This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
Mind you... if you don't know ruby, you risk running into confusion between what bits are ruby and what bits are rails, and a lot of things in rails will seem very mysterious... like magic. That said -- there are enormous amounts of tutorials and help available online, so it's certainly possible to just go ahead and start.