use warnings;
use strict;

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

print "@unpacked";
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Prints:

1 4 3
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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.