my %output_hash;
my $pk = "SomeString";
foreach my $pool ( @pools ) {
   my @machines = qx/Some command that gets me a list of machines/;
   #Some code here to check for cmd errors, etc. Convert output to an array of hashes (decode_json is involved);
   my $machine_aref = decode_json $machines[0];
   print "$#{machine_aref} lines returned\n";
   foreach my $row ( @{$machines_aref} ) {
            unless ( defined $row->{$pk} ) {
               print "'$pk'\n";
               print Dumper $row;
               print "$pk, $row\n";
               print "Bad return: Some command from above\n";
               print "HERE: " . $row->{"$pk"} . "\n";
               die;
            }
      $output_hash{$row->{$pk}} = 1;
   }
}

my @output_array = keys %output_hash;

return \@output_array;