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


       perlmodlib - constructing new Perl modules and finding existing ones


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

       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 sub-
       routines within a particular file rather than just a block.  Such dec-
       larations are effective for the entire file for which they were
       declared.  You cannot rescind them with "no vars" or "no subs".

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

       attributes  Get/set subroutine or variable attributes

       attrs       Set/get attributes of a subroutine (deprecated)

       autouse     Postpone load of modules until a function is used

       base        Establish IS-A relationship with base class 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

       constant    Declare constants

       diagnostics Produce verbose warning diagnostics

       encoding    Allows you to write your script in non-ascii or non-utf8

       fields      Compile-time class fields

       filetest    Control the filetest permission operators

       if          "use" a Perl module if a condition holds

       integer     Use integer arithmetic instead of floating point

       less        Request less of something from the compiler

       lib         Manipulate @INC at compile time

       locale      Use and avoid POSIX locales for built-in operations

       open        Set default PerlIO layers for input and output

       ops         Restrict unsafe operations when compiling

       overload    Package for overloading perl operations

       re          Alter regular expression behaviour

       sigtrap     Enable simple signal handling

       sort        Control sort() behaviour

       strict      Restrict unsafe constructs

       subs        Predeclare sub names

       threads     Perl extension allowing use of interpreter based threads
                   from perl

                   Perl extension for sharing data structures between threads

       utf8        Enable/disable UTF-8 (or UTF-EBCDIC) in source code

       vars        Predeclare global variable names (obsolete)

       vmsish      Control VMS-specific language features

       warnings    Control optional warnings

                   Warnings 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

                   Simpler definition of attribute handlers

       AutoLoader  Load subroutines only on demand

       AutoSplit   Split a package for autoloading

       B           The Perl Compiler

       B::Asmdata  Autogenerated data about Perl ops, used to generate byte-

                   Assemble Perl bytecode

       B::Bblock   Walk basic blocks

       B::Bytecode Perl compiler’s bytecode backend

       B::C        Perl compiler’s C backend

       B::CC       Perl compiler’s optimized C translation backend

       B::Concise  Walk Perl syntax tree, printing concise info about ops

       B::Debug    Walk Perl syntax tree, printing debug info about ops

       B::Deparse  Perl compiler backend to produce perl code

                   Disassemble Perl bytecode

       B::Lint     Perl lint

       B::Showlex  Show lexical variables used in functions or files

       B::Stackobj Helper module for CC backend

       B::Stash    Show what stashes are loaded

       B::Terse    Walk Perl syntax tree, printing terse info about ops

       B::Xref     Generates cross reference reports for Perl programs

       Benchmark   Benchmark running times of Perl code

       ByteLoader  Load byte compiled perl code

       CGI         Simple Common Gateway Interface Class

       CGI::Apache Backward compatibility module for

       CGI::Carp   CGI routines for writing to the HTTPD (or other) error log

       CGI::Cookie Interface to Netscape Cookies

       CGI::Fast   CGI Interface for Fast CGI

       CGI::Pretty Module to produce nicely formatted HTML code

       CGI::Push   Simple Interface to Server Push

       CGI::Switch Backward compatibility module for defunct CGI::Switch

       CGI::Util   Internal utilities used by CGI module

       CPAN        Query, download and build perl modules from CPAN sites

                   Utility for CPAN::Config file Initialization

       CPAN::Nox   Wrapper around without using any XS module

       Carp        Warn of errors (from perspective of caller)

       Carp::Heavy No user serviceable parts inside

       Class::ISA  Report the search path for a class’s ISA tree

                   Declare struct-like datatypes as Perl classes

       Config      Access Perl configuration information

       Cwd         Get pathname of current working directory

       DB          Programmatic interface to the Perl debugging API (draft,
                   subject to

       DB_File     Perl5 access to Berkeley DB version 1.x

                   Stringified perl data structures, suitable for both print-
                   ing and "eval"

                   A Perl code profiler


       Devel::Peek A data debugging tool for the XS programmer

                   Generate stubs for a SelfLoading module

       Digest      Modules that calculate message digests

       Digest::MD5 Perl interface to the MD5 Algorithm

                   Digest base class

       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

                   Alias definitions to encodings

                   Single Byte Encodings

                   Internally used by Encode::??::ISO_2022_*

       Encode::CN  China-based Chinese Encodings

                   Internally used by Encode::CN

                   Internally used by Encode

                   EBCDIC Encodings

                   Object Oriented Encoder

                   Encode Implementation Base Class

                   Guesses encoding from data

       Encode::JP  Japanese Encodings

                   Internally used by Encode::JP::2022_JP*

                   Internally used by Encode::JP

       Encode::KR  Korean Encodings

                   Internally used by Encode::KR

                   MIME ’B’ and ’Q’ header encoding

                   A detailed document on Encode and PerlIO

                   Encodings supported by Encode

                   Symbol Encodings

       Encode::TW  Taiwan-based Chinese Encodings

                   Various Unicode Transformation Formats

                   UTF-7 encoding

       English     Use nice English (or awk) names for ugly punctuation vari-

       Env         Perl module that imports environment variables as scalars
                   or arrays

       Errno       System errno constants

       Exporter    Implements default import method for modules

                   Exporter guts

                   Utilities to replace common UNIX commands in Makefiles etc.

                   Commands for the MM’s to use in Makefiles

                   Generate XS code to import C header constants

                   Utilities for embedding Perl in C/C++ applications

                   Install files from here to there

                   Inventory management of installed modules

                   Determine libraries to use and how to use them

                   OS adjusted ExtUtils::MakeMaker subclass

                   Platform-agnostic MM methods

                   Methods to override UN*X behaviour in ExtUtils::MakeMaker

                   Methods to override UN*X behaviour in ExtUtils::MakeMaker

                   DOS specific subclass of ExtUtils::MM_Unix

                   Methods to override UN*X behaviour in ExtUtils::MakeMaker

                   Methods to override UN*X behaviour in ExtUtils::MakeMaker

                   Methods to override UN*X behaviour in ExtUtils::MakeMaker

                   U/WIN specific subclass of ExtUtils::MM_Unix

                   Methods used by ExtUtils::MakeMaker

                   Methods to override UN*X behaviour in ExtUtils::MakeMaker

                   Methods to override UN*X behaviour in ExtUtils::MakeMaker

                   Method to customize MakeMaker for Win9X

                   ExtUtils::MakeMaker subclass for customization

                   Create a module Makefile

                   Frequently Asked Questions About MakeMaker

                   Writing a module with MakeMaker



                   Utilities to write and check a MANIFEST file

                   Make a bootstrap file for use by DynaLoader

                   Write linker options files for dynamic extension

                   Manage .packlist files

                   Add blib/* directories to @INC

       Fatal       Replace functions with equivalents which succeed or die

       Fcntl       Load the C Fcntl.h defines

                   Split a pathname into pieces

                   Run many filetest checks on a tree

                   Compare files or filehandles

       File::Copy  Copy files or filehandles

                   DOS like globbing and then some

       File::Find  Traverse a directory tree.

       File::Glob  Perl extension for BSD glob routine

       File::Path  Create or remove directory trees

       File::Spec  Portably perform operations on file names

                   Methods for Cygwin file specs

                   Methods for Epoc file specs

                   Portably perform operations on file names

                   File::Spec for Mac OS (Classic)

                   Methods for OS/2 file specs

                   File::Spec for Unix, base for other File::Spec modules

                   Methods for VMS file specs

                   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

                   Simplified source filtering

                   Perl Source Filter Utility Module

       FindBin     Locate directory of original perl script

       GDBM_File   Perl5 access to the gdbm library.

                   Extended processing of command line options

       Getopt::Std Process single-character switches with switch clustering

       Hash::Util  A selection of general-utility hash subroutines

                   Compare 8-bit scalar data according to the current locale

                   Functions for dealing with RFC3066-style language tags

                   Tags and names for human languages

                   Query locale information

       IO          Load various IO modules

       IO::Dir     Supply object methods for directory handles

       IO::File    Supply object methods for filehandles

       IO::Handle  Supply object methods for I/O handles

       IO::Pipe    Supply object methods for pipes

       IO::Poll    Object interface to system poll call

                   Supply seek based methods for I/O objects

       IO::Select  OO interface to the select system call

       IO::Socket  Object interface to socket communications

                   Object interface for AF_INET domain sockets

                   Object interface for AF_UNIX domain sockets

       IPC::Open2  Open a process for both reading and writing

       IPC::Open3  Open a process for reading, writing, and error handling

       IPC::SysV   SysV IPC constants

                   SysV Msg IPC object class

                   SysV Semaphore IPC object class

       List::Util  A selection of general-utility list subroutines

                   Constants for Locale codes

                   ISO codes for country identification (ISO 3166)

                   ISO three letter codes for currency identification (ISO

                   ISO two letter codes for language identification (ISO 639)

                   Framework for localization

                   Article about software localization

                   ISO codes for script identification (ISO 15924)

                   Encoding and decoding of base64 strings

                   Encoding and decoding of quoted-printable strings

                   Arbitrary size floating point math package

                   Arbitrary size integer math package

                   Pure Perl module to support Math::BigInt

                   Arbitrarily big rationals

                   Complex numbers and associated mathematical functions

       Math::Trig  Trigonometric functions

       Memoize     Make functions faster by trading space for time

                   Glue to provide EXISTS for AnyDBM_File for Storable use

                   Plug-in module for automatic expiration of memoized values

                   Test for Memoize expiration semantics

                   Test for Memoize expiration semantics

                   Glue to provide EXISTS for NDBM_File for Storable use

                   Glue to provide EXISTS for SDBM_File for Storable use

                   Store Memoized data in Storable database

       NDBM_File   Tied access to ndbm files

       NEXT        Provide a pseudo-class NEXT (et al) that allows method

       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

       Net::FTP    FTP Client class

       Net::NNTP   NNTP Client class

       Net::Netrc  OO interface to users netrc file

       Net::POP3   Post Office Protocol 3 Client class (RFC1939)

       Net::Ping   Check a remote host for reachability

       Net::SMTP   Simple Mail Transfer Protocol Client

       Net::Time   Time and daytime network client interface

                   By-name interface to Perl’s built-in gethost*() functions

                   Libnet Frequently Asked Questions

       Net::netent By-name interface to Perl’s built-in getnet*() functions

                   By-name interface to Perl’s built-in getproto*() functions

                   By-name interface to Perl’s built-in getserv*() functions

       O           Generic interface to Perl Compiler backends

       ODBM_File   Tied access to odbm files

       Opcode      Disable named opcodes when compiling perl code

       POSIX       Perl interface to IEEE Std 1003.1

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

                   Encoding layer

                   In-memory IO, scalar IO

       PerlIO::via Helper class for PerlIO layers implemented in perl

                   PerlIO layer for quoted-printable strings

                   Check pod documents for syntax errors

       Pod::Find   Find POD documents in directory trees

                   Group Perl’s functions a la perlfunc.pod

       Pod::Html   Module to convert pod files to HTML

                   Objects representing POD input paragraphs, commands, etc.

       Pod::LaTeX  Convert Pod data to formatted Latex

       Pod::Man    Convert POD data to formatted *roff input

                   Parse an L<> formatting code in POD text

                   Helpers for POD parsing and conversion

       Pod::Parser Base class for creating POD filters and translators

                   Let Perldoc check Pod for errors

                   Let Perldoc render Pod as man pages

                   Let Perldoc convert Pod to nroff

                   Let Perldoc render Pod as ... Pod!

                   Let Perldoc render Pod as RTF

                   Let Perldoc render Pod as plaintext

                   Let Perldoc use Tk::Pod to render Pod

                   Let Perldoc render Pod as XML

                   Convert POD data to formatted ASCII text

                   Perl extension for converting Pod to old style Pod.

       Pod::Select Extract selected sections of POD from input

       Pod::Text   Convert POD data to formatted ASCII text

                   Convert POD data to formatted color ASCII text

                   Convert POD data to formatted overstrike text

                   Convert POD data to ASCII text with format escapes

       Pod::Usage  Print a usage message from embedded pod documentation

       SDBM_File   Tied access to sdbm files

       Safe        Compile and execute code in restricted compartments

                   A selection of general-utility scalar subroutines

                   Search for key in dictionary file

       SelectSaver Save and restore selected file handle

       SelfLoader  Load functions only on demand

       Shell       Run shell commands transparently within perl

       Socket      Load the C socket.h defines and structure manipulators

       Storable    Persistence for Perl data structures

       Switch      A switch statement for Perl

       Symbol      Manipulate Perl symbols and their names

                   Try every conceivable way to get hostname

       Sys::Syslog Perl interface to the UNIX syslog(3) calls

                   Color screen output using ANSI escape sequences

       Term::Cap   Perl termcap interface

                   Perl word completion module

                   Perl interface to various "readline" packages.

       Test        Provides a simple framework for writing test scripts

                   Backend for building test libraries

                   Run Perl standard test scripts with statistics

                   Simple assert

                   Internal Test::Harness Iterator

                   Detailed analysis of test results

       Test::More  Yet another framework for writing test scripts

                   Basic utilities for writing tests.

                   A tutorial about writing really basic tests

                   Create an abbreviation table from a list

                   Extract delimited text sequences from strings.

                   Parse text into an array of tokens or array of arrays

                   Implementation of the Soundex Algorithm as Described by

       Text::Tabs  Expand and unexpand tabs per the unix expand(1) and unex-

       Text::Wrap  Line wrapping to form simple paragraphs

       Thread      Manipulate threads in Perl (for old code only)

                   Thread-safe queues

                   Thread-safe semaphores

                   Start a thread which runs signal handlers reliably (for old

                   Thread-specific keys

       Tie::Array  Base class for tied arrays

       Tie::File   Access the lines of a disk file via a Perl array

       Tie::Handle Base class definitions for tied handles

       Tie::Hash   Base class definitions for tied hashes

                   Add data to hash when needed

                   Use references as hash keys

       Tie::Scalar Base class definitions for tied scalars

                   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

                   By-name interface to Perl’s built-in gmtime() function

                   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 Collation Algorithm

                   Unicode Normalization Forms

                   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

       Win32       Interfaces to some Win32 API Functions

       XS::APItest Test the perl C API

       XS::Typemap Module to test the XS typemaps distributed with perl

       XSLoader    Dynamically load C libraries into Perl code

       To find out all modules installed on your system, including those with-
       out documentation or outside the standard release, just use the follow-
       ing 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 sys-
       tem 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 Make-
       Maker install process.)

       Extension Modules

       Extension modules are written in C (or a mix of Perl and C).  They are
       usually dynamically loaded into Perl if and when you need them, but may
       also be linked in statically.  Supported extension modules include
       Socket, Fcntl, and POSIX.

       Many popular C extension modules do not come bundled (at least, not
       completely) due to their sizes, volatility, or simply lack of time for
       adequate testing and configuration across the multitude of platforms on
       which Perl was beta-tested.  You are encouraged to look for them on
       CPAN (described below), or using web search engines like Alta Vista or


       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 occa-
       sional binary distributions for these.   Search engines for CPAN can be
       found at

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

       ·   Language Extensions and Documentation Tools

       ·   Development Support

       ·   Operating System Interfaces

       ·   Networking, Device Control (modems) and InterProcess Communication

       ·   Data Types and Data Type Utilities

       ·   Database Interfaces

       ·   User Interfaces

       ·   Interfaces to / Emulations of Other Programming Languages

       ·   File Names, File Systems and File Locking (see also File Handles)

       ·   String Processing, Language Text Processing, Parsing, and Searching

       ·   Option, Argument, Parameter, and Configuration File Processing

       ·   Internationalization and Locale

       ·   Authentication, Security, and Encryption

       ·   World Wide Web, HTML, HTTP, CGI, MIME

       ·   Server and Daemon Utilities

       ·   Archiving and Compression

       ·   Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing

       ·   Mail and Usenet News

       ·   Control Flow Utilities (callbacks and exceptions etc)

       ·   File Handle and Input/Output Stream Utilities

       ·   Miscellaneous Modules

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


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

       You should try to choose one close to you.


       South Africa







       Russian Federation

       Saudi Arabia


       South Korea



       Central America

       Costa Rica




       Bosnia and Herzegovina



       Czech Republic


























       United Kingdom

       North America



           Nova Scotia



       United States




           District of Columbia







           New Jersey

           New York

           North Carolina












       New Zealand

       United States

       South America




       RSYNC Mirrors


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

Modules: Creation, Use, and Abuse

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

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

       A module is a file that (by convention) provides a class of the same
       name (sans the .pm), plus an import method in that class that can be
       called to fetch exported symbols.  This module may implement some of
       its methods by loading dynamic C or C++ objects, but that should be
       totally transparent to the user of the module.  Likewise, the module
       might set up an AUTOLOAD function to slurp in subroutine definitions on
       demand, but this is also transparent.  Only the .pm file is required to
       exist.  See perlsub, perltoot, 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 con-
           structor, 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 appropri-
           ate.  Split large methods into smaller more flexible ones.  Inherit
           methods from other modules if appropriate.

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

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

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

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

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

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

           Always use -w.

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

           Always use -w.

           Follow the guidelines in the perlstyle(1) manual.

           Always use -w.

       ·   Some simple style guidelines

           The perlstyle manual supplied with Perl has many helpful points.

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

           Use underscores to separate words.  It is generally easier to read
           $var_names_like_this than $VarNamesLikeThis, especially for non-
           native speakers of English. It’s also a simple rule that works con-
           sistently 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 lead-
           ing 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 pos-
           sible.  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 any-
           one (though having 23 called Sort::Quick is only marginally better
           :-).  Imagine someone trying to install your module alongside many
           others.  If in any doubt ask for suggestions in

           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 stan-
           dards for naming modules and the interface to methods in those mod-

           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

       ·   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 sugges-
           tions, is to ask someone who knows. Comp.lang.perl.misc is read by
           just about all the people who develop modules and it’s the best
           place to ask.

           All you need to do is post a short summary of the module, its pur-
           pose 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 oth-
           ers 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 docu-
           mentation 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 incompatibili-

           ·         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, Copy-
           ing, 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, Copy-
               ing, 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

           ·   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 pack-
               age variable called $VERSION.  This should be a floating point
               number with at least two digits after the decimal (i.e., hun-
               dredths, e.g, "$VERSION = "0.01"").  Don’t use a "1.3.2" style
               version.  See Exporter for details.

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

           ·   How to release and distribute a module.

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

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

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

               FTP Archives for Perl Modules:

               Follow the instructions and links on:


               or upload to one of these sites:


               and notify <>.

               By using the WWW interface you can ask the Upload Server to
               mirror your modules from your ftp or WWW site into your own
               directory on CPAN!

               Please remember to send me an updated entry for the Module

           ·   Take care when changing a released module.

               Always strive to remain compatible with previous released ver-
               sions.  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 con-
           tinue 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)’ ...
                % perl -mModule::Name ...    (in perl5.002 or higher)


       Perl does not enforce private and public parts of its modules as you
       may have been used to in other languages like C++, Ada, or Modula-17.
       Perl doesn’t have an infatuation with enforced privacy.  It would pre-
       fer 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.

perl v5.8.6                       2004-11-05                     PERLMODLIB(1)

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