str=`sed -n -e '/^MemTotal:/p' -e '/^MemFree:/p' -e '/^Buffers:/p' -e '/^Cached:/p' /proc/meminfo | awk '{print $2}' | xargs echo`; arr=($str); echo $((${arr[0]} - ${arr[1]} - ${arr[2] - ${arr[3]}}))