Is there any reason why you would want to use exec or eval? In any language? I have never seen the need for it, but have seen plenty of very poor uses of eval in PHP and JavaScript. Are there any legitimate ones, aside from writing a debugger of some kind?
A nugget from an old version of WordPress:<p><pre><code> eval('$v_result = '.$p_options[PCLZIP_CB_PRE_EXTRACT].'(PCLZIP_CB_PRE_EXTRACT, $v_local_header);')</code></pre>