template in unpack

[uva]

hello monks,, can you tell what the use of using x2 template in unpack. i read in the documentation as, x A null byte. X Back up a byte. but i didnt understand crealy. i also tried with the example. can you please give me some code which explain that.

[GrandFather]

use warnings;
use strict;

my $str = '1234567890';
my @unpacked = unpack 'A1 x2 A1 X2 A1', $str;

print "@unpacked";

Prints:

1 4 3

A1 gets the first character (1), x2 skips two (23), A1 gets one character (4), X2 backs up two characters (43), A1 gets one character (3).

BTW print "@unpacked"; prints the elements in @unpacked with spaces between them as print join ' ', @unpacked; would.