Re: pipe on stderr

[Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>]

Didier Verna wrote:
>         I've only recently discovered that there's no simple way, in any
> shell, to pipe stderr on another process. As you can write `foo 2> foo.err',
> wouldn't it be nice to be able to write `foo 2| bar' ?

Trouble is, it gets into quite serious trouble with existing syntax, since
you don't need a space before the pipe --- think about 
  echo 2| foo
so although it could be an option there's probably still too much scope for
confusion.

As you may already have discovered, you can swap file descriptors:
  echo foo 3>&1 1>&2 2>&3 | sed 's/foo/bar/'
which has the effect you want provided 1 and 2 were originally going to the
same place, i.e. what used to be 1 still goes there but what used to be 2
now goes to the pipe.  But agree it's not simple (and in zsh you have to
`unsetopt multios').

-- 
Peter Stephenson <pws@xxxxxxxxxxxxxxxxx>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56127 Pisa, Italy