Docker environment hack, to put the names of running containers in /etc/hosts

update-hosts.sh

#!/bin/bash
# An alternative to "links", run this script after starting or stopping any
# container. It's a hack to update the host machine (vagrant) /etc/hosts with
# the current active docker containers and tell dnsmasq to refresh.
#
# Then start each machine with "-dns ${DOCKER_HOST_IP}", e.g.
#    $ docker run -d -name mycontainer1 -dns 10.0.3.1 MYPRODUCT
# You can't seem to set the DNS during "docker build".
#
# Diagnostic command to run in host or while logged into containers:
#    # dig @10.0.3.1 mycontainer1
#
cd ${0%/*}

function dip() { docker inspect $1 | grep IPAddress | cut -d '"' -f 4 ; }

cat /etc/hosts | grep -v '#DOCKER-DELETE-ME' > /etc/hosts.docker.tmp
RESULT="$?"
if [ ${RESULT} = 0 ]; then
   echo "Checking for running docker containers..."
else
   echo "Error modifying /etc/hosts, try running with sudo."
   exit 1
fi

echo "# Below are the docker hosts running at $(date). #DOCKER-DELETE-ME" >> /etc/hosts.docker.tmp


docker ps -q | while read CONTAINERID
do
   IP=$(docker inspect ${CONTAINERID} | jq -r '.[0].NetworkSettings.Networks as $in | $in | keys[] | $in[.].IPAddress')
   if [ -n "${IP}" ] ; then
     NAME=$(docker inspect ${CONTAINERID} | jq -r '.[0].Name' | cut -c 2-)
    for i in ${IP}; do
      echo "${i}    ${NAME}  #DOCKER-DELETE-ME" >> /etc/hosts.docker.tmp
    done
   fi
done

mv -f /etc/hosts.docker.tmp /etc/hosts
echo 'Updated /etc/hosts with current ("docker ps") entries...'
tail -10 /etc/hosts

Updated to docker 18.05, should work with older versions as well.
Uses jq to ease up processing and speed.