I think your problem is that instead of

my $rh_set = IO::Select->select($read_set, undef, undef, 0);
foreach my $rh (@$rh_set) {
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you want

my($rh_set) = IO::Select->select($read_set, undef, undef, 0);
foreach my $rh (@$rh_set) {
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or

my @rh_set = $read_set->can_read();
foreach my $rh (@rh_set) {
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The original code can't work, because it's not defined what the IO::Select->select method returns in scalar context (you're calling it like that), and in list context it returns a list of three references to arrays, the first being a reference to the array of readable handles.