Cataloguing Perl Module Dependencies

So you have a bunch of Perl scripts and modules you’ve written over time, and you’d like to quickly determine what non-core Perl modules are required to make them run. Devel::Modlist to the rescue.

$ perl -d:Modlist=nocore some-funky-script
Module::ExtractUse 0.27
Module::ExtractUse::Grammar 0.25
Parse::RecDescent 1.967009
Pod::Strip 1.02
version::vxs 0.95

Unfortunately Devel::Modlist is not itself a core module, but it’s an easy install since it doesn’t have any dependencies of its own. The way it works is pretty clever. Rather than trying to parse the Perl scripts and modules, looking for “use” statements, it loads the code into the Perl debugger. This is a smart approach since the common wisdom is only perl can parse Perl.

But this is not a perfect solution. For one, this only works for code that already runs on your system, so you can’t use it to quickly list what modules are needed for some bit of Perl you just downloaded. It also cannot find and report on modules that get loaded dynamically, as would happen if you do something like:

if ($magicRequired) { require Magic; castSpell(); }

And finally this module is not designed to be used from inside of a Perl script since it would cause the dependency reporting every time that script is executed. The shell command line example shown above is the normal usage model for this module.

But even with those caveats, this is still a handy little tool to have in your Perl toolbox.

2 Responses to “Cataloguing Perl Module Dependencies”

  1. I’ve just been bitten by module version discrepancies across environments. Thanks so much for posting this; it’s going directly into my release and deployment routines.

    I’ve also been looking at local::lib and Carton, for allowing your Perl program to use alternate CPAN module versions that what your Perl has installed.

  2. Here is an excellent review of various Perl dependency checkers available on CPAN:

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