This table might help. The ksh (AIX/OpenBSD default shell) does not differ that much from POSIX, the csh does.
zsh: massive extensions on top of sh but different ones to bash
csh: a completely different shell to sh, contemporary in origin, mostly different syntax
tcsh: extensions on top of csh
fish: a completely different shell again, cut-down syntax and features mostly targeted at interactive users
So, yeah, it's important to specify which shell you're targeting.
Thanks for the info. I've updated the posts with shell reqs. 😊
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