CPAN Module Distributions

CAUTION It is important to include all modules that your module uses 

in PREREQ_PM, even ones that come with Perl. Unfortunately, many pack 

agers of Perl choose to not include some or all of the optional modules 

usually included with Perl. Thus, even if a module is installed by default 

on your system, some of your users may need to install the module 

from CPAN.

NOTE There is no way to specify that your module needs an exact 

version of another module and won't work with a later, higher num 

bered version. To do this you'll need to add code to your Makefile.PL

to explicitly check for the version you need.

The next section is somewhat curious:

    ($] >= 5.005 ?    ## Add these new keywords supported since 5.005

      (ABSTRACT_FROM   =>  Counter.pm , # retrieve abstract from module

       AUTHOR          =>  A. U. Thor  ) : ()),

It checks to see if the Perl version is 5.005 or greater and then defines some parameters 

if it is. This seems to be at odds with the module file that h2xs generates. Although 

Makefile.PL goes out of its way to support older versions of Perl, the generated 

module file will only work with rather new versions! In fact, it would be better if the 

required Perl version were checked in Makefile.PL rather than in the module file 

itself. That way version incompatibility is discovered as early as possible, saving 

users from downloading prerequisite modules for a module that they won't be able 

to use. For example, to include a version check for Perl 5.6.0, I add this line at the 

top of Data::Counter's Makefile.PL:

use 5.006;

This is needed since Data::Counter uses the new our keyword, which isn't available 

before version 5.6.0.

The parameters that are set inside the check for 5.005 are ABSTRACT_FROM and 

AUTHOR. ExtUtils::MakeMaker uses ABSTRACT_FROM to search for a one line description of 

your module. It does so by looking for a line that starts with your module name and 

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