error handling

hi,

im working with php 4 and postgresql 8 and i would like to know how to
handle certain errors generated. in postgresql, i've written a stored
function that selects a record from a table and in case no record is found i
'raise an exception'. fine, now in my php script i call that the stored
function which works properly when there is a record but when the record
doesnt exist, i would like to be able to place my own error message and not
e.g 'fatal error, .....'. how do i capture(in php) the exception i raised
in postgres so that i know the record doesnt exist?

thanx.