How to break out of a sourced Bash script's function

Question

I have a Bash script that is sourced. When this script is sourced, it runs a function in the Bash script. This function should terminate the script if a certain condition is matched. How can this be done without terminating the shell in which the script is sourced?

To be clear: I want the termination action to be completed by the function in the sourced shell script, not in the main body of the sourced shell script. The problems that I can see are that return simply returns from the function to the main of the script while exit 1 terminated the calling shell.

The following minimal example illustrates the problem:

main(){
    echo "starting test of environment..."
    ensure_environment
    echo "environment safe -- starting other procedures..."
}

ensure_environment(){
    if [ 1 == 1 ]; then
        echo "environment problemm -- terminating..."
        # exit 1 # <-- terminates calling shell
        return   # <-- returns only from function, not from sourced script
    fi
}

main

Answer 1

You can return from a sourced shell script. POSIX spec

So, while you can't return from the function directly to get what you want you can return from the main body of the script if your function returns non-zero (or some other agreed upon value).

For example:

$ cat foo.sh
f() {
    echo in f "$@"
}

e() {
    return 2
}

f 1
e
f 2
if ! e; then
    return
fi
f 3
$ . foo.sh
in f 1
in f 2