rx/tx eth0 monitor

Pre-requisites:

/run/user/user_id directory
terminal "clear" command may be busybox only (it is what I run). I should use the terminal ANSI escape code.
Should run in dash shell too (avoid bash like hell of course, don't be corpo naughty).

Code:

#!/bin/sh
f0=$(mktemp -p /run/user/$(id -u) -u)

cleanup ()
{
        rm -f $f0 
        exit
}

trap cleanup 2

cp -f /proc/net/dev $f0
receive_prev=$(grep -F eth0 $f0  | cut -F 3)
transmit_prev=$(grep -F eth0 $f0  | cut -F 11)

sleep 10

while true
do
        cp -f /proc/net/dev $f0
        receive_new=$(grep -F eth0 $f0  | cut -F 3)
        transmit_new=$(grep -F eth0 $f0  | cut -F 11)

        clear
        printf "RECEIVE:$(( ($receive_new - $receive_prev)*8/10000 ))\n"
        printf "TRANSMIT:$(( ($transmit_new - $transmit_prev)*8/10000 ))"

        receive_prev=$receive_new
        transmit_prev=$transmit_new

        sleep 10
done