ERB comes by default with ruby, you only need to require it:
require 'erb'
Create a template file ./template/steak.erb:
A large steak, <%= @how_done %>, please!
<%- 3.times do -%>
And another!
<%- end -%>
And read it into a variable:
tempalte = File.read('./template/steak.erb')
Now you can bind instance variables and pass them to the renderer:
renderer = ERB.new(template, nil, '-')
@how_done = 'medium rare'
puts renderer.result(binding)