COPY does not handle empty arguments well

[joepvd]

cat <<EOF >Dockerfile
FROM centos
COPY Dockerfile "" /tmp/
RUN ls /
RUN ls /tmp
EOF
imagebuilder .

This will create a file /tmpDockerfile. in / docker build ignores the empty string.

Use case: An empty ARG variable that could be used to copy extra files in.

[derekhiggins]

This will create a file /tmpDockerfile. in / docker build ignores the empty string.

Just to add to this, imagebuilder puts anything in the source directory on the host into / (not limited to Dockerfile)
docker/podman build does something similar, but instead puts all the files into /tmp

[nalind]

@joepvd which version of docker build are you testing with? When I run your reproducer with a file other than Dockerfile in the build context directory with 19.03.12 (say, by running touch NOT-THIS-FILE first), docker build copies it to the destination directory, too, as if the empty quoted value was being treated as * rather than being ignored.

[nalind]

@derekhiggins Thanks for clearing things up!