Learn Enough Command Line to Be Dangerous Ebooks

I'm linking this news post mainly because it offers a 50% launch discount, but you can find the completed Learn Enough Command Line to Be Dangerous tutorial here:

http://learnenough.com/command-line

Thanks to HN for the previous discussion (https://news.ycombinator.com/item?id=10245033), which led to several significant improvements in the text.