passing unused data to syswrite() seems like an odd thing to do.

Since you can't control how many bytes actually get written, it makes it very easy to use syswrite:

my $to_write = length($msg);
while ($to_write) {
    my $written = syswrite($fh, $msg, $to_write, -$to_write)
        or die "syswrite: $!\n";
    $to_write -= $written;
}
[download]