Howdy,

It's easier if you just search by column:

my $data = do { local $/; <DATA> };

my $p1 = qr(.{1}#);
my $p2 = qr(#);
my $p3 = qr(.{2}#\.);

for my $column (0 .. 80) {
    my $start = qr(.{$column});
    my $next = qr(.*\n$start);
    my $target = qr($start(?=$p1$next$p2$next$p3));
    while ( $data =~ m/^$target/mg) {
        my $row = () = substr($data,0,pos $data) =~ /\n/g;
        print "[row: $row|column: $column]\n";
    }
}

__DATA__
#..#.....#.
..#...##...
.#....#..##
#..#....#..
..#...#..#.
.......#.#.
...........
[download]

[row: 2|column: 0]
[row: 1|column: 1]
[row: 1|column: 6]
[download]