php regex to get string inside href tag

I need a regex that will give me the string inside an href tag and inside the quotes also.

For example i need to extract theurltoget.com in the following:

<a href="theurltoget.com">URL</a>

Additionally, I only want the base url part. I.e. from http://www.mydomain.com/page.html i only want http://www.mydomain.com/