make a sql script which only outputs the single value you want:
set timing off
set feedback off
set pages 0
select sysdate from dual;
make a bat file as follows:
FOR /F "usebackq delims=!" %%i IN (`sqlplus -s u/p@db @t`) DO set xresult=%%i
the bat file will assign the final line of output to the variable xresult.
the "-s" option will prevent the "disconnected" message
in the FOR command, the "delims" option is used to override the default delimitor of whitespaces. this allows a string with spaces to be parsed as one variable (if you expect a "!", then choose something else, or leave it out completely if you won't haev whitespaces)
Give a man a fish, you feed him for a day. Club him over the head with a fish, he'll leave you alone.