okay, so the search form submits from outside, i see…
i believe EE introduces a number of hidden fields to the search for, for example:
<form method="post" action="http://domain.com/index.php" >
<div class='hiddenFields'>
<input type="hidden" name="ACT" value="2" />
<input type="hidden" name="XID" value="hashstring5b87c938f58cd7f0d8f73442ba0d" />
<input type="hidden" name="RES" value="10" />
<input type="hidden" name="meta" value="longhashstringrNXWN45xkaPUqK" />
<input type="hidden" name="site_id" value="1" />
</div>
<input type="text" name="keywords" id="keywords" value="Search…" />
<input type="submit" name="g" id="g" value="Go" />
</form>
So i would imagine that you cannot pass anything pretending to be this form from outside EE as otherwise it would be a great way to DDOS an EE site!
However, that would not stop you writing your own code to query the database directly.