Thank you, Laurent_R. If it is the case that grep outputs the values themselves that are true, how is it that the  next unless grep !/(.).*\1/, @list;line appears to be doing what I want it to in this:

for (sort keys %words) {
  my @list = sort @{$words{$_}};
  next unless @list > 1; 
  next unless grep !/(.).*\1/, @list;
  print "@list\n";
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If grep outputs the words themselves, why is the "next unless" part working?