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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 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-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 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 backslash.


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 separated):

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


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 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.


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.

Finding packages and VERSION

This module presumes that all packages on CPAN


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 defined:

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 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.

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 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 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)

1 POD Error

The following errors were encountered while parsing the POD:

Around line 3717:

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