php写入文件做日志

public function dump_log(){
    $time = date('Y-m-d');
    $file = "mac/".$time.".txt";
    $f = fopen($file,"a");
    fwrite($f,"----------------------$this->cmd---------------------------"."\n");
    fwrite($f,"-----imei-----"."\n".$this->imei."\n");
    fwrite($f,"-----cmd-----"."\n".$this->cmd."\n");
    fwrite($f,"-----data-----"."\n");
    ob_start();
    print_r(json_decode(htmlspecialchars_decode($this->data)));
    $result = ob_get_clean();
    fwrite($f,"$result"."\n");
    fwrite($f,"-----time-----"."\n".date("Y-m-d H:i:s")."\n\n\n\n");
    fclose($f);
}