#!/usr/bin/perl
use strict;
use warnings;

my $output = "Fmd.txt";
my $seq    = "BATCATEATFATRAT";
my $result = splitSequence($seq, 3);

print "\nResult:\n$result\n";

open my $outFile, '>', $output or die qq{Cannot open file "$output": $!.\n};
print $outFile "Formatted Data:\n$result\n\n";
close $outFile;


sub splitSequence {
    my ($sequence, $length) = @_;
    my $result;

    while (length $sequence) {
        $result .= substr($sequence, 0, $length, '') . "\n";
    }

    return $result;
}