[kdmccormick]

Got it. I'm the dev tools guy at my job right now, and we have a mix of Linux and Mac users, so I've gotta make sure that any shell I write works on both. For me, POSIX seems to be a good indicator of the intersection between the two OSs, even though the true intersection is neither a superset nor subset of POSIX (eg, Mac has bash, which isn't POSIX shell). Oh well. It's close enough to be useful, and I test it all manually anyway.

[tannhaeuser]

Mac OS ships zsh since 10.15 as default shell as I'm sure you know, with the (restricted ksh subset called) POSIX shell pretty much the intersection of what works on both Linux and Mac OS. There you have the usefulness of POSIX/SUS.