Two images

1.Dockerfile

FROM alpine:3.12

ADD file-1.txt /

2.Dockerfile

FROM alpine:3.12

COPY --from=image-1 /file-1.txt /
ADD file-2.txt /

CMD cat /file-1.txt /file-2.txt

README.md

This demonstrates how to use COPY --from in a Dockerfile to include arbitrary data from another image. For instance when building a Git repository, a Docker image can be used as a resulting artefact so some data from that repository can also be used in another image, built from another repository at a different time.

file-1.txt

This file is originally from image-1.

file-2.txt

This file is from image-2.

run.sh

#! /usr/bin/env bash

# Build two images. The first one contains some file (e.g. obtained from a
# repository not available during the second image build).
# The second image is built with a COPY --from to obtain that file.

set -e

docker build -t image-1 -f 1.Dockerfile .
docker build -t image-2 -f 2.Dockerfile .
docker run image-2