Install ruby-sdl by entering the following commands in the terminal:
sudo apt update sudo apt install ruby-sdl
Description:
Ruby/SDL interface for Ruby
Ruby/SDL is the ruby extension library to use SDL. SDL (Simple DirectMedia Layer) is a cross-platform multimedia library designed to provide fast access to the graphics framebuffer and audio device.
Homepage: http://ohai.github.io/rubysdl/
Version: 2.2.0-1build2
Section: universe/ruby