Probably Trivial: Finding Largest Primary Key used in Table

Hi All,

This may sound trivial...but I've been trying to find out how to find 
the largest primary key that's been assigned/used within a table.

I'm new to DB development while I have done some DBA.

It would save me trouble when I want to keep control of the primary 
keys, make sure that when I insert a new record I can assign a unique 
primary key.

I would like to do this using a perl script...not as some stored 
procedure or constraint so as to keep it as DB independent (regardless 
of Sybase, MySQL, Oracle, etc) as possible.

Best Regards,
Jay