Re: [Help-bash] shell redirection

[Christof Warlich]

Am 19.10.2016 um 20:09 schrieb Greg Wooledge:

> On Wed, Oct 19, 2016 at 07:28:24PM +0200, Christof Warlich wrote:
> > I want my script(s) to print stderr to the terminal, while both stdout
> > _/and/_ stderr should go to a logfile.
> Not possible without hacks that will break synchronization between the
> streams.
>
> > Any ideas how this could be done, ideally without using any temporary
> > files or named pipes?
> A temp file probably wouldn't help, because you'd lose *all* sync
> information.  Instead of having
>
> stdOut1
> stdErr1
> O2
> E2
>
> you'd end up with
>
> O1
> O2
> O3
> E1
> E2
> E3
>
> Probably not what you want.
>
> You could set up two piped readers, one for each stream, and have them
> both write to your log file (opened in *append* mode by each one).
> Then the stderr reader (but not the stdout reader) would also write
> to the terminal.
>
> So, two process substitutions (which are roughly equivalent to named
> pipes), and each one is reading in (presumably) a line-oriented way.
> That's the best you're likely to get.
Thanks for the quick response: Thus, as much as I understand,
a line-oriented piped reader approach would avoid mixing output
of stdout and stderr _within_ lines, but the sequence of whole lines
w.r.t. stdout and stderr may still be garbeled ...?!

That's really rather disappointing: My idea was to make the
sequence of commnds executed by my scripts (and possible
errors) visible on the terminal by employing set -x, while writing
a logfile containing _all_ information for "debugging" purpose
if needed.

This would be particularly usefull for scripts that produce loads
of output, e.g. when generating toolchains.

Anyhow, thanks for caring :-)

Chris