I use Maatkit for a lot of grunt work and thought you might appreciate this quick tip. Suppose you have a bazillion tables to convert from MyISAM to InnoDB, but they are mixed in with other tables that are already InnoDB, or are another storage engine that you don’t want to touch.
mk-find <db_name> --engine MyISAM --exec "ALTER TABLE %D.%N ENGINE=INNODB" --print
Here’s a bonus tip, while I’m at it. I had a client a while back whose application creates tables as needed, so they had about 90,000 tables in a bunch of different databases, all named things like user_123_456_friends. I wanted to add an index to them — but not to the ones named friends_123_456_user.
mk-find <db_name> --tblregex '^user_\d+_\d+_friends$' --exec 'ALTER TABLE %D.%N ADD KEY(site_id)'
Boy, is that a lot easier than adding indexes to 90k tables by hand!