export file stream in PHP

export.php

<?php 

$fileName = 'somefile.csv';

header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header('Content-Description: File Transfer');
header("Content-type: text/csv");
header("Content-Disposition: attachment; filename={$fileName}");
header("Expires: 0");
header("Pragma: public");

$fh = @fopen( 'php://output', 'w' );