echo off
setlocal
for %%i IN (e,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v) do (
if not defined second (call :TESTDRIVE %%i) else (goto :ALLDONE)
)
goto :eof
:TESTDRIVE
if exist %1: echo %1 is already a driveletter
if not exist %1: echo %1 USABLE DRIVELETTER && call :MOUNTDRIVE %1
goto :eof
:MOUNTDRIVE
if not defined first (set first=%1) else (set second=%1)
echo this is where we would mount drive %1
goto :eof
:ALLDONE
echo All done, first driveletter is %first%, second is %second%
endlocal