Username Fields, and how to avoid dodgy chars

[nexgen_x]

I'm making a registration form.

What functions can I use to make sure people only use the letters a-z, numbers 0-9, underscores and hyphons?

[drew010]

use regular expressions to match that and give an error if they dont match

[silent]

More specifically, here is one that only allows A-Z, a-z, and 0-9

if (!eregi('[[:alnum:]]',$your_input)) {
  //do some error stuff here
}

If you need to allow spaces, just change [[:alnum:]] to [[:alnum:][:space:]]

Hope this helps