my %inventory_hash = ();
open DataFile, "Inventory.csv" or die ("Inventory.csv $!");
while (my $inventory_line = <DataFile>) {
  my @inventory_fields = split /,/,$inventory_line;
  my $inventory_key = shift @inventory_fields;
  if (exists($inventory_hash{$inventory_key})) {
    print "Warning! Duplicate inventory key detected: $inventory_key\n";
    next;
  }
  $inventory_hash{$inventory_key} = \@inventory_fields;
}
close DataFile;
open DataFile, "clients.txt" or die ("clients.txt $!");
while (my $line = <DataFile>) {
  my @fields = split(/,/, $line);
  if (exists($inventory_hash{$fields[3]})) {
    my @sys = @{$inventory_hash{$fields[3]}};
    # do stuff with the contents of @sys, print, whatever
    delete $inventory_hash{$fields[3]};
  }
}