case

Match a variable against string literals to decide which command to run

$ case [$COUNTRULE] in [words]) [wc --words README] ;; [lines]) [wc --lines README] ;; esac

$ case [$COUNTRULE] in [[wW]|words]) [wc --words README] ;; [[lL]|lines]) [wc --lines README] ;; *) [echo "what?"] ;; esac

$ case [$ANIMAL] in [cat]) echo "It's a cat" ;;& [cat|dog]) echo "It's a cat or a dog" ;;& *) echo "Fallback" ;; esac

$ case [$ANIMAL] in [cat]) echo "It's a cat" ;& [dog]) echo "It's either a dog or cat fell through" ;& *) echo "Fallback" ;; esac

$ help case

case value in
pattern1) commands1 ;;
pattern2) commands2 ;;
...
*) default_commands ;;
esac

value
    The variable or expression to be evaluated.

pattern
    A pattern to match against the value. Can include literals, wildcards (*, ?, []), or alternation (|).

commands
    The commands to execute if the corresponding pattern matches the value.

;;
    Terminates the command list for a specific pattern, preventing fallthrough to the next pattern.

*)
    A wildcard pattern that matches any value not matched by the previous patterns. It defines the default case.

The case command in Linux is a control flow statement that allows you to execute different commands based on the value of a variable or expression. It provides a more readable and structured alternative to nested if-then-else statements when dealing with multiple conditions. The case command works by comparing a specified value against a series of patterns. When a pattern matches the value, the corresponding commands are executed. The case statement ends with the esac keyword (case reversed). The patterns can include literal values, wildcard characters (*, ?, []), and alternation (|). It is commonly used in shell scripts to handle different input options, system states, or user choices. The case statement offers improved script readability and maintainability by organizing conditional logic in a clear and concise manner.

If multiple patterns match the value, only the commands associated with the first matching pattern are executed. It's important to order patterns carefully to avoid unintended behavior.

While the case statement supports wildcards, it's important to note they are not regular expressions. The '*' matches zero or more characters, '?' matches any single character, and '[]' defines a character class. For more complex pattern matching, consider using tools like grep or regular expression constructs within the shell.

The exit status of the case statement is the exit status of the last command executed within the matching pattern. If no pattern matches, the exit status is 0.

The case statement is a fundamental part of the Bourne shell and its descendants (Bash, Zsh, etc.). It has been a standard feature of Unix-like operating systems since the early days of shell scripting, providing a structured way to handle multiple conditional branches.

if(1), test(1)