How to strip anything except for numbers, letters and spaces?

[JohnSaunders]

Can someone tell me how to remove anything from a variable except for letters, numbers, or spaces? For example, if it has & or dashes or anything else like that i don't want it to remain in the string.

[AlienDev]

I know this isnt what you asked for, but heres the regex for checking if the variable only has letters, numbers or spaces in it:

if (preg_match("/[^a-zA-Z0-9 ]/",$var)) {
echo 'You may only use letters, numbers and spaces!';
} else {
echo 'Heres a cookie';
} 

[logic_earth]

Or can change that to

$data = preg_replace('/[^a-z0-9 ]/i', '', $data);