[Linux] How to tell a bash script is sourced or executed?

In bash, a script can be both executed and sourced.

An example script as follows:

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#!/bin/bash

if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
    echo "I am being executed"
    sourced=0
else
    echo "I am being sourced"
    sourced=1
fi

# this variable setting has no effect if executed, because
# the execution is in a sub-shell
export VAR_SOURCE="Only effective if sourced"

if [[ $sourced -gt 0 ]]; then
  echo "Done in source"
  return 0
else
  # call exit when sourcing a file will exit the terminal
  echo "Done in execute"
  exit 0
fi

Distinguish between the two

To tell whether a script is being sourced or not, one can use the test [[ "${BASH_SOURCE[0]}" == "$0" ]], where ‘${BASH_SOURCE[0]}’ is the current script filename, and ‘$0’ is the same if being executed but empty string "" if sourced, as shown in the above code.

Some differences between sourcing and executing

export: the command export has no effect for the calling environment because it is executed in a sub-shell. To set variables in current environment, source the script.
exit and return: calling ‘exit’ when sourcing a script will close the terminal, use ‘return’ instead.

References

Discussion of ‘$BASH_SOURCE’ on stackoverflow: https://stackoverflow.com/questions/41837948/can-a-bash-script-determine-if-its-been-sourced

Last modified on 2021-06-03