Upload & Download speed in Tmux status line

You can call a shell script from tmux's status line, specifying your required interface like so:

set -g status-left '#[fg=blue]#(speed eth0)#[default]'

And place this script, speed¹, in your $PATH:

#!/bin/bash

iface=$1
RXB=$(</sys/class/net/"$iface"/statistics/rx_bytes)
TXB=$(</sys/class/net/"$iface"/statistics/tx_bytes)
sleep 2 
RXBN=$(</sys/class/net/"$iface"/statistics/rx_bytes)
TXBN=$(</sys/class/net/"$iface"/statistics/tx_bytes)
RXDIF=$(echo $((RXBN - RXB)) )
TXDIF=$(echo $((TXBN - TXB)) )

echo -e "$((RXDIF / 1024 / 2))K/s $((TXDIF / 1024 / 2))K/s"

^{1. Can't remember where I found this...}

I wanted the answer above by jasonwryan to deal with all interfaces so I made this modification:

#!/bin/bash

RXB=0
TXB=0

for rxbytes in /sys/class/net/*/statistics/rx_bytes ; do
  let RXB+=$(<$rxbytes)
done

for txbytes in /sys/class/net/*/statistics/tx_bytes ; do
  let TXB+=$(<$txbytes)
done

sleep 2 

RXBN=0
TXBN=0

for rxbytes in /sys/class/net/*/statistics/rx_bytes ; do
  let RXBN+=$(<$rxbytes)
done

for txbytes in /sys/class/net/*/statistics/tx_bytes ; do
  let TXBN+=$(<$txbytes)
done    

RXDIF=$(echo $((RXBN - RXB)) )
TXDIF=$(echo $((TXBN - TXB)) )

echo -e "$((RXDIF / 1024 / 2))K/s $((TXDIF / 1024 / 2))K/s"

You can obviously change the wildcard to only do all eth* or wlan* interfaces, or use find to make a more complicated match of the two.

Building on the Above, this should display up and down indicators using ^ and v, use the correct symbol (Ki is binary Kilobytes, etc) change to Mi and Gi as needed, and also display non zero fractional values of one decimal place.

https://github.com/gryftir/tmux-networkspeed