http://www.perlmonks.org?node_id=586

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

If you're storing your dates as epoch seconds then simply subtract one from the other. If you've got a structured date (distinct year, day, month, hour, minute, seconds values) then use one of the Date::Manip and Date::Calc modules from CPAN.