How to extract links from a web content?

I have download a web page and I want to extract all the links in that file. this links include absolutes and relatives. for example we have :

<script type="text/javascript" src="/assets/jquery-1.8.0.min.js"></script>

or

<a href="http://ift.tt/gbk8l4" />

so after reading the file, what should I do?