ทำการ export file excel อยากจะให้ไฟล์ที่ export ไปอยู่ในโฟลเดอร์ที่กำหนด อย่างไรค่ะ

public function exportXLS(){ 
	
		function filterData(&$str)
		{
			$str = htmlspecialchars_decode($str);
			$str = preg_replace("/\t/", "", $str);
			$str = preg_replace("/\r?\n/", "", $str);
			$str = str_replace('\r','',$str);
			$str = str_replace('\n','',$str);
			$str = str_replace(',','',$str);
		}
	
		$data = $this->home_model->customer_tech_call_csv();
		
		// file name for download
		$fileName = "test" . date('Ymd') . ".xls";
		
		// headers for download
		//header("Content-Disposition: attachment; filename=\"$fileName\"");
		header("Content-Type: application/vnd.ms-excel");
		header("Content-Type: text/html; charset=utf-8");
		
		$file_url = ('./doc/xls/'.$fileName);
		file_put_contents($file_url,$fileName);
		
		$header = array("Contact type","Cust Problem");
		
		$flag = false;
		$bom =( chr(0xEF) . chr(0xBB) . chr(0xBF) );
		foreach($data as $row) {
			if(!$flag) {
				// display column names as first row
				echo implode(",", $header) . "\n";
				$flag = true;
			}
			// filter data
			array_walk($row, 'filterData');
			//echo iconv('UTF-8', 'TIS-620', implode(",", $row)) . "\n";
			echo implode(",",array(
				iconv('UTF-8', 'TIS-620', $row['contact_type']),
				iconv('UTF-8', 'TIS-620', $row['cust_problem'])	)). "\n";
			//var_dump ($row);

		}
		

	}