#!/usr/bin/perl
use strict;
use warnings;

my $octetstr = join '', map chr(), 0xab, 0xcd, 0x00, 0x1d, 0x94, 0x56;

my $val;
map { $val .= sprintf("%02x",$_) } unpack "CCCCCC", $octetstr;
my $mac=join(".",unpack("a4 a4 a4",$val));

print "MAC1: $mac\n";

########################
####  Exactly the same thing with foreach instead of map{}
########################

$val='';
foreach my $decimal_value (unpack "CCCCCC", $octetstr)
{ 
   $val .= sprintf("%02x",$decimal_value); # makes 2 digit Hex

   print "Decimal_value: $decimal_value \tval(hex string)=$val\n";
}
my $mac2=join(".",unpack("a4 a4 a4",$val));
print "MAC2: $mac2\n";

# the a4 unpack for $mac2 could be done in other, slower ways
# like with a regex (a very,very slow way, but just a hypothetical)
#

my $mac3 = $val;
$mac3 =~ s/^([0-9a-f]{4})([0-9a-f]{4})([0-9a-f]{4})/$1\.$2\.$3/;
print "MAC3: $mac3\n";

#######################
### BrowserUk, AnomalousMonk ideas with either H2 or H4
### far better!! One step, fast. Clearly the right way
### for this specific problem!
#######################

my $mac4 = join '.', unpack '(H4)*', $octetstr;
print "MAC4: $mac4\n";

__END__
All of these MAC's are the same:

MAC1: abcd.001d.9456
Decimal_value: 171 	val(hex string)=ab
Decimal_value: 205 	val(hex string)=abcd
Decimal_value: 0 	val(hex string)=abcd00
Decimal_value: 29 	val(hex string)=abcd001d
Decimal_value: 148 	val(hex string)=abcd001d94
Decimal_value: 86 	val(hex string)=abcd001d9456
MAC2: abcd.001d.9456
MAC3: abcd.001d.9456
MAC4: abcd.001d.9456