Can a Bash Script Determine if it's Been Sourced?

Question

In Python, the common idiom is to write code like this:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

def main():
    pass

if __name__ == "__main__":
    main()

This is done so that if a Python script is imported rather than executed, its main method won't run.

Is there a similar idiom in Bash?

Answer 1

You can use this snippet at top of your script to determine if script is being sourced in:

#!/bin/bash

if [[ ${BASH_SOURCE[0]} != $0 ]]; then
   printf "script '%s' is sourced in\n" "${BASH_SOURCE[0]}"
fi

When script is sourced then $0 becomes -bash, which holds otherwise the name of the script itself.

Answer 2

There is a special bash variable meant for this,

BASH_SOURCE

An array variable whose members are the source filenames where the corresponding shell function names in the FUNCNAME array variable are defined. The shell function ${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]} and called from ${BASH_SOURCE[$i+1]}

It is literally an array variable, that holds a stack trace of sources, where ${BASH_SOURCE[0]} is the latest one.

An example shamelessly stolen from this-site, just for demonstration purposes,

Script aaa.sh

#!/bin/bash
echo "from ${BASH_SOURCE[0]} : BASH_SOURCE = ${BASH_SOURCE[*]}"
source bbb.sh

Script bbb.sh

#!/bin/bash
echo "from ${BASH_SOURCE[0]} : BASH_SOURCE = ${BASH_SOURCE[*]}"
source ccc.sh

Script ccc.sh

#!/bin/bash
echo "from ${BASH_SOURCE[0]} : BASH_SOURCE = ${BASH_SOURCE[*]}"
for i in ${BASH_SOURCE[@]}; do
    readlink -f $i
done

Running aaa.sh produces,

from aaa.sh : BASH_SOURCE = aaa.sh                
from bbb.sh : BASH_SOURCE = bbb.sh aaa.sh
from ccc.sh : BASH_SOURCE = ccc.sh bbb.sh aaa.sh
/tmp/ccc.sh                                       # -> first element showing the latest script sourced 
/tmp/bbb.sh
/tmp/aaa.sh