sub Fetch_w_callback{ # Main DBI retrieval mechanism----
   my ($sql, $callback) = @_;
   my $state = $_[2] ||= {}; # ** This THIRD param is CALL-by-ref **
   $debug{SQL} = $sql;
   (my $sth=$dbh->prepare($sql))->execute();
   
   $state->{ROW} = 0; 
   while (my $row = $sth->fetchrow_hashref()){
      $debug{ROW} = $state->{ROW}++;
      last if $callback->($row,$state) < 0; # Return negative to quit
   }
   $sth->finish;
 }
## Sample call, later in the code ....
Fetch_w_callback( "select client_name from xxx where cid='some-cid'",
                sub{ $row->{whatever} =  $_[0]->{client_name}; # SET
                    #Process  other values );