I wrote this and it seems to work... Do you think it's correct?

if($initial_string=~/((-*)(B+)(-*))/)
{
    $total=$1;
        $position_total=index($initial_string, $total);
        $substring_until_total=substr($initial_string,0,$position_tota
+l);

    $blank_left=$2;
    $b_region=$3;
    $blank_right=$4;
    
    if(length($blank_left)>200)
    {
        substr($blank_left, -200, 200, ('B' x 200));
    }

    else
    {
        $blank_left=~s/\-/B/g;
    }

    if(length($blank_right)>200)
    {
        substr($blank_right, 0, 200, ('B' x 200));
    }

    else
    {
        $blank_right=~s/\-/B/g;
    }

    print $substring_until_total.$blank_left.$b_region.$blank_right."\
+n";
}
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