Many bash scripts you’ll see in the wild often have some variation of set -euxo pipefail at the top of the file. These settings make your scripts fail loudly and early when something goes wrong

I’m constantly looking this up whenever I come across it, so here are my quick notes for us to refer back to if/when we need a quick refresher.

set -e (Exit on Error)

The set -e option instructs Bash to immediately exit if any command (excluding certain contexts like while or if conditions, or the right-hand side of a pipeline) returns a non-zero exit status.

Bash will continue even if a command fails. set -e brings Bash closer to the behavior of other languages, ensuring that a failing command stops the script right away.

set -u (Unset Variables are Errors)

When set -u is active, referencing any variable that hasn’t been previously defined (with exceptions for $* and $@) will cause the script to immediately exit with an error.

By default, Bash silently uses an empty string for the unset/mistyped variables. This flag prevents common typos from creating new, empty variables without you realizing it.

set -x (Print Commands)

This option enables trace mode, printing each command’s expanded form to standard error immediately before it is executed. set -x helps you visualize the flow of your script by showing exactly which commands are being run and with what arguments.

set -o pipefail (Fail on Pipeline Errors)

By default, the exit status of a pipeline (command1 | command2) is the exit status of the last command, even if an earlier command in the pipeline failed. set -o pipefail changes this, ensuring that the entire pipeline’s exit status is that of the first non-zero exit status encountered.

This flag prevents errors in the middle of a pipeline from being silently ignored. For instance, if grep fails to find a file but pipes its (empty) output to sort, sort will succeed, and the pipeline would report success. With pipefail, the pipeline would correctly report grep’s failure.