You can use something that looks like a hash, but provides ordered results: Tie::IxHash

$ demo() {
   perl -e'
      use v5.18;
      use Tie::IxHash qw( );
      my %h;
      tie %h, Tie::IxHash:: if $ARGV[0];
      ++$h{ $_ } for "a".."z";
      say keys %h;
   ' -- "$1"
}

$ demo 0
lukphmweqsiorxvnbdfajyczgt

$ demo 0
dpbwuxlvticosyngmrzajefqkh

$ demo 1
abcdefghijklmnopqrstuvwxyz

$ demo 1
abcdefghijklmnopqrstuvwxyz
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You'd have to tie not just %hash, but the hashes referenced by the values of %hash.