#! perl -slw
use strict;
use Data::Dumper;

my $b = "abefcdghijklmn";
my @a = (
    [ 'start 0', unpack '(A1x)*', $b ],
    [ 'start 1', unpack '(xA1)*', $b ]
);

print Dumper \@a;
__END__
C:\test>539664
$VAR1 = [
    [ 'start 0', 'a', 'e', 'c', 'g', 'i', 'k', 'm' ],
    [ 'start 1', 'b', 'f', 'd', 'h', 'j', 'l', 'n' ]
];