I have inherited some code from a guy whose favorite past time was to shorten every line to its absolute minimum (and sometimes only to make it look cool). His code is hard to understand but I managed to understand (and rewrite) most of it.

Now I have stumbled on a piece of code which, no matter how hard I try, I cannot understand.

my @heads = grep {s/\.txt$//} OSA::Fast::IO::Ls->ls($SysKey,'fo','osr/tiparlo',qr{^\d+\.txt$}) || ();
my @selected_heads = ();
for my $i (0..1) {
   $selected_heads[$i] = int rand scalar @heads;
   for my $j (0..@heads-1) {
      last if (!grep $j eq $_, @selected_heads[0..$i-1]);
      $selected_heads[$i] = ($selected_heads[$i] + 1) % @heads; #WTF?
   }
   my $head_nr = sprintf "%04d", $i;
   OSA::Fast::IO::Cp->cp($SysKey,'',"osr/tiparlo/$heads[$selected_heads[$i]].txt","$recdir/heads/$head_nr.txt");
   OSA::Fast::IO::Cp->cp($SysKey,'',"osr/tiparlo/$heads[$selected_heads[$i]].cache","$recdir/heads/$head_nr.cache");
}

From what I can understand, this is supposed to be some kind of randomizer, but I never saw a more complex way to achieve randomness. Or are my assumptions wrong? At least, that's what this code is supposed to do. Select 2 random files and copy them.

=== NOTES ===

The OSA Framework is a Framework of our own. They are named after their UNIX counterparts and do some basic testing so that the application does not need to bother with that.