Regular expression to only allow lower-case letters [duplicate]

Question

Possible Duplicate:
Regular Expressions: low-caps, dots, zero spaces

How could I change the regular expression below to only allow lower-case letters?

function valid_username($username, $minlength = 3, $maxlength = 30)
{

    $username = trim($username);

    if (empty($username))
    {
        return false; // it was empty
    }
    if (strlen($username) > $maxlength)
    {
        return false; // to long
    }
    if (strlen($username) < $minlength)
    {

        return false; //toshort
    }

    $result = ereg("^[A-Za-z0-9_\-]+$", $username); //only A-Z, a-z and 0-9 are allowed

    if ($result)
    {
        return true; // ok no invalid chars
    } else
    {
        return false; //invalid chars found
    }

    return false;

}

Answer 1

You have both A-Z and a-z in your character class, just omit the A-Z to only allow for the a-z (lowercase) letters. I.e.

"^[a-z0-9_\-]+$"

Answer 2

You just remove the A-Z from the regular expression.

Also, since you are already using a regular expression you can just put everything into it, like this:

function valid_username($username, $minlength = 3, $maxlength = 30)
{
    $regex = "/^[a-z0-9_\-]{{$minlength},{$maxlength}}$/";

    return preg_match($regex, trim($username)) === 1;
}

It will make sure that the username is not empty, is of the permitted length, and that it only contains allowed characters.