set -eux is a super useful bash trick I’ve been using in Chef and Rex tasks. I’m going to break it down and explain it one option at a time:

set -e


cmd1 && cmd2 && cmd3

is equivalent to this

set -e

set -u

The shell prints a message to stderr when it tries to expand a variable that is not set. Also it immediately exits. An interactive shell will not exit. I think this is similar to Perl’s use strictures which is something Moo enables.

set -x

The shell prints each command in a script to stderr before running it. I think this would be particularly useful in Rex. And Chef.

set -x
echo hey
echo woah


+ echo hey
+ echo woah

set -o pipefail

Pipelines fail on the first command which fails instead of dying later on down the pipeline. This is especially good when cmd3 is a command that always succeeds (like echo):

cmd1 | cmd2 | cmd3

See also