Let's create a new image, on an existing repository, to install bash:

host      $ cd <repository path>
host      $ ship alpine:latest
container $ apk add --no-cache bash
container $ exit
Dockerfile written successfully!
host      $ cat Dockerfile
# Generated by https://github.com/augustohp/ship
FROM alpine:latest
LABEL maintainer="Augusto Pascutti <augusto.hp@gmail.com>"

RUN apk add --no-cache bash

What happened?

1. The container specified was executed in iterative mode
2. bash (prefered) or ash shell are detected and history configured
3. The current directory was mounted at /home/developer
4. The history of the container was converted to RUN instructions in the Dockefile
5. Your Git credentials become LABEL maintainer, if they are available

Supported images are (other images might work if they have bash available):

• alpine
• ubuntu/debian
• fedora

This is a single-file script, you can rename it freely to anything memorable for you. An easy one-line install is available through sinister:

sh <(curl -sSL https://git.io/fjjvu) --name ship --local --chmod 755 --url https://git.io/fjhO5

The above one-liner will install the script just for the current user. If you want it globally, remove --local option.

You should be able to execute ship now, for example ship --help:

Usage: ship [-o <filename>] [-f] <image>
       ship <-d | --detect-shell> <image>
       ship <-h | --help>
       ship <-v | --version>

Eases the creation of a Dockerfile by transforming the history
into RUN instructions.

Arguments:
  image                    The name of Dockerimage to be executed. 
                           The image must have bash installed.
Options:
  -o | --out <filename>    The name of the Dockerfile to be creared.
                           Default: Dockerfile.
  -f | --force             Re-creates Dockerfile if it
                           already exists.
  -d | --detect-shell      Outputs the shell available in the image.
                           Shells tested: bash ash

Requirements, trying to be minimal, are:

• Docker
• If Git is available, you get the maintainer label in the Dockerfile
• A POSIX (compatible) Shell (bash, for example)

There is a Makefile to automate checks on the script:

• make lint runs shellcheck
• make test runs bats tests

Feel free to hack the ship script. It uses sh not bash to run, so try to avoid bashisms. Almost everything inside the script is on a function to be friendly even if you've never done any shell-scripting before.

Please, feel free to report bugs, ideas or feature requests through an issue.