作为对先前答案的更新，当前的dockerbuild 接受--build-arg传递环境变量的方式，例如http_proxy 不将其保存在生成??的映像中。
例：
# get squid
docker run --name squid -d --restart=always \
--publish 3128:3128 \
--volume /var/spool/squid3 \
sameersbn/squid:3.3.8-11
# optionally in another terminal run tail on logs
docker exec -it squid tail -f /var/log/squid3/access.log
# get squid ip to use in docker build
SQUID_IP=$(docker inspect --format '{{ .NetworkSettings.IPAddress }}' squid)
# build your instance
docker build --build-arg http_proxy=http://$SQUID_IP:3128 .
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