Re: [9fans] echo -n

["Francisco J Ballesteros" <nemo@lsub.org>]

Isn´t it that a write of zero bytes should just not write, instead
of meaning a write of zero bytes?

Or did I miss something?


On 11/20/06, Russ Cox <rsc@swtch.com> wrote:
> > Why is read from a closed pipe not considered an error, though?
>
> The same reason that reading from the end of a disk file is not an error.
> Try running your program reading /dev/null instead of a pipe.
>
> >         close(fd[0]);
> >         for(int i=0; i<5; i++){
> >                 n = read(fd[1], buf, 8);
> >                 print("%d: read %ld bytes: %r\n", i, n);
> >         }
> > produces:
> >         0: read 0 bytes:
> >         1: read 0 bytes:
> >         2: read 0 bytes:
> >         3: read -1 bytes: i/o on hungup channel
> >         4: read -1 bytes: i/o on hungup channel
> > where I expected errstr to be set on the first read after pipe
> > closure.
>
> Errstr is only set when a system call returns -1.
>
> > Is there really no way to immediately determine that a
> > pipe has been closed?  Why would read be so implemented?
>
> It's a clumsy hack to work around exactly this problem.
> It's not read in general that is implemented this way,
> just the read implementation for pipes and network data files.
>
> The only real solution is to change the interface so that
> end-of-file is not signaled by a zero-length read.  But that
> convention is far too entrenched to go anywhere any time soon.
>
> Russ
>
>