To manipulate dates use the Date::Manip package. It's big and slow but the most functional date handling package that I've seen in any language.

I once had a problem installing a module using CPAN on Red Hat 9. The makefile that was generated by MakeMaker had bogus data in it, like lines with a single quote that wasn't terminated, etc. This page http://dbforums.com/arch/96/2003/7/753440 indicated that the problem was caused by RH setting the LANG environment to en_US.UTF-8 and sure enough, when I unset LANG and ran it again it worked.