#!/bin/sh

# grab previous stats
cache="/tmp/cpuload"

[ ! -f "$cache" ] || touch "$cache"

# get the currents cpu stats variables
curr_stats=$(head -n 1 /proc/stat)
prev_stats=$(cat "$cache")

# get the stats

curr_idle=$(echo "$curr_stats" | awk ' { print $5 } ')
prev_idle=$(echo "$prev_stats" | awk ' { print $5 } ')

curr_sum=$(echo "$curr_stats" | awk '{ print ($2+$3+$4+$5+$6+$7+$8+$9+$10) }')
prev_sum=$(cat "$cache" | awk '{ print ($2+$3+$4+$5+$6+$7+$8+$9+$10) }')

if [ -n "$prev_sum" ] ; then
        # get the delta by subtracting the the current total from the previous total
        delta=$(($curr_sum - $prev_sum))
        # calculate idle delta
        idle=$(($curr_idle - $prev_idle))
        # caclulate working time
        used=$(($delta - $idle))

        # caculate usage
        cpu_usage=$((100 * $used / $delta))

        echo "$cpu_usage%"
fi

echo "$curr_stats" > "$cache"