Validate Username & Print Out Bad Characters

[rivka]

I have a simple check to see if someone is using any non-allowed characters in their usernames:

if(!preg_match("!^[a-z0-9_~]{1,30}$!i", $uname))
{
		echo "You have entered an invalid username.";
}

But in addition to that, I would like to be able to print out which specific characters were bad. Any suggestions on how to do that?

[Weedpacket]

if(preg_match_all('/[^a-z0-9_~]/i', $uname, $invalid))
{
   echo "Your requested username contains invalid characters: ".join('',array_unique($invalid[0]));
}

It doesn't check the length of the username, but that's what strlen() is for.

[rivka]

This is awesome! Thank you! One last question -- is there a way to make it print out something like [space] if one of the invalid characters is a space?