Example Squash

Dockerfile

FROM    ubuntu:14.04

RUN     echo "Secrets" > /opt/data.secret
RUN     rm /opt/data.secret

squash.sh

#!/bin/bash
# 
# Example Docker "Squash" hack.  develop@cjhanks.name

set -e

log_file=out.log
docker build . | tee $log_file

# Get the name of the image id from the logs
raw_image_id=$(cat $log_file | grep Successfully | awk '{ print $3 }')

# Launch an image into a detached bash state, this is necessary since
# export operates on running containers, not images.
echo "Launching $raw_image_id"
machine_id=$(docker run -d -t $raw_image_id bash)

# export the machine and import through a pipe
echo "ExImporting the machine"
docker export $machine_id | docker import - my_image:tag

# cleanup
echo "Beginning cleanup"
docker stop $machine_id
docker rm $machine_id
docker rmi $raw_image_id