if ($file_name =~ m#
      (?<=/a/)
      (\d{2,4})(\d{2})(\d{2})(?:ag)?#x) {
   @date{'YEAR', 'MONTH', 'DAY'} = ((
         length($1) == 2
         ? '19' . $1
         : $1), $2, $3
       ),$2,$3);
}