use strict;
use warnings;
use Data::Dumper;

my @lookback;
for my $line (1..5) {
    push @lookback, [ map { "$line.$_" } 0..10 ]; 
}

print Dumper \@lookback;

my $col = 3;
my @column = map { $_->[$col] } @lookback;

print Dumper \@column;