Here's a snippet I use a lot at home-

use Date::Calc "Delta_Days";

my $first = shift || die "Give two date strings YYYYMMDD YYYYMMDD\n";
my $second = shift || die "Give two date strings YYYYMMDD YYYYMMDD\n";

my $days = Delta_Days( $first =~ /(\d\d\d\d)(\d\d)(\d\d)/,
                       $second =~ /(\d\d\d\d)(\d\d)(\d\d)/ );

print $days, $/;
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Though I love the DateTime stuff when anything gets much hairier than that.