Re: [Help-bash] shell redirection

[Russell Lewis]

As others have mentioned, there's no way to ensure that the lines reach the
logfile in order (that problem exists even in the source program, but also
in the tee command below).  But here's a command line which seems to work
(under trivial testing):
    { echo "fred"; echo "wilma" 1>&2; } 2> >(tee -a logfile) 1>>logfile

Basically, it redirects stderr to a process substitution (that is, it
connects stderr to the stdin of tee).  The process substitution's stdout is
of course the same as the current shell - so stderr goes both to the log
file and to the tty; then we redirect stdout to point to the logfile as
well.

I used -a on the tee command, and >> on the redirection of stdout, so that
neither would crop the log file (and presumably destroy the output of the
other), but I'm not well versed in what happens when there are multiple
open file pointers to the same file on disk.  From trivial testing, it
seems to work, but I worry that perhaps there are race conditions I haven't
explored.  (I originally thought about using some magic with /dev/fd to
duplicate file pointers, but I wasn't sure that it was necessary complexity
- or that I could get it totally correct.)

Russ

On Wed, Oct 19, 2016 at 6:32 PM, John McKown <address@hidden>
wrote:

> On Wed, Oct 19, 2016 at 12:28 PM, Christof Warlich <address@hidden>
> wrote:
>
> > Hi,
> > looks like I still haven’t fully gasped shell redirection:
> > I want my script(s) to print stderr to the terminal, while both stdout
> > _/and/_ stderr should go to a logfile. I thought that this is an easy
> task,
> > but so far, I failed miserably.
> > Any ideas how this could be done, ideally without using any temporary
> > files or named pipes?
> > Many thanks,
> > Chris
> >
> >
> ​I've read all the replies. And tried some really strange things myself.
> The closest that I can come to what you want (and it is not all that close)
> is to use the "script" program to run your program.
>
> script -c 'somecmd p1 parm2 --option' logfile.txt
>
> Both stdout & stderr come to the terminal & get written to logfile.txt​ .
> There is no way, that I know of, to put stdout into "logfile.txt" but
> suppress it from the terminal.
>
>
> --
> Heisenberg may have been here.
>
> Unicode: http://xkcd.com/1726/
>
> Maranatha! <><
> John McKown
>