@lower =  qw(a b c d e f g h i j k l m n o p q r s t u v w x y z);
@upper = map { uc($_) } @lower;
@eligibles = (@upper, @lower, q{_});
@chars = (@eligibles, 0..9);

%eligibles = map {$_,1} @eligibles;
%chars = map {$_,1} @chars;