Almost right,

sub fn {
    my ($fn_x, $fn_y) = @_;
    ($$fn_x, $$fn_y) = ('x', 'y');

    my $rc = 0;
    $rc = 1 if $$fn_x ne 'x';
    return 0;
}
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is what you want though. The references $fn_x and $fn_y should be dereferenced if you want to access/change the values they refer to. For a scalar, dereferencing is done with $, while @, % and & are used to dereference lists, hashes and functions respectively. E.g. suppose that $r_list is a reference to a list, you'd get the list it refers to using @$r_list while you'd get the second element of the list using $r_list->[1].

For the ocmplete story, have a look at perlref.

Incidently, you might want to die inside the function fn since this is where the exception actually occurs. The if statement can be replaced by eval {...}; and you can test for an error by checking the value of the variable $@.

Hope this helps, -gjb-