title: Hidden features of Ruby
body: <p>Continuing the "Hidden features of ..." meme, let's share the lesser-known but useful features of Ruby programming language.</p>
  
  <p>Try to limit this discussion with core Ruby, without any Ruby on Rails stuff.</p>
  
  <p>See also:</p>
  
  <ul>
  <li><a href="https://stackoverflow.com/questions/9033/hidden-features-of-c">Hidden features of C#</a></li>
  <li><a href="https://stackoverflow.com/questions/15496/hidden-features-of-java">Hidden features of Java</a></li>
  <li><a href="https://stackoverflow.com/questions/61088/hidden-features-of-javascript">Hidden features of JavaScript</a></li>
  <li><a href="https://stackoverflow.com/questions/709679/hidden-features-of-ruby-on-rails">Hidden features of Ruby on Rails</a></li>
  <li><a href="https://stackoverflow.com/questions/101268/hidden-features-of-python">Hidden features of Python</a></li>
  </ul>
  
  <p>(Please, just <em>one</em> hidden feature per answer.)</p>
  
  <p>Thank you</p>