the option when a pipeline is created that controls the way the exit
status of the pipeline is calculated. Previously it was the state of
the option when the exit status of the pipeline was collected.
This makes no difference at all for foreground pipelines (there is
no way to change the option between starting and completing the
pipeline) but it does for asynchronous (background) pipelines.
This was always the right way to implement it - it was originally
done the other way as I could not find any other shell implemented
this way - they all seemed to do it our previous way, and I could
not see a good reason to be the sole different shell.
However, now I know that ksh93 works as we will now work, and I
am told that if the option is added to the FreeBSD shell (apparently
the code exists, uncommitted) it will be the same.
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