bug#21919: tee enhancement

[Pádraig Brady]

On 14/11/15 16:00, Tim Shaw wrote:
> If I am using stdout redirection of a shell block to capture some text I am 
> generating, errors need to go to stderr, but it would also be good if they 
> went into the generated output. For example
> for i in files*; do
>   if there_is_an_error; then
>     echo big long complicated error message goes here >&2
>     echo big long complicated error message goes here
>     continue
>   fi
>    stuff_producing_text_on_stdout
> done > file_i_am_creating
>  
> I do not like duplicating code, such as the big long error message echo. So, 
> I could create a temp file or a temp shell var to save the message, but that 
> makes things more complicated than just duplicating the code, and also is 
> just not my style for something transient like this.
>  
> What I would like to do is add a parameter to tee, "-2", that copies to 
> stderr in addition to stdout, just like "-" copies to stdout twice. 

Note `tee -` now copies to a file called '-' rather than
duplicating to stdout, since v8.24 as discussed at:
http://lists.gnu.org/archive/html/coreutils/2015-02/msg00085.html

> So the code becomes
>     echo big long complicated error message goes here | tee -2
> Simple, eh?
>  
> Where's the tee source? I know this would not be POSIX compliant, but it 
> would work for me, and I hate having to rewrite everything from scratch for 
> trivial stuff like this.

Maybe shell constructs like this would suffice?

  { echo error | tee >(cat >&2); }

cheers,
Pádraig.