1160 lines
32 KiB
Plaintext
1160 lines
32 KiB
Plaintext
=head1 NAME
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perlmodlib - constructing new Perl modules and finding existing ones
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=head1 DESCRIPTION
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=head1 THE PERL MODULE LIBRARY
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A number of modules are included the Perl distribution. These are
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described below, and all end in F<.pm>. You may also discover files in
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the library directory that end in either F<.pl> or F<.ph>. These are old
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libraries supplied so that old programs that use them still run. The
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F<.pl> files will all eventually be converted into standard modules, and
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the F<.ph> files made by B<h2ph> will probably end up as extension modules
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made by B<h2xs>. (Some F<.ph> values may already be available through the
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POSIX module.) The B<pl2pm> file in the distribution may help in your
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conversion, but it's just a mechanical process and therefore far from
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bulletproof.
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=head2 Pragmatic Modules
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They work somewhat like pragmas in that they tend to affect the compilation of
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your program, and thus will usually work well only when used within a
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C<use>, or C<no>. Most of these are lexically scoped, so an inner BLOCK
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may countermand any of these by saying:
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no integer;
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no strict 'refs';
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which lasts until the end of that BLOCK.
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Unlike the pragmas that effect the C<$^H> hints variable, the C<use
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vars> and C<use subs> declarations are not BLOCK-scoped. They allow
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you to predeclare a variables or subroutines within a particular
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I<file> rather than just a block. Such declarations are effective
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for the entire file for which they were declared. You cannot rescind
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them with C<no vars> or C<no subs>.
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The following pragmas are defined (and have their own documentation).
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=over 12
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=item use autouse MODULE => qw(sub1 sub2 sub3)
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Defers C<require MODULE> until someone calls one of the specified
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subroutines (which must be exported by MODULE). This pragma should be
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used with caution, and only when necessary.
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=item blib
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manipulate @INC at compile time to use MakeMaker's uninstalled version
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of a package
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=item diagnostics
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force verbose warning diagnostics
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=item integer
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compute arithmetic in integer instead of double
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=item less
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request less of something from the compiler
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=item lib
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manipulate @INC at compile time
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=item locale
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use or ignore current locale for builtin operations (see L<perllocale>)
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=item ops
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restrict named opcodes when compiling or running Perl code
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=item overload
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overload basic Perl operations
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=item re
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alter behaviour of regular expressions
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=item sigtrap
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enable simple signal handling
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=item strict
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restrict unsafe constructs
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=item subs
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predeclare sub names
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=item vmsish
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adopt certain VMS-specific behaviors
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=item vars
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predeclare global variable names
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=back
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=head2 Standard Modules
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Standard, bundled modules are all expected to behave in a well-defined
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manner with respect to namespace pollution because they use the
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Exporter module. See their own documentation for details.
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=over 12
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=item AnyDBM_File
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provide framework for multiple DBMs
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=item AutoLoader
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load functions only on demand
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=item AutoSplit
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split a package for autoloading
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=item Benchmark
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benchmark running times of code
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=item CPAN
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interface to Comprehensive Perl Archive Network
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=item CPAN::FirstTime
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create a CPAN configuration file
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=item CPAN::Nox
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run CPAN while avoiding compiled extensions
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=item Carp
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warn of errors (from perspective of caller)
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=item Class::Struct
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declare struct-like datatypes
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=item Config
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access Perl configuration information
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=item Cwd
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get pathname of current working directory
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=item DB_File
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access to Berkeley DB
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=item Devel::SelfStubber
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generate stubs for a SelfLoading module
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=item DirHandle
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supply object methods for directory handles
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=item DynaLoader
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dynamically load C libraries into Perl code
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=item English
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use nice English (or awk) names for ugly punctuation variables
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=item Env
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import environment variables
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=item Exporter
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implements default import method for modules
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=item ExtUtils::Embed
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utilities for embedding Perl in C/C++ applications
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=item ExtUtils::Install
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install files from here to there
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=item ExtUtils::Liblist
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determine libraries to use and how to use them
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=item ExtUtils::MM_OS2
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methods to override Unix behaviour in ExtUtils::MakeMaker
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=item ExtUtils::MM_Unix
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methods used by ExtUtils::MakeMaker
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=item ExtUtils::MM_VMS
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methods to override Unix behaviour in ExtUtils::MakeMaker
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=item ExtUtils::MakeMaker
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create an extension Makefile
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=item ExtUtils::Manifest
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utilities to write and check a MANIFEST file
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=item ExtUtils::Mkbootstrap
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make a bootstrap file for use by DynaLoader
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=item ExtUtils::Mksymlists
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write linker options files for dynamic extension
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=item ExtUtils::testlib
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add blib/* directories to @INC
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=item Fatal
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make errors in builtins or Perl functions fatal
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=item Fcntl
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load the C Fcntl.h defines
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=item File::Basename
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split a pathname into pieces
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=item File::CheckTree
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run many filetest checks on a tree
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=item File::Compare
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compare files or filehandles
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=item File::Copy
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copy files or filehandles
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=item File::Find
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traverse a file tree
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=item File::Path
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create or remove a series of directories
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=item File::Spec
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portably perform operations on file names
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=item File::Spec::Functions
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function call interface to File::Spec module
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=item File::stat
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by-name interface to Perl's builtin stat() functions
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=item FileCache
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keep more files open than the system permits
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=item FileHandle
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supply object methods for filehandles
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=item FindBin
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locate directory of original Perl script
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=item GDBM_File
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access to the gdbm library
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=item Getopt::Long
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extended processing of command line options
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=item Getopt::Std
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process single-character switches with switch clustering
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=item I18N::Collate
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compare 8-bit scalar data according to the current locale
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=item IO
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load various IO modules
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=item IO::File
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supply object methods for filehandles
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=item IO::Handle
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supply object methods for I/O handles
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=item IO::Pipe
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supply object methods for pipes
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=item IO::Seekable
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supply seek based methods for I/O objects
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=item IO::Select
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OO interface to the select system call
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=item IO::Socket
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object interface to socket communications
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=item IPC::Open2
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open a process for both reading and writing
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=item IPC::Open3
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open a process for reading, writing, and error handling
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=item Math::BigFloat
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arbitrary length float math package
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=item Math::BigInt
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arbitrary size integer math package
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=item Math::Complex
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complex numbers and associated mathematical functions
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=item Math::Trig
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simple interface to parts of Math::Complex for those who
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need trigonometric functions only for real numbers
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=item NDBM_File
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tied access to ndbm files
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=item Net::Ping
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Hello, anybody home?
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=item Net::hostent
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by-name interface to Perl's builtin gethost*() functions
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=item Net::netent
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by-name interface to Perl's builtin getnet*() functions
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=item Net::protoent
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by-name interface to Perl's builtin getproto*() functions
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=item Net::servent
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by-name interface to Perl's builtin getserv*() functions
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=item Opcode
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disable named opcodes when compiling or running Perl code
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=item Pod::Text
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convert POD data to formatted ASCII text
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=item POSIX
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interface to IEEE Standard 1003.1
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=item SDBM_File
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tied access to sdbm files
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=item Safe
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compile and execute code in restricted compartments
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=item Search::Dict
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search for key in dictionary file
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=item SelectSaver
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save and restore selected file handle
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=item SelfLoader
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load functions only on demand
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=item Shell
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run shell commands transparently within Perl
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=item Socket
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load the C socket.h defines and structure manipulators
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=item Symbol
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manipulate Perl symbols and their names
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=item Sys::Hostname
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try every conceivable way to get hostname
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=item Sys::Syslog
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interface to the Unix syslog(3) calls
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=item Term::Cap
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termcap interface
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=item Term::Complete
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word completion module
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=item Term::ReadLine
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interface to various C<readline> packages
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=item Test::Harness
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run Perl standard test scripts with statistics
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=item Text::Abbrev
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create an abbreviation table from a list
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=item Text::ParseWords
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parse text into an array of tokens
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=item Text::Soundex
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implementation of the Soundex Algorithm as described by Knuth
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=item Text::Tabs
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expand and unexpand tabs per the Unix expand(1) and unexpand(1)
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=item Text::Wrap
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line wrapping to form simple paragraphs
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=item Tie::Hash
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base class definitions for tied hashes
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=item Tie::RefHash
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base class definitions for tied hashes with references as keys
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=item Tie::Scalar
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base class definitions for tied scalars
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=item Tie::SubstrHash
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fixed-table-size, fixed-key-length hashing
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=item Time::Local
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efficiently compute time from local and GMT time
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=item Time::gmtime
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by-name interface to Perl's builtin gmtime() function
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=item Time::localtime
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by-name interface to Perl's builtin localtime() function
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=item Time::tm
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internal object used by Time::gmtime and Time::localtime
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=item UNIVERSAL
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base class for ALL classes (blessed references)
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=item User::grent
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by-name interface to Perl's builtin getgr*() functions
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=item User::pwent
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by-name interface to Perl's builtin getpw*() functions
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=back
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To find out I<all> the modules installed on your system, including
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those without documentation or outside the standard release, do this:
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% find `perl -e 'print "@INC"'` -name '*.pm' -print
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They should all have their own documentation installed and accessible via
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your system man(1) command. If that fails, try the I<perldoc> program.
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=head2 Extension Modules
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Extension modules are written in C (or a mix of Perl and C) and may be
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statically linked or in general are
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dynamically loaded into Perl if and when you need them. Supported
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extension modules include the Socket, Fcntl, and POSIX modules.
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Many popular C extension modules do not come bundled (at least, not
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completely) due to their sizes, volatility, or simply lack of time for
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adequate testing and configuration across the multitude of platforms on
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which Perl was beta-tested. You are encouraged to look for them in
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archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their
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authors before randomly posting asking for their present condition and
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disposition.
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=head1 CPAN
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CPAN stands for the Comprehensive Perl Archive Network. This is a globally
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replicated collection of all known Perl materials, including hundreds
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of unbundled modules. Here are the major categories of modules:
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=over
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=item *
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Language Extensions and Documentation Tools
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=item *
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Development Support
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=item *
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Operating System Interfaces
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=item *
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Networking, Device Control (modems) and InterProcess Communication
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=item *
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Data Types and Data Type Utilities
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=item *
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Database Interfaces
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=item *
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User Interfaces
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=item *
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Interfaces to / Emulations of Other Programming Languages
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=item *
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File Names, File Systems and File Locking (see also File Handles)
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=item *
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String Processing, Language Text Processing, Parsing, and Searching
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=item *
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Option, Argument, Parameter, and Configuration File Processing
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=item *
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Internationalization and Locale
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=item *
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Authentication, Security, and Encryption
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=item *
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World Wide Web, HTML, HTTP, CGI, MIME
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=item *
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Server and Daemon Utilities
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=item *
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Archiving and Compression
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=item *
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Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
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=item *
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Mail and Usenet News
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=item *
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Control Flow Utilities (callbacks and exceptions etc)
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=item *
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File Handle and Input/Output Stream Utilities
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=item *
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Miscellaneous Modules
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=back
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The registered CPAN sites as of this writing include the following.
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You should try to choose one close to you:
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=over
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=item *
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Africa
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South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
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ftp://ftpza.co.za/pub/mirrors/cpan/
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=item *
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Asia
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Armenia ftp://sunsite.aua.am/pub/CPAN/
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China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
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Hong Kong ftp://ftp.hkstar.com/pub/CPAN/
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Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
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Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
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ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
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ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
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ftp://ftp.meisei-u.ac.jp/pub/CPAN/
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ftp://mirror.nucba.ac.jp/mirror/Perl/
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Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
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South Korea ftp://ftp.bora.net/pub/CPAN/
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ftp://ftp.nuri.net/pub/CPAN/
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Taiwan ftp://ftp.wownet.net/pub2/PERL/
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ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
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Thailand ftp://ftp.cs.riubon.ac.th/pub/mirrors/CPAN/
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ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
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=item *
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Australasia
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Australia ftp://cpan.topend.com.au/pub/CPAN/
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ftp://ftp.labyrinth.net.au/pub/perl/CPAN/
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ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
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ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
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New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
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ftp://sunsite.net.nz/pub/languages/perl/CPAN/
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=item *
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Central America
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Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
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=item *
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Europe
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Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
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Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
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Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
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Croatia ftp://ftp.linux.hr/pub/CPAN/
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Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
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ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
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Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
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Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
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Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
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France ftp://ftp.lip6.fr/pub/perl/CPAN/
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ftp://ftp.oleane.net/pub/mirrors/CPAN/
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ftp://ftp.pasteur.fr/pub/computing/CPAN/
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|
Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
|
|
ftp://ftp.gmd.de/packages/CPAN/
|
|
ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
|
|
ftp://ftp.leo.org/pub/comp/programming/languages/script/perl/CPAN/
|
|
ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
|
|
ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
|
|
ftp://ftp.uni-erlangen.de/pub/source/CPAN/
|
|
ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
|
|
Greece ftp://ftp.ntua.gr/pub/lang/perl/
|
|
Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
|
|
Ireland ftp://sunsite.compapp.dcu.ie/pub/perl/
|
|
Italy ftp://cis.uniRoma2.it/CPAN/
|
|
ftp://ftp.flashnet.it/pub/CPAN/
|
|
ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
|
|
Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
|
|
ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
|
|
Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
|
|
ftp://sunsite.uio.no/pub/languages/perl/CPAN/
|
|
Poland ftp://ftp.man.szczecin.pl/pub/perl/CPAN/
|
|
ftp://ftp.man.torun.pl/pub/doc/CPAN/
|
|
ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
|
|
ftp://sunsite.icm.edu.pl/pub/CPAN/
|
|
Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
|
|
ftp://ftp.ua.pt/pub/CPAN/
|
|
Romania ftp://ftp.dntis.ro/pub/mirrors/perl-cpan/
|
|
ftp://ftp.dnttm.ro/pub/CPAN/
|
|
Russia ftp://cpan.npi.msu.su/CPAN/
|
|
ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
|
|
Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
|
|
Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
|
|
Spain ftp://ftp.etse.urv.es/pub/perl/
|
|
ftp://ftp.rediris.es/mirror/CPAN/
|
|
Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
|
|
Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
|
|
Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
|
|
United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
|
|
ftp://ftp.flirble.org/pub/languages/perl/CPAN/
|
|
ftp://ftp.plig.org/pub/CPAN/
|
|
ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
|
|
ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/
|
|
|
|
=item *
|
|
North America
|
|
|
|
Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
|
|
California ftp://ftp.cdrom.com/pub/perl/CPAN/
|
|
ftp://ftp.digital.com/pub/plan/perl/CPAN/
|
|
Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
|
|
Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
|
|
Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
|
|
Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
|
|
ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
|
|
Manitoba ftp://theory.uwinnipeg.ca/pub/CPAN/
|
|
Massachusetts ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
|
|
ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
|
|
Mexico D.F. ftp://ftp.msg.com.mx/pub/CPAN/
|
|
New York ftp://ftp.rge.com/pub/languages/perl/
|
|
North Carolina ftp://ftp.duke.edu/pub/perl/
|
|
Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
|
|
Ontario ftp://ftp.crc.ca/pub/packages/perl/CPAN/
|
|
Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
|
|
Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
|
|
Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
|
|
Utah ftp://mirror.xmission.com/CPAN/
|
|
Virginia ftp://ftp.perl.org/pub/perl/CPAN/
|
|
ftp://ruff.cs.jmu.edu/pub/CPAN/
|
|
Washington ftp://ftp.spu.edu/pub/CPAN/
|
|
|
|
=item *
|
|
South America
|
|
|
|
Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
|
|
Chile ftp://ftp.ing.puc.cl/pub/unix/perl/CPAN/
|
|
ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/
|
|
|
|
=back
|
|
|
|
For an up-to-date listing of CPAN sites,
|
|
see F<http://www.perl.com/perl/CPAN> or F<ftp://ftp.perl.com/perl/>.
|
|
|
|
=head1 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 F<.pm> file is required to
|
|
exist. See L<perlsub>, L<perltoot>, and L<AutoLoader> for details about
|
|
the AUTOLOAD mechanism.
|
|
|
|
=head2 Guidelines for Module Creation
|
|
|
|
=over 4
|
|
|
|
=item 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.
|
|
|
|
=item Try to design the new module to be easy to extend and reuse.
|
|
|
|
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: C<die "Invalid" unless ref $ref eq 'FOO'>.
|
|
Generally you can delete the "C<eq 'FOO'>" part with no harm at all.
|
|
Let the objects look after themselves! Generally, avoid hard-wired
|
|
class names as far as possible.
|
|
|
|
Avoid C<$r-E<gt>Class::func()> where using C<@ISA=qw(... Class ...)> and
|
|
C<$r-E<gt>func()> would work (see L<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 $@ unless caller();
|
|
|
|
Does your module pass the 'empty subclass' test? If you say
|
|
"C<@SUBCLASS::ISA = qw(YOURCLASS);>" your applications should be able
|
|
to use SUBCLASS in exactly the same way as YOURCLASS. For example,
|
|
does your application still work if you change: C<$obj = new YOURCLASS;>
|
|
into: C<$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 B<-w>. Try to C<use strict;> (or C<use strict qw(...);>).
|
|
Remember that you can add C<no strict qw(...);> to individual blocks
|
|
of code that need less strictness. Always use B<-w>. Always use B<-w>!
|
|
Follow the guidelines in the perlstyle(1) manual.
|
|
|
|
=item 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
|
|
$no_caps_here function scope my() or local() variables
|
|
|
|
Function and method names seem to work best as all lowercase.
|
|
e.g., C<$obj-E<gt>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.
|
|
|
|
=item 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 C<$blessed_ref-E<gt>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:
|
|
C<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.
|
|
|
|
=item 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 in any doubt ask for suggestions in comp.lang.perl.misc.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
=item 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. 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
|
|
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!
|
|
|
|
=item 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:
|
|
|
|
=over 10
|
|
|
|
=item *
|
|
A description of the module/package/extension etc.
|
|
|
|
=item *
|
|
A copyright notice - see below.
|
|
|
|
=item *
|
|
Prerequisites - what else you may need to have.
|
|
|
|
=item *
|
|
How to build it - possible changes to Makefile.PL etc.
|
|
|
|
=item *
|
|
How to install it.
|
|
|
|
=item *
|
|
Recent changes in this release, especially incompatibilities
|
|
|
|
=item *
|
|
Changes / enhancements you plan to make in the future.
|
|
|
|
=back
|
|
|
|
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.
|
|
|
|
=over 4
|
|
|
|
=item 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). 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.
|
|
|
|
=item 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 $VERSION. This should be a floating point
|
|
number with at least two digits after the decimal (i.e., hundredths,
|
|
e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version.
|
|
See Exporter.pm in Perl5.001m or later 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.
|
|
|
|
=item 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 you should place the module into a major ftp archive and
|
|
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 processed before announcing its
|
|
location.
|
|
|
|
FTP Archives for Perl Modules:
|
|
|
|
Follow the instructions and links on
|
|
|
|
http://franz.ww.tu-berlin.de/modulelist
|
|
|
|
or upload to one of these sites:
|
|
|
|
ftp://franz.ww.tu-berlin.de/incoming
|
|
ftp://ftp.cis.ufl.edu/incoming
|
|
|
|
and notify <F<upload@franz.ww.tu-berlin.de>>.
|
|
|
|
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 list!
|
|
|
|
=item 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 behaviour if people rely on it. Document incompatible changes.
|
|
|
|
=back
|
|
|
|
=back
|
|
|
|
=head2 Guidelines for Converting Perl 4 Library Scripts into Modules
|
|
|
|
=over 4
|
|
|
|
=item 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.
|
|
|
|
=item 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?
|
|
|
|
=item 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.
|
|
|
|
=item 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:
|
|
|
|
=over 10
|
|
|
|
=item *
|
|
Adds the standard Module prologue lines
|
|
|
|
=item *
|
|
Converts package specifiers from ' to ::
|
|
|
|
=item *
|
|
Converts die(...) to croak(...)
|
|
|
|
=item *
|
|
Several other minor changes
|
|
|
|
=back
|
|
|
|
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!
|
|
|
|
=back
|
|
|
|
=head2 Guidelines for Reusing Application Code
|
|
|
|
=over 4
|
|
|
|
=item Complete applications rarely belong in the Perl Module Library.
|
|
|
|
=item 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.
|
|
|
|
=item Break-out the reusable code into one or more separate module files.
|
|
|
|
=item Take the opportunity to reconsider and redesign the interfaces.
|
|
|
|
=item 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:
|
|
|
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% perl -e 'use Module::Name; method(@ARGV)' ...
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or
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% perl -mModule::Name ... (in perl5.002 or higher)
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=back
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=head1 NOTE
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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.
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|
|
|
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 C<use RedefineTheWorld> that
|
|
you're redefining the world and willing to take the consequences.
|