how to make a function readonly

Question

Having a sample function

function functionName ()
{
    echo "Hello World"
}

How can I avoid it to be overwritten by a following function with the same name?

function functionName ()
{
    echo "this is another function"
}

Answer 1

You need to use the -f option to make corresponding function readonly and syntax is:

readonly -f functionName

After this, if you ever try to update the function an error will be fired:

bash: functionName: readonly function