Stream a large file download without exhausting memory in PHP

$path = '/var/exports/orders-2013.csv';
$fh   = fopen($path, 'rb');

header('Content-Type: text/csv');
header('Content-Disposition: attachment; filename="orders-2013.csv"');
header('Content-Length: ' . filesize($path));

while (!feof($fh)) {
    echo fread($fh, 8192);
    flush();
}

fclose($fh);