title: Simplest way to check if a command-line program is installed?
body: <p>Specifically perl.
  Something along the lines of </p>
  
  <pre><code>if(perl) { "You have perl installed, we may continue" }
  </code></pre>
  
  <p>Would be good, but it (understandably) runs the perl utility. Is there a way to  simply check if the perl command would be found in the current context?</p>