stream_filter_remove

<?

$filename = "stream_filter_remove.txt";
$mode = "w+";

$handle = fopen($filename, $mode);

    $filtername = "string.rot13";

    $stream_filter = stream_filter_append($handle, $filtername);

    fwrite($handle, "Hello");

    stream_filter_remove($stream_filter);

    fwrite($handle, " World!");
    rewind($handle);
    fpassthru($handle);

fclose($handle);

Hello Jbeyq!