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The Code 
#!perl
use strict;
use warnings;

sub both_byte_orders_32 {
    my $data = shift;
    $data = pack 'H*', sprintf '%08x', $data;
    return reverse($data).$data
}

print both_byte_orders_32(305419896);

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Currently...
I need to format an integer into an 8-byte hexadecimal string as follows: if hex representation is (st uv wx yz) the formatted string must be (yz wx uv st st uv wx yz).

e.g. 305419896 in hex is (12345678) so formatted string should be (78 56 34 12 12 34 56 78)

The Question
although this works I have a nagging suspicion that this isn't The Best Way (tm) - is there some way to incorporate the reversing (little/big endian or something) into the pack/sprintf somehow - pack is still mysterious to me!