rbenv is a version manager tool for the Ruby programming language on Unix-like
systems. It is useful for switching between multiple Ruby versions on the same
machine and for ensuring that each project you are working on always runs on
the correct Ruby version.

After rbenv injects itself into your PATH at installation time, any invocation
of `ruby`, `gem`, `bundler`, or other Ruby-related executable will first
activate rbenv. Then, rbenv scans the current project directory for a file
named `.ruby-version`. If found, that file determines the version of Ruby that
should be used within that directory. Finally, rbenv looks up that Ruby version
among those installed under `~/.rbenv/versions/`.
