case语句：选择结构
case SWITCH in
value1)
statement
...
;;
value2)
statement
...
;;
*)
statement
...
;;
esac
case $1 in
[0-9])
echo "A digit." ;;
[a-z])
echo "Lower" ;;
[A-Z])
echo "upper" ;;
*)
echo "Special character."
esac
