Hi, Thanks for all the replies - most informative!

I've now got working code, something like this:

# Declaration of the data structure
my %packet_fields = (
   $Idents{ Format_7 } => [qw(    ident
                x
                    y
                    flight_level
                chksum
                    )],
   $Idents{ Rotation_Marker } => [qw(    ident
                            site_x
                            site_y
                            chksum
                      )],
);

# This structure listed for completeness of this example!
my %packet_template = (
    $Idents{ Rotation_Marker } => "C3 n n n n n n n n n n n n C3",
    $Idents{ Format_7 }                => "C B16 n2 A4 A8 A2 A A A3 C2
+",
);
# Referencing the data structure
# code here to read $buffer from STDIN
# $ident is extracted from $buffer
    @packet{ @{$packet_fields{ $ident }} } =
        unpack ( $packet_template{ $ident }, $buffer);
[download]

I've got one further question about creating and accessing a hash of hashes.

I'm currently using the following structures:

my %ARP_GLA = (
    x    =>    247866.9,
    y    =>    666999.7,
);

my %ARP_EDI = (
    x    =>    314382.0,
    y    =>    673841.9,
[download]

I'd like to combine these into one data structure which I guess is a hash of hashes.

I believe I know enough to create the hash. This should do the trick:

my %ARP = (
    GLA => {
        x    =>    247866.9,
        y    =>    666999.7
        },
    EDI => {
        x    =>    314382.0,
        y    =>    673841.9
        }
);
[download]

How do I now access the elements in this structure?

Is it something like:

my $edi_arp = $ARP{EDI}->{x};
[download]

Thanks.

R.

--
Robin Bowes | http://robinbowes.com