use Date::Set;

# when the event occurs: every friday.
my $set = Date::Set->event ( rule => 'FREQ=WEEKLY;BYDAY=FR');

# in what period we want occurences: december 2002
my $period = Date::Set->period (time => ['20021201', '20021231']);

my @occurs = $set->during (at => $period)->list;
print "occurences on ", join (" ,", @occurs), "\n";