Getting the value of a config parameter in runtime

Hi all!

Sorry to ask this, I had it noted down but now I cannot find it and
I've been googling for 30 minutes now without success. There is a way
to query the system database to get the current value of a
configuration parameter, something in the form of SELECT value FROM
some_table WHERE field_name = 'archive_command', or similar, can't
remember, honestly. Or perhaps something more generic which was
filtered with greps, tails, heads and cuts.

Would someone be so kind as to point me at the right page or remind me
the way it was done?

Thanks in advance.

--
Jaume Sabater
http://linuxsilo.net/

"Ubi sapientas ibi libertas"