Conditional COPY/ADD in Dockerfile?

Question

Inside of my Dockerfiles I would like to COPY a file into my image if it exists, the requirements.txt file for pip seems like a good candidate but how would this be achieved

Answer 1

Copy all files to a throwaway dir, hand pick the one you want, discard the rest.

COPY . /throwaway
RUN cp /throwaway/requirements.txt . || echo 'requirements.txt does not exist'
RUN rm -rf /throwaway

You can achieve something similar using build stages, which relies on the same solution, using cp to conditionally copy. By using a build stage, your final image will not include all the content from the initial COPY.

FROM alpine as copy_stage
COPY . .
RUN mkdir /dir_for_maybe_requirements_file
RUN cp requirements.txt /dir_for_maybe_requirements_file &>- || true

FROM alpine
# Must copy a file which exists, so copy a directory with maybe one file
COPY --from=copy_stage /dir_for_maybe_requirements_file /
RUN cp /dir_for_maybe_requirements_file/* . &>- || true
CMD sh