#!/bin/sh

set -eu

DISPLAY_DECIMAL_PLACES=2

MEBI=1024
GIBI=$((MEBI * MEBI))
TEBI=$((GIBI * MEBI))

display_kib_unit() {
	size_kib=$1
	decimal_places=$2

	if [ "$size_kib" -lt "$MEBI" ]; then
		size=$size_kib
		unit="K"
	elif [ "$size_kib" -lt "$GIBI" ]; then
		size=$(printf 'scale=%s; %s / %s\n' "$decimal_places" "$size_kib" "$MEBI" | bc)
		unit="M"
	elif [ "$size_kib" -lt "$TEBI" ]; then
		size=$(printf 'scale=%s; %s / %s\n' "$decimal_places" "$size_kib" "$GIBI" | bc)
		unit="G"
	else
		size=$(printf 'scale=%s; %s / %s\n' "$decimal_places" "$size_kib" "$TEBI" | bc)
		unit="T"
	fi

	printf '%.*f%s' "$decimal_places" "$size" "$unit"
}

mem_total=
mem_free=
mem_buffers=
mem_cached=
mem_sreclaimable=
mem_shmem=

while read -r type value _; do
	case $type in
	MemTotal:) mem_total=$value ;;
	MemFree:) mem_free=$value ;;
	Buffers:) mem_buffers=$value ;;
	Cached:) mem_cached=$value ;;
	SReclaimable:) mem_sreclaimable=$value ;;
	Shmem:) mem_shmem=$value ;;
	esac
done </proc/meminfo

mem_used=$((mem_total - mem_free))
mem_non_cache_buffer=$((mem_used - (mem_buffers + (mem_cached + mem_sreclaimable - mem_shmem))))

printf 'MEM %s' $(display_kib_unit "$mem_non_cache_buffer" "$DISPLAY_DECIMAL_PLACES")