replacing urls with links

[Anon]

I have a function that is intended to replace urls having the formats below with an appropriate link.

http://yahoo.com
http://www.yahoo.com
www.yahoo.com

Also the regex should ignore existing anchors.

This works but doesn't ignore the anchors:
$this->data[$name] = eregi_replace("(((http://)(www.)?)|(www.))([a-z0-9-]+(.[a-z0-9-]+)(.[a-z]{2,3})((/|\?)[a-z0-9~#%&\/'_+=:\?.-])*)", "<a href=\"http://www.\6\">\0</a>", $this->data[$name]);

So I tried to require the url string to start with either http:// or www. by adding a ^ at the beginning of the expression. This ignores anchors but does only replace urls starting with http://www.

I hope you'll be able to help me out :-)

[majik-sheff]

This replaces any text that:
begins with http://
ends with yahoo.com (case insensitive)
is not preceded by ", ', or =
is not proceeded by ", ', or >

$output = preg_replace("/(?![\"'\=].)(http:\/\/.*yahoo.com)(?![\"'>])/i", "<A HREF=\"\1\">\1</A>", $input);