Erm, let the OS do it. (localtime( $time_t ))[8] should be correct for the native time zone. If you need that for a time zone other than the system's naitive one use do { local $ENV{TZ} = "XYZ"; (localtime( $time_t ))[8]} instead.

Getting your date as a time_t is of course an exercise for the reader (see Time::Local or something like Date::Parse).