case - macOS

Overview

The case command in macOS is a shell builtin that performs conditional matching against strings. It is used primarily within shell scripts or command line to execute different commands based on the value of a given string. This command is particularly effective in scenarios where multiple conditional checks are required, and it can simplify scripting decisions compared to multiple if-elif-else statements.

Syntax

The basic syntax of the case command is as follows:

case <expression> in
    <pattern1>)
        <commands1>
        ;;
    <pattern2>)
        <commands2>
        ;;
    *)
        <default_commands>
        ;;
esac

<expression> is the variable or value you want to test.
<pattern> can include literal strings, wildcards, and other patterns that are matched against the expression.
<commands> are executed if the expression matches the corresponding pattern.
*) defines a default block that executes if no other pattern matches (optional).
esac ends the case block.

Options/Flags

The case command does not have options or flags as it is a shell control structure rather than an executable command. Its behavior is solely determined by the patterns and expressions specified in the script.

Examples

Simple Example:

#!/bin/bash
a="test"
case $a in
    test)
        echo "Pattern matched for test."
        ;;
    *)
        echo "No match found."
        ;;
esac

Complex Example with Wildcard:

#!/bin/bash
file_name="example.txt"
case $file_name in
    *.txt)
        echo "File is a text file."
        ;;
    *.jpg | *.png)
        echo "File is an image file."
        ;;
    *)
        echo "File type is not recognized."
        ;;
esac

Common Issues

Pattern not matching: Ensure that patterns cover the expected range of input values, including considering case sensitivity or using wildcards for partial matches.
Forget the double semicolon (;;): Each pattern block must end with ;;, or it will result in a syntax error.

Integration

case statements can be integrated into scripts that involve file manipulation, user input processing, or any other conditional logic. Here’s an example using case within a script that processes input options:

#!/bin/bash
option="$1"
case $option in
    start | -s)
        echo "Starting the process."
        # Commands to start the process
        ;;
    stop | -t)
        echo "Stopping the process."
        # Commands to stop the process
        ;;
    *)
        echo "Option is not recognized."
        ;;
esac

if: Used for conditional execution based on the success or failure of commands.
[ ] and [[ ]]: Test constructs used within if and while constructs to test string, arithmetic, and file conditions.

Further Reading:

Bash Reference Manual provides a detailed guide and reference to Bash scripting, where case statements are frequently used.