Make sure username contains only: A-Z, a-z, ., _, -, 0-9 (no comma) PHP [closed]
if(preg_match("/[^w-.?]/", $user)){
    // invalid character
}
if(!filter_var($email, FILTER_VALIDATE_EMAIL) || strstr($email,'@yahoo.com')) {
    // either invalid email, or it contains in @yahoo.com
}

<?php

    // The validator class

    class Validator
    {
        public function isValidUsername($username)
        {
            if(preg_match('/^[a-zA-Z0-9_-.]+$/', $username)) {
                return true;
            }
            return false;
        }

        public function isYahooMail($mail) {
            if(preg_match('/^[a-zA-Z0-9_-.]+@yahoo.com$/', $mail)) {
                return true;
            }
            return false;
        }
    }

    // The way to use this class

    $username = "otporan_123";
    $email = "otporan@gmail.com";

    $badUsername = "otporan*bad";
    $yahooEmail = "otporan@yahoo.com";

    $validator = new Validator();

    var_export($validator->isValidUsername($username));
    echo "<br />";

    var_export($validator->isValidUsername($badUsername));
    echo "<br />";

    var_export($validator->isYahooMail($email));
    echo "<br />";

    var_export($validator->isYahooMail($yahooEmail));
    echo "<br />";

?>

if(preg_match("/[^-A-Za-z0-9._ ]/", $userName)){
    // there are one or more of the forbidden characters (the set of which is unknown)
}

if (!preg_match('/w-/', $username) {
    //throw error
}