UNIX Unleashed: this is a huge (1600 pages!) book on Unix, written by many different people. The fact that so many people contributed is its advantage, because no one section assumes that you've read another section. So, what you have are self-contained 60 page synopses of major topics. The 56 page section on Perl is still my major reference when I've forgotten what command does what. When I really needed to dig in to Unix Internet software (such as majordomo) I turned to O'Reilly's Managing Internet Information Services. O'Reilly's TCP/IP Network Administration was also useful for issues like DNS and routing. I prefer Teach Yourself Perl in 21 days to the venerable Camel Book, though you'll probably need both if you really dig in. The Camel Book is too quick on some subjects. The Teach Yourself... book is very complete, and if it covers your topic it'll do a very good job.