Hi.

nahi> 'erb' is a Ruby library thus is easy to embed in Ruby application.
nahi> 'erb' offers lightweight library named ERbLight which compiles only '<%= %>'.

ERb sample code is here.
  http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/1731


In ERb and eruby, "$stdout.write" means that it inserts 
a string in this place.

'<% print "hello" %>' and '<%= "hello" %>', These are 
equivalent in meaning.

In ERbLight, "$stdout.write" is write to standard output.
e.g.
---- prompt.rb ----
require 'erb/erb'
require 'erb/erbl'

script = <<EOS
<%
   puts "What's your name?"
   s = readline.chomp
%>
Hi, <%= s %>.
EOS

puts "ERbLight:"
erb = ERbLight.new(script)
p erb.result

puts

puts "ERb:"
erb = ERb.new(script)
p erb.result
--------------------


BTW
erb.rb and erbl.rb are executable script.

  o execute eRuby script.
    % ruby erb.rb <eRubyScript>
    % ruby erbl.rb <eRubyScript>

  o print converted Ruby script.
    % ruby erb.rb -x <eRubyScript>
    % ruby erbl.rb -x <eRubyScript>


-- 
Masatoshi SEKI