while

until

#!/bin/bash
#
cat << EOF
d|D) show disk usage
m|M) show memory usage
s|S) show swap usage
q|Q) quited
EOF
read Input
until [ $Input == q -o $Input == Q ];do
        case $Input in
                d|D)
                   df -h
                   echo " d|D) show disk usage"
                   echo " m|M) show memory usage"
                   echo " s|S) show swap usage"
                   echo " q|Q) quited"
                   read Input
                   ;; 
                m|M)
                   free -m | grep 'Mem'
                   echo " d|D) show disk usage"
                   echo " m|M) show memory usage"
                   echo " s|S) show swap usage"
                   echo " q|Q) quited"
                   read Input
                   ;; 
                s|S)
                   free -m | grep 'Swap'
                   echo " d|D) show disk usage"
                   echo " m|M) show memory usage"
                   echo " s|S) show swap usage"
                   echo " q|Q) quited"
                   read Input
                   ;; 
                *) 
                   echo "Usage: {[d|D],[m|M],[s|S],[q|Q]}"
                   read Input
                   ;; 
        esac
done