Bash Case Statement

Linuxize.com ^ | 28 February 2019 | Linuxize

[ShadowAce]

Bash case statements are generally used to simplify complex conditionals when you have multiple different choices. Using the case statement instead of nested if statements will help you make your bash scripts more readable and easier to maintain.

The Bash case statement has a similar concept with the Javascript or C switch statement. The main difference is that unlike the C switch statement the Bash case statement doesn’t continue to search for a pattern match once it has found one and executed statements associated with that pattern.

In this tutorial, we will cover the basics of the Bash case statements and show you how to use them in your shell scripts.

Case Statement Syntax

The Bash case statement takes the following form:

case EXPRESSION in

PATTERN_1) STATEMENTS ;;

PATTERN_2) STATEMENTS ;;

PATTERN_N) STATEMENTS ;;

*) STATEMENTS ;;
esac

• Each case statement starts with the case keyword followed by the case expression and the in keyword. The statement ends with the esac keyword.
• You can use multiple patterns separated by the | operator. The ) operator terminates a pattern list.
• A pattern can have special characters.
• A pattern and its associated commands are known as a clause.
• Each clause must be terminated with ;;.
• The commands corresponding to the first pattern that matches the expression are executed.
• It is a common practice to use the wildcard asterisk symbol (*) as a final pattern to define the default case. This pattern will always match.
• If no pattern is matched the return status is zero. Otherwise, the return status is the exit status of the executed commands.

Case Statement Example

Here is an example using the case statement in a bash script that will print the official language of a given country:

languages.sh

#!/bin/bash

echo -n "Enter the name of a country: "
read COUNTRY

echo -n "The official language of $COUNTRY is "

case $COUNTRY in

Lithuania)
echo -n "Lithuanian"
;;

Romania | Moldova)
echo -n "Romanian"
;;

Italy | "San Marino" | Switzerland | "Vatican City")
echo -n "Italian"

*)
echo -n "unknown"
;;

esac

Save the custom script as a file and run it from the command line.

The script will ask you to enter a country. For example, if you type “Lithuania” it will match the first pattern and the echo command in that clause will be executed.

The script will print the following output:

Enter the name of a country: Lithuania
The official language of Lithuania is Lithuanian

If you enter a country that doesn’t match any other pattern except the default wildcard asterisk symbol, let’s say Argentina the script will execute echo command inside the default clause.

Enter the name of a country: Argentina
The official language of Argentina is unknown

Conclusion

By now you should have a good understanding of how to write bash case statements. They are often used to pass parameters to a shell script from the command line. For example, the init scripts are using case statements for starting, stopping or restarting services.

[ShadowAce]

[Skywise]

Lol - read that as “Bush case statement” and was wondering what W had said now :)

[zeugma]

The case statement is extremely powerful, and can greatly simplify iterating over multiple options, as opposed to using long 'if ... then ... else' loops. Personally, I think it can make a script more legible than nested loops, which can easily get out of hand. Also, the final "*)" construct makes it easy to validate input. If your input doesn't fit the rather sharply defined criteria, you have an easy place to handle it.

ShadowAce, I'd recommend a post on 'while' loops next, as they are related IMO, one on functions would be cool too.

[DUMBGRUNT]

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