CPAN(3)                Perl Programmers Reference Guide                CPAN(3)

       CPAN - query, download and build perl modules from CPAN sites

       Interactive mode:

         perl -MCPAN -e shell;

       Batch mode:

         use CPAN;

         autobundle, clean, install, make, recompile, test

       The CPAN module is designed to automate the make and install of perl
       modules and extensions. It includes some searching capabilities and
       knows how to use Net::FTP or LWP (or lynx or an external ftp client) to
       fetch the raw data from the net.

       Modules are fetched from one or more of the mirrored CPAN
       (Comprehensive Perl Archive Network) sites and unpacked in a dedicated

       The CPAN module also supports the concept of named and versioned
       'bundles' of modules. Bundles simplify the handling of sets of related
       modules. See BUNDLES below.

       The package contains a session manager and a cache manager. There is no
       status retained between sessions. The session manager keeps track of
       what has been fetched, built and installed in the current session. The
       cache manager keeps track of the disk space occupied by the make
       processes and deletes excess space according to a simple FIFO

       All methods provided are accessible in a programmer style and in an
       interactive shell style.

       Interactive Mode

       The interactive mode is entered by running

           perl -MCPAN -e shell

       which puts you into a readline interface. You will have the most fun if
       you install Term::ReadKey and Term::ReadLine to enjoy both history and
       command completion.

       Once you are on the command line, type 'h' and the rest should be self-

       The most common uses of the interactive modes are

       Searching for authors, bundles, distribution files and modules
         There are corresponding one-letter commands a, b, d, and m for each
         of the four categories and another, i for any of the mentioned four.
         Each of the four entities is implemented as a class with slightly
         differing methods for displaying an object.

         Arguments you pass to these commands are either strings exactly
         matching the identification string of an object or regular
         expressions that are then matched case-insensitively against various
         attributes of the objects. The parser recognizes a regular expression
         only if you enclose it between two slashes.

         The principle is that the number of found objects influences how an
         item is displayed. If the search finds one item, the result is
         displayed as object->as_string, but if we find more than one, we
         display each as object->as_glimpse. E.g.

             cpan> a ANDK
             Author id = ANDK
                 EMAIL        a.koenig@franz.ww.TU-Berlin.DE
                 FULLNAME     Andreas König

             cpan> a /andk/
             Author id = ANDK
                 EMAIL        a.koenig@franz.ww.TU-Berlin.DE
                 FULLNAME     Andreas König

             cpan> a /and.*rt/
             Author          ANDYD (Andy Dougherty)
             Author          MERLYN (Randal L. Schwartz)

       make, test, install, clean  modules or distributions
         These commands take any number of arguments and investigate what is
         necessary to perform the action. If the argument is a distribution
         file name (recognized by embedded slashes), it is processed. If it is
         a module, CPAN determines the distribution file in which this module
         is included and processes that.

         Any make or test are run unconditionally. An

           install <distribution_file>

         also is run unconditionally. But for

           install <module>

         CPAN checks if an install is actually needed for it and prints module
         up to date in the case that the distribution file containing the
         module doesn't need to be updated.

         CPAN also keeps track of what it has done within the current session
         and doesn't try to build a package a second time regardless if it
         succeeded or not. The force command takes as a first argument the
         method to invoke (currently: make, test, or install) and executes the
         command from scratch.


             cpan> install OpenGL
             OpenGL is up to date.
             cpan> force install OpenGL
             Running make

         A clean command results in a

           make clean

         being executed within the distribution file's working directory.

       readme, look module or distribution
         These two commands take only one argument, be it a module or a
         distribution file. readme unconditionally runs, displaying the README
         of the associated distribution file. Look gets and untars (if not yet
         done) the distribution file, changes to the appropriate directory and
         opens a subshell process in that directory.

       Signals installs signal handlers for SIGINT and SIGTERM. While you
         are in the cpan-shell it is intended that you can press ^C anytime
         and return to the cpan-shell prompt. A SIGTERM will cause the cpan-
         shell to clean up and leave the shell loop. You can emulate the
         effect of a SIGTERM by sending two consecutive SIGINTs, which usually
         means by pressing ^C twice.
 ignores a SIGPIPE. If the user sets inactivity_timeout, a
         SIGALRM is used during the run of the perl Makefile.PL subprocess.


       The commands that are available in the shell interface are methods in
       the package CPAN::Shell. If you enter the shell command, all your input
       is split by the Text::ParseWords::shellwords() routine which acts like
       most shells do. The first word is being interpreted as the method to be
       called and the rest of the words are treated as arguments to this
       method. Continuation lines are supported if a line ends with a literal


       autobundle writes a bundle file into the
       $CPAN::Config->{cpan_home}/Bundle directory. The file contains a list
       of all modules that are both available from CPAN and currently
       installed within @INC. The name of the bundle file is based on the
       current date and a counter.


       recompile() is a very special command in that it takes no argument and
       runs the make/test/install cycle with brute force over all installed
       dynamically loadable extensions (aka XS modules) with 'force' in
       effect. The primary purpose of this command is to finish a network
       installation. Imagine, you have a common source tree for two different
       architectures. You decide to do a completely independent fresh
       installation. You start on one architecture with the help of a Bundle
       file produced earlier. CPAN installs the whole Bundle for you, but when
       you try to repeat the job on the second architecture, CPAN responds
       with a "Foo up to date" message for all modules. So you invoke CPAN's
       recompile on the second architecture and you're done.

       Another popular use for recompile is to act as a rescue in case your
       perl breaks binary compatibility. If one of the modules that CPAN uses
       is in turn depending on binary compatibility (so you cannot run CPAN
       commands), then you should try the CPAN::Nox module for recovery.

       The four CPAN::* Classes: Author, Bundle, Module, Distribution

       Although it may be considered internal, the class hierarchy does matter
       for both users and programmer. deals with above mentioned four
       classes, and all those classes share a set of methods. A classical
       single polymorphism is in effect. A metaclass object registers all
       objects of all kinds and indexes them with a string. The strings
       referencing objects have a separated namespace (well, not completely

                Namespace                         Class

          words containing a "/" (slash)      Distribution
           words starting with Bundle::          Bundle
                 everything else            Module or Author

       Modules know their associated Distribution objects. They always refer
       to the most recent official release. Developers may mark their releases
       as unstable development versions (by inserting an underbar into the
       visible version number), so the really hottest and newest distribution
       file is not always the default.  If a module Foo circulates on CPAN in
       both version 1.23 and 1.23_90, offers a convenient way to
       install version 1.23 by saying

           install Foo

       This would install the complete distribution file (say
       BAR/Foo-1.23.tar.gz) with all accompanying material. But if you would
       like to install version 1.23_90, you need to know where the
       distribution file resides on CPAN relative to the authors/id/
       directory. If the author is BAR, this might be BAR/Foo-1.23_90.tar.gz;
       so you would have to say

           install BAR/Foo-1.23_90.tar.gz

       The first example will be driven by an object of the class
       CPAN::Module, the second by an object of class CPAN::Distribution.

       Programmer's interface

       If you do not enter the shell, the available shell commands are both
       available as methods (CPAN::Shell->install(...)) and as functions in
       the calling package (install(...)).

       There's currently only one class that has a stable interface -
       CPAN::Shell. All commands that are available in the CPAN shell are
       methods of the class CPAN::Shell. Each of the commands that produce
       listings of modules (r, autobundle, u) returns a list of the IDs of all
       modules within the list.

         The IDs of all objects available within a program are strings that
         can be expanded to the corresponding real objects with the
         CPAN::Shell->expand("Module",@things) method. Expand returns a list
         of CPAN::Module objects according to the @things arguments given. In
         scalar context it only returns the first element of the list.

       Programming Examples
         This enables the programmer to do operations that combine
         functionalities that are available in the shell.

             # install everything that is outdated on my disk:
             perl -MCPAN -e 'CPAN::Shell->install(CPAN::Shell->r)'

             # install my favorite programs if necessary:
             for $mod (qw(Net::FTP MD5 Data::Dumper)){
                 my $obj = CPAN::Shell->expand('Module',$mod);

             # list all modules on my disk that have no VERSION number
             for $mod (CPAN::Shell->expand("Module","/./")){
                 next unless $mod->inst_file;
                 # MakeMaker convention for undefined $VERSION:
                 next unless $mod->inst_version eq "undef";
                 print "No VERSION in ", $mod->id, "\n";

       Methods in the four

       Cache Manager

       Currently the cache manager only keeps track of the build directory
       ($CPAN::Config->{build_dir}). It is a simple FIFO mechanism that
       deletes complete directories below build_dir as soon as the size of all
       directories there gets bigger than $CPAN::Config->{build_cache} (in
       MB). The contents of this cache may be used for later re-installations
       that you intend to do manually, but will never be trusted by CPAN
       itself. This is due to the fact that the user might use these
       directories for building modules on different architectures.

       There is another directory ($CPAN::Config->{keep_source_where}) where
       the original distribution files are kept. This directory is not covered
       by the cache manager and must be controlled by the user. If you choose
       to have the same directory as build_dir and as keep_source_where
       directory, then your sources will be deleted with the same fifo


       A bundle is just a perl module in the namespace Bundle:: that does not
       define any functions or methods. It usually only contains

       It starts like a perl module with a package declaration and a $VERSION
       variable. After that the pod section looks like any other pod with the
       only difference being that one special pod section exists starting with

               =head1 CONTENTS

       In this pod section each line obeys the format

               Module_Name [Version_String] [- optional text]

       The only required part is the first field, the name of a module (e.g.
       Foo::Bar, ie. not the name of the distribution file). The rest of the
       line is optional. The comment part is delimited by a dash just as in
       the man page header.

       The distribution of a bundle should follow the same convention as other

       Bundles are treated specially in the CPAN package. If you say 'install
       Bundle::Tkkit' (assuming such a bundle exists), CPAN will install all
       the modules in the CONTENTS section of the pod. You can install your
       own Bundles locally by placing a conformant Bundle file somewhere into
       your @INC path. The autobundle() command which is available in the
       shell interface does that for you by including all currently installed
       modules in a snapshot bundle file.


       If you have a local mirror of CPAN and can access all files with
       "file:" URLs, then you only need a perl better than perl5.003 to run
       this module. Otherwise Net::FTP is strongly recommended. LWP may be
       required for non-UNIX systems or if your nearest CPAN site is
       associated with an URL that is not ftp:.

       If you have neither Net::FTP nor LWP, there is a fallback mechanism
       implemented for an external ftp command or for an external lynx

       Finding packages and VERSION

       This module presumes that all packages on CPAN

       · declare their $VERSION variable in an easy to parse manner. This
         prerequisite can hardly be relaxed because it consumes far too much
         memory to load all packages into the running program just to
         determine the $VERSION variable. Currently all programs that are
         dealing with version use something like this

             perl -MExtUtils::MakeMaker -le \
                 'print MM->parse_version($ARGV[0])' filename

         If you are author of a package and wonder if your $VERSION can be
         parsed, please try the above method.

       · come as compressed or gzipped tarfiles or as zip files and contain a
         Makefile.PL (well, we try to handle a bit more, but without much


       The debugging of this module is pretty difficult, because we have
       interferences of the software producing the indices on CPAN, of the
       mirroring process on CPAN, of packaging, of configuration, of
       synchronicity, and of bugs within

       In interactive mode you can try "o debug" which will list options for
       debugging the various parts of the package. The output may not be very
       useful for you as it's just a by-product of my own testing, but if you
       have an idea which part of the package may have a bug, it's sometimes
       worth to give it a try and send me more specific output. You should
       know that "o debug" has built-in completion support.

       Floppy, Zip, and all that Jazz works nicely without network too. If you maintain machines that
       are not networked at all, you should consider working with file: URLs.
       Of course, you have to collect your modules somewhere first. So you
       might use to put together all you need on a networked machine.
       Then copy the $CPAN::Config->{keep_source_where} (but not
       $CPAN::Config->{build_dir}) directory on a floppy. This floppy is kind
       of a personal CPAN. on the non-networked machines works nicely
       with this floppy.

       When the CPAN module is installed, a site wide configuration file is
       created as CPAN/ The default values defined there can be
       overridden in another configuration file: CPAN/ You can
       store this file in $HOME/.cpan/CPAN/ if you want, because
       $HOME/.cpan is added to the search path of the CPAN module before the
       use() or require() statements.

       Currently the following keys in the hash reference $CPAN::Config are

         build_cache        size of cache for directories to build modules
         build_dir          locally accessible directory to build modules
         index_expire       after this many days refetch index files
         cpan_home          local directory reserved for this package
         gzip               location of external program gzip
         inactivity_timeout breaks interactive Makefile.PLs after this
                            many seconds inactivity. Set to 0 to never break.
                            if true, does not print the startup message
         keep_source        keep the source in a local directory?
         keep_source_where  directory in which to keep the source (if we do)
         make               location of external make program
         make_arg           arguments that should always be passed to 'make'
         make_install_arg   same as make_arg for 'make install'
         makepl_arg         arguments passed to 'perl Makefile.PL'
         pager              location of external program more (or any pager)
         tar                location of external program tar
         unzip              location of external program unzip
         urllist            arrayref to nearby CPAN sites (or equivalent locations)
         wait_list          arrayref to a wait server to try (See CPAN::WAIT)

       You can set and query each of these options interactively in the cpan
       shell with the command set defined within the o conf command:

       o conf <scalar option>
         prints the current value of the scalar option

       o conf <scalar option> <value>
         Sets the value of the scalar option to value

       o conf <list option>
         prints the current value of the list option in MakeMaker's neatvalue

       o conf <list option> [shift⎪pop]
         shifts or pops the array in the list option variable

       o conf <list option> [unshift⎪push⎪splice] <list>
         works like the corresponding perl commands.

       CD-ROM support

       The urllist parameter of the configuration table contains a list of
       URLs that are to be used for downloading. If the list contains any file
       URLs, CPAN always tries to get files from there first. This feature is
       disabled for index files. So the recommendation for the owner of a
       CD-ROM with CPAN contents is: include your local, possibly outdated
       CD-ROM as a file URL at the end of urllist, e.g.

         o conf urllist push file://localhost/CDROM/CPAN will then fetch the index files from one of the CPAN sites that
       come at the beginning of urllist. It will later check for each module
       if there is a local copy of the most recent version.

       There's no strong security layer in helps you to
       install foreign, unmasked, unsigned code on your machine. We compare to
       a checksum that comes from the net just as the distribution file
       itself. If somebody has managed to tamper with the distribution file,
       they may have as well tampered with the CHECKSUMS file. Future
       development will go towards strong authentification.

       Most functions in package CPAN are exported per default. The reason for
       this is that the primary use is intended for the cpan shell or for

       We should give coverage for _all_ of the CPAN and not just the PAUSE
       part, right? In this discussion CPAN and PAUSE have become equal -- but
       they are not. PAUSE is authors/ and modules/. CPAN is PAUSE plus the
       clpa/, doc/, misc/, ports/, src/, scripts/.

       Future development should be directed towards a better integration of
       the other parts.

       If a Makefile.PL requires special customization of libraries, prompts
       the user for special input, etc. then you may find CPAN is not able to
       build the distribution. In that case, you should attempt the
       traditional method of building a Perl module package from a shell.

       Andreas König <>

       perl(1), CPAN::Nox(3)

3rd Berkeley Distribution    perl 5.005, patch 02                      CPAN(3)