How do I determine my data dir for a created database for pg_ctl?

Hi,

I have a database I can psql into... How can I determine what its
absolute path is so I can use pg_ctl on it to restart it?  Because
when I use pg_ctl, it tells me I have to provide it in the -D flag as
an argument.

Thanks,
matt

--
It is from the wellspring of our despair and the places that we are
broken that we come to repair the world.
-- Murray Waas