Hi, I am successfully using the following data structures: 
# List all packet types that this script knows about
my %Idents = (
    Rotation_Marker => 0x90,
    Format_7    => 0x87,
);

# List packet lengths of each of the packet types (Ident char to check
+sum, inclusive)
my %Packet_Length = (
    $Idents{ Rotation_Marker }    => 30,
    $Idents{ Format_7 }        => 28,
);

# unpack templates to use for each packet type (not including the pack
+et Ident)
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",
);

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So far so good. I can read an ident from a file and then use construct like $packet_template{ $ident } I am also using the following data structures: 
my @packet_fields = qw(    ident
            flags
            x
            y
            mode3
            callsign
            route
            spare1
            spare2
            flight_level
            terminator
            chksum
            );
my @rotation_packet_fields = qw(ident
                RDP_Ident
                Radar_Site_Ident
                site_x
                site_y
                Useful_Vol_Upper
                Useful_Vol_Lower
                Useful_Vol_North
                Useful_Vol_South
                Useful_Vol_East
                Useful_Vol_West
                Rotation
                Rotation_x
                Rotation_y
                Reserved
                QNH_Datum
                terminator
                chksum
                );

[download]
I use these as follows: 
if ($ident == $Idents{ Rotation_Marker }) {
   @packet{ @rotation_packet_fields } = unpack (
   $packet_template{ $ident }, $buffer);
   ...

if ($ident == $Idents{ Format_7 }) {
   @packet{ @packet_fields } = unpack (
   $packet_template{ $ident }, $buffer);

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Now, what I'd like to do is to create a hash of these arrays and refer to them in a similar fashion to the way I refer to the %packet_template hash. However, I can't work out how to do it. I've come up with the following declaration to create the hash, but I don't know how to re-reference it: 
my %packet_fields = (
   $Idents{ Format_7 }    => qw(    ident
            flags
            x
            y
            mode3
            callsign
            route
            spare1
            spare2
            flight_level
            terminator
            chksum
            ),
   $Idents{ Format_7 } => qw(ident
                RDP_Ident
                Radar_Site_Ident
                site_x
                site_y
                Useful_Vol_Upper
                Useful_Vol_Lower
                Useful_Vol_North
                Useful_Vol_South
                Useful_Vol_East
                Useful_Vol_West
                Rotation
                Rotation_x
                Rotation_y
                Reserved
                QNH_Datum
                terminator
                chksum
                ),
);

[download]
Is this correct? How do I use it in my code, e.g. this doesn't work: 
   @packet{$%packet_fields{ $ident} } = unpack (
   $packet_template{ $ident }, $buffer);

[download]
What should I use? Thanks, R.
-- Robin Bowes | http://robinbowes.com

In reply to Help with hash/array data structure by robinbowes

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