Measure bandwidth with tcpstat + gnuplot

measure.sh

# Measure traffic with tcpstat
tcpstat -i em1 -o "%r\t%b\n" -s 30 0.1 > traffic.txt

# Create plot using the below script
gnuplot traffic.script > traffic.png

# Display plot
qlmanage -p 2>/dev/null traffic.png

traffic.script

        set term png small
        set grid
        set yrange [ -10 :  ]
        set title "Traffic"
        set xlabel "seconds"
        set ylabel "bits/s"
        plot    "traffic.txt" using 1:2 smooth csplines title "Bandwidth"