example-
$filename = 'filename.ext';
$upload_dir = 'uploads';
$docroot = $ENV{'DOCUMENT_ROOT'};
$FullFileSpec = "$docroot/$upload_dir/$filename";
If your site is on a shared server, most likely $ENV{'DOCUMENT_ROOT'} will return something like-
/c3p0/user/foobar/www
(if your domain was foobar.com and you were on a server named C3P0...)
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