title: ruby how to find mkmf?
body: <p>When I do:</p>
  
  <pre><code>ruby extconf.rb
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code>extconf.rb:24:in 'require': no such file to load -- mkmf (LoadError)
  </code></pre>
  
  <p>When I start up <code>irb</code> and execute all commands from <code>extconf.rb</code> line by line it works fine (including <code>require 'mkmf'</code>).</p>
  
  <p>How do I tell <code>ruby</code> where to find <code>mkmf</code> when obviously <code>irb</code> can find it.
  I compiled ruby from source (1.9.1) and it's intalled in "non standard location".</p>