While @Gary is technically correct that the only thing returned is the ERRORLEVEL, sqlcmd
does also display its results to STDOUT. Armed with that, you could do something like this in a batch file:
set SERVERNAME=yoursqlserver
for /f "skip=2" %%x in ('sqlcmd -S %SERVERNAME% -Q "select count(*) from active_connections" ^| findstr /v /c:"rows affected"') do set COUNT=%%x
echo There are %COUNT% records in the active_connections table.