return boolean in Bash

In Bash programming, the return command is used to exit a function and return a value to the calling section of the code. A boolean value is a type of variable with only two possible values: true or false.

Syntax

The syntax of the return command in Bash is as follows:

return [n]

Where n represents the exit status of the function. The exit status is a numeric value that indicates success or failure of the function. By convention, an exit status of 0 indicates success, while any other value represents failure.

Example

Suppose we want to create a function that checks whether a given file exists. We can use the return command to indicate whether the file exists or not:

#!/bin/bash

check_file_existence() {
    if [ -f "$1" ]; then
        return 0  # file exists
    else
        return 1  # file does not exist
    fi
}

# call the function
check_file_existence "/etc/passwd"
if [ $? -eq 0 ]; then
    echo "File exists"
else
    echo "File does not exist"
fi

In this example, the check_file_existence function takes a filename as an argument, and checks whether the file exists using the -f operator. If the file exists, the function returns 0; otherwise, it returns 1. The ?$ syntax is used to get the exit status of the function, which is then used to determine whether the file exists or not.

Conclusion

The return boolean command is used to return a boolean value from a Bash function. By convention, a 0 exit status represents success, while any other value represents failure. The return command can be used to indicate success or failure based on some condition in the function.