Saving a file on the disk

i have writen data to a file in php and now i want to save the file automatically on the disk?

i have used this following code :

header("Content-Disposition: attachment; filename=" . $textFileName);
header('Content-type: application/zip');
header('Content-Length: ' . $textFileName);
readfile($textFileName);

but it has some problem , can u help me in sorting it out......