The Art of UNIX Programming (Addison-Wesley Professional Computing Series)

The Art of Unix Programming attempts to capture the engineering wisdom and philosophy of the Unix community as it's applied today — not merely as it has been written down in the past, but as a living "special transmission, outside the scriptures" passed from guru to guru. Accordingly, the book doesn't focus so much on "what" as on "why", showing the connection between Unix philosophy and practice through case studies in widely available open-source software. [Authors Site][1]

[1]: catb.org/~esr/writings/taoup/