A very inconsistent book. It varies wildly between chapters what kind of technical background the book assumes, and for the most part it ends up explaining things well below the level of any "Unix geek".

In one chapter it explains how to use filenames with spaces in a terminal, and how to use sudo. This is elementary level Unix knowledge that belongs more in a book for Unix beginners, rather than an introduction to a different Unix-like system for people with Unix knowledge. Then in another it goes in-depth with porting C applications, and the differences between object formats on OS X (Mach-O) versus other Unixes (mostly ELF).

Some parts of the book are by now wildly out of date, which is to be expected, but many of the Mac-specific Unix quirks are still accurate, but it requires you to go through the book explaining basic Unix usage in order to find them.

If you're a long time Unix user that wants to learn about the specifics of macOS, this simply isn't the book for you. If you're a novice Unix user, this might be helpful.