Hello @kartik.
PHP has built-in extensions for dealing with compressed files. There should be no need to use system calls for this. ZipArchive is one option.
$zip = new ZipArchive;
$res = $zip->open('file.zip');
if ($res === TRUE) {
  $zip->extractTo('/myzips/extract_path/');
  $zip->close();
  echo 'woot!';
} else {
  echo 'doh!';
}
Also, as others have commented, $HTTP_GET_VARS has been deprecated since version 4.1 which was a really long time ago. Don't use it. Use the $_GET superglobal instead.
Finally, be very careful about accepting whatever input is passed to a script via a $_GET variable.
Hope it helps!!
Thank you!!