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case
In bash, multiple-choice compound command is called case. It has the following syn- tax:
case word in
[pattern [| pattern]...) commands ;;]...
esac
If we look at the read-menu program from Chapter 28, we see the logic used to act on a user’s selection:
#!/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
#!/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
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
Using case, we can replace this logic with something simpler:
#!/bin/bash
# case-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] > "
case $REPLY in
0) echo "Program terminated." exit
;;
#!/bin/bash
# case-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] > "
case $REPLY in
0) echo "Program terminated." exit
;;
1) echo "Hostname: $HOSTNAME" uptime
;;
2) df -h
;;
3) 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
;;
*) echo "Invalid entry" >&2 exit 1
;;
esac
1) echo "Hostname: $HOSTNAME" uptime
;;
2) df -h
;;
3) 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
;;
*) echo "Invalid entry" >&2 exit 1
;;
esac
The case command looks at the value of word, in our example, the value of the REPLY variable, and then attempts to match it against one of the specified patterns. When a match is found, the commands associated with the specified pattern are executed. After a match is found, no further matches are attempted.