Simple Username Creation Validation with PHP

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When I create login areas (mostly intranets) for small websites, I'm always asked by the customer to keep usernames to letters and numbers. That means no email addresses as usernames and special characters like "_", "-", and ".". This, in my customer's mind, keeps the login easy for their users and limits the number of support calls they will receive. While I don't recommend disallowing common username characters like the ones cited above, I do understand their need for simplicity. Here's how, using PHP, I validate that a username is only letters and numbers.

The PHP

function validate_username($input,$pattern = '[^A-Za-z0-9]')
{
	return !ereg($pattern,$input);
}

It's as easy as that. I don't go as far as using this for passwords, but you could if you wanted to. I'll also mention that if I want to allow non-alphanumeric characters, I just need to change the function's pattern. Easy enough!

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Discussion

  1. I like the approach — instead of matching a word boundary e.g. ^[a-zA-z0-9]*$ you match the first invalid character. I wonder what the speed difference is…

    BTW, you can use [^\w\d] insead ;) It’s lazier

  2. My bad. You cant use \w since it matches _ as well. On the other hand \w handles \d, so if you are looking for something quick for chars, digits and _ — you can use \w.

  3. Brian

    You could also use PHP’s ctype_alnum to match only alphanumeric characters
    which matches (ever so slightly) faster than its equivalent regular expression,
    and still retain future flexibility by using something like:

    function username($input, $pattern = false)
    {
           return ($pattern) ? !ereg($pattern, $input) : ctype_alnum($input);
    }
    

    Of course the speed difference is on the order of nanoseconds,
    but it is faster nonetheless.

  4. Jeff Hartman

    A better method name would be useful. ;)

  5. @Jeff: Ooops. I have this function within a class. I actually use it like this:

    if($valid->username($input)) {
      // move on...
    }
    

    I simply didn’t rename it for the blog. I’ll do that quick!

  6. A word of warning, ereg is being removed in PHP6 because of the more powerful and usually faster preg. Altering your code to work with pregs is easy and safer should the server you’re on upgrade to PHP6 sometime in the future:

    function validate_username($input, $pattern = '/[^A-Za-z0-9]/')
    {
        return !preg_match($pattern, $input);
    }
    
  7. ereg will be deprecated in php 5.3 and removed in 6, use preg instead

  8. ereg is not available in php 5.3.0

    any alternative for this ?

  9. Nolan Hawkins

    I’m rather new to regexp, and am just trying to get something exactly like this to work, but it just isn’t. I got annoyed, and then simplified as much as possible to this:


    and it isn’t responding anything except 0, no matter what I try.

  10. Nolan Hawkins

    Oops sorry. Anyways, it’s just a text input that posts to itself, and it deals with the post by doing

     if(!is_null($_POST["f"])){
    $input=$_POST["f"];
    $pattern = '[^A-Za-z0-9]';
    $a=preg_match($pattern,$input);
    echo $a;
    }
  11. 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;
            }
        }
    

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