Back-up script and folder capitalisation

Question

I have a site backup script that I am using, and it's working fine - apart from one issue. It does not respect and follow folder capitalisation, so "l" and "L" are compressed into one folder. Is there a way around that? The function is below.

Many thanks!

function BackupSite() {

$archname = './fullsite_' . date("Y-m-d-H-i-s") . '.tar.gz';

$command = 'tar -';
$command .= '-exclude ' . $archname . ' -czf ' . $archname . ' .';

$output = shell_exec($command);

$size = round(filesize($archname)/1000);