Copy your ssh public key to authorized keys for root on a system running dropbear (e.g. OpenWRT)

ssh_dropbear_key_copy.sh

#!/bin/bash

if [ "$#" -ne "1" ]; then
  echo "" > /dev/stderr
  echo "Error: Invalid number of arguments" > /dev/stderr
  echo "" > /dev/stderr
  echo "Usage: $0 ip_or_hostname" > /dev/stderr
  echo "" > /dev/stderr
  exit 1
fi

rhost=$1
ssh root@$rhost "tee -a /etc/dropbear/authorized_keys" < ~/.ssh/id_rsa.pub