PHP Regex Pattern Problem

You'll need to do it in two steps really. First step, strip out everything except non-alpha characters and spaces.

$newString = preg_replace("/[^a-zA-Z0-9\s]/", "", $oldString);

Then replace all spaces with dashes (the below will replace a series of spaces with a single dash)

$newerString = preg_replace("/\s+/", "-", $newString);

Of course you can combine them into one statement, but it can be quite unreadable.

$newString =  preg_replace("/\s+/", "-", (preg_replace("/[^a-zA-Z0-9\s]/", "", $oldString));

It's useful to get a regex testing utility (there are loads of browser plugins for it) as creating the correct regex is usually the hardest part of this code.