So what?

Well, you can use the global variable DATA to get the contents of what you wrote after the __END__ block. DATA is actually a File object to just that piece of text in your script.

How about a little sample to make things a little clearer?

#!/usr/bin/env ruby
%w(yaml pp).each { |dep| require dep }

obj = YAML::load(DATA)

pp obj

__END__
---
-
  name: Adam
  age: 28
  admin: true
-
  name: Maggie
  age: 28
  admin: false

So with this, I was able to embed a little bit of YAML directly into my script. I added the YAML after __END__. YAML::load will accept a File object, so I just passed it DATA and now I have a reconstituted array.

Maybe that’s not the most practical use of this information; however, Sinatra provides a really awesome use of this.  With Sinatra, you can create a whole web application that lives in one single, solitary ruby file.  Sinatra can use in-file templates.  In-file templates are added into the space after __END__ where each view file is annotated with @@view_name.

require 'rubygems'
require 'sinatra'

get '/' do
  haml :index
end

__END__

@@ layout
%html
  = yield

@@ index
%div.title Hello world!!!!!

Not bad for a useless trick!