User priveledges

I have what may be a fairly simple question for the group, but for the life
of me I missed it in the documentation.

In writing some perl cgi scripts for postgres, I found that I would get an
error message if a user without certain priveledges tried to do a select,
insert, delete or whatever.

What I would like to do is a quick scan prior to executing a perl script
that would look at the user and see if they have the priveledge for the
action they are about to attempt.  An example would be that prior to a
screen coming up that handles deletions, a query is made to see if the user
even has this priveledge and the result is somehow captured so that they
can either go on to a subroutine generating a HTML screen for deletion or a
subroutine informing them they do not have the correct priveledge status,
etc....

Any hints?

Regards - Bob Kruger