why bother with the temporary variables, especially inside map? Heck, you'd also screen out a small subset of invalid data.
print  map {$_ =~ /(\d\d)-(\d\d)-(\d{4})/ && "$3-$1-$2"; } ("01-02-1999");
of course, using this kind of code, you'd need to make sure that your dataset's valid -- you won't get Date::Manip's heavy duty "Am I valid datetime or not" routines.