Just to let you know, if you’re learning Clojure from the Clojure For The Brave and True website when they they tell you to download Leiningen from the website, please do that. At least on Ubuntu 18.04, the apt package is severely out-of-date, it installs Clojure 1.8, whereas the current version is 1.10. Version 1.8 is from 2016. But come to think of it, the book was copyrighted back in 2015, so it says in the book:

As of this writing, it’s at version 1.9.0, and development is going strong. If you’re reading this book in the far future and Clojure has a higher version number, don’t worry! This book covers Clojure’s fundamentals, which shouldn’t change from one version to the next. There’s no need for your robot butler to return this book to the bookstore.

By the way the Brave and True Book has a stupid title, but it’s probably the best book out if you’re looking to learn Clojure, and the book  website seems to has the whole text of the book that you can read for free. Can’t beat the price.