Or

#! /usr/bin/perl
#
use strict ;
use warnings ;
my $b = "abcdefghijklm" ;

my @a ;

$a[0]->[0] = "start 0" ;
$a[1]->[0] = "start 1" ;

for(my $i = 0; $i < 14; $i += 2) {
    push (@{$a[0]}, $_) for unpack("x$i A1", $b) ;
    push (@{$a[1]}, $_) for unpack("x".($i+1)." A1", $b) ;
}

foreach ( @{$a[0]} ) {
    print "$_\n" ;
}
foreach ( @{$a[1]} ) {
    print "$_\n" ;
}
[download]

Somehow I have the feeling this can be done all at once!!
And is there an other way to use the ($i+1) inside unpack ?

Luca