PHP ftp_cdup function

// set up basic connection
$conn_id = ftp_connect($ftp_server);
 
// login with username and password
$login_result = ftp_login($conn_id, $ftp_user_name, $ftp_user_pass);
 
// change the current directory to html
ftp_chdir($conn_id, 'html');
 
echo ftp_pwd($conn_id); // /html 
 
// return to the parent directory
if (ftp_cdup($conn_id)) { 
  echo "cdup successful\n";
} else {
  echo "cdup not successful\n";
}
 
echo ftp_pwd($conn_id); // /
 
ftp_close($conn_id);