A common type of interactivity is called menu driven. In menu-driven programs, the user is presented with a list of choices and is asked to choose one. For example, we could imagine a program that presented the following:

Please Select:

1. Display System Information
2. Display Disk Space
3. Display Home Space Utilization
0. Quit

Enter selection [0-3] >

Using what we learned from writing our sys_info_page program, we can construct a menu-driven program to perform the tasks on the above menu:

#!/bin/bash

# read-menu: a menu driven system information program

clear
echo "
Please Select:

1. Display System Information
2. Display Disk Space
3. Display Home Space Utilization
0. Quit
"
read -p "Enter selection [0-3] > "

if [[ $REPLY =˜ ^[0-3]$ ]]; then
        if [[ $REPLY == 0 ]]; then
                echo "Program terminated."
                exit
        fi
        if [[ $REPLY == 1 ]]; then
                echo "Hostname: $HOSTNAME"
                uptime
                exit
        fi
        if [[ $REPLY == 2 ]]; then
                df -h
                exit
        fi
        if [[ $REPLY == 3 ]]; then
                if [[ $(id -u) -eq 0 ]]; then
                        echo "Home Space Utilization (All Users)"
        ....