#!/bin/bash

uptime=$(cat /proc/uptime)
let secs=${uptime%%.*}
let mins=$(($secs/60%60))
let hours=$(($secs/(60*60)%24))
let days=$(($secs/(60*60*24)))

if [[ "$days" -ne 0 ]]; then
    echo -n "${days}d"
fi
echo -n "${hours}h${mins}m"