Regex that does not allow consecutive dots
<p>I have a Regex to allow alphanumeric, underscore and dots but not consecutive dots:</p>

<pre><code>^(?!.*?[.]{2})[a-zA-Z0-9_.]+$
</code></pre>

<p>I also need to now allow dots in the first and last character of the string.</p>

<p>How can I do this?</p>