Clean unneeded dependencies on Homebrew

Let’s say you’ve uninstalled a formula with Hombrebrew that it’s no longer needed. Homebrew won’t clean the associated dependencies that are no longer needed. You can do this by running:

$ brew rm $(join <(brew leaves) <(brew deps <FORMULA>))

This calls for the formula dependencies and does a join with the installed packages that are not dependencies of other packages, and uninstall the resulting list of packages.

CAVEAT EMPTOR: This method uninstalled Qt from my computer, and I needed it for Capybara. This happened because brew only takes into account dependencies of programs installed with brew. Any dependency from outside brew is ignored.