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 directory.

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 mechanism.

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 most fun if you install Term::ReadKey and Term::ReadLine to enjoy both history and completion.

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

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 matching exact 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 regualar 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, we display the result of 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 do indeed exist just as written above. Each of them takes any number of arguments and investigates for each what it might be. Is it a distribution file (recognized by embedded slashes), this file is being processed. Is it a module, CPAN determines the distribution file where this module is included and processes that.

Any make, test, and readme are run unconditionally. A

  C<install E<lt>distribution_fileE<gt>>

also is run unconditionally. But for

  C<install E<lt>moduleE<gt>>

CPAN checks if an install is actually needed for it and prints Foo up to date in case 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 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
readme, look module or distribution

These two commands take only one argument, be it a module or a distribution file. readme displays 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.


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.


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. 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 will be glad to run recompile in 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.

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(...)). The programmer's interface has beta status. Do not heavily rely on it, changes may still be necessary.

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 mechanism.


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

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, that one special pod section exists starting with (verbatim):

        =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 (eg. 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 distributions.

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.

There is a meaningless Bundle::Demo available on CPAN. Try to install it, it usually does no harm, just demonstrates what the Bundle interface looks like.


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 command.

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 by 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 enthusiasm).


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 byproduct 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 defined:

  build_cache        size of cache for directories to build modules
  build_dir          locally accessible directory to build modules
  index_expire       after how 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 that
                     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  where keep the source (if we do)
  make               location of external program make
  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)

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 format.

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.


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 oneliners.


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 intergration of the other parts.


Andreas König <>


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

1 POD Error

The following errors were encountered while parsing the POD:

Around line 2588:

Non-ASCII character seen before =encoding in 'König'. Assuming CP1252