To count the rows, use scalar In general, if you need to count the number of columns in each row (since they need not be the same), you could use a for loop:

use strict;
use warnings;
my @AoA=(
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [0, 0, 0, 1]
     );

print 'Number of rows = ', scalar @AoA, "\n";
for my $aref (@AoA) {
    print 'Number of cols = ', scalar @{$aref}, "\n";
}

__END__

Number of rows = 3
Number of cols = 4
Number of cols = 4
Number of cols = 4
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See also:

• perldsc
• References quick reference