my $written = syswrite($test_file, $buf, length($buf));
die("Unable to write to file: $!\n")
   if not defined $written;
die("Unable to write whole string in one call\n")
   if $written != length($buf);

##</code><code>##

my $offset   = 0;
my $to_write = length($buf);
while ($to_write > 0) {
   my $written = syswrite($test_file, $buf, $to_write, $offset);
   die("Unable to write to file: $!\n")
      if not defined $written;
   $to_write -= $written;
   $offset   += $written;
}