validate input (no special characters)

[beavis82]

Hi,

I'm sure this is really simple, but I can't find an answer anywhere!

I have a site in which users register a username. I want to validate their input so that their username is no less than 4 characters, no more than 12, and contains only numbers, letters or underscores. how can I do this?

Cheers in advance for any advice!

[cahva]

Heres a little script that I made for you:

if (strlen($username)>12 || strlen($username)<4)
{
die("Username must contain less than 12 and more than 4 letters.");
}

// In $letters you put characters that are allowed
$letters="ABCDEFGHIJKLMOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890_";

for ($i=0; $i < strlen($username); $i++)
{
	$pos=strrpos($letters,$username{$i});
	if ($pos===false)
	{
	die ("illegal letters!");
	}
}

[beavis82]

Thank you so so much! That's done the trick!

Cheers!