OS/X (Mac) is Mach-derived   I think you do it a disservice to call it BSD-derived.    While the kernel-to-application interface was compatible with 4.2 BSD, the kernel is largely of CMU’s only creation.

The thing came layered with Doug Gwyn’s (where is he? I invited him) BRL SV on BSD user environment to silence the critics that it wasn’t SVID compatible.    I hadn’t even realized it until I got a few Mach kerneled machines (notably our NeXT cube) and found that it had my version of the Bourne shell with job control and command line editing hacked in (to battle the tcsh guys at BRL because I detested the csh syntax and Korn’s shell hadn’t gotten out of the labs yet at that point).