title: When should we be wary of backticks in PHP?
body: <p><a href="http://php.net/manual/en/language.operators.execution.php" rel="nofollow">The fine manual</a> states thus:</p>
  
  <blockquote>
    <p>Unlike some other languages, backticks cannot be used within double-quoted strings.</p>
  </blockquote>
  
  <p>However, empirical testing finds no problems:</p>
  
  <pre><code>$ cat test.php 
  #!/usr/bin/php -q
  &lt;?php
  echo "O`reilly\n";
  echo `ls`;
  echo "\n";
  ?&gt;
  
  $ ./test.php 
  O`reilly
  test.php
  
  $ php --version
  PHP 5.3.6-13ubuntu3.7 with Suhosin-Patch (cli) (built: May  4 2012 00:50:06) 
  Copyright (c) 1997-2011 The PHP Group
  Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies
      with Xdebug v2.1.0, Copyright (c) 2002-2010, by Derick Rethans
  </code></pre>
  
  <p>Obviously safe mode is off due to the backticks working in the <code>ls</code> line, and I see that sage mode is disabled in php.ini. On other servers with safe mode I have used backticks in SQL queries and I do not recall ever having an issue. So why does the manual have the warning about backticks in double-quoted strings?</p>