Unofficially, you shouldn't use modules in perl golf unless specifically called for or given as an option in the problem. (Hypothetically, you could write a module that does the bulk of the work though still be of utility to others outside of the golf, release it to CPAN, then use that module in your golf to crush the other players). Typically golfs with 70 or more characters will be benefitted by a module use, while for golfs less than that, the module might be more trouble (as you have to add 5 + lenght(module name) automatically to use the module.

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Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
"I can see my house from here!"
It's not what you know, but knowing how to find it if you don't know that's important