php实现时间显示方式（2秒前）

header("Content-type:text/html;charset=utf-8"); function relative_date($date) {    if (!preg_match('/^\d+$/', $date)) $date = strtotime(trim($date));    $sec = time() - $date;    switch(true){    case $sec < 60:    return 60 - $sec. '秒前';        case $sec < 3600:            return round($sec/60). '分钟前';        case $sec < 86400:            return round($sec/3600). '小时前';        case $sec < (86400 * 7):            return round($sec/86400). '天前';        case $sec < (86400 * 7 * 4):            return round($sec/(86400*7)). '周前';         default:            return date("Y年n月d日",$date);    }}$date = '2014-11-20 13:36:12';echo relative_date($date);