use warnings;
use strict;

sub two_d_search{
    my $amount_of_data = shift;
    my @data = splice @_, 0, $amount_of_data;
    my @pattern = ();
    my ($arg, $indentation, $string);
    my $i = 0;
    
    while (@_){
        $arg = shift;
        if ($arg eq "\n"){
            $i++;
            $arg = shift;
            }
        $indentation = $arg;
        $string = shift;
        $pattern[ $i ] .= ".{$indentation}" if $indentation;
        $pattern[ $i ] .= $string;
        print "($i: $pattern[ $i ])", "\n";
        }
    
    my $pos;
    my $match = 0;
    my @matches = ();
    
    for my $i (0 .. @data - 1){
        undef pos $data[ $i ];
        
        OUT_2:
        while ($data[ $i ] =~ m/$pattern[0]/g){
            ($pos) = @-;
            # matches can overlap, so 'pos' increases only by +1:
            (pos $data[ $i ]) = $pos + 1;
            
            for my $j (1 .. @pattern - 1){
                pos ($data[ $i + $j ]) = $pos;
                if ($data[ $i + $j ] =~ m/\G$pattern[$j]/){
                    # do nothing
                    }
                else {
                    next OUT_2
                    }
                }
            $match ++;
            push @matches, "[row: $i|column: $pos]";
            }
        
        }
    $" = "\n"; # set list output separator to "\n"
    return     "Number of matches: $match;", 
            "Upper-left corners match at:\n@matches"
    }

my @data = <DATA>;
chomp @data;

my @info = &two_d_search(
    scalar @data,
    @data,

#    indentation; string; argument of line separation
    1, '#', "\n",    # two_d_regex first line
    0, '#', "\n",    # two_d_regex second line
    2, '#\.'    # two_d_regex third line
    );

print "@info",$/;

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

OUTPUT:
(0: .{1}#)
(1: #)
(2: .{2}#\.)
Number of matches: 3;
Upper-left corners match at:
[row: 1|column: 1]
[row: 1|column: 6]
[row: 2|column: 0]
[download]