The Cathedral and the Bizaar and the Open Sources books, give a nice historical background. The Open Sources book have many nice essays from different contributors. I particulary enjoyed reading about the history of Unix transforming into a free OS, and Larry Wall's onion analogy.

A lot of the stuff in it is out of date, but `Unix Text Processing' is a great read, if only to get a feel for the concepts and ideas.

That title caught my eye also. Not much difference between Unix text processing then, and now.

Definitely 'the cathedral and the bazaar' which is imho a classic.