Check links to make valid

[onlyican]

Hey people
I forgot how to do this.

Here is the situation

We built a script for someone to send out newsletters, and they keep forgetting to add http:// on the links

I forgot, how do I check that when there is a www.something.something
I can make it
http://www.something.something
But if there is a http://, then leave it

The links are in the middle of text blocks

[ToonMariner]

preg_replace('/(?!http(s)?\/\/)www/', 'http://www' , $string);

Or something like that anyway.