Frequently Asked Question

What does set -euo pipefail do and should I always use it?

The line set -euo pipefail enables three of bash's strictest error-handling options at once. -e (errexit) tells the shell to exit immediately if any simple command returns a non-zero exit status, instead of stumbling onward. -u (nounset) makes the shell error out if you reference an unset variable, catching typos like $USRNAME` for `$USERNAME before they silently become an empty string. -o pipefail changes how pipelines report failure: by default, cmd1 | cmd2 exits with cmd2's status only, so a crashed cmd1 is invisible; with pipefail, the pipeline returns the first non-zero status in the chain.

Together these turn bash from a forgiving glue language into something that stops loudly on the first problem, which is almost always what you want for an automation script. It is not a silver bullet, set -e has notorious edge cases around conditional contexts, and you sometimes have to disable it locally with cmd || true for commands whose non-zero exits are expected, but it is a massive improvement over the default. Treat it as the standard prelude for any script you intend to keep.