@echo off
if %1.==. goto noparams
goto drvid

:noparams

for %%a in (d e f g h i j k l m n o p q r s t u v w x y z) do call %0 %%a

:drvid
echo Checking if backup drive is mounted as drive %1:
if exist %1:\drvid.txt goto found
goto end

:found
Set DRVID=%1
echo Drive found as %DRVID%:

**PUT BACKUP CODE HERE. SUBSTITUTE DRIVE LETTER FOR %DRIVID%, SO E.G. USE: XCOPY C:\Windows %DRVID%:\Windows

:end