#template.rb
require 'erb'

class Template
  def initialize(foo, bar)
    @foo = foo
    @bar = bar
  end

  def open_template
    puts ERB.new(File.read(templates_path), nil).result(binding)
  end

  def templates_path
    File.expand_path("../template.erb", __FILE__)
  end
end

Template.new('hi', 'hello').open_template

#template.erb
1. <%= @foo %>
2. <%= @bar %>

#執行
ruby template.rb
#1. hi
#2. hello