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use strict;
use warnings;
...
for my $k (sort keys %UH){
  print "Hash contains key '$k'\n";
}

use strict;
use warnings;
my @items = ('ü','ü','ä', 'Ä');
my @unique_items = sort keys %{ {map { $_ => 1 } @items} };
print "@unique_items\n";