Alexander Barton [Fri, 30 Jun 2023 12:29:36 +0000 (14:29 +0200)]
Use bash and fix shellcheck warnings
We need to use bash, because the "-ot" test is not defined in POSIX sh.
And fix quite a few other shellcheck warnings (but mute SC2250 "Prefer
putting braces around variable references even when not strictly
required" for now).