official PostgresSQL docker images - create multiple databases

create-postgresql-databases.sh

#!/bin/bash
set -e

if [ -n "$POSTGRES_DATABASES" ]; then
  echo "POSTGRES_DATABASES provided. Creating multiple databases..." >&2
  IFS=', '; for db in $POSTGRES_DATABASES; do
    echo "Creating '$db'" >&2
    psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" <<-ESQL
      CREATE USER "$db";
      CREATE DATABASE "$db";
      GRANT ALL PRIVILEGES ON DATABASE "$db" TO "$db";
ESQL
  done
fi

docker-compose.yml

---
version: '3.7'

services:
  postgres:
    image: postgres:11.7
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_DATABASES: database-larry, database_curly, moe
    volumes:
      - create-postgresql-databases.sh:/docker-entrypoint-initdb.d/create-postgresql-databases.sh:ro