docker-machine-update-hosts.sh

#!/usr/bin/env bash

list=( $(docker-machine ls | grep Running | awk '{ print $1 }') )

for i in "${list[@]}"; do
    ip=$(docker-machine ip $i)
    #remove line matching ip
    sudo sed -i '' '/'$ip'/d' /etc/hosts
    #insert ip/host on last line
    sudo sed -i -e '$a\    
    '"$ip"' '"$i"'' /etc/hosts
done

FYI this also removes any other lines in the /etc/hosts file that were pointing to the same ip for any other host names other than the docker machine's name.

Yes, you are correct. Some additional logic could be added to search for host+ip.