Получить корректный размер используемой памяти из /proc/meminfo

free -h

mem=/proc/meminfo; \
cut="cut -c17-24"; \
echo $(($(grep "MemTotal" $mem|$cut)-$(grep "MemFree" $mem|$cut)\
-$(grep "Buffers" $mem|$cut)-$(grep "^Cached" $mem|$cut)\
-$(grep "Slab" $mem|$cut)+$(grep "SUnreclaim" $mem|$cut))); free

mem=$(mktemp);\
cut="cut -c17-24";\
cat /proc/meminfo > $mem & free;\
echo $(($(grep "MemTotal" $mem|$cut)-$(grep "MemFree" $mem|$cut)\
-$(grep "Buffers" $mem|$cut)-$(grep "^Cached" $mem|$cut)\
-$(grep "Slab" $mem|$cut)+$(grep "SUnreclaim" $mem|$cut))); rm $mem

declare -A mi; \
while read key value unit; do mi[${key%:}]=$value; done < /proc/meminfo; \
echo $((
  ${mi[MemTotal]}
  - ${mi[MemFree]}
  - ${mi[Buffers]}
  - ${mi[Cached]}
  - ${mi[Slab]}
  + ${mi[SUnreclaim]}
  ))