to execute commands against a running container use docker exec.

to copy a file (ex: dump.sql) into a container, use docker cp

So your approach might look something like this:

docker cp ./dump.sql pg_test:/docker-entrypoint-initdb.d/dump.sql
docker exec -u postgres pg_test psql postgres postgres -f docker-entrypoint-initdb.d/dump.sql

here it is in generic form:

docker cp ./localfile.sql containername:/container/path/file.sql
docker exec -u postgresuser containername psql dbname postgresuser -f /container/path/file.sql

And note that if you need to seed your database every time it is run, the folder /docker-entrypoint-initdb.d/ does have special significance, if you're using the offical postgres image

That's a feature of the standard postgres image; it's not something you get if you install PostgreSQL by hand in a plain Ubuntu container.

If you build a custom image for this, you can just start from that image and add your initialization file. This is a complete Dockerfile:

FROM postgres:9.6
COPY ./scripts/test.sql /docker-entrypoint-initdb.d/

I might not build a custom image for this. Instead, you can use the docker run -v option or the Docker Compose volumes: option to push the script into the container when it starts up (treating it as a configuration file).

(Also remember that these init scripts only run the very first time the database container starts up; if there is already database data they will not re-run.)

docker exec -it yiialkalmi_postgres_1 psql -U project -W project

Some explanation

• docker exec -it The command to run a command to a running container. The it flags open an interactive tty. Basically it will cause to attach to the terminal. If you wanted to open the bash terminal you can do this

docker exec -it yiialkalmi_postgres_1 bash

• yiialkalmi_postgres_1 The container name (you could use the container id instead, which in your case would be 40e39bd0329a )

• psql -U project -W project The command to execute to the running container

• U user

• W Tell psql that the user needs to be prompted for the password at connection time. This parameter is optional. Without this parameter, there is an extra connection attempt which will usually find out that a password is needed, see the PostgreSQL docs.

• project the database you want to connect to. There is no need for the -d parameter to mark it as the dbname when it is the first non-option argument, see the docs: -d "is equivalent to specifying dbname as the first non-option argument on the command line."

These are specified by you here

environment:
    POSTGRES_DB: project
    POSTGRES_USER: project
    POSTGRES_PASSWORD: project