Add support for ps2pdf(1) command of the Ghostscript suite
This not only makes this script useful on Linux and BSD systems but is
important on current macOS systems as well, as Apple dropped PostScript
support from macOS starting with version 14, "Sonoma", and no longer
ships a `pstopdf` command with the system!
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).