"Finally, it is a pleasure to acknowledge our debt to the Unix operating system, developed at Bell Labs by Ken Thompson and Dennis Ritchie. We wrote the text, tested the programs, and typeset the manuscript, all within Unix. Many of the tools we describe are based on Unix models. Most important, the ideas and philosophy are based on our experience as Unix users. Of all the operating systems we have used, Unix is the only one that has been a positive help in getting a job done instead of an obstacle to be overcome. The world-wide acceptance of Unix indicates that we are not the only ones who feel this way."
— "Software Tools in Pascal", 1981, by Brian W. Kernighan, P.J. Plauger
As every neckbearded n-gate reader will now rush to well-actually at me, BWK's experience writing this book led to Why Pascal Is Not My Favorite Programming Language, but note this rant is about "standard" ANSI Pascal, not the somewhat improved P-Code Pascal of the '70s or the free-wheeling super-powered Turbo Pascal of the early '80s, and nothing like modern FreePascal. Standard Pascal was a deliberately simplified pedagogical language, not a systems programming language, which the later ones are.
Anyway, the book's interesting as a problem-solving exercise, but the Unix part amused me. And no, Linux is Not Unix. Buy a Mac or install BSD if you want UNIX®.