On Sun, Jan 22, 2023 at 09:20:26PM +0100, Otto Moerbeek wrote:
> On Sun, Jan 22, 2023 at 02:44:47PM +0100, S??ren Tempel wrote:
>
> > Hi Otto,
> >
> > Thanks for your fast reply. Remarks below.
> >
> > Otto Moerbeek <o...@drijf.net> wrote:
> > > Some observations:
> > >
> > > - You are reading from stdout.
> >
> > Sorry, small mistake that slipped in while reformatting the code for the ML.
> >
> > > - Since you are reading one char at the time, the moment the EOF is
> > > processed the buffer is empty, so no pending chars. I'll take that as
> > > a valid interpretation of Posix.
> >
> > I am no expert on the interpretation of the POSIX standard, but Section
> > 11.1.9 explicitly talks about "bytes waiting to be read" and not about
> > bytes in the buffer of the process "the moment the EOF is processed".
> >
> > > - If you modify your program to read 4 chars at the time (see below),
> > > you will see your expected behaviour.
> > >
> > > -Otto
> > >
> > > #include <unistd.h>
> > > #include <stdio.h>
> > >
> > > int main(void)
> > > {
> > > for (;;) {
> > > char c[4];
> > > ssize_t r = read(0, c, sizeof(c));
> > > if (r == 0)
> > > break; /* EOF */
> > > printf("read: %zd chars\n", r);
> > > }
> > > }
> >
> > While this program works for the input "foo<ctrl-d>" it does (just like
> > my original program) also terminate on the input "foo1<ctrl-d>" since
> > the buffer is, once again, empty when the EOF is received. However, POSIX
> > mandates that read(2) should only return a byte count of zero if "the
> > EOF occurred at the beginning of a line" and for the input
> > "foo1<ctrl-d>" the EOF does not occur at the beginning of the line but
> > OpenBSD read(2) still returns zero.
> >
> > Greetings,
> > S??ren
>
> I'd have to check a FreeBSD machine (I can do so tomorrow), but macOS
> follows the same logic as OpenBSD. So this maye vey well be
> established BSD behaviour.
>
> The text in our man page are almost verbatim copies of the Posix text
> (same for the man pages of macOS and FreeBSD). I do wonder why they do
> not describe the slightly different BSD semantics.
>
> I'll post the FreeBSD results tomorrow.
>
> -Otto
>
Confirmed, FreeBSD has the same behaviour as macOS and OpenBSD.
-Otto
