Question 413654 in Docker Question posted in
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How can I copy/clone only the folder structure between images using Docker?

For the sake of simplicity, let’s say I have the following structure in the source image:

files/
    folder1/
        file1
        file2
    folder2/
        file1
        file2

I want to have a result where only the directory structure is copied to my other image during build. The result should therefore look like this:

files/
    folder1/
    folder2/

How can this be achieved?

Background: You might ask why I want to do this. Well, in reality the directory structure is much more complex and I need to maintain consistency between both source and destination image. And as there are significant amounts of data in the source image I cannot simply copy over everything and then remove the files (as this would take a lot of time).

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2

Answers


  1. Chosen as BEST ANSWER
    0

    Actually Pádraig Galvin and KamilCuk pointed to what I wanted to achieve. This how I did it in the end:

    # Some dummy image that would hold data in real life
FROM alpine:latest AS some_image
RUN mkdir -p /my/dir/structure/is/deep

# Export the folder structure
FROM some_image AS source
RUN find /my -type d > dir_export.txt

# Import to destination image
FROM alpine:latest AS destination
COPY --from=source ./dir_export.txt /.
RUN xargs mkdir -p < /dir_export.txt
RUN rm /dir_export.txt

    It gives the same structure in "some_image" and "destination":

    / # tree my
my
└── dir
    └── structure
        └── is
            └── deep

  2. 0

    How can this be achieved?

    Dynamic programming:

    1. get the list of directories
    2. create them

    So something along:

    (cd dir1 && find . -depth -type d) | (cd dir2 && xargs mkdir -p)

    The specifics, programming language, the representation of "the list of directories", quoting and anything may change – the algorithm stays.

    You can do it better by zero separated list:

    (cd dir1 && find . -depth -type d -print0) | (cd dir2 && xargs -0 mkdir -p)

    And you can prepend docker to it:

    docker exec image1 sh -c 'cd dir1 && find . -depth -type d -print0' | docker exec -i image2 sh -c 'cd dir2 && xargs -0 mkdir -p'

    Or you could save the list to a file and then use it in dockerfile:

    # on host
$ docker run -ti --rm image1 sh -c 'cd dir1 && find . -depth -type d -print0' > dirlist.bin

# in Dockerfile
COPY dirlist.bin ./
RUN cd dir2 && xargs -0 mkdir -p <dirlist.bin
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