Expose the netns of a docker container to the host.

docker_netns.sh

#!/usr/bin/env bash

if [ "$1" == "" ]; then
  echo "usage: $0 <docker_id>"
  echo "Exposes the netns of a docker container to the host"
  exit 1
fi
ppid=`docker inspect $1 | grep Pid | awk '{print $2 + 0}'`
if [ "$ppid" == "" ]; then
  echo "lxc parent pid not found"
  exit 1
fi
pid=`ps --ppid $ppid -o pid | tail -n1`
if [ "$pid" == "" ]; then
  echo "lxc child pid not found"
  exit 1
fi
sudo mkdir -p /var/run/netns
sudo rm -f /var/run/netns/$1
sudo ln -s /proc/$pid/ns/net /var/run/netns/$1

echo "Container netns exposed as $1"
echo "For example try: sudo ip netns exec $1 ip addr"

You could extract the pid of the container with docker inspect directly without any grep/awk magic:

ppid=$(docker inspect --format '{{.State.Pid}}' $1)

Also, why do you query for any child processes?