how to pass argument to dockerfile from a file

Question

I am trying to pass an argument from a file to docker file.

I tried to the copy the file into docker container and use source command.

Dockerfile

COPY docker.env .
RUN /bin/bash -c "source docker.env"

Docker.env

BuildMode="release"

another try which also did not work

export BuildMode="release"

There is no error but when I tried to print ECHO $BuildMode, it is not printing the value inside it, it is like it did not get the value inside of it.

But if I create a docker container and try the same codes inside docker container, then it is working.

Answer 1

Then you can use --build-arg, it will pass parameters with --build-arg key=value to dockerfile when build, refer to this.

You just need to use sed to get from your env file & combine them to the format --build-arg key=value when build the dockerfile, example as next:

Dockefile:

FROM ubuntu:16.04

ARG BuildMode
ENV BuildMode=${BuildMode}

RUN echo $BuildMode

docker.env:

BuildMode="release"

Command:

docker build -t abc:1 $(cat docker.env | sed 's@^@--build-arg @g' | paste -s -d " ") . --no-cache

Output:

shubuntu1@shubuntu1:~/1$ docker build -t abc:1 $(cat docker.env | sed 's@^@--build-arg @g' | paste -s -d " ") . --no-cache
Sending build context to Docker daemon  3.072kB
Step 1/4 : FROM ubuntu:16.04
 ---> 13c9f1285025
Step 2/4 : ARG BuildMode
 ---> Running in 3bc49fbb0af4
Removing intermediate container 3bc49fbb0af4
Step 3/4 : ENV BuildMode=${BuildMode}
 ---> Running in 4c253fba0b36
Removing intermediate container 4c253fba0b36
 ---> c70f7f535d1f
Step 4/4 : RUN echo $BuildMode
 ---> Running in 5fef72f28975
"release"
Removing intermediate container 5fef72f28975
 ---> 4b5555223b5b
Successfully built 4b5555223b5b
Successfully tagged abc:1