blink(1) script to light up osx network usage

blink_osx_network_monitor.sh

#!/bin/bash
# Quick hack to get blink(1) to light up while monitoring osx network usage
# Based on "Simple script to monitor network usage on OSX - Joe McManus 2011/03/30 joe@cert.org"

#Interval between tests in seconds, change this to whatever you want
interval=1

if [ -z $1 ]
then
	echo "ERROR: No interface specified"
	echo "USAGE: $0 interface_name" 
	exit
else
	interface=$1
fi

intcount=`ifconfig $interface | wc -l`

if [ $intcount == 0 ] 
then
	echo "ERROR: Interface $interface not found" 
	exit
fi

#echo "Monitoring: $interface "
#echo "Hit CTRL-C to stop" 

i=1
while [ 1 -ne 0 ]
do
	now=`date +'%Y-%m-%d %H:%M:%S'`
	intinfo=`netstat -b -I $interface | grep ^$interface | sort -u`
	inbound=`echo $intinfo | awk ' {print $7 } ' `
	outbound=`echo $intinfo | awk ' {print $10 } ' `

	if [ $i -eq 1 ]
	then
		#We dont have any data yet, so lets just set the starting point
	 	lastin=$inbound
		lastout=$outbound
		totalin=0
		totalout=0
		outmaxxxx=0
		inmaxxxx=0
	else
		diffin=`expr $inbound - $lastin`
		diffpersecin=`expr $diffin / $interval`
		totalin=`expr $totalin + $diffin`

		diffout=`expr $outbound - $lastout`
		diffpersecout=`expr $diffout / $interval`
		totalout=`expr $totalout + $diffout`

		#echo "Time: $now, In: $diffin, Out: $diffout, In/Sec: $diffpersecin, Out/Sec: $diffpersecout, Total In: $totalin, Total Out, $totalout"

		outtotal=$diffout
		intotal=$diffin

    # These seem to be the max in and out...at least on my computer + connection.
    inmax=235574
    outmax=73122
    colormax=255
      
	  # slope of a line 
    # normalize 0-255 for coloring [y-b/m] where b=0
    in_m=`echo $inmax / $colormax | bc -l`
    out_m=`echo $outmax / $colormax | bc -l`

    # And now normalize output
  	outcolor=`echo $outtotal / $out_m | bc -l`
		if [ ${outcolor/.*} -gt ${colormax/.*} ]; then
		  outcolor=$colormax
		fi

    # And now normalize input
		incolor=`echo $intotal / $in_m | bc -l`
		if [ ${incolor/.*} -gt ${colormax/.*} ]; then
		  incolor=$colormax
		fi

    # show the input and output colors, red and green on blink(1) device
    blink_cmd="./blink1-tool -m 300 --rgb $incolor,$outcolor,0"
    eval $blink_cmd

		lastin=$inbound
		lastout=$outbound
	fi
	
  	i=`expr $i + 1`
	sleep 0.03
done