@HWUSI-EAS1734_0032_FC620F7AAXX:5:1:18184:1176#CGATGT/1
GGATTTCTCGTGGANACCATTTGTTGGTCAANNNNNNNNNNGTGTTNGNCTTCANNGNNATTGAAAATGNTCATTCGTGGCTATTTTCGCNNNNNATNNNN
+HWUSI-EAS1734_0032_FC620F7AAXX:5:1:18184:1176#CGATGT/1
gggfggggfgeeecB```^]gffgegadcgBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
@HWUSI-EAS1734_0032_FC620F7AAXX:5:1:1934:1185#CGATGT/1
GTCATCCTTAATTANCGTATGTGCTCTTCCTNCNNNNNNNNGCTGCTANTTATTTCTNNGCAGCTTTGCTCTTATTAGTTACGAACATGCCNNNNTANNNN
+HWUSI-EAS1734_0032_FC620F7AAXX:5:1:1934:1185#CGATGT/1
acdad`^ddd^aa^B_\VZZfcfccaffBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
..........


##</code><code>##

    if (-e "$ARGV[0].idx") {
        open (INDEXFQ1, "$ARGV[0].idx") or die $!;
    }
    else {
        open (INDEXFQ1, "+>$ARGV[1].idx") or die $!;
        build_index(*FQ1, *INDEXFQ1);
    }

##</code><code>##

 print OQ10_1 line_with_index(*FQ1, *INDEXFQ1, $line);

##</code><code>##

741:20058#ATCACG/1
GTTCGTGAGAGCTCTAGGTTGTCGTCTCCCAGTCAACTATGGTCGCTGTAACGCGCTGACTT
41:20058#ATCACG/1
dgggg_ddadbaggedbXdd]^[UVYX]XR_BBBBBBBBBBBBBBBBBBBBBBBBBBBBBB

##</code><code>##

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>);
}