1 2EMPTY= 3 4check-empty: 5 @${MAKE} -f ${MAKEFILE} do-$@ 6 @${MAKE} -f ${MAKEFILE} -j2 do-$@ 7 @${MAKE} -f ${MAKEFILE} -j2 -B do-$@ 8 9do-check-empty: 10 ${EMPTY} 11 @${EMPTY} 12 @-${EMPTY} 13