There are no required textbooks for this course. That said, you may find these two books helpful. The first is the standard reference work for the Ruby programming language. Every programming language has one, and for Ruby, it's the book Rubyists refer to as "The Pickaxe Book:"
The second is a brief guide to the UNIX operating system. This one is far less obligatory than the first (there's nothing in it that you can't find online), but you may find it helpful when trying to figure out how to do something on the command line.
These books are not available in the UNL bookstore, but you can easily find them at your favorite online retailer (or wherever geeky books are sold). Please make sure the titles, edition numbers, and ISBNs match before purchasing.