while ( $offset < length( $pieces ) ) {
  # do some stuff
}
# do some more stuff
foreach my $p ( @pieces ) {
  # do some more stuff
  print "[dothis:] Piece $counted: $p \n";
  # do some more stuff
  while ($n = read (F, $data, $piece_length)  != 0) { 
     # yet more stuff
     print "[dothat] Hash2:" .  sha1_hex($data) . "\n\n";
     # yet more stuff
  }
}