The guest contributors (Ken Arnold, Steven M. Bellovin, Stuart Feldman, Jim Gettys, Steve Johnson, Brian Kernighan, David Korn, Mike Lesk, Doug McIlroy, Marshall Kirk McKusick, Keith Packard, Henry Spencer, and Ken Thompson) added a great deal of value to this book. Doug McIlroy, in particular, went far beyond the call of duty in the thoroughness of his critique and the depth of his contributions, displaying the same care and dedication to excellence which he brought to managing the original Unix research group thirty years ago.

Special thanks go to Rob Landley and to my wife Catherine Raymond, both of whom delivered intensive line-by-line critiques of manuscript drafts. Rob's insightful and attentive commentary actually inspired more than one entire chapter in the final manuscript, and he had a lot to do with its present organization and range; if he had written all the text he pushed me to improve, I would have to call him a co-author. Cathy was my test audience representing non-technical readers; to the extent this book is accessible to people who aren't already programmers, that's largely her doing.

This book benefited from discussions with many other people over the five years it took me to write it. Mark M. Miller helped me achieve enlightenment about threads. John Cowan supplied some insights about interface design patterns and drafted the case studies of wily and VM/CMS, and Jef Raskin showed me where the Rule of Least Surprise comes from. The UIUC System Architecture Group contributed useful feedback on early chapters. The sections on What Unix Gets Wrong and Flexibility in Depth were directly inspired by their review. Russell J. Nelson contributed the material on Bernstein chaining in Chapter 7. Jay Maynard contributed most of the material in the MVS case study in Chapter 3. Les Hatton provided many helpful comments on the Languages chapter and motivated the portion of Chapter 4 on Optimal Module Size. David A. Wheeler contributed many perceptive criticisms and some case-study material, especially in the Design part. Russ Cox helped develop the survey of Plan 9. Dennis Ritchie corrected me on some historical points about C.

Hundreds of Unix programmers, far too many to list here, contributed advice and comments during the book's public review period between January and June of 2003. As always, I found the process of open peer review over the Web both intensely challenging and intensely rewarding. Also as always, responsibility for any errors in the resulting work remains my own.

The expository style and some of the concerns of this book have been influenced by the design patterns movement; indeed, I flirted with the idea of titling the book Unix Design Patterns. I didn't, because I disagree with some of the implicit central dogmas of the movement and don't feel the need to use all its formal apparatus or accept its cultural baggage. Nevertheless, my approach has certainly been influenced by Christopher Alexander's work^[3] (especially The Timeless Way of Building and A Pattern Language), and I owe the Gang of Four and other members of their school a large debt of gratitude for showing me how it is possible to use Alexander's insights to talk about software design at a high level without merely uttering vague and useless generalities. Interested readers should see Design Patterns: Elements of Reusable Object-Oriented Software [GangOfFour] for an introduction to design patterns.

The title of this book is, of course, a reference to Donald Knuth's The Art of Computer Programming. While not specifically associated with the Unix tradition, Knuth has been an influence on us all.

Editors with vision and imagination aren't as common as they should be. Mark Taub is one; he saw merit in a stalled project and skillfully nudged me into finishing it. Copy editors with a good ear for prose style and enough ability to improve writing that isn't like theirs are even less common, but Mary Lou Nohr makes that grade. Jerry Votta seized on my concept for the cover and made it look better than I had imagined. The whole crew at Addison-Wesley gets high marks for making the editorial and production process as painless as possible, and for cheerfully accommodating my control-freak tendencies not just over the text but deep into the details of the book's visual design, art, and marketing.