You are assigning the result of split() to a %hash

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

   ## which means...
   my %hash_list = (
      # key         # value
      " Bill 34" => " Jane 28",
      " John 20" => " Tom 19",
      " Wall 18  => undef
   );
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Upon upon further inspection, if you just want to sort these in alphabetical order, you do not need to assign them to a hash... just use a simple sort, and you're done:

   print sort ( split( /,/, $names ) );
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However, if you want to sort them by, say, the number to the right of the name, then you do need to use a hash:

    my $names    = "John 20, Bill 34... etc";
    my @elems    = split( /\s*,\s*/, $names );
    my %num2name = map{ reverse split( /\s/, $_ ) } @elems;

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