How to determine current database?

I am using postgres 7.3.4 and need to be able to determine which
database a query is being run in (from a script). pg_database lists
databases but doesn't tell me which one is currently active. Is there a
query I can use along the lines of:
UPDATE tblUpdates SET xxx=1234 WHERE pg_current = TRUE;
or
UPDATE tblUpdates SET xxx=1234 WHERE pg_current = thisDBname;

We have about 15 databases all set up identically and when the structure
changes I run scripts to update them to ensure that they are all the
same. I need to create two new databases which have slight changes
(different default values - for now) and want to be able to have my
scripts be able to determine which database their running from.

Thanks

Ron