use warnings;
use strict;

while (<DATA>) {
    chomp;
    my $template = 'A3' x 20;
    my @nums = unpack $template, $_;
}

__DATA__
 -8-18 -9-10 -8 -7 -9-10 -9 -6 -5 -8 12 -7-10 -8 -8 -8 -8 -6
 -3  2  2 -2 -8  1 -2 -5 -1 -4 -6  6 -4 -6 -5 -1  0 -8 -6 -6
  3 -6 -3 -6 -2 -5 -5 -5 -4  4 -3 -2 -2 -3 -5  1  3 -7 -4  3
  1 -6 -5 -6  4 -5 -6 -5 -6  3  1 -5 -3 -2 -5 -1  3 -4 -3  4
  2 -8 -6 -7 -8 -8 -8  7 -8 -9 -9 -7 -8 -6 -8 -4 -7 -9 -9 -8
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I added a single space to the beginning of every line so that each number would occupy 3 columns. If that is not the case with your actual input, the template just needs to be adjusted.