Bash question - redirect stderr to a variable

[James Mcphee]

If you just want to assign stderr to a file and don't care about stdout,
then the following works.

 $ var="$(cat bah 3>&1 1>&2 2>&3)"
 $ echo $var
cat: bah: No such file or directory


On Tue, Mar 15, 2011 at 12:54 AM, der.hans <PLUGd at lufthans.com> wrote:

> Am 14. Mar, 2011 schwätzte Bryan O'Neal so:
>
> moin moin,
>
>
>  Ok - if I want to direct stranded out, standard error, or both to a
>>
>
> Gotta love stranded out :).
>
>
>  file I can do that. If I want to redirect standard out to a variable
>> for latter use, I can do that. But how do I redirect standard error to
>> a variable?
>>
>
> If all else fails, you can redirect STDERR to STDOUT, '2>&1'.
>
> If you control whatever's giving the errors you can have it set variables
> that are used later.
>
> As to capturing both to variables without using a temporary file, see the
> bottom of the following page.
>
> http://mywiki.wooledge.org/BashFAQ/002
>
> If you can do everything you need for one of them in a subshell, then it
> is possible.
>
> ( exec 3>&1; fred=$( { output=$( ls -d /tmp /ztmp 2>&1 1>&3- ); } 3>&1;
> echo "{$output}" | sed -re 's,/ztmp (.+),/zztop \1,'; ); echo "<$fred>"
>
> ( exec 3>&1; fred=$( { output=$( ls -d /tmp /ztmp 2>&1 1>&3- ); } 3>&1;
> echo "{$output}" | sed -re 's,/ztmp (.+),/zztop \1,' >&2; ); echo
> "<$fred>" )
> {ls: Zugriff auf /zztop nicht möglich: Datei oder Verzeichnis nicht
> gefunden}
> </tmp>
>
> The sed is just to show that I'm mangling the STDERR output once it's been
> tossed into a variable.
>
> Since $output is in a subshell you can't get to it from the normal shell,
> but you could call a fx() to handle the data.
>
> ( mungestderr() { echo "{$output}" | sed -re 's,/ztmp (.+),/zztop \1,'; };
> exec 3>&1; fred=$( { output=$( ls -d /tmp /ztmp 2>&1 1>&3- ); } 3>&1;
> mungestderr "$output" ); echo "<$fred>" )
> </tmp
> {ls: Zugriff auf /zztop nicht möglich: Datei oder Verzeichnis nicht
> gefunden}>
>
> ( mungestderr() { echo "{$output}" | sed -re 's,/ztmp (.+),/zztop \1,' >&2;
> }; exec 3>&1; fred=$( { output=$( ls -d /tmp /ztmp 2>&1 1>&3- ); } >3>&1;
> mungestderr "$output" ); echo "<$fred>" )
> {ls: Zugriff auf /zztop nicht möglich: Datei oder Verzeichnis nicht
> gefunden}
> </tmp>
>
> To keep it clear you might just want to toss it into a file or named pipe.
>
> ciao,
>
> der.hans
> --
> #  http://www.LuftHans.com/        http://www.LuftHans.com/Classes/
> #  ABLEconf - 2011Apr02 - Free Software for Free Enterprise
> #  "Backups are irrelevant. Only restorals matter." -- der.hans
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-- 
James McPhee
jmcphe at gmail.com
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