Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!exodus!appserv!slovax.Eng.Sun.COM!lm
From: lm@slovax.Eng.Sun.COM (Larry McVoy)
Newsgroups: comp.lang.perl
Subject: perl 4.0beta bug in sysread/syswrite?
Message-ID: <536@appserv.Eng.Sun.COM>
Date: 6 Apr 91 03:45:43 GMT
Sender: news@appserv.Eng.Sun.COM
Reply-To: lm@sun.UUCP (Larry McVoy)
Organization: Sun Microsystems, Mountain View
Lines: 36


I ran into a weird bug, I think.  I narrowed it down to sysread and/or
syswrite.  I can't read what I wrote:

#!/bin/perl4.000

# open a temp file, write some lines.
open(F, ">/tmp/test") || die "create";
$foo = "perl is the greatest!\n";
for $i (0..3) {
	syswrite(F, $foo, length($foo), $i * length($foo)) || die "write";
}
close(F);

# reopen a temp file, make sure the lines are the same.
open(F, "/tmp/test") || die "create";
for $i (0..3) {
	sysread(F, $buf, length($foo), $i * length($foo)) || die "read";
	if ($buf ne $foo) {
		print "buf $i is wrong: \"$buf\"\n";
	}
}
close(F);

The trace output looks like so:

write (3, "perl is the greatest!\n", 22) = 22
write (3, "".., 22) = 22
write (3, "".., 22) = 22
write (3, "".., 22) = 22
read (3, "perl is the greatest!\n", 22) = 22
read (3, "".., 22) = 22
read (3, "".., 22) = 22
read (3, "".., 22) = 22
---
Larry McVoy, Sun Microsystems     (415) 336-7627       ...!sun!lm or lm@sun.com