set tag=ABC/DEF
if not exist /%tag% if exist (hd0,0)/%tag% root (hd0,0)
if not exist /%tag% if exist (hd0,1)/%tag% root (hd0,1)
if not exist /%tag% find --set-root --ignore-floppies --ignore-cd /%tag% || set _=
if not exist /%tag% if exist (hd0)/%tag% root (hd0)
if not exist /%tag% find --set-root /%tag% || set _=