How to determine if Python script was run via command line?

If you’re running it without a terminal, as when you click on “Run” in Nautilus, you can just check if it’s attached to a tty:

import sys
if sys.stdin and sys.stdin.isatty():
    # running interactively
    print("running interactively")
else:
    with open('output','w') as f:
        f.write("running in the background!\n")

But, as ThomasK points out, you seem to be referring to running it in a terminal that closes just after the program finishes. I think there’s no way to do what you want without a workaround; the program is running in a regular shell and attached to a terminal. The decision of exiting immediately is done just after it finishes with information it doesn’t have readily available (the parameters passed to the executing shell or terminal).

You could go about examining the parent process information and detecting differences between the two kinds of invocations, but it’s probably not worth it in most cases. Have you considered adding a command line parameter to your script (think --interactive)?