Case statement in Bash

case expression in
  pattern1) execute commands;;
  pattern2) execute commands;;
  pattern3) execute commands;;
  pattern4) execute commands;;
  * ) execute else or nothing
;;

esac

echo "Enter a letter"
read letter
case "$letter" in
  "a"|"A") echo "Yoou entered vowel a" ;;
  "b"|"B") echo "You entered a consonant b" ;;
  *) echo "you entered somthing else" ;;
esac