Case Statement in Bash Script

case statement in bash shell is similar to switch statement in C++. It can be used to test simple values like integers and characters. Bash shell checks the condition, and controls the flow of the program. The case construct also allows us to test strings against patterns that can contain wild card characters.

Syntax

Below is the syntax of case statement in shell script

case  $variable-name  in
    pattern1)
        ...
        ....
        ;;
    pattern2)
        ...
        ....
        ;;            
    pattern4|pattern5|pattern6)
        ...
        ....
        ;;
    patternN)
        ...
        ....
        ;;
    *)
        ...
        ....				
        ;;
esac 

$variable-name is compared against the patterns until a match is found. *) acts as default and it is executed if no match is found. The pattern can include wildcards. When a match is found all of the associated statements until the double semicolon (;;) are executed. esac indicate end of case statement.

Example

Consider below example. Below example checks if user has passed any argument to this script. If the valid argument is passed, type of the vehicle is printed. | is or operator, it matches multiple conditions.

#!/bin/bash

# -z switch will test if the expansion of "$1" is a null string or not. 
# If it is a null string then the body is executed.
if [ -z "$1" ]
    then
        echo "Unknown vehicle"
        exit
elif [ -n $1 ]
    then
        # otherwise set first arg
        vehicle=$1

        # use case statement to make decision
        case $vehicle in
        "car"|"van") echo "Four wheeler";;
        "bicycle") echo "Two wheeler";;
        *) echo "No match found!";;
        esac
fi

Upon executing this script with argument it will generate below output.

./exp.sh
Unknown vehicle

./exp.sh "car"
Four wheeler

./exp.sh "Rail"
No match found!

Interactive Script

During software installation or license agreement, we need to ask yes or no input from user. The following code snippet is one of the way to get the yes or no input from user.

#!/bin/bash

echo -n "Select [yes or no]: "
read yno
case $yno in
    [yY]|[yY][Ee][Ss] )
            echo "Yes"
            ;;
    [nN]|[nN][Oo] )
            echo "No";
            ;;
    *) echo "Invalid input"
        ;;
esac

Above script ask a user to choose yes or no. If user selects ‘yes’ or ‘no’, it prints the corresponding value on the terminal. For other values entered by the user, it prints Invalid input. Below snippet shows the output of this script for some of the sample inputs.

./exp.sh
Select [yes or no]: Yes
Yes

./exp.sh
Select [yes or no]: No
No