Switch (Case) Statment in Bash

Switch (Case) Statement in Bash

The case statement in Bash is a conditional construct that simplifies checking multiple conditions. It’s often used when comparing a variable or expression against multiple patterns and executing corresponding commands.

Why Use a Case Statement?

Readability: Easier to understand compared to nested if-elif statements.
Efficiency: Suitable for matching multiple cases quickly.
Flexibility: Supports pattern matching with wildcards and ranges.

Syntax

case variable in
    pattern1)
        # Commands for pattern1
        ;;
    pattern2)
        # Commands for pattern2
        ;;
    *)
        # Default commands (optional)
        ;;
esac

Key Points:

variable is the value to evaluate.
pattern is the condition to match. It can include wildcards (*, ?) or ranges ([a-z]).
;; marks the end of a block of commands.
* serves as the default case (executed if no other pattern matches).
esac marks the end of the case block.

Basic Example: Menu Selection

echo "Choose an option:"
echo "1) Start"
echo "2) Stop"
echo "3) Exit"
read -r choice

case $choice in
    1)
        echo "Starting the process..."
        ;;
    2)
        echo "Stopping the process..."
        ;;
    3)
        echo "Exiting..."
        ;;
    *)
        echo "Invalid option. Please choose 1, 2, or 3."
        ;;
esac

Output (if user inputs 1):

Starting the process...

Advanced Example: File Type Checker

read -p "Enter a filename: " filename

case $filename in
    *.txt)
        echo "This is a text file."
        ;;
    *.jpg | *.png)
        echo "This is an image file."
        ;;
    *.sh)
        echo "This is a shell script."
        ;;
    *)
        echo "Unknown file type."
        ;;
esac

Output (if user inputs image.jpg):

This is an image file.

Example: Using Ranges

read -p "Enter a number: " num

case $num in
    [1-5])
        echo "You entered a number between 1 and 5."
        ;;
    [6-9])
        echo "You entered a number between 6 and 9."
        ;;
    *)
        echo "Number is out of range."
        ;;
esac

Case Statement with Command Substitution

You can evaluate the result of a command using case:

os_type=$(uname)

case $os_type in
    Linux)
        echo "You are using Linux."
        ;;
    Darwin)
        echo "You are using macOS."
        ;;
    *)
        echo "Unknown operating system."
        ;;
esac

Handling Multiple Patterns

You can combine patterns using | (logical OR):

read -p "Enter a fruit: " fruit

case $fruit in
    apple|banana|cherry)
        echo "This is a common fruit."
        ;;
    mango|pineapple)
        echo "This is a tropical fruit."
        ;;
    *)
        echo "Unknown fruit."
        ;;
esac

Output (if user inputs apple):

This is a common fruit.

Using Functions with Case Statements

You can pair functions with case to keep your script modular:

start_service() {
    echo "Starting the service..."
}

stop_service() {
    echo "Stopping the service..."
}

case $1 in
    start)
        start_service
        ;;
    stop)
        stop_service
        ;;
    *)
        echo "Usage: $0 {start|stop}"
        ;;
esac

Conclusion

The case statement in Bash is a powerful tool for handling multiple conditions elegantly. It’s versatile, supports pattern matching, and is much cleaner than using multiple if-elif statements. Whether you're writing a menu-driven script, checking file types, or handling user input, the case statement is your go-to solution.

Let me know if you'd like additional examples or adjustments!

Souy Soeng