title: What is the difference between Perl subroutines with "&" (ampersand) and without
body: <p>What is the difference between the next two lines in Perl:</p>
  
  <pre><code>PopupMsg("Hello");
  
  &amp;PopupMsg("Hello");
  
  ...
  
  sub PopupMsg
  {
      subroutines code here...
  }
  </code></pre>
  
  <p>please notice that in some cases I must use the first line and in some the second, other wise I get an error.</p>