Just to clarify: I think your main confusion is about how the C, a and A templates for (un)pack work. Observe:

#! /usr/bin/perl 

use strict ;
use warnings ;

my $bindata = pack("CaA", 65, "B", "C");

print "$bindata\n";

print join(", ",unpack("H2H2H2",$bindata)),"\n";

print join(", ",unpack("C*",$bindata)),"\n";

print join(", ",unpack("A1A1A1",$bindata)),"\n";

print join(", ",unpack("a1a1a1",$bindata)),"\n";
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