So "Q" is not supported on my architecture and my file is 100GB+ with variable length lines. I'm a little confused with your code. is $i the offset?<\p>

If I wanted to rebuild the entire index with the following code what would I change.

sub build_index {
        my $data_file = shift;
        my $index_file = shift;
        my $offset = 0;

        while (<$data_file>) {
                print $index_file pack("N", $offset);
                $offset = tell($data_file);
        }
}

sub line_with_index {
        my $data_file = shift;
        my $index_file = shift;
        my $line_number = shift;

        my $size;
        my $i_offset;
        my $entry;
        my $d_offset;

        $size = length(pack("N", 0));
        $i_offset = $size * ($line_number-1);
        seek($index_file, $i_offset, 0) or return;
        read($index_file, $entry, $size);
        $d_offset = unpack("N", $entry);
        seek($data_file, $d_offset, 0);
        return scalar(<$data_file>);
}
[download]