title: what is the use of "#!/usr/local/bin/ruby -w" at the start of a ruby program
body: <p>what is the use of writing the following command at the start of a ruby program ?</p>
  
  <pre><code>#!/usr/local/bin/ruby -w
  </code></pre>
  
  <p>Is it OS specific command? Is it valid for ruby on windows ? if not, then what is an equivalent command in windows ?</p>