MySQL partial backup

Hi folks.  I want to setup a backup script for a MySQL database, as such 
things are generally regarded as Good.  mysqldump is the standard tool there, 
but as near as I can tell there is no way to export only the structure of 
certain tables.  It's all-or-nothing.  Easily half the data in my database is 
active session records, logs, cache tables, and other such volatile data that 
has no business being in a routine backup, but I've yet to figure out from the 
mysqldump man page how to only get the structure of those tables instead of 
the full data.

Has anyone else done that?  Any links to recommend, or alternate approaches?

The database is of a size that I'll want to compress the backups as well and 
ideally rotate them.  I don't know how do to proper rotation to clear out old 
backups yet, but I figure one step at a time.  (Pointers for that would be 
great, too, though.)
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