this is an old script that i have:
$filename = "/blah/blah/message.txt";
$newMsg = "place new message here";
$fileOpen = fopen($filename, "r");
$oldMsg = fread($fileOpen, filesize($filename));
fclose($fileOpen);
$newConent = "$newMsg \n $oldMsg";
$fileOpen = fopen($filename, "w");
fputs($fileOpen, $newContent);
fclose($fileOpen);