A question About Array Indexing

[ccelt09]

If one has an array can you assign the length of its current index value from the beginning to a scalar variable?

Essentially I am reprinting a text file made of one long string of 0's and N's with no spaces. At the positions along this string that lie outside of certain intervals, I want all the elements reprinted as N's.

 input file looks like this: 0000000NNNN00NNN0NNN0N0N0NN0N

#-------------------------------------------------

my $population = "all28_males";

my $count = 0; 
my $position = 0;
my ($n, $data, @info, $info, $buf);

my $filtered_sites = "/Users/logancurtis-whitchurch/Dropbox/thesis_fol
+der/galaxy_chrX_data/filtered_chrX_rawdata.interval";
open (INTERVAL, "<$filtered_sites") or die "can't open $filtered_sites
+";

open(MASK, "/Users/logancurtis-whitchurch/Dropbox/thesis_folder/consen
+sus_files/filtered_mask_files/filtered.mask."."$population".".txt") o
+r die "can't open     masked file\n";

my $mask = <MASK>;
chomp ($mask);

for each (my @interval = <INTERVAL>); { 

    chomp (@interval); 
    my @positions = split(/\t/, $interval[$count]);
    my $start = $positions[1];
    my $end = $positions[2]; 

    while (($n = read MASK, $data, 100000) != 0) {
        
        my @info =  split(//, $data);
        my $length = 1;
                                    
        foreach $info (@info){
                        
            if ( $length < $start]) {
                substr($mask,($info),1,'N');
                $length++;
            }

            if (( $length >= $start) && ($length <= $end)) {
                next; 
                $length++
            }

            if ($length > $end) {
                $count++;
            }
        }
        $buf .= $data;
        print OUT "$mask";
        close OUT; 
        close MASK;
    }
}