I would like to read contents of a file specified by an environment variable and pass it to docker-compose as build arg.
So then in my Dockerfile I can do:
ARG MY_FILE
RUN echo "$MY_FILE" > /my-file
This works perfectly:
docker-compose -f ./docker-compose.yml build --build-arg MY_FILE="$(cat $PATH_TO_MY_FILE)"
However, if I try to do this in docker-compose.yml like so:
build:
context: .
args:
- MY_FILE="$(cat $PATH_TO_MY_FILE)"
it fails with this error:
ERROR: Invalid interpolation format for "build" option in service "my-service": "MY_FILE="$(cat $PATH_TO_MY_FILE)""
Any idea how do I have to construct this string to have the same effect? I tried $$ etc, but doesn't seem to work...
Thanks for your help :)
Docker compose doesn't support this, so you have to use a workaround only. Which would either mean pre-processing the compose file or generate the command you ran by reading the yaml and interpolating by generating the command in bash
You can use something like yq and parse the parameters from docker-compose.yml and generate your command. But honestly what you are doing right now is simple and effective.
In docker service 3, you can do that now.
web:
image: xxxx
env_file:
- web-variables.env
If you have specified a Compose file with docker-compose -f FILE, paths in env_file are relative to the directory that file is in.