grant select on all databases except one mysql

Run the output of the following query:

SELECT CONCAT("GRANT SELECT ON ",SCHEMA_NAME,".* TO 'test_user'@'localhost';")
FROM information_schema.SCHEMATA 
WHERE SCHEMA_NAME NOT LIKE 'mysql';

Since you have 200 databases and you do not want to grant one by one. Fastest way to do that would be

GRANT SELECT ON *.* TO 'test_user'@'localhost';
FLUSH PRIVILEGES;

And then just revoke the privilege in mysql db

REVOKE SELECT ON mysql.* FROM 'test_user'@'localhost' ;
FLUSH PRIVILEGES;

But when I selectively GRANT and then REVOKE on mysql.* . Then it is working

user@ubuntu:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 150
Server version: 5.5.41-0ubuntu0.12.04.1 (Ubuntu)

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> CREATE USER 'mysqlrockstar'@'localhost';
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW GRANTS FOR 'mysqlrockstar'@'localhost';
+---------------------------------------------------+
| Grants for mysqlrockstar@localhost                |
+---------------------------------------------------+
| GRANT USAGE ON *.* TO 'mysqlrockstar'@'localhost' |
+---------------------------------------------------+
1 row in set (0.00 sec)

mysql> GRANT SELECT ON mysql.* TO 'mysqlrockstar'@'localhost';
Query OK, 0 rows affected (0.00 sec)

mysql> exit;
Bye
user@ubuntu:~$ mysql -u mysqlrockstar
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 151
Server version: 5.5.41-0ubuntu0.12.04.1 (Ubuntu)

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
+--------------------+
2 rows in set (0.06 sec)

mysql> exit;
Bye
user@ubuntu:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 152
Server version: 5.5.41-0ubuntu0.12.04.1 (Ubuntu)

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> REVOKE SELECT  ON mysql.* FROM 'mysqlrockstar'@'localhost';
Query OK, 0 rows affected (0.00 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

mysql> exit;
Bye
user@ubuntu:~$ mysql -u mysqlrockstar
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 153
Server version: 5.5.41-0ubuntu0.12.04.1 (Ubuntu)

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
+--------------------+
1 row in set (0.00 sec)

mysql> use mysql;
ERROR 1044 (42000): Access denied for user 'mysqlrockstar'@'localhost' to database 'mysql'