Add apt proxy to docker container

add-apt-proxy.sh

#!/bin/bash -ex
#
# Add to your Dockerfile:
#
#    RUN chmod +x add-apt-proxy.sh && ./add-apt-proxy.sh
#
# For additional information see:
#
# https://github.com/sameersbn/docker-apt-cacher-ng
# https://gist.github.com/dergachev/8441335

CONFPATH=/etc/apt/apt.conf.d/01proxy 
APT_PROXY_PORT=${1:-3142}
HOST_IP=$(awk '/^[a-z0-9]+\t00000000/ { printf("%d.%d.%d.%d\n", int("0x" substr($3, 7, 2)), int("0x" substr($3, 5, 2)), int("0x" substr($3, 3, 2)), int("0x" substr($3, 1, 2)));exit }' < /proc/net/route)

if [[ ! -z "$APT_PROXY_PORT" ]] && [[ ! -z "$HOST_IP" ]]; then
    cat > $CONFPATH <<-EOL
	Acquire::HTTP::Proxy "http://${HOST_IP}:${APT_PROXY_PORT}";
	Acquire::HTTPS::Proxy "false";
EOL
    cat $CONFPATH
    echo "Using host's apt proxy."
else
    echo "Not using apt proxy."
fi