As Corion correctly said, the error lies in the condition:

die unless ( $answer eq 'Y' or 'y' );
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which does not work because of the low precedence of or (compared to eq), so that this is parsed essentially as if you had written:

die unless (  ($answer eq 'Y') or ('y')  );
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The right-hand part of the or operator is always true so that even if the user type "N", the condition will always be true. (Note that even using the higher precedence || operator would not help, because its precedence is still lower than the precedence of the eq operator.)

Deparsing the statement shows this:

$ perl -MO=Deparse,-p -e  'die unless ( $answer eq "Y" or  "y");'
((($answer eq 'Y') or 'y') or die);
-e syntax OK
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In Perl 6, though, using an any junction infix operator would allow you to do something similar that would work the way you expected:

> my $answer = "y";
y
> say "true" if $answer eq 'Y' | 'y';
true
> say "true" if $answer eq 'N' | 'y';
true
> say "true" if $answer eq 'N' | 'n';
Nil
>
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