Bash: Functions

Functions allow you to group a set of commands to be reused multiple times throughout your script, making your code more organized and readable.

Defining a Function

Basic function syntax

function greet {
    echo "Hello, world!"
}

The `function` keyword is optional, but it improves readability. The commands go between curly braces `{}`.

Calling a Function

Calling the function by name

greet

To run the function, simply call its name as you would a regular command.

Functions with Parameters

Passing parameters to a function

function greet_user {
    echo "Hello, $1!"
}

greet_user "Alice"

Inside a function, parameters are accessed using `$1`, `$2`, etc., just like in a regular script.

Return Values

Returning a status code

function check_file {
    if [ -f "$1" ]; then
        return 0 # Success
    else
        return 1 # Failure
    fi
}

check_file "my_file.txt"
if [ $? -eq 0 ]; then
    echo "File exists."
fi

Functions use the `return` command to exit with a status code. A status of `0` typically means success, and a non-zero status means failure. The special variable `$?` holds the status code of the last executed command or function.

Since [] itself already returns success/failure, you can shorten the 'check_file' function:

function check_file { [ -f "$1" ]; }

check_file "my_file.txt"
if [ $? -eq 0 ]; then
    echo "File exists."
fi