Re: Forwarding stdout/stderr of a child process in batch mode

[Bruno Barbier]

Hi Paul,

Paul Pogonyshev <pogonyshev@gmail.com> writes:

> So, I got to separating stdout and stderr, but I get them in a wrong
> order now...  Here is an example Python program that I use to generate
> output (store as `10.py'):
...

> When I run the Emacs script, I receive all stderr output line-by-line
> (which is fine), but all stdout output comes in one chunk at the very
> end, which is not...
>

You may want to pass the "-u" option to Python, so that it uses
unbuffered outputs.

You're example is working for me, when using the "-u" option; i.e. I'm
getting interleaved chunks of stderr/stdout.

Bruno

> I cannot really use `pty' connection type, because I want (in real
> usecase, not in the script) to additionally keep stdout and stderr in
> separate buffers, for possible later processing.  Also, with pty I
> wouldn't be able to use `message' or `princ' depending on the stream
> used by the child process.
>
> Is there any way to fix this?
>
> Paul
>
>
> On Sun, 6 Dec 2020 at 22:40, Paul Pogonyshev <pogonyshev@gmail.com> wrote:
>
>> Thank you, this seems to work (haven't tried separating stderr from
>> stdout yet). Is there a normal way to wait for asynchronous process to
>> terminate? Currently I have managed to make it work by throwing from
>> sentinel, but this feels a bit hackish, maybe there is something
>> better?
>>
>> Currently I have something like this:
>>
>>     (let ((process (make-process ... :sentinel (lambda (_process
>> _event) (throw 'done nil)))))
>>       (catch 'done
>>         (while (process-live-p process)
>>           (accept-process-output nil 60)))
>>       ...
>>
>> Paul
>>
>> On Sun, 6 Dec 2020 at 14:37, Zhu Zihao <all_but_last@163.com> wrote:
>> >
>> >
>> > IMO, in batch mode, `message` writes to stderr, `princ` writes to
>> > stdout. You can install a filter for childprocess, and run functions I
>> > mentioned above to forward these outputs.
>> >
>> >
>> > Paul Pogonyshev writes:
>> >
>> > > Hi,
>> > >
>> > > I'm using Emacs in batch mode. I need to invoke a child process that
>> > > is a longish operation (a few minutes). During this time, it writes to
>> > > its stdout, so user will see that it is working and what exactly is
>> > > being done. However, if I invoke it from Emacs (e.g. using
>> > > `call-process') I see no way of forwarding this output to the "real"
>> > > stdout. So, for a user this looks like the process (or batch Emacs on
>> > > top of it) is hung.
>> > >
>> > > Am I missing a way to forward output?
>> > >
>> > > Paul
>> >
>> >
>> > --
>> > Retrieve my PGP public key: https://meta.sr.ht/~citreu.pgp
>> >
>> > Zihao
>>