Except... it's not '*nix' as everyone knows it (or more importantly as deployed in production). Even while working on a mac I do all of my linux development on a VM, because the differences are always such a stumbling block for me. Half the utilities do not support long args, no real repos (resulting in broken or missing tools), old versions of utilities... ugh.
I still use one, but I'm seriously considering dual booting centos on the hardware.
And that's the way Unix was before Linux. Solaris, Irix, BSD.. all had different implementations of the basic unix tools. You're actually referring to the GNU tools and not the operating system.
Linux came along and everyone was using distros of Linux + GNU tools installed. You could in theory compile non-GNU tools and run a linux kernel and you'd be just as perplexed as running on a mac.
PROTIP: you can take any modern OS (Windows, Linux, Mac, Solaris) and compile/install the GNU utilities and get long arg support and have all the tools behave the same way. In fact, if you were building an OS from scratch your fasted bootstrap would be kernel -> compile the GNU tools -> distribute.
Trademark UNIX is like an expensive country club for vendor-proprietary "extensions" of BSD & SysV sensibilities. I'm suprised Apple wasn't a member sooner!
I still use one, but I'm seriously considering dual booting centos on the hardware.