Just lowercase the $id you use for the hash lookup: 

   my $id = $ID[0];
   my $id_lc = lc $id;
   if ($ids{$id_lc}) {
       print "'$id' is duplicate\n";
   } else {
      $ids{$id_lc} = 1;
   }

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In reply to Re^3: Search a hash case insensitive by Eliya
in thread Search a hash case insensitive by Saved

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