my $read = read($fh_in, $buf, $blk_size, length($ofs));

##</code><code>##

   my $read = read($fh_in, $newbuf, $blk_size);
   ...
   $buf .= $newbuf;

##</code><code>##

   my $read = read($fh_in, $buf, $blk_size, length($buf));