Re: Return codes and pipelines

[Randall R Schulz <rrschulz at cris dot com>]

Rolf,

One posting is enough, really.

There is no guaranteed or specified parent child relationship between the 
processes in a pipeline. This means that you cannot predict which process's 
status will be the one returned as that of the pipeline as a whole.

You can force this in your contrived example by adding an exit call.

All of these will print "true:"

(true | true; exit 0) && echo true || echo false
(false | true; exit 0) && echo true || echo false
(true | false; exit 0) && echo true || echo false
(false | false; exit 0) && echo true || echo false


Randall Schulz


At 14:09 2003-01-12, Rolf Campbell wrote:
> /home/rcampbell> (true | true) && echo true || echo false
> true
> /home/rcampbell> (true | false) && echo true || echo false
> false
> /home/rcampbell> (false | true) && echo true || echo false
> true
> /home/rcampbell> (false | false) && echo true || echo false
> false
>
> The third test above yields different results when run on Linux.  I'm
> wondering if this was the desired result or not?  (This is not a new
> problem, it's been around for at least a year of releases).  It makes
> some makefiles not work as expected, specifically, the GCC manual
> describes how to perform auto-dependency analysis like:
>
> gcc ... | sed ...
>
> But, if gcc fails, sed will still work, thus make will not consider it a
> failure and will continue.
>
> I know there are many ways to avoid this specific problem, already
> implemented one.  Just wanted to let you guys know.
>
>
> -Rolf Campbell