threads / patch / 12453

patchRedirect stderr to a pipe before redirecting stdout to stderr

Subject: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr

## tl;dr

4 messages between Mar 3, 2008 and Mar 3, 2008. Diffs are folded; open one to read it.

replies: 3people: 3as markdown or json

Christian Couder· Mar 3, 2008, 07:21 UTC · lore

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).
Show changes to run-command.c +7 −6
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· Mar 3, 2008, 07:33 UTC · re: Christian Couder · lore

Re: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr

Christian Couder <chriscool@tuxfamily.org> wrote:
Show 12 quoted lines
> 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· Mar 3, 2008, 07:52 UTC · re: Shawn O. Pearce · lore

Re: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr

Le lundi 3 mars 2008, Shawn O. Pearce a écrit :
Show 16 quoted lines
> 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· Mar 3, 2008, 08:07 UTC · re: Christian Couder · lore

Re: [PATCH] Redirect stderr to a pipe before redirecting stdout to stderr

Christian Couder schrieb:
Show 12 quoted lines
> 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

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