Writing a bash script, how do I stop my session from exiting when my script exits?

Question

bash scripting noob here. I've found this article: https://www.shellhacks.com/print-usage-exit-if-arguments-not-provided/ that suggests putting
[ $# -eq 0 ] && { echo "Usage: $0 argument"; exit 1; }

at the top of a script to ensure arguments are passed. Seems sensible.

However, when I do that and test that that line does indeed work (by running the script without supplying any arguments: . myscript.sh) then the script does indeed exit but so does the bash session that I was calling the script from. This is very irritating.

Clearly I'm doing something wrong but I don't know what. Can anyone put me straight?

It's not clear what exactly you are doing. I guess that you run that line in your shell which was started as part of the session, and when it hits exit 1 that shell is closed. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Mar 9, 2018 at 14:30
Yes I think you're right, is there a way to prevent that from happening? — jamiet
– jamiet, Commented Mar 9, 2018 at 14:31

Thomas · Accepted Answer · 2018-03-09 14:47:18Z

4

. myscript.sh is a synonym for source myscript.sh, which runs the script in the current shell (rather than as a separate process). So exit terminates your current shell. (return, on the other hand, wouldn't; it has special behaviour for sourced scripts.)

Use ./myscript.sh to run it "the normal way" instead. If that gives you a permission error, make it executable first, using chmod a+x myscript.sh. To inform the kernel that your script should be run with bash (rather than /bin/sh), add the following as the very first line in the script:

#!/usr/bin/env bash

You can also use bash myscript.sh if you can't make it executable, but this is slightly more error-prone (somebody might do sh myscript.sh instead).

edited Mar 9, 2018 at 14:47

answered Mar 9, 2018 at 14:34

Thomas

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3 Comments

jamiet Over a year ago

Perfect. Thanks @Thomas.

Ulrich Eckhardt Over a year ago

Well, the other obvious alternative is bash myscript.sh, which doesn't require executable bit or hashbang line.

chepner Over a year ago

Note that if your script does need to be executed with source, you can use return instead of exit.

Nahuel Fouilleul · Accepted Answer · 2018-03-09 14:33:26Z

1

Question seems not clear if you're sourcing script source script_name or . script_name it's interpreted in current bash process, if you're running a function it's the same it's running in same process, otherwise, calling a script, caller bash forks a new bash process and waits until it terminates (so running exit doesn't exit caller process), but when running exit builtin in in current bash it exits current process.

answered Mar 9, 2018 at 14:33

Nahuel Fouilleul

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