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CPAN Module
Written by Philip L Yuson   

Who is this for
This article is for those who want to be familiar with the CPAN module.

What you need to know
Skills in compilation and linking

One of the features of Perl is its extensibility. This feature allows you to extend the capabilities of the Perl language beyond its core functions. Examples of these extensions are the DBI, Tk and CGI modules. These have been discussed in this site in previous months.

These and the other modules have to be installed. The simplest and easiest way is to find a distribution for these modules and installing them. Different distributions of Linux provide their own methods of distributing these modules. Likewise, different distributions of Perl in Windows have their own way of installing these modules. As I said, the simplest way to install these modules is to use the method provided by the distribution.

Another way of installing the modules is by configuring and make-ing these modules yourselves. This requires compilation and link process knowledge. For simple modules, it would be straightforward, at most, 4 steps (configure or create the make file, make, make test and make install). But for modules with pre-requisites, you will need to first determine the pre-requisites before you can install them.

To install the modules yourself, you might need the compiler and maker. You might also need include files from other components of your system.

To make your life simpler, install modules from any pre-built modules.

You also need to download the modules from the CPAN website (http://www.cpan.org).

CPAN shell
CPAN is an acronym for Comprehensive Perl Archive Network. Perl provides a process to simpify installing CPAN modules. It uses the CPAN module and you can install other modules using the shell or directly from the Perl command line.

This article discusses the CPAN shell.

Starting the CPAN Shell

On the command line type this:

perl -MCPAN -e shell

The first time you start CPAN, it will ask you several questions. You can take the default and it would be fine. Make sure that you have write access to your Perl directories. You should always use the same userid wen using the CPAN shell.

Getting Help
When you start the CPAN shell, you can enter commands to control its operation. The most important command is h. This lists all the commands that you can use in the CPAN shell.

Displaying Modules
To display modules whose name has a given string, you can use the m or i commands:

m /string/ or i /string/

The string is any valid regular expression. You can also browse all modules from the CPAN website. Modules names appear before the :: characters.

Installing modules
One of the reasons for using CPAN is to simplify installation. If your module requires other modules and these requisite modules are not installed, CPAN will install them automatically for you.

To install modules, type:

install modulename

When you install a module, CPAN will create the makefile, make the module, test it and then install it in one step.

To install the Tk module, you can do this:

install DBI

To install the HTML::Mason module, you do this:

install HTML::Mason

Forcing Installation
There will be times when the CPAN install would not work. You might have to force the installation ONLY if you are sure that the error is acceptable. Otherwise, you will have to manually install the module.

To force installation, you can type:

force install modulename

This will install the module even if CPAN encounters errors during testing.

Copyright: © 2017 Philip Yuson