Bash Scripting: Case Statements

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What is a Case Statement?

The case statement is used in Bash to perform pattern matching against a single value. It is similar to the switch statement in other languages, such as C or Java. The case statement can match strings, but it can't directly compare numeric values. However, it can be combined with other constructs to do numeric comparisons.

The case statement is useful when you need to make complex decisions in your scripts. It can make your code cleaner and easier to read.

Syntax

The syntax of a Bash case statement is:

case expression in
    pattern1)
        commands
        ;;
    pattern2)
        commands
        ;;
    pattern3)
        commands
        ;;
    *)
        commands
        ;;
esac

• expression: This is the value that you are trying to match against.
• pattern1, pattern2, pattern3: These are the patterns that you are trying to match. The patterns can be literal strings or wildcard expressions.
• commands: These are the commands that will be executed if the pattern matches.
• ;;: This is used to terminate each case.
• *): This is a catch-all case that will match any value. It is optional but is usually included as the last case. It is similar to the default case in a switch statement in other languages.
• esac: This is used to end the case statement.

Basic Case Statement

#!/bin/bash

read -p "Enter a fruit: " fruit

case $fruit in
    "apple")
        echo "Apple is tasty."
        ;;
    "banana")
        echo "Banana is sweet."
        ;;
    "orange")
        echo "Orange is sour."
        ;;
    *)
        echo "I don't know about that fruit."
        ;;
esac

In this script, you are prompted to enter a fruit. The script then checks the entered fruit against the cases and outputs a message depending on the fruit entered.

Case Statement with Wildcard Patterns

#!/bin/bash

read -p "Enter a filename: " filename

case $filename in
    *.txt)
        echo "This is a text file."
        ;;
    *.sh)
        echo "This is a shell script."
        ;;
    *.py)
        echo "This is a Python script."
        ;;
    *)
        echo "Unknown file type."
        ;;
esac

In this script, you are prompted to enter a filename. The script then checks the file extension against the cases and outputs a message depending on the file type.

Case Statement with Multiple Patterns

#!/bin/bash

read -p "Enter a day: " day

case $day in
    "Monday"|"Tuesday"|"Wednesday"|"Thursday"|"Friday")
        echo "It's a weekday."
        ;;
    "Saturday"|"Sunday")
        echo "It's a weekend."
        ;;
    *)
        echo "Invalid day."
        ;;
esac

In this script, you are prompted to enter a day. The script then checks the entered day against the cases and outputs a message depending on the day entered.

Conclusion

The case statement is a powerful tool in Bash that allows you to perform complex decisions based on pattern matching. It can be used to match literal strings or wildcard patterns, and it can be combined with other constructs to perform numeric comparisons.

• Bash Scripting
• Bash Scripting: Introduction
• Variables
• Basic Math
• Control Statements
• For Loops
• While Loops
• Functions
• Arguments

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Version 1.0

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