2009/4/3, Russ Cox <r...@swtch.com>:
> > But when you do something like
> > cmd1 | cmd2 |[2] cmd3
> > you get cmd1's stdout piped to cmd2's stdin; but my confusion begins
> > here: is it cmd1's or cmd2's stderr that gets redirected to cmd3's
>
> > stdin? maybe both? my guess is that ...
>
> why guess?
>
> % {echo cmd1 >[1=2]} | {echo cmd2 >[1=2]} | sed 's/^/cmd3: /'
> cmd1
> cmd2
> % {echo cmd1 >[1=2]} | {echo cmd2 >[1=2]} |[2] sed 's/^/cmd3: /'
> cmd3: cmd1
> cmd3: cmd2
> %
>
> not what i expected, but there you have it.
> and it makes sense: cmd1 and cmd2 are both
> writing to the same stderr, so redirecting it
> redirects both.
>
>
> > how can I redirect cmd1's stderr to cmd3's stdin instead
> > of cmd2's? or both?
>
>
> if you don't care about cmd2's stderr, then you can get rid of it
>
> % {echo cmd1 >[1=2]} | {echo cmd2 >[2]/dev/null} |[2] sed 's/^/cmd3: /'
> cmd2
> cmd3: cmd1
>
> %
>
> > It's easy to think of more complex cases.
>
>
> it's easy to think of elephants.
>
> rc does its general-purpose job very well.
> if you have special-purpose needs,
> as lucio suggests, write a c program.
>
>
> russ
>
>
ok, thanks
--
Hugo
