using envsubst in Dockerfile

Dockerfile

FROM ubuntu:trusty
RUN \
  apt-get update \
  && apt-get -y install gettext-base \
  && apt-get clean \
  && rm -rf /var/lib/apt/lists/*

ENV VALUE=foo
ENV VALUE1=boo
COPY config.txt source_config.txt
RUN envsubst < "source_config.txt" > "config.txt"

I don't think you'd be able to RUN the envsubst. Well I mean you can run it, but it won't have the environment variables that are passed when the container is launched, which is probably what you'd want otherwise you should use build args. Maybe you mean CMD on that last line instead of RUN?

I don't think you'd be able to RUN the envsubst. Well I mean you can run it, but it won't have the environment variables that are passed when the container is launched, which is probably what you'd want otherwise you should use build args. Maybe you mean CMD on that last line instead of RUN?

lol man :)

You can run it, but must have it in the same line - so they will be in the same context.

RUN export VALUE=foo && \
    export VALUE1=$(cmd to get value1) && \
    envsubst < "source_config.txt" > "config.txt"

Update available packages in Debian

RUN apt-get update

CMD export VALUE=foo &&
export VALUE1=$(cmd to get value1) &&
envsubst < "source_config.txt" > "config.txt"