Dockerfile: how to set env variable from file contents

Question

I want to set an environment variable in my Dockerfile.

I\'ve got a .env file that looks like this: FOO=bar.

Inside my Dockerfile,

Answer 1

Environment Variables

If you want to set a number of environment variables into your docker image (to be used within the containers) you can simply use env_file configuration option in your docker-compose.yml file. With that option, all the entries in the .env file will be set as the environment variables in image and hence into containers.

More Info about env_file

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Build ARGS

If your requirement is to use some variables only within your Dockerfile then you specify them as below

ARG FOO
ARG FOO1
ARG FOO2
etc...

And you have to specify these arguments under the build key in your docker-compose.yml

build: context: . args: FOO: BAR FOO1: BAR1 FOO2: BAR2

More info about args

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Accessing .env values within the docker-compose.yml file

If you are looking into passing some values into your docker-compose file from the .env then you can simply put your .env file same location as the docker-compose.yml file and you can set the configuration values as below;

ports: - "${HOST_PORT}:80"
So, as an example you can set the host port for the service by setting it in your .env file

Please check this