Bash: Print usage statement & exit; otherwise continue using Bash shorthand operators
 

I'm trying to write a Bash script using some shorthand Bash operators.

I want a short script to test for a commandline argument.
- If $1 is not present, then print a Usage statement and exit from the function.
- If there is a value, then continue with the rest of the function.

Here's the problem. If I run the command with no arguments, the 'echo "FOO=$1"' is still printed.

I know this is simple, but I just can't wrap my head around it this morning. It's been a long week.

Any help is appreciated.

-= Stefan

Try this:

I think the reason you were still getting the "FOO=" output is that ( echo "Usage: testIt foo"; exit 0 ; ) runs in a subshell because of the brackets. It exits from the subshell at your exit statement and continues with the script. dogpatch's example executes in one level...

Thanks Dogpatch. The 'if ; then; fi' certainly works.

I was just trying to figure out how to do this with the shorthand operators like [[ TEST ]] || and && .

Since I write these sorts of scripts often, I was hoping to find a one-liner to do this. Plus, it'd slick.

It *should* work at some level, right?

Hrm, I'll have to work on this more.

Here is one way to do it:

[[ -n "$1" ]] && echo "FOO=$1" || echo "Usage: testIt foo"

You are missing the exit requirement.

This statement will exit from the current shell. And actually, this is probably the preferred behavior within a shell script-- the script spawns a subshell (e.g. #!/bin/bash ), and the script & subshell will exit if it encounters an error.

However, if I put this in function within my current interactive shell, my current shell will exit.

I'm not saying that your solution is wrong ;) It is just an interesting thing to notice.

If you want only the function to be exited, here's a way:

Thank you jlliagre. Both of your solutions work.

Thanks!