When should we be wary of backticks in PHP?
<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>
