Grab value from .env file with dotenv and pass them into a docker run command

Question

I have the following .env file:

MY_SECRET_POSTGRES_PASSWORD=hello

I installed dotenv to load variables from this env file and run the docker command as follows:

dotenv -- docker run --name postgresql-container -p 5432:5432 -e POSTGRES_PASSWORD=$MY_SECRET_POSTGRES_PASSWORD -d postgres

When I run the command, I get the following error:

Error: Database is uninitialized and superuser password is not specified.

       You must specify POSTGRES_PASSWORD to a non-empty value for the

       superuser. For example, "-e POSTGRES_PASSWORD=password" on "docker run".

However, when I just run the following command to ensure that the env is loaded, it shows up fine:

dotenv -- bash -c 'echo "$MY_SECRET_POSTGRES_PASSWORD"'

I know I can use --env-file to pass in the entire env file but I rather like to pick the values that I pass is so that I do not expose anything unnecessary to the container.

Answer 1

See the difference in output:

MIHAI=test bash -c "echo Var is: $MIHAI"

Var is:

MIHAI=test bash -c 'echo Var is: $MIHAI'

Var is: test

The difference is the single and double quotes.

When you run this:

dotenv -- docker run --name postgresql-container \
  -p 5432:5432 -e POSTGRES_PASSWORD=$MY_SECRET_POSTGRES_PASSWORD -d postgres

MY_SECRET_POSTGRES_PASSWORD gets evaluated before it is sent to dotenv. So dontenv does not receive a $... but an empty value.

Correct:

dotenv -- bash -c 'docker run --name postgresql-container -p 5432:5432 -e POSTGRES_PASSWORD=$MY_SECRET_POSTGRES_PASSWORD -d postgres'

This way what is between the single quotes is sent as is to dotenv.