title: Hidden features of Bash
body: <p>Shell scripts are often used as glue, for automation and simple one-off tasks. What are some of your favorite "hidden" features of the Bash shell/scripting language?</p>
  
  <ul>
  <li>One feature per answer</li>
  <li>Give an example and short description of the feature, not just a link to documentation</li>
  <li>Label the feature using bold title as the first line</li>
  </ul>
  
  <p>See also:</p>
  
  <ul>
  <li><a href="https://stackoverflow.com/questions/132241/hidden-features-of-c">Hidden features of C</a></li>
  <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/75538/hidden-features-of-c">Hidden features of C++</a></li>
  <li><a href="https://stackoverflow.com/questions/102254/hidden-features-of-delphi">Hidden features of Delphi</a></li>
  <li><a href="https://stackoverflow.com/questions/101268/hidden-features-of-python">Hidden features of Python</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/63998/hidden-features-of-ruby">Hidden features of Ruby</a></li>
  <li><a href="https://stackoverflow.com/questions/61401/hidden-features-of-php">Hidden features of PHP</a></li>
  <li><a href="https://stackoverflow.com/questions/161872/hidden-features-of-perl">Hidden features of Perl</a></li>
  <li><a href="https://stackoverflow.com/questions/102084/hidden-features-of-vbnet">Hidden features of VB.Net</a></li>
  </ul>