$readonlyfields is hiding value when assigned to variable

Hi Forum,

Need Help again. No docs on $readonlyfields.

I'm trying to do this:
$car = $readonlyfields["carrier"];

$ui="You rcvd a $car E-mail from Blah";

$File = "/var/www/hosts/blah.com/httpdocs/testfile";;

$Handle = fopen($File, 'w');

fwrite($Handle, $ui);

fclose($Handle);
OUtput of the file is

"You rcvd a E-mail from Blah"

The $readonlyfields does not provide the value of the field if set as readonly type.

I also tried $values. Same exact thing.
TIA!!!