Capture stderr to variable without new process

Capture stderr to variable without new process

[rahul]

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I guess the typical way would be:

   ERR=$(popd 2>&1)

However, the command cannot run in a sub-shell as it would have no effect
in the current shell.
Is writing to a file the only way ?

-- 
 rahul

Re: Capture stderr to variable without new process

[Phil Pennock]

On 2013-01-22 at 01:41 +0530, rahul wrote:
> I guess the typical way would be:
> 
>    ERR=$(popd 2>&1)
> 
> However, the command cannot run in a sub-shell as it would have no effect
> in the current shell.
> Is writing to a file the only way ?

If the output can only be one line and you have an unbuffered cat(1) (-u
option).

% coproc cat -u
[1] 6550
% popd 2>&p
% read -p foo
% echo $foo
popd: directory stack empty
% coproc -

Otherwise, you need to script a cat-command which can exit on a sentinel
line; I don't know of a way to close the coproc's stdin while leaving
the coproc running to collect its output later.  Perhaps someone else
does?  If you could send EOF on the coproc's stdin, then you could just
use:
  popd_stderr="$(cat <&p)"
after closing its stdin.

-Phil

Re: Capture stderr to variable without new process

[Han Pingtian]

On Mon, Jan 21, 2013 at 06:35:49PM -0500, Phil Pennock wrote:
> On 2013-01-22 at 01:41 +0530, rahul wrote:
> > I guess the typical way would be:
> > 
> >    ERR=$(popd 2>&1)
> > 
> > However, the command cannot run in a sub-shell as it would have no effect
> > in the current shell.
> > Is writing to a file the only way ?
> 
> If the output can only be one line and you have an unbuffered cat(1) (-u
> option).
> 
> % coproc cat -u
> [1] 6550
> % popd 2>&p
> % read -p foo
> % echo $foo
> popd: directory stack empty
Good method. I think we can improve it by using a loop and add
a timeout to read:

% coproc cat
% git abc 2>&p
% while read -t 2 -p line;do ERR+=$line$'\n';done
% print "$ERR"
git: 'abc' is not a git command. See 'git --help'.

Did you mean this?
add

%
> % coproc -
This is interesting. How could we figure out this method, please?
> 
> Otherwise, you need to script a cat-command which can exit on a sentinel
> line; I don't know of a way to close the coproc's stdin while leaving
> the coproc running to collect its output later.  Perhaps someone else
> does?  If you could send EOF on the coproc's stdin, then you could just
> use:
>   popd_stderr="$(cat <&p)"
> after closing its stdin.
> 
> -Phil