I'm not sure what you intend, so I'll try PSI::ESP. On the first five iterations of the loop, there won't be anything in @AoA at index 5. There's your uninitialized value right there.

Additionally, your split doesn't make a lot of sense. If you want to split on whitespace, you can avoid any regex at all. Otherwise, if you want an array slice, the syntax would be @tmp = (split)[0 .. 7];

Here's how I would do things:

while(<DATA>){
    push @AoA, [split];
}
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This gives you a list of five lines, with each number in a separate slot.