Is there a way to watch a mysql database for changes using perl?

If you add a TRIGGER to the table(s) you're interested in, you can use that to alert the watching application. You could do that in a number of ways:

1. Create an audit table in the database, and have the trigger write the relevant info there; and have your watching application poll the audit table for new entries. You're still polling, but in a controlled way which won't hit the server too hard.
2. Have the trigger call an external app through a UDF.

As far as MyISAM tables go you can watch information_schema.TABLES.UPDATE_TIME. That would save you from polling all tables you're interested in. For InnoDB, watching binlog is the best I can think of.

Another approach is to do a push/signal instead of a DB poll. Have whatever process updates the database, notify your Perl code that an update was done via any IPC you pick (heck, a log file being appended to with name of table being changed might do the trick well enough).

This is especially effective if the updates a fairly rare/low volume yet the reaction time to them must be quick.

An additional benefit is portability - works for any MySQL backend or for any other DB engine.