Adding the Brightbox PPA to the system.

First install python-software-properties like this:

sudo aptitude install python-software-properties

Next add the Brightbox PPA repository to the system like this:

sudo add-apt-repository ppa:brightbox/ruby-ng

With that done, run aptitude update to get the new repository picked up like this:

sudo aptitude update

Install various versions of Ruby via the Brightbox PPA.

Install Ruby 1.8:

sudo aptitude install ruby1.8 ruby1.8-dev

Install Ruby 1.9:

sudo aptitude install ruby1.9 ruby1.9-dev

Install Ruby 2.0:

sudo aptitude install ruby2.0 ruby2.0-dev

Install Ruby 2.1:

sudo aptitude install ruby2.1 ruby2.1-dev

Install Ruby 2.2:

sudo aptitude install ruby2.2 ruby2.2-dev