Why is trap in bash throwing an error when empty variable is assigned

Question

I have been using the trap function for a while now, but am running into an issue I don't understand.

Here is a reprex:

err_report() {
    
    echo -e "ERROR LINE $1"
    exit 1;
}
trap 'err_report ${LINENO}' ERR

existing=$(echo test | grep -oP "x")

This will throw an error because the result of the grep is empty. When I run the code without the trap, all works fine. I tried setting set +u but that didn't help..

What am I doing wrong here?

Thanks

Thanks a lot! That did the trick :) I had no idea it was the grep's fault ... — pieterjanvc, Nov 04 '20 at 15:06

score 4 · Accepted Answer · answered Nov 04 '20 at 15:07

4

When grep fails to match anything, it'll exit with a non-zero exit status, triggering the ERR trap. Since you're not interested in grep's exit status here, this should do the trick:

existing=$(echo test | grep -oP 'x' || true)

answered Nov 04 '20 at 15:07

Ted Lyngmo

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Why is trap in bash throwing an error when empty variable is assigned

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