It would be something like:

%mysqlimport -d forums_db /path/to/your/template.sql

A few notes:
the "-d" argument deletes all the data in the table you are importing to
whatever your your backup file is called, that's the table it will be loaded into in your database. So if you named your file "mybackup.sql", mysqlimport will strip the ".sql" part and load the contents into the "mybackup" table - so you'll probably want to make sure that you call your backup file "template.sql".

BACKUP YOUR EXISTING DB BEFORE DOING THIS

-jim