If unix and linux are supposed to be so different, why are they sharing a category on this web site? This pairing of two OS on one stackexchange topic makes it seem that they are indistinguishable and a question concerning Linux can apply to Unix.
Unix is not an operating system, it's a family of operating systems. Linux is not an operating system, it's the kernel found in a number of Unix-like and non-Unix-like operating systems.
There's as much difference between one non-Linux-based Unix system and the next as between one Linux-based one and the next, but they all share very similar interfaces and have a lot concepts in common.
It makes sense to have both. I find the Unix & Linux name confusing and misleading myself though because it mixes operating systems and kernels and seem to imply that things like GNU would be off-topic and that your TV, printer or smart phone running Linux would be on-topic.
Unix-like operating systems would have been a better name IMO.
I suppose the name was chosen because few people suspect Debian or Fedora for instance are Unix-like operating systems, while more may have heard that they are built around a Linux kernel (though for Debian, Linux is not the only supported kernel).
The name is a useful reminder that GNU/Linux is not the only unix-like environment around and that, unless a particular flavour of unix or particular Linux distribution is mentioned in the question, answers should be careful to at least make note of any non-POSIX features used in the answer or provide both POSIX and non-POSIX versions of the answer.
e.g. if your answer includes a shell script that uses features only available in bash, then mention that it is a
bash script, not a
sh script. Similarly, if you use features of
grep or some other tool that are only available in the GNU versions of that tool, then mention it. Bonus points for providing a variation of your answer that works using only POSIX features of the tool(s).
GNU/Linux is a UNIX clone. UNIX is a big family and consist other family such as BSD, systemV, SVR and so on. for more information you can visit: unix history