$offset = 0;
        while (read(DATA, $data, BLOCKLEN, $offset)) {
                my $blockhdr = unpack "H*", substr($data, 0, BLOCKHDR);
                my $blockdt  = unpack "H*", substr($data, BLOCKHDR, BLOCKDATA);
                my $cdrdata  = unpack "H*", substr($data, BLOCKHDR+BLOCKDATA, CDRLENGTH);
...
                        $offset += BLOCKLEN;
...
                        $offset += BLOCKLEN;
                        $offset -= 286;