PostgresSQL
from bash
su potgres
createdb target_db
pg_dump source_db | psql target_db
or from psql
postgres=# CREATE DATABASE target_db WITH TEMPLATE source_db;
MySQL
echo "create database target_db" | mysql [-u user -ppasswd]
mysqldump source_db [-u user -ppasswd] | mysql target_db [-u user -ppasswd]