There is a form field where users *should* input domain names in the form of "google.com".

However, taking into consideration confused users, I want to be able to clean the input to the exact form of "google.com" in case they type in the following cases:

```
http://www.google.com
http://google.com
google.com/blah
www.google.com
..and other incorrect forms

```

What is the best way to accomplish this?

Thanks in advance!