Although recovering a LoadError is not a preferred approach in Ruby development, sometimes its needed when you are building one-off command line scripts. It simplifies the installation of gems as the user is running the script.

Below is the approach, to run the GemRunner directly:

begin 
 require 'sass'
rescue LoadError
 require 'rubygems/gem_runner'
 gemrunner = Gem::GemRunner.new 
 gemrunner.run(['install', 'nokogiri','--bindir',"#{File.expand_path File.dirname(__FILE__)}/bins"])
 require 'sass'      	
end

Again, typically you would want to define all your libraries in a Gemfile and use bundle.