取中间字符

function cut($begin,$end,$str){
    $b = mb_strpos($str,$begin) + mb_strlen($begin);
    $e = mb_strpos($str,$end) - $b;
    return mb_substr($str,$b,$e);
}

判断是否包含字符

$email = 'user@example.com';
$domain = strstr($email, '@');