foreach my $num (1..5) {
 foreach my $letters ( ('TS','SA') ) {
  my $name = "cluster".$num."_".$letters;
  foreach ( @{$cluster{$name}}) {
   do_action($_);
  }
 }
}
[download]

I feel that's missing something, but I can't think what.. Update: It's missing a 2-D array.
Double Update: Looking at Ovid solution, another idea presents itself - if all the clusters have the same number of computers, just do a modulo on the array index to find the one you have to treat specially. Consider:

my @clusters = 
(       
        ['h1', 'h2', ... ],
 ['h8', 'h9', ... ],
 ['h16', 'h17', ... ],
 ['h24', 'h25', ... ],
 ['h32', 'h33', ... ],
);
[download]

and now iterate over the array. Or even better

my @clusters = 
(       
        'h1', 'h2', ... ,
 'h8', 'h9', ... ,
 'h16', 'h17', ... ,
 'h24', 'h25', ... ,
 'h32', 'h33', ... ,
);
[download]

Of course you have to go to the effort of making each of the 'h's do something. It depends on the rest of your code how you want to attack it.

____________________
Jeremy
I didn't believe in evil until I dated it.