my @table2 = [[7, 8, 9], [10, 11, 12]]; # using array

To assign to an array you need parentheses, not square brackets.

my @table2 = ([7, 8, 9], [10, 11, 12]);
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The following code might help you with accessing array references.

johngg@abouriou:~/perl/Monks$ perl -Mstrict -Mwarnings -MData::Dumper 
+-E '
my $raTable = [
   [ 1, 2, 3 ],
   [ 4, 5, 6 ],
   ];

say qq{\nNumber 4 is found at \$raTable->[ 1 ]->[ 0 ] - $raTable->[ 1 
+]->[ 0 ]};

push @{ $raTable->[ 0 ] }, 8;
push @{ $raTable->[ 1 ] }, 9;

print Data::Dumper->Dumpxs( [ $raTable ], [ qw{ raTable } ] );'

Number 4 is found at $raTable->[ 1 ]->[ 0 ] - 4
$raTable = [
             [
               1,
               2,
               3,
               8
             ],
             [
               4,
               5,
               6,
               9
             ]
           ];
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I hope this is helpful.