set -euf -o pipefail

[davidchambers]

set -euf -o pipefail is equivalent to:

set -o errexit      # Exit immediately if a command exits with a non-zero status.

set -o nounset      # Treat unset variables as an error when substituting.

set -o noglob       # Disable file name generation (globbing).

set -o pipefail     # The return value of a pipeline is the status of
                    # the last command to exit with a non-zero status,
                    # or zero if no command exited with a non-zero status.

We already have errexit enabled. ShellCheck asserts statically what nounset checks at run time, so this option should be safe to enable. We don't currently use any globbing or piping, so enabling noglob and pipefail should not change the behaviour of the program.

[davidchambers]

Although this change is not necessary, using =~ is consistent with the way in which matching is performed elsewhere in the program ([[ $increment =~ ^pre ]], for example).

[davidchambers]

I have not yet merged this pull request due to concern that this change could affect the behaviour of scripts provided via --script. Since opening the pull request I have determined that changes to shell options are not inherited, so I'm now ready to merge.