use MatchRegex qw( digits UCalpha );

$filename = join "", (
  digits(2),     # \d{2}
  UCalpha(2,5),  # [A-Z]{2,5}
  '_',           # _
  digits(2),     # \d{2}
  digits(2),     # \d{2}
  digits(4),     # \d{4}
);