[Linux] C Shell (csh) switch用法: Conditional branching in scripts

Overview

The switch command in C Shell (csh) is used for conditional branching, allowing users to execute different blocks of code based on the value of a variable. It simplifies the process of making decisions in scripts by providing a cleaner syntax compared to multiple if statements.

Usage

The basic syntax of the switch command is as follows:

switch (expression)
    case pattern1:
        commands
        breaksw
    case pattern2:
        commands
        breaksw
    default:
        commands
        breaksw
endsw

Common Options

• case pattern:: Defines a pattern to match against the expression.
• breaksw: Exits the switch block after executing the matched case.
• default:: A fallback case that executes if no patterns match.

Common Examples

Example 1: Basic Switch Statement

set color = "red"
switch ($color)
    case "red":
        echo "Color is red"
        breaksw
    case "blue":
        echo "Color is blue"
        breaksw
    default:
        echo "Color is unknown"
        breaksw
endsw

Example 2: Matching Multiple Patterns

set fruit = "apple"
switch ($fruit)
    case "apple":
    case "banana":
        echo "This is a fruit"
        breaksw
    default:
        echo "Not a fruit"
        breaksw
endsw

Example 3: Using Default Case

set day = "Monday"
switch ($day)
    case "Saturday":
        echo "It's the weekend!"
        breaksw
    case "Sunday":
        echo "It's the weekend!"
        breaksw
    default:
        echo "It's a weekday."
        breaksw
endsw

Tips

• Always include a default case to handle unexpected values.
• Use breaksw to prevent fall-through behavior, ensuring only the matched case executes.
• Keep your patterns simple and clear for better readability and maintenance of your scripts.