> I don't know why we should say that is the only valid definition and ignore the validity of the other three.
For "trademark UNIX": very few of the systems within are small, comprehensible or elegant.
For "heritage/genealogical UNIX": Windows 10 may have the heritage of DOS, but I wouldn't call it "DOS with a GUI."
For "UNIX-like/UNIX-compatible": nothing is really UNIX-compatible or all that UNIX-like. Do you define it as "source compatibility?" Nothing from v7 or before will compile; it's before standardization of C. Do you define it as "script compatibility?" UNIX never consistently stuck to a shell, which is why POSIX requires POSIX sh which is in many ways more limited than the Bourne shell.
I personally take McIllroy's view on the UNIX philosophy:
A number of maxims have gained currency among the builders and users of the UNIX system to explain and promote its characteristic style:
* Make each program do one thing well. To do a new job, build afresh rather than complicate old programs by adding new "features."
* Expect the output of every program to become the input to another, as yet unknown, program. Don't clutter output with extraneous information. Avoid stringently columnar or binary input formats. Don't insist on interactive input.
* Design and build software, even operating systems, to be tried early, ideally within weeks. Don't hesitate to throw away the clumsy parts and rebuild them.
* Use tools in preference to unskilled help to lighten a programming task, even if you have to detour to build the tools and expect to throw some of them out after you've finished using them.
Throwing out things that don't work is a good idea, which is why the modern backwards-compatible-ish hell is far from UNIX (in this regard, I'll admit illumos doesn't qualify).
I fully agree with you that Plan 9 is closer to UNIX than Linux and FreeBSD!
Would the original authors of Unix agree with your opinions on how to define the term?
Does AT&T's c. 1980 port of Unix to run on top of IBM's TSS/370 mainframe operating system [0] count as a real Unix? It appears that Ritchie did think it was a Unix, he linked to the paper from his page on Unix portability [1].
So is your definition of "Unix" broad enough to include that system? If not, you are defining the term differently from how Ritchie defined it; in which case I think we should prefer Ritchie's definition to yours. (McIlroy's maxims are explicating the Unix philosophy, but I don't read him as saying that systems which historically count as Unix aren't really Unix if they fall short in following his maxims.)
> McIlroy's maxims are explicating the Unix philosophy
This is why I used the quote, not for this reason:
> but I don't read him as saying that systems which historically count as Unix aren't really Unix if they fall short in following his maxims.
I'd say yes, a port of v7 is fine, because it's not meaningfully more complex. It can still be comprehended by a single individual (unlike FreeBSD, Linux, everything currently called Certified Commercial UNIX trademark symbol, etcetera).
> I'd say yes, a port of v7 is fine, because it's not meaningfully more complex
I think AT&T's port of V7 (or something close to V7, I guess it was probably actually a variant of PWB) to run on top of TSS/370 really is meaningfully more complex because in order to understand it you also have to understand IBM TSS/370 and the interactions between TSS/370 and Unix.
For "trademark UNIX": very few of the systems within are small, comprehensible or elegant.
For "heritage/genealogical UNIX": Windows 10 may have the heritage of DOS, but I wouldn't call it "DOS with a GUI."
For "UNIX-like/UNIX-compatible": nothing is really UNIX-compatible or all that UNIX-like. Do you define it as "source compatibility?" Nothing from v7 or before will compile; it's before standardization of C. Do you define it as "script compatibility?" UNIX never consistently stuck to a shell, which is why POSIX requires POSIX sh which is in many ways more limited than the Bourne shell.
I personally take McIllroy's view on the UNIX philosophy:
Throwing out things that don't work is a good idea, which is why the modern backwards-compatible-ish hell is far from UNIX (in this regard, I'll admit illumos doesn't qualify).I fully agree with you that Plan 9 is closer to UNIX than Linux and FreeBSD!