$ sudo apt-get update
$ sudo apt-get install ruby-gnome2 

ruby-gnome2 is installed in your system.

Make ensure the ruby-gnome2 package were installed using the commands given below,

$ sudo dpkg-query -l | grep ruby-gnome2 *

You will get with ruby-gnome2 package name, version, architecture and description in a table

ruby-gnome2 package basic information: