Fail bash script when command expansion fails

Question

I'd like to be able to warn and fail if the following command expansion fails:

#!/usr/bin/env bash
set -Eeuo pipefail

echo "$(invalid_cmd)"
echo "$?"

Instead of failing, I get the following output:

./script.sh: line 5: invalid_cmd: command not found

0

Please paste your script at shellcheck.net and try to implement the recommendations made there. — Cyrus
– Cyrus, Commented Oct 10, 2023 at 21:16

KamilCuk · Accepted Answer · 2023-10-10 21:24:11Z

1

Use a temporary variable. The exit status of variable assignment is the exit status of last command executed - in this case $(...).

tmp="$(invalid_cmd)"
ret="$?"  # won't get here, set -e will trigger
echo "$tmp"
echo "$ret"

Overall, echo "$(stuff)" is just stuff. Just run the command, no need to get the to command output to print it, command already prints it.

invalid_cmd
echo "$?"

answered Oct 10, 2023 at 21:24

KamilCuk

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3 Comments

UncleCarl Over a year ago

I believe OP was getting the return value of the echo command, not invalid_cmd.

tjm3772 Over a year ago

They were, which is why set -e didn't trigger. However, based on the context of their question, that's probably not their intention.

kporter Over a year ago

Ah! I'll be able to use this in the actual problem - I guess I should have provided a more detail. The example above was meant to be the most basic reproduction of my problem. Thanks for inferring the problem. The actual problem is a bit more complicated - I've been using bash as a "no dependency" template engine (probably a bad idea :)). Recently, a template change contained an error and the "template engine" didn't fail the way I'd expected which caused problems downstream. Thanks for the help.

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