ ftp://ftp.wayne.edu/CPAN/
New Hampshire: http://mirror.metrocast.net/cpan/
New Jersey: http://mirror.datapipe.net/CPAN/ ftp://mirror.datapipe.net/pub/CPAN/ http://www.hoovism.com/CPAN/ ftp://ftp.hoovism.com/CPAN/ http://cpan.mirror.nac.net/
New York: http://mirror.cc.columbia.edu/pub/software/cpan/ ftp://mirror.cc.columbia.edu/pub/software/cpan/ http://cpan.belfry.net/ http://cpan.erlbaum.net/ ftp://cpan.erlbaum.net/CPAN/ http://cpan.hexten.net/ ftp://cpan.hexten.net/ http://mirror.nyi.net/CPAN/ ftp://mirror.nyi.net/pub/CPAN/ http://noodle.portalus.net/CPAN/ ftp://noodle.portalus.net/CPAN/ http://mirrors.rit.edu/CPAN/ ftp://mirrors.rit.edu/CPAN/
North Carolina: http://httpupdate140.cpanel.net/CPAN/ http://mirrors.ibiblio.org/CPAN/
Oregon: http://ftp.osuosl.org/pub/CPAN/ ftp://ftp.osuosl.org/pub/CPAN/ http://mirror.uoregon.edu/CPAN/
Pennsylvania: http://cpan.pair.com/ ftp://cpan.pair.com/pub/CPAN/ http://cpan.mirrors.ionfish.org/
South Carolina: http://cpan.mirror.clemson.edu/
Texas: http://mirror.uta.edu/CPAN/
Utah: http://cpan.cs.utah.edu/ ftp://cpan.cs.utah.edu/CPAN/ ftp://mirror.xmission.com/CPAN/
Virginia: http://mirror.cogentco.com/pub/CPAN/ ftp://mirror.cogentco.com/pub/CPAN/ http://mirror.jmu.edu/pub/CPAN/ ftp://mirror.jmu.edu/pub/CPAN/ http://mirror.us.leaseweb.net/CPAN/ ftp://mirror.us.leaseweb.net/CPAN/
Washington: http://cpan.llarian.net/ ftp://cpan.llarian.net/pub/CPAN/
Wisconsin: http://cpan.mirrors.tds.net/ ftp://cpan.mirrors.tds.net/pub/CPAN/

South America

Argentina: http://cpan.mmgdesigns.com.ar/
Brazil: http://cpan.kinghost.net/ http://linorg.usp.br/CPAN/ http://mirror.nbtelecom.com.br/CPAN/
Chile: http://cpan.dcc.uchile.cl/ ftp://cpan.dcc.uchile.cl/pub/lang/cpan/

RSYNC Mirrors

rsync://ftp.is.co.za/IS-Mirror/ftp.cpan.org/ rsync://mirror.ac.za/CPAN/ rsync://mirror.zol.co.zw/CPAN/ rsync://mirror.dhakacom.com/CPAN/ rsync://mirrors.ustc.edu.cn/CPAN/ rsync://mirrors.xmu.edu.cn/CPAN/ rsync://kambing.ui.ac.id/CPAN/ rsync://ftp.jaist.ac.jp/pub/CPAN/ rsync://mirror.jre655.com/CPAN/ rsync://ftp.kddilabs.jp/cpan/ rsync://ftp.nara.wide.ad.jp/cpan/ rsync://ftp.riken.jp/cpan/ rsync://mirror.neolabs.kz/CPAN/ rsync://mirror.qnren.qa/CPAN/ rsync://ftp.neowiz.com/CPAN/ rsync://mirror.0x.sg/CPAN/ rsync://ftp.yzu.edu.tw/pub/CPAN/ rsync://ftp.ubuntu-tw.org/CPAN/ rsync://mirrors.digipower.vn/CPAN/ rsync://cpan.inode.at/CPAN/ rsync://ftp.byfly.by/CPAN/ rsync://mirror.datacenter.by/CPAN/ rsync://ftp.belnet.be/cpan/ rsync://cpan.mirror.ba/CPAN/ rsync://mirrors.neterra.net/CPAN/ rsync://mirrors.netix.net/CPAN/ rsync://mirror.dkm.cz/cpan/ rsync://mirrors.nic.cz/CPAN/ rsync://cpan.mirror.vutbr.cz/cpan/ rsync://rsync.nic.funet.fi/CPAN/ rsync://ftp.ciril.fr/pub/cpan/ rsync://distrib-coffee.ipsl.jussieu.fr/pub/mirrors/cpan/ rsync://cpan.mirrors.ovh.net/CPAN/ rsync://mirror.de.leaseweb.net/CPAN/ rsync://mirror.euserv.net/cpan/ rsync://ftp-stud.hs-esslingen.de/CPAN/ rsync://ftp.gwdg.de/pub/languages/perl/CPAN/ rsync://ftp.hawo.stw.uni-erlangen.de/CPAN/ rsync://cpan.mirror.iphh.net/CPAN/ rsync://mirror.netcologne.de/cpan/ rsync://ftp.halifax.rwth-aachen.de/cpan/ rsync://ftp.ntua.gr/CPAN/ rsync://mirror.met.hu/CPAN/ rsync://ftp.heanet.ie/mirrors/ftp.perl.org/pub/CPAN/ rsync://rsync.panu.it/CPAN/ rsync://mirror.as43289.net/CPAN/ rsync://rsync.cs.uu.nl/CPAN/ rsync://mirror.nl.leaseweb.net/CPAN/ rsync://ftp.nluug.nl/CPAN/ rsync://mirror.transip.net/CPAN/ rsync://cpan.uib.no/cpan/ rsync://cpan.vianett.no/CPAN/ rsync://cpan.perl-hackers.net/CPAN/ rsync://cpan.perl.pt/cpan/ rsync://mirrors.m247.ro/CPAN/ rsync://mirrors.teentelecom.net/CPAN/ rsync://cpan.webdesk.ru/CPAN/ rsync://mirror.yandex.ru/mirrors/cpan/ rsync://mirror.sbb.rs/CPAN/ rsync://ftp.acc.umu.se/mirror/CPAN/ rsync://rsync.pirbot.com/ftp/cpan/ rsync://cpan.ip-connect.vn.ua/CPAN/ rsync://rsync.mirror.anlx.net/CPAN/ rsync://mirror.bytemark.co.uk/CPAN/ rsync://mirror.sax.uk.as61049.net/CPAN/ rsync://rsync.mirrorservice.org/cpan.perl.org/CPAN/ rsync://ftp.ticklers.org/CPAN/ rsync://mirrors.uk2.net/CPAN/ rsync://CPAN.mirror.rafal.ca/CPAN/ rsync://mirror.csclub.uwaterloo.ca/CPAN/ rsync://mirrors.namecheap.com/CPAN/ rsync://mirrors.syringanetworks.net/CPAN/ rsync://mirror.team-cymru.org/CPAN/ rsync://debian.cse.msu.edu/cpan/ rsync://mirrors-usa.go-parts.com/mirrors/cpan/ rsync://rsync.hoovism.com/CPAN/ rsync://mirror.cc.columbia.edu/cpan/ rsync://noodle.portalus.net/CPAN/ rsync://mirrors.rit.edu/cpan/ rsync://mirrors.ibiblio.org/CPAN/ rsync://cpan.pair.com/CPAN/ rsync://cpan.cs.utah.edu/CPAN/ rsync://mirror.cogentco.com/CPAN/ rsync://mirror.jmu.edu/CPAN/ rsync://mirror.us.leaseweb.net/CPAN/ rsync://cpan.mirror.digitalpacific.com.au/cpan/ rsync://mirror.internode.on.net/cpan/ rsync://uberglobalmirror.com/cpan/ rsync://cpan.lagoon.nc/cpan/ rsync://mirrors.mmgdesigns.com.ar/CPAN/

For an up-to-date listing of CPAN sites, see https://www.cpan.org/SITES or ftp://www.cpan.org/SITES.

Modules: Creation, Use, and Abuse

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

Perl implements a class using a package, but the presence of a package doesn’t imply the presence of a class. A package is just a namespace. A class is a package that provides subroutines that can be used as methods. A method is just a subroutine that expects, as its first argument, either the name of a package (for static methods), or a reference to something (for virtual methods).

A module is a file that (by convention) provides a class of the same name (sans the .pm), plus an import method in that class that can be called to fetch exported symbols. This module may implement some of its methods by loading dynamic C or C++ objects, but that should be totally transparent to the user of the module. Likewise, the module might set up an AUTOLOAD function to slurp in subroutine definitions on demand, but this is also transparent. Only the .pm file is required to exist. See perlsub, 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 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.