#!/bin/sh

if [ "$1" = "-h" ]; then
	cat <<EOF>&2
Usage: ${0##*/}

Return the CPU usage. Linux only.

EOF
	exit
fi

if [ ! "$(uname)" = "Linux" ]; then
	echo >&2 "Linux only."
	exit 1
fi


## CPU usage
##
## A typical CPU array is (on Linux Kernel 3.0)
##   cpu  158150 0 52354 18562746 1472 0 10198 0 0 0
##
## The meanings of the columns are as follows, from left to right:
##
##   user: normal processes executing in user mode
##   nice: niced processes executing in user mode
##   system: processes executing in kernel mode
##   idle: twiddling thumbs
##   iowait: waiting for I/O to complete
##   irq: servicing interrupts
##   softirq: servicing softirqs
##   ... (see 'man 5 proc' for further details)
##
## Only the first 4 values are interesting here.

cpuarray="$(grep '^cpu ' /proc/stat)"
## We start at field #3 since there are 2 spaces after 'cpu'.
f1=$(echo "$cpuarray" | cut -f3 -d' ')
f2=$(echo "$cpuarray" | cut -f4 -d' ')
f3=$(echo "$cpuarray" | cut -f5 -d' ')
f4=$(echo "$cpuarray" | cut -f6 -d' ')

totalA=$((f1+f2+f3+f4))
idleA=$f4
sleep 1

cpuarray="$(grep '^cpu ' /proc/stat)"
f1=$(echo "$cpuarray" | cut -f3 -d' ')
f2=$(echo "$cpuarray" | cut -f4 -d' ')
f3=$(echo "$cpuarray" | cut -f5 -d' ')
f4=$(echo "$cpuarray" | cut -f6 -d' ')

totalB=$((f1+f2+f3+f4))
idleB=$f4

totaldiff=$((${totalB:-0}-${totalA:-0}))

if [ $totaldiff -eq 0 ]; then
	echo 0
else
	echo "$((100 - 100 * (idleB-idleA) / totaldiff))"
fi