in reply to Random read/write on a block device

I don't know the answer to your main question. Although if you provide code written in a different language, we could help you translate it.

I know syswrite() and seek() are mutually incompatible.

But sysseek isn't.

Does the 4th parameter to syswrite() do the same as seek() on the file handle?

No. As documented, "An OFFSET may be specified to write the data from some part of the string other than the beginning."

That means syswrite($fh, "abcdef", 2, 3) will write three bytes starting at index 2: de.

FYI, [doc://funcname] links to better (up to date) documentation. [funcname] finds rather old documentation which isn't rendered particularly well.

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Re^2: Random read/write on a block device
by FloydATC (Deacon) on Jun 25, 2009 at 12:13 UTC
    See, I missed sysseek() completely... very impressive.

    About the docs you refer to, that's what I thought it meant but I was unsure since it overlaps with what substr() does, and passing unused data to syswrite() seems like an odd thing to do. Thanks for clearing it up :-)

    -- Time flies when you don't know what you're doing
[reply]

      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;
}

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