psql client in a container

Set the context:

PSQL_USER=user \
PSQL_PASSWORD=password \
PSQL_HOST=datamart.rds.amazonaws.com \
PSQL_PORT=5432 \
PSQL_DB=db_default

Then:

docker run -it --rm jbergknoff/postgresql-client \
  "postgresql://${PSQL_USER}:${PSQL_PASSWORD}@${PSQL_HOST}:${PSQL_PORT}/${PSQL_DB}" \
  -P pager=off -c "select count(*) from pg_class"