A helper script for patching docker images

docker-patch

#!/bin/bash
# Dependencies:
#   - docker (obviously)
#   - jq (json parsing)

docker_patch_usage() {
  echo 'Usage: docker-patch'
  echo '  CONTAINER=$(docker-patch start your/tag)'
  echo '  # apply patch to $CONTAINER (docker container)'
  echo '  docker-patch commit ${CONTAINER} your/patched-tag'
}

docker_patch_start() {
  IMAGE=$1
  IMAGE_ENTRYPOINT=$(docker inspect ${IMAGE} | jq -rc '.[0] | .Config.Entrypoint')
  IMAGE_CMD=$(docker inspect ${IMAGE} | jq -rc '.[0] | .Config.Cmd')
  if [ "${IMAGE_ENTRYPOINT}" == "null" ]; then
    docker run -id ${IMAGE} /bin/sh
  elif [ "${IMAGE_CMD}" == "null" ]; then
    docker run --entrypoint= -id ${IMAGE} /bin/sh
  else
    docker run --entrypoint= -id ${IMAGE} /bin/sh
  fi
}

docker_patch_commit() {
  CONTAINER="${@: -2:1}"
  NEW_IMAGE="${@: -1:1}"
  IMAGE=$(docker inspect ${CONTAINER} | jq -rc '.[0].Config.Image')
  IMAGE_ENTRYPOINT=$(docker inspect ${IMAGE} | jq -rc '.[0] | .Config.Entrypoint')
  IMAGE_CMD=$(docker inspect ${IMAGE} | jq -rc '.[0] | .Config.Cmd')
  if [ "${IMAGE_ENTRYPOINT}" == "null" ]; then
    set -- "${@:1:$#-2}" -c "CMD ${IMAGE_CMD}" "${CONTAINER}" "${NEW_IMAGE}"
    docker commit "$@"
  elif [ "${IMAGE_CMD}" == "null" ]; then
    set -- "${@:1:$#-2}" -c "ENTRYPOINT ${IMAGE_ENTRYPOINT}" -c "CMD []" "${CONTAINER}" "${NEW_IMAGE}"
    docker commit "$@"
  else
    set -- "${@:1:$#-2}" -c "ENTRYPOINT ${IMAGE_ENTRYPOINT}" -c "CMD ${IMAGE_CMD}" "${CONTAINER}" "${NEW_IMAGE}"
    docker commit "$@"
  fi
}

ARG=$1
shift
if [ "${ARG}" == "start" ]; then
  docker_patch_start "$@"
elif [ "${ARG}" == "commit" ]; then
  docker_patch_commit "$@"
else
  docker_patch_usage