Dockerfile - set ENV to result of command

Question

Is it possible to set a docker ENV variable to the result of a command? Like:

ENV MY_VAR whoami

i want MY_VAR to get the value \"root\" or

Answer 1

Not sure if this is what you were looking for, but in order to inject ENV vars or ARGS into your .Dockerfile build this pattern works.

in your my_build.sh:

echo getting version of osbase image to build from
OSBASE=$(grep "osbase_version" .version | sed 's/^.*: //')

echo building docker
docker build -f \
--build-arg ARTIFACT_TAG=$OSBASE \
PATH_TO_MY.Dockerfile \
-t my_artifact_home_url/bucketname:$TAG .

for getting an ARG in your .Dockerfile the snippet might look like this:

FROM scratch
ARG ARTIFACT_TAG
FROM my_artifact_home_url/bucketname:${ARTIFACT_TAG}

alternatively for getting an ENV in your .Dockerfile the snippet might look like this:

FROM someimage:latest
ARG ARTIFACT_TAG
ENV ARTIFACT_TAG=${ARTIFACT_TAG}

the idea is you run the shell script and that calls the .Dockerfile with the args passed in as options on the build.