Bash Case Statement

Bash Case Statement

In Bash scripting, the case statement allows you to make decisions based on the value of a variable. It provides a way to simplify complex conditional operations by matching a variable against multiple patterns.

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Syntax

case "$variable" in
    pattern1)
        # commands for pattern1
        ;;
    pattern2)
        # commands for pattern2
        ;;
    *)
        # default commands
        ;;
esac

The basic syntax involves using case followed by the variable in double quotes, patterns to match against, and the commands to execute for each pattern. The ;; marks the end of each pattern's commands, and esac ends the case statement.

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Example Bash Case Statements

Let's look at some examples of how to use case statements in Bash:

1. Case Statement for Day of the Week

This script checks the value of the variable day and prints a message based on the day of the week.

#!/bin/bash

day="Monday"

case "$day" in
    "Monday")
        echo "Today is Monday."
        ;;
    "Tuesday")
        echo "Today is Tuesday."
        ;;
    "Wednesday")
        echo "Today is Wednesday."
        ;;
    *)
        echo "It's another day."
        ;;
esac

In this script, the variable day is assigned the value 'Monday'. The case statement checks the value of day and matches it against the patterns 'Monday', 'Tuesday', and 'Wednesday'. If none of these patterns match, the default case prints a message indicating it's another day.

2. Case Statement for User Input

This script prompts the user to enter a number between 1 and 3 and prints a corresponding message.

#!/bin/bash

read -p "Enter a number between 1 and 3: " number

case "$number" in
    1)
        echo "You entered one."
        ;;
    2)
        echo "You entered two."
        ;;
    3)
        echo "You entered three."
        ;;
    *)
        echo "Invalid input."
        ;;
esac

In this script, the user is prompted to enter a number between 1 and 3. The case statement checks the value of number and matches it against the patterns 1, 2, and 3. If none of these patterns match, the default case prints a message indicating invalid input.

3. Case Statement for File Type

This script checks the extension of a filename and prints a message based on the file type.

#!/bin/bash

filename="document.txt"

case "$filename" in
    *.txt)
        echo "It's a text file."
        ;;
    *.jpg)
        echo "It's an image file."
        ;;
    *.sh)
        echo "It's a shell script."
        ;;
    *)
        echo "Unknown file type."
        ;;
esac

In this script, the variable filename is assigned the value 'document.txt'. The case statement checks the extension of filename and matches it against the patterns '*.txt', '*.jpg', and '*.sh'. If none of these patterns match, the default case prints a message indicating an unknown file type.

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Conclusion

The Bash case statement is a powerful tool for simplifying complex conditional operations in shell scripting. Understanding how to use case statements can help you create more efficient and readable scripts.