Bring up all services:

./cjl up -d

Connect via psql:

./cjl run --rm postgresql_db "psql -h postgresql_db -U postgres"

The above command will prompt you to enter the database password.

SQL script backup via pg_dump:

export PGPASSWORD=$(printf '%s' "$POSTGRES_PASSWORD")
./cjl run --rm -e PGPASSWORD='$PGPASSWORD' postgresql_db "pg_dump -h postgresql_db -U postgres -p 5432"