Switch Case in Shell Scripting

The case statement in shell scripting provides a way to perform conditional branching based on the value of a variable or an expression. It’s similar to a series of if-elif-else statements, but it can be more concise and readable in certain situations.

Here’s a detailed breakdown of the case statement:

Syntax:

case expression in
    pattern1)
        # Code to execute if expression matches pattern1
        ;;
    pattern2)
        # Code to execute if expression matches pattern2
        ;;
    ...
    *)
        # Default code to execute if none of the patterns match
        ;;
esac

case expression in
    pattern1)
        # Code to execute if expression matches pattern1
        ;;
    pattern2)
        # Code to execute if expression matches pattern2
        ;;
    ...
    *)
        # Default code to execute if none of the patterns match
        ;;
esac

• case: Indicates the start of the case statement.
• expression: This is the value that you want to compare against the patterns. It can be a variable, a command substitution, or any expression that yields a result.
• in: Marks the beginning of the pattern matching section.
• pattern1), pattern2), …: These are the patterns that are compared against the expression. If a pattern matches the expression, the corresponding block of code is executed. Patterns are typically strings, but they can also be regular expressions.
• ;;: This signals the end of a block of code for a particular pattern. It’s important to include this after each block of code to prevent “fall-through” (i.e., executing code for subsequent patterns if a match is found).
• *): The asterisk (*) is a wildcard pattern that matches anything. The default case is executed if none of the previous patterns match.
• esac: This marks the end of the case statement.

Example:

#!/bin/bash

fruit="apple"

case $fruit in
    "apple")
        echo "It's an apple."
        ;;
    "banana")
        echo "It's a banana."
        ;;
    "cherry")
        echo "It's a cherry."
        ;;
    *)
        echo "It's something else."
        ;;
esac

#!/bin/bash

fruit="apple"

case $fruit in
    "apple")
        echo "It's an apple."
        ;;
    "banana")
        echo "It's a banana."
        ;;
    "cherry")
        echo "It's a cherry."
        ;;
    *)
        echo "It's something else."
        ;;
esac

In this example, the value of the variable fruit is compared against different fruit names using the case statement. If a match is found, the corresponding message is printed. Otherwise, the default case (“It’s something else.”) is executed.

case statements are useful when you have a series of conditions to check against a single variable. They can make your code more readable and organised compared to a series of if-elif-else statements, especially when dealing with multiple cases.