first value, second value, third value
fourth value, fifth value, sixth value

<?php
$row[] = 'first value';
$row[] = 'second value';
$row[] = 'third value';
$data .= join(',', $row)."\n"; // Join all values without any trailing commas and add a new line

$row = ''; // We must clear the previous values
$row[] = 'fourth value';
$row[] = 'fifth value';
$row[] = 'sixth value';
$data .= join(',', $row)."\n";

// Output the headers to download the file
header("Content-type: application/x-msdownload");
header("Content-Disposition: attachment; filename=log.csv");
header("Pragma: no-cache");
header("Expires: 0");
echo $data;
?>

<?php
$row = 'first value,';
$row .= 'second value,';
$row .= 'third value';
$data .= $row."\n";

$row = 'fourth value,';
$row .= 'fifth value,';
$row .= 'sixth value';
$data .= $row."\n";

// Output the headers to download the file
header("Content-type: application/x-msdownload");
header("Content-Disposition: attachment; filename=log.csv");
header("Pragma: no-cache");
header("Expires: 0");
echo $data;
?>