~ perl6 -e 'sub MAIN (Int $month where 1 <= $month <= 12) {say "Success";}' 4
Success

~ perl6 -e 'sub MAIN (Int $month where 1 <= $month <= 12) {say "Success";}' 14
Usage:
  -e '...' <month>

~ perl6 -e 'sub MAIN (Int $month where 1 <= $month <= 12) {say "Success";}' 8.5
Usage:
  -e '...' <month>