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Menus
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] >
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] > "
#!/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 [[ $(id -u) -eq 0 ]]; then
echo "Home Space Utilization (All Users)" du -sh /home/*
else
echo "Home Space Utilization ($USER)" du -sh $HOME
fi exit
fi else
echo "Invalid entry." >&2 exit 1
fi
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 [[ $(id -u) -eq 0 ]]; then
echo "Home Space Utilization (All Users)" du -sh /home/*
else
echo "Home Space Utilization ($USER)" du -sh $HOME
fi exit
fi else
echo "Invalid entry." >&2 exit 1
fi
This script is logically divided into two parts. The first part displays the menu and inputs the response from the user. The second part identifies the response and carries out the se- lected action. Notice the use of the exit command in this script. It is used here to pre- vent the script from executing unnecessary code after an action has been carried out. The presence of multiple exit points in a program is generally a bad idea (it makes program logic harder to understand), but it works in this script.