my $mask_input = ;
...
my $lastEnd = 1;
while ( ) {
my (undef, $start, $end) = split '\s', $_;
## change everything from the end of the last range
## to the start of this range to 'N'
substr( $mask_input, $lastEnd, $start ) =~ tr[\x00-\xff][N];
$lastEnd = $end;
}
...
print OUT "$mask_input";