Break on

$fileold = "D:\xfer.txt"
$filenew = "D:\xfer_new.txt"

$rc = Open (1, $fileold, 2)
$rc = Open (2, $filenew, 5)
$line = ReadLine (1)
$OldString= "%" + "windir" + "%"
$line = ReadLine (1)
While @ERROR = "0"
	Select
		Case %windir% = "c:\windows"
			$newstring = "%" + "systemdrive" + "%\windows"
		Case %windir% = "c:\winnt"
			$newstring = "%" + "systemdrive" + "%\winnt"
	EndSelect
	$newline = Replace($line,$oldstring,$newstring)
	$rc = WriteLine (2, $newline + @CRLF)
	$line = ReadLine (1)
Loop
$rc = Close (1)
$rc = Close (2)
Del $fileold
Move $filenew $fileold