check if bash script was sourced

To determine whether a Bash script was sourced or executed directly, you can utilize specific built-in Bash variables. Understanding how to distinguish between these two methods of running a script is crucial, especially when you want to control the behavior of the script based on its execution context.

Understanding Sourcing vs. Executing

When you source a script, it runs in the current shell environment, allowing any functions or variables defined in the script to be available in the current session. Conversely, executing a script runs it in a new shell instance, isolating its environment from the calling shell.

Checking if a Bash Script was Sourced

The key to detecting whether a script was sourced involves comparing two special variables: $0 and ${BASH_SOURCE[0]}.

The Check

You can perform this check by using the following conditional statement within your script:

if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
    echo "Script is executed directly"
else
    echo "Script is sourced"
fi

Explanation of the Variables

• ${BASH_SOURCE[0]}: Contains the path of the script being executed or sourced. When sourcing, it reflects the script's actual path.
• $0: Represents the name of the current shell or script running. If the script is sourced, $0 will still point to the parent shell, not to the script itself.

Practical Example

Here's a complete example of how you can implement this check in a script:

#!/bin/bash

if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
    echo "Executed directly"
else
    echo "Sourced"
fi

Additional Considerations

• Function Definitions: If your script defines functions you intend to use in the current shell, sourcing is necessary.
• Exit Behavior: You might want to control whether the script can terminate the shell (for example, using exit statements) based on whether it was sourced or executed directly.

Conclusion

By incorporating this simple check ([[ "${BASH_SOURCE[0]}" == "${0}" ]]) into your Bash scripts, you can easily determine how they are being run. This capability is particularly advantageous for scripts designed to serve dual purposes—either executing in isolation or enhancing the current shell environment when sourced.

Understanding and using these techniques will help you write more robust and flexible Bash scripts tailored to varying execution scenarios.