automatically dump a table when it is updated

Hi All,

I need to dump a modified column (rpad(id, 19 ) || 'X' AS data) of a table to a
text file after that table has been updated.  I thought that a trigger might
work but I would like an external script to post process the file.  The LISTEN
and NOTIFY commands might do the job but I have no idea how to use them.  Can
someone assist me or point me in the direction of a clear 'How To' type document?

Kind Regards,
Keith