Programming Perl, 3rd Edition

Time::Local

use Time::Local;
$time = timelocal($sec,$min,$hours,$mday,$mon,$year);
$time = timegm($sec,$min,$hours,$mday,$mon,$year);

$time = timelocal(50, 45, 3, 18, 0, 73);
print "Scalar localtime gives: ", scalar(localtime($time)), "\n";
$time += 28 * 365.2425 * 24 * 60 * 60;
print "Twenty-eight years of seconds later, it's now\n\t",
    scalar(localtime($time)), "\n";

This prints:

Scalar localtime gives: Thu Jan 18 03:45:50 1973
Twenty-eight years of seconds later, it's now
        Wed Jan 17 22:43:26 2001

The Time::Local module provides two functions, timelocal and timegm, that work like inverse functions for the standard localtime and gmtime functions, respectively. That is, they take a list of numeric values for the various components of what localtime returns in list context and figure out what input to localtime would produce those values. You might do this if you wanted to compare or run calculations on two different dates. Although these are not general-purpose functions for parsing dates and times, if you can arrange to have your input in the right format, they often suffice. As you can see from the example above, however, time has its oddities, and even simple calculations often fail to do the job intended due to leap years, leap seconds, and the phase of the moon. Two large but fully featured CPAN modules address these issues and more: Date::Calc and Date::Manip.