вы можете использовать echo cmd как:
echo "CREATE USER 'test' @ '%' IDENTIFIED BY '123456'; GRANT ALL PRIVILEGES ON *. * TO 'test' @ '%'; FLUSH PRIVILEGES; " | mysql -u root
или использовать опцию -e
mysql -u root -e "CREATE USER 'test' @ '%' IDENTIFIED BY '123456'; GRANT ALL PRIVILEGES ON *. * TO 'test' @ '%'; FLUSH PRIVILEGES;"