A CPAN client that works like a charm

How to use and configure properly a CPAN client.

Perl

cpan

The Comprehensive Perl Archive Network CPAN is a collection of freely available Perl modules. Perl comes with a builtin CPAN client, named ehm cpan.

Be aware that your configuration is stored in the ~/.cpan/CPAN/MyConfig.pm file.

Do not edit that file, use o conf instead from the cpan interactive shell, see below.

First run

It is really easy to start, just launch

$ cpan

CPAN.pm requires configuration, but most of it can be done automatically.
If you answer 'no' below, you will enter an interactive dialog for each
configuration option instead.

Would you like to configure as much as possible automatically? [yes]

and hit enter (two times) to accept defaults. It will be enough to let you prompt into an interactive shell so you can start install modules.

Give it a try installing Perl::Tidy

cpan[1] install Perl::Tidy

If it ends with an OK you are done, just type q to exit interactive shell.

...
  SHANCOCK/Perl-Tidy-20130922.tar.gz
  /home/bi/software/make/current/bin/make install   OK

cpan[2] q
Terminal does not support GetHistory.
Lockfile removed.

Continue with Configuration if cpan is working and you want to configure it to achieve greater user experience

or go to cpanminus if you want a zero config, minimal and efficient CPAN client

otherwise read Troubleshooting if you had problems during installation.

Troubleshooting

ATTENTION

Two things could not work: network or permissions.

The quickest workaround is to check your network configuration and launch commands using sudo.

I really recommend to avoid using cpan and perl provided by your system. See Install your own Perl with your own CPAN or dotsoftware to know how to install Perl in some location your user owns.

local::lib approach

By the way, cpan will realize if you have not write permission and will ask what approach do you want: default is local::lib that is a good idea if you don’t want to build your own Perl.

For example, I use it on Codio and works great: just keep hitting enter and cpan will install local::lib for you.

After installation, you need to modify your environment manually. Just launch

cd ~/perl5/lib/perl5
perl -Mlocal::lib >> ~/.bash_profile
source ~/.bash_profile # or reconnect

Help

Just type h in a cpan shell

cpan> h

Configuration

You can reconfigure all cpan client options by launching

cpan> o conf init

CPAN.pm requires configuration, but most of it can be done automatically.
If you answer 'no' below, you will enter an interactive dialog for each
configuration option instead.

Would you like to configure as much as possible automatically? [yes] no

type no and follow instructions.

In particular, if you need cpan pick mirrors for you, launch

cpan> o conf init urllist

Get CPAN latest version

STRONGLY RECOMMENDED

First of all, make sure you have CPAN.pm module updated to latest version

cpan> install CPAN
...
cpan> reload CPAN

Autocommit

OPTIONAL

Always commit changes to config variables to disk.

cpan> o conf auto_commit 1
For the rest of this article I assume auto_commit is on.
Note that auto_commit is disabled by default, so you should launch o conf commit to confirm configuration changes.

Command number in prompt

PERSONAL

Disable the command number in the prompt.

cpan> o conf commandnumber_in_prompt 0

Enable history

RECOMMENDED

You need to install the following modules

cpan> install Term::ReadLine::Perl Term::ReadKey

YAML

RECOMMENDED

Install YAML Perl module

cpan> install YAML

and try to install a faster YAML implementation

cpan> install YAML::XS

It will need a C compiler installed on your system. If installation is successful, tell cpan which YAML implementation you prefer.

cpan> o conf yaml_module YAML::XS

LWP

RECOMMENDED

Make sure LWP is installed and up to date

install LWP

so cpan will use it to fetch files from Internet.

CPAN::SQLite

OPTIONAL

CPAN::SQLite is a layer between the index files that are downloaded from the CPAN and CPAN.pm that speeds up metadata queries and reduces memory consumption of CPAN.pm considerably.

To use CPAN::SQLite launch

install CPAN::SQLite

cpan> o conf use_sqlite yes

Build prerequisites automatically

RECOMMENDED

The CPAN.pm module can detect when a module which you are trying to build depends on prerequisites. If this happens, I prefer it builds the prerequisites automatically instead of asking for confirmation.

I prefer to install prerequisites also when it is only needed for building or testing in order to save time on future installations.

cpan> o conf prerequisites_policy follow
cpan> o conf build_requires_install_policy yes

Enable colors

PERSONAL

cpan> o conf colorize_output yes
cpan> o conf colorize_print bold white on_black
cpan> o conf colorize_warn bold red on_black
cpan> o conf colorize_debug green on_black

or choose your favourite colors

cpan> o conf init /colorize/

Character set

PERSONAL

In general, CPAN is English speaking territory, so the character set does not matter much but some modules have names that are outside the ASCII range. Since my terminal supports UTF-8, I set

cpan> o conf term_is_latin no

Upgrade modules

Print modules that can be upgraded.

cpan> r

and

cpan> upgrade

Both commands accept a /regexp/ as argument. See Help.

Distroprefs

Distroprefs is a great feature that let you customize module building.

cpanminus

App::cpanminus is a gift from Perl community angel Tatsuhiko Miyagawa.

It’s dependency free (can bootstrap itself), requires zero configuration, and stands alone. When running, it requires only 10MB of RAM.

I assuming you already have a working cpan client, so to install cpanminus just launch

cpan App::cpanminus

and use cpanm instead of cpan from now on. It is light, fast and minimal CPAN client, but, it has many features too: see cpanm or cpanm -h to see what cpanminus can do.

Remember that you should probably pick a mirror and set mirror-only to get consistent results. PERL_CPANM_OPT is your friend for such things.

You can use App::cpanoutdated to detect outdated CPAN modules in your environment.

Install it

cpanm App::cpanoutdated

then update all modules with

cpan-outdated | cpanm

Note that also cpan has the upgrade modules feature but cpan-outdated is faster, uses less memory and is integrated with cpanm.

See also