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   ## your code is effectively this:
   my %hash_list = ( " Bill 34", " Jane 28", " John 20", " Tom 19", " 
+Wall 18" );
...
      " John 20" => " Tom 19",
      " Wall 18  => undef
   );

   print sort ( split( /,/, $names ) );

    my $names    = "John 20, Bill 34... etc";
    my @elems    = split( /\s*,\s*/, $names );
...

    my @sorted   = map{ $num2name{$_} } sort { $a <=> $b } keys %num2n
+ame;
    print "@sorted\n";