# 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);