php 擷取給定日期的前一天日期

 /**     *      * 擷取給定日期的前一天     * @param string $date     * @return string $yesterday     */    public function getYesterday($date)    {        if(empty($date))         {            $yesterday = date("Y-m-d",strtotime("-1 day"));        }else{            $arr = explode('-', $date);            $year = $arr[0];            $month = $arr[1];            $day = $arr[2];            $unixtime = mktime(0,0,0,$month,$day,$year)-86400;            $yesterday = date('Y-m-d',$unixtime);        }                return $yesterday;    }

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