How to validate a textbox for a filepath entry? : <p>the cases are </p>

<ul>
<li>compulsory '\' char at the first</li>
<li>followed by alphanumeric </li>
<li>compulsory '\' char at the last</li>
</ul>

<p>eg:\abc\bvc\</p>

<p>\abc4\abc3\abc2\abc1\</p>
