Here's another approach that you might find instructive:

my $text = "0 X X X ...";
my @items = split(' ', $text);
my @array;
while (@items) {
  push(@array, [ splice(@items, 0, 8) ]);
}
pp \@array; use Data::Dumper;
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The basic idea is:

1. Split the input string into an array (@items).
2. Remove the first 8 elements of @items, create an array ref out of those elements, and push that array ref onto the end of @array
3. Repeat step 2 until @items is empty.

To make sure you have a full matrix, you can check the length of the last row with:

die "incomplete last row\n"
   unless (scalar(@{$array[-1]} == 8);
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