PHP username validation

Question

I am working on writing a PHP login system. I have everything that I need working, but I would like to verify that a username entered during the registration only contains alphanumeric characters. So how could I take a variable, say $username, and ensure that it contained only alphanumeric characters?

Answer 1

if(preg_match('/^\w{5,}$/', $username)) { // \w equals "[0-9A-Za-z_]"
    // valid username, alphanumeric & longer than or equals 5 chars
}

OR

if(preg_match('/^[a-zA-Z0-9]{5,}$/', $username)) { // for english chars + numbers only
    // valid username, alphanumeric & longer than or equals 5 chars
}

Answer 2

The Best way I recommend is this :-

$str = "";
function validate_username($str) 
{
    $allowed = array(".", "-", "_"); // you can add here more value, you want to allow.
    if(ctype_alnum(str_replace($allowed, '', $str ))) {
        return $str;
    } else {
        $str = "Invalid Username";
        return $str;
    }
}

Answer 3

If you don't care about the length, you can use:

if (ctype_alnum($username)) {
   // Username is valid
}

http://www.php.net/manual/en/function.ctype-alnum.php