Docker exec - cannot call postgres with environment variables

Question

I have multiple Environment Variables defined on my Postgres container, such as POSTGRES_USER. The container is running and I want to connect to Postgres from the command line using exec.

I'm unable to connect with the following:

docker exec -it <CONTAINER-ID> psql -U $POSTGRES_USER -d <DB NAME>

I understand that the variable is defined on the container and the following does work:

docker exec -it <CONTAINER-ID> bash -c 'psql -U $POSTGRES_USER  -d <DB NAME>'

Is there a way for me to execute the psql command directly from docker exec and call the environment variable on the container?

docker exec -it <CONTAINER-ID> psql -U ????? -d <DB NAME>

Answer 1

Depending on your use case, what you could do, instead of passing a user to the psql command is to define the environment variable PGUSER to the container at boot time.

This way, it will be the default user for PostgreSQL, if you do not specify any, so you won't even have to specify it in order to connect:

$ docker run --name postgres -e POSTGRES_PASSWORD=bar -e POSTGRES_USER=foo -e PGUSER=foo -d postgres
e250f0821613a5e2021e94772a732f299874fc7a16b340ada4233afe73744423

$ docker exec -ti postgres psql -d postgres                                                          
psql (12.4 (Debian 12.4-1.pgdg100+1))
Type "help" for help.

postgres=#