{
  my $FName='default.log';
  my $fh;
  sub _open {
     open $fh, '+>', $FName or die "Can't open $FName: $!";
  }
  sub write {
     my $data = shift;
     _open() if !defined $fh;
     syswrite($fh, $data) 
          or die "write() error: $FName: $!";
  }
  sub move {
     my ($src_pos, $dest_pos, $bytes) = @_;
     sysseek($fh, $src_pos, SEEK_SET);
     my $data;
     sysread($fh,$data,$bytes);
     sysseek($fh, $dest_pos, SEEK_SET);
     syswrite($fh, $data); 
     sysseek($fh, 0, SEEK_END);
  }
  # other stuff as needed (setting name,...)
}