replace certain characters

[fnbcprog]

How do I replace all characters except:
1. Letters/Numbers
2. Underscores
3. Periods
4. @

Thanks for the help!

[NogDog]

You don't say what you want to replace them with, so for this example I'll replace them with an underscore:

$newString = preg_replace('/[^a-z0-9_.@]/i', '_', $oldString);