I don’t think of the book is focused on Ruby-only Unix programming, I think it’s it’s focused on Unix programming concepts. It certainly appeals most to Ruby programmers because I use Ruby code to drive the examples in the book.
However, if you’re a user of Perl or Python then the examples in the book should work with pretty minimal tweaking for syntax.
On the note of ‘preferred language’ I’ve actually considered shipping several different versions of the text with just the examples rewritten in different languages. I quickly realized that that wasn’t sustainable :P The more I thought about it, the more I realized that the book is about Unix programming concepts and shouldn’t try to show you how to call your system in language X. Once you understand what your system can do and how you want to use it, then, unfortunately in your case, it’s left as an exercise for the reader to figure out how language X supports that.