Yeah, variance between different system utilities is one of the biggest underrated perils of shell scripting. For a long time, I worked on a team that mostly used Macs to administer Linux servers, which led to some confusing issues when people tested certain commands locally and then tried to use them on a server.

It would be nice if shellcheck had checks to detect common BSD/GNU incompatibilities and warn about them so you don't have to catch them in the moment.