# [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr

4 messages from 2008-03-03 to 2008-03-03. Participants: Christian Couder, Shawn O. Pearce, Johannes Sixt.
Thread: https://gitlist.dev/t/12453

## Christian Couder, 2008-03-03 07:21

Subject: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr
Message-ID: <20080303082111.24d3ea73.chriscool@tuxfamily.org>
URL: https://gitlist.dev/e/20080303082111.24d3ea73.chriscool%40tuxfamily.org

```
With this patch, in the 'start_command' function after forking
we now take care of stderr in the child process before stdout.

This way if 'start_command' is called with a 'child_process'
argument like this:

	.err = -1;
	.stdout_to_stderr = 1;

then stderr will be redirected to a pipe before stdout is
redirected to stderr. So we can now get the process' stdout
from the pipe (as well as its stderr).

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 run-command.c |   14 +++++++-------
 1 files changed, 7 insertions(+), 7 deletions(-)

	This patch should make my previous patch:

	[PATCH 1/2] help: add "man.viewer" config var to use "woman" or "konqueror"

	work as expected (at least with Emacs 21 and 22).

diff --git a/run-command.c b/run-command.c
index 743757c..44100a7 100644
--- a/run-command.c
+++ b/run-command.c
@@ -91,6 +91,13 @@ int start_command(struct child_process *cmd)
 			close(cmd->in);
 		}
 
+		if (cmd->no_stderr)
+			dup_devnull(2);
+		else if (need_err) {
+			dup2(fderr[1], 2);
+			close_pair(fderr);
+		}
+
 		if (cmd->no_stdout)
 			dup_devnull(1);
 		else if (cmd->stdout_to_stderr)
@@ -103,13 +110,6 @@ int start_command(struct child_process *cmd)
 			close(cmd->out);
 		}
 
-		if (cmd->no_stderr)
-			dup_devnull(2);
-		else if (need_err) {
-			dup2(fderr[1], 2);
-			close_pair(fderr);
-		}

```

## Shawn O. Pearce, 2008-03-03 07:33

Subject: Re: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr
Message-ID: <20080303073307.GG8410@spearce.org>
URL: https://gitlist.dev/e/20080303073307.GG8410%40spearce.org
In-Reply-To: <20080303082111.24d3ea73.chriscool@tuxfamily.org>

```
Christian Couder <chriscool@tuxfamily.org> wrote:
> With this patch, in the 'start_command' function after forking
> we now take care of stderr in the child process before stdout.
> 
> This way if 'start_command' is called with a 'child_process'
> argument like this:
> 
> 	.err = -1;
> 	.stdout_to_stderr = 1;
> 
> then stderr will be redirected to a pipe before stdout is
> redirected to stderr. So we can now get the process' stdout
> from the pipe (as well as its stderr).

I'm in favor of this patch.  My series to add sideband support
to send-pack/receive-pack (aka push) needed it for the hooks.

-- 
Shawn.

```

## Christian Couder, 2008-03-03 07:52

Subject: Re: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr
Message-ID: <200803030852.43254.chriscool@tuxfamily.org>
URL: https://gitlist.dev/e/200803030852.43254.chriscool%40tuxfamily.org
In-Reply-To: <20080303073307.GG8410@spearce.org>

```
Le lundi 3 mars 2008, Shawn O. Pearce a écrit :
> Christian Couder <chriscool@tuxfamily.org> wrote:
> > With this patch, in the 'start_command' function after forking
> > we now take care of stderr in the child process before stdout.
> >
> > This way if 'start_command' is called with a 'child_process'
> > argument like this:
> >
> > 	.err = -1;
> > 	.stdout_to_stderr = 1;
> >
> > then stderr will be redirected to a pipe before stdout is
> > redirected to stderr. So we can now get the process' stdout
> > from the pipe (as well as its stderr).
>
> I'm in favor of this patch.  My series to add sideband support
> to send-pack/receive-pack (aka push) needed it for the hooks.

Now that you say it, I remember having seen your patch, so please take 
ownership of this patch.

Thanks,
Christian.

```

## Johannes Sixt, 2008-03-03 08:07

Subject: Re: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr
Message-ID: <47CBB1C7.8010201@viscovery.net>
URL: https://gitlist.dev/e/47CBB1C7.8010201%40viscovery.net
In-Reply-To: <20080303082111.24d3ea73.chriscool@tuxfamily.org>

```
Christian Couder schrieb:
> With this patch, in the 'start_command' function after forking
> we now take care of stderr in the child process before stdout.
> 
> This way if 'start_command' is called with a 'child_process'
> argument like this:
> 
> 	.err = -1;
> 	.stdout_to_stderr = 1;
> 
> then stderr will be redirected to a pipe before stdout is
> redirected to stderr. So we can now get the process' stdout
> from the pipe (as well as its stderr).

Makes sense. All current users of .stdout_to_stderr don't modify the
stderr channel, so this patch should not make a difference.

But please also adjust Documentation/technical/api-run-command.txt because
it documents the behavior that you are modifying.

-- Hannes

```