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Subject: |
Process filters received stderr output, not documented |
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Date: |
Mon, 22 Aug 2016 13:35:25 -0400 |
The documentation for Process Filter Functions mentions that process
filters receive the standard output from their associated processes. It
does not mention that the filters also receive standard error output.
In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
of 2016-04-17 on lgw01-04, modified by Debian
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--- End Message ---
--- Begin Message ---
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Subject: |
Re: bug#24287: Process filters received stderr output, not documented |
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Date: |
Wed, 24 Aug 2016 17:44:04 +0300 |
> From: Clément Pit--Claudel <address@hidden>
> Date: Tue, 23 Aug 2016 17:47:16 -0400
>
> > That is described in the parent section:
> >
> > It is impossible to separate the standard output and standard error
> > streams of the subprocess, because Emacs normally spawns the subprocess
> > inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If
> > you want to keep the output to those streams separate, you should
> > redirect one of them to a file—for example, by using an appropriate
> > shell command.
>
> Hi Eli,
>
> Am I misunderstanding something? This section sounds misleading, at least
> for Emacs 25 (I'm not sure about Emacs 24). The documentation of
> make-process (which is new in Emacs 25, right?) says:
>
> :stderr STDERR
> Associate STDERR with the standard error of the process.
> STDERR is either a buffer or a pipe process created with
> ‘make-pipe-process’.
>
> The docstring of start-process was updated accordingly:
>
> If you want to separate standard output from standard error, use
> ‘make-process’ or invoke the command through a shell and redirect
> one of them using the shell syntax.
>
> Both of these suggest that the impossibility that the manual mention only
> applies to the pty case (the manual recommends against using PTYs for
> non-user-facing processes anyway). What about something like this:
>
> It is impossible to separate the standard output and standard error
> streams
> of a subprocess spawned inside a pseudo-TTY, as pseudo-TTYs have only one
> output channel. If you want to keep the output to those streams separate,
> you should either use `make-process' with the :stderr argument, or
> redirect
> one of the streams to a file—for example, by using
> start-process-shell-command with an appropriate redirection.
>
> Additionally, we could update the documentation of make-process: right now,
> it starts with "This function is like ‘start-process’, but takes keyword
> arguments.", but from what I understand it can actually do more than
> start-process. What about this:
>
> This function is like ‘start-process’, but takes keyword arguments, and
> can
> separate output to standard output and standard error.
Actually, the situation was much worse than those minor changes could
handle. The documentation of process-related APIs was not reviewed in
its entirety for quite some time, and as result bit-rotted quite a
lot. I fixed that.
This is what happens and will continue to happen if people will not
volunteer to review documentation during the pretest, certainly when a
major version is about to be released. For Emacs 25.1, only a single
individual volunteered, and a single *.texi file was reviewed. I
expect the accuracy and the overall quality of our documentation to go
downhill if we don't see more volunteers.
> Btw, was there a way in Emacs 24 to separate these streams if the process was
> run after setting process-connection-type to nil? (I can't think of one).
No, I don't think so.
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