# First make a hash to hold it all
  my %p = ();   # p is short for people so I can type less.

  #  bob, fred, peter and john are keys of %p, and refs to 
  # hashes we didn't predeclare.  This is what makes hashes 
  # of hashes (or arrays) so useful, they are easily 
  # populated from unknown data.

  $p{bob}{birth_order}   = 1;
  $p{fred}{birth_order}  = 2;
  $p{peter}{birth_order} = 3;
  $p{john}{birth_order}  = 4;

  $p{bob}{salary}   = 50000;
  $p{fred}{salary}  = 60000;
  $p{peter}{salary} = 70000;
  $p{john}{salary}  = 80000;
  
  # to sort by the people's names:
  for my $name ( sort keys %p ){
    # do something here
  }

  # to sort by the people's birth order:
  for my $name ( sort { $p{$a}{birth_order} <=> $p{$b}{birth_order} } keys %p ) {
    print "$p{$name}{birth_order}, $name\n";
  }