Re: How to safely pipe output to tee?

[Steven W. Orr]

On 3/7/2011 2:02 PM, Micah Cowan wrote:
> (03/07/2011 10:31 AM), Steven W. Orr wrote:
> > I want to compute a command string which will end up in foo.
> >
> > Then I want to run that command and cause stdout and stderr to be piped
> > to tee for safe keeping while it also goes to the screen.
> >
> > After the command finishes, I need tee to exit.
> >
> > It sounds easy, but it's not.
> >
> > eval "$foo" 2>&1 | tee filename
> >
> > will cause a hang. Why? Because what $foo does is to start lots of child
> > processes and services which do not end. I just want to proceed to the
> > next command as soon as $foo completes.
>
> It seems to me that tee hangs around because its pipe is still open on
> the other end (courtesy of these background processes you mention).
>
> In that case, can't you just redirect all these background processes, so
> that they're not writing to that same stdout file descriptor?
>
> For instance,
>
>    foo='sleep 100&'
>
> poses an issue, but
>
>    foo='sleep 100>&- 2>&-&'
>
> shouldn't.

Sorry, but I'm not sure I see why this helps.

I think it says (I assume you meant a space between the 100 and the greater 
than, otherwise you're just trying to close channel 100):

foo='sleep 100 >&- 2>&- &'

"Sleep for 100 seconds and then close channel 1 and channel 2."

Maybe. But how do I harvest the status of the command, since the sleep will 
always succeed?

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