A Dark And Stormy Night ... - Page 165

You sit alone, at the keyboard, staring at the prompt:

[lonelyone@badhost]$

Friday night is here, and you're juiced up to script some Perl (we're just kidding, of course, you are well-liked and popular with all genders). It's a good idea, both for future reference and future pickup lines, to know which version of Perl is installed on this system:

[lonelyone@badhost]$ perl -v

This is perl, v5.6.1 built for i686-linux

Let's hustle to the farmer's market that is CPAN. To visit CPAN, you'll need to use the CPAN module. Apropos for a farmer's market, it looks like we might have the chicken and egg paradox on our hands — you need a module to retrieve modules — but in this case, the answer is "the chicken". The CPAN module has been part of the standard Perl distribution for awhile now. If the following command does not work, and thus CPAN is not part of your ISP's old, crusty version of Perl, I would raise hell.

perl -MCPAN -e shell

The above command will launch Perl with the CPAN module (the -M argument), and execute (-e) the command 'shell'. This brings us into the CPAN "interactive shell", a mini-environment for executing CPAN-specific commands.

When CPAN runs for the first time, it will try to create a configuration file. For most users, this will be ~yourhome/.cpan, and a message to this effect appears in the welcome output:

/home/lonelyone/.cpan/CPAN/MyConfig.pm initialized.

Following the welcome text, we are given the chance to engage in manual or automatic configuration. It's a good idea to say 'yes' to manual configuration, especially because we want to build Perl modules in our private home directory, rather than the Perl installation tree. The value in square brackets following the question is CPAN's default answer, which you can simply hit Enter to accept, or else type your alternate choice.

Are you ready for manual configuration? [yes] yes

As you'll see between configuration questions, CPAN is very talkative. Following more chatter, we're asked to confirm a local directory for CPAN to work in — it needs a place to save and build modules. Unless you have a strong objection, the default is fine.

From here on in, we won't detail every question that the CPAN interrogation asks, because there are many. Most of the time, we choose the defaults. Below, let's go over the questions that need specific, non-default responses:

Policy on building prerequisites (follow, ask or ignore)? [follow]

Some modules require other modules to be installed. If CPAN detects that you need new or upgraded modules, it can automatically retrieve and install them, or ask you for permission for each prerequisite module. In many cases, "follow" will work fine and save you the hassle of approving each decision. However, there are cases where module dependencies might contain mistakes, causing CPAN to go on a wild goose chase, or down a path you'd rather not go down. The safe choice is "ask", thus embracing you in the process.

Parameters for the 'perl Makefile.PL' command?

This is a very important configuration item. We want CPAN to install Perl modules in a special place, not the Perl installation tree. So the answer to this question is crucial. Imagine that our home directory is ~lonelyone. Within, we've created perl, for all our Perl stuff, and within that modules, for just the module stuff. So, we'll want ~lonelyone/perl/modules to be where CPAN installs Perl modules, and where Perl will look for these modules when we run scripts out of there.

Your choice: []
PREFIX=~lonelyone/perl/modules LIB=~lonelyone/perl/modules

[The lines above are one line. It has been split for formatting purposes.]

We've supplied two parameters, PREFIX and LIB. This will ensure that CPAN builds modules in our home directory, and later we'll see how to instruct Perl to find the modules there.

Continuing with the configuration questions (again, we choose the defaults), eventually CPAN will ask you to choose some CPAN sites. When you finally complete the interrogation, you'll land at the CPAN shell prompt.

The Perl You Need to Know Part 23: CPAN, a Farmer's Market for Perl - Page 164
The Perl You Need to Know
Inside CPAN - Page 166