Starting robust reliable and maintainable bash scripts

The set and shopt commands in bash are pretty powerful. One of the ways they can help you is by turning on some shell options that will make your bash scripts much more robust, reliable and maintainable. Aaron Maxwell has a nice discussion about this, but here I’ll record my own set of commands that I use at the top of my scripts.

#!/usr/bin/env bash

set -o errexit                # Exit on error. Append || true if you expect an error.
                              # Equivalent to `-e`.
set -o errtrace               # Exit on error inside any functions or subshells.
                              # Equivalent to `-E`.
set -o noclobber              # Don't allow overwriting files. Equivalent to `-C`.
set -o nounset                # Don't allow use of undefined vars.
                              # Use ${VAR:-} to use an undefined VAR. Equivalent to `-u`.
set -o pipefail               # Produce a failure return code if any pipeline command errors.
shopt -s failglob             # Cause globs that don't get expanded to cause errors.
shopt -s globstar 2>/dev/null # Match all files and zero or more sub-directories.

Note that I use the long names rather than the short equivalents. When writing scripts (as opposed to typing one-off commands), I prefer to use the long names, as I easily forget what short options refer to.

Another useful option is set -o xtrace or set -x, which will print a trace of commands in the script – though you may find this overkill, and I typically don’t include it.