Ruby

Ruby is a programming language, it is required for software like Rails, passenger, and GitLab.

Installation
Install :

make.conf
Several packages built against ruby such as passenger require ruby targets to be defined in

Slots
Ruby is slotted in Portage, to view which installed version slot the system is currently using, run:

To change the selected slot, issue:

Upgrades
To upgrade Ruby, first add the new Ruby target into. For example, if upgrading from Ruby 2.2 to Ruby 2.3, add  to the RUBY_TARGETS variable:

Next, ask Portage to rebuild the @world set:

After that, update the slot to the newly installed version (2.3 in this case) using as mentioned above.

Finally, as long as no packages are still using the old version, it should be removable by asking Portage to do a dependency clean:

Remove old ruby version
First verify, that no package depends on this specific version.

For example, if removing Ruby 2.2, remove  from the RUBY_TARGETS variable:

Next, ask Portage to rebuild the @world set without the old Ruby version with

and remove no longer needed packages again

External resources

 * Codecademy's Ruby course
 * http://iwanttolearnruby.com/