bg behaves differently depending on order of arguments if any are invalid #3909
Description
Let's say you have some jobs:
> sleep 30 &; sleep 50 &; sleep 90 &
> kill -SIGSTOP %sleep
Job 3, 'sleep 90 &' has stopped
Job 2, 'sleep 50 &' has stopped
Job 1, 'sleep 30 &' has stopped
> jobs
Job Group State Command
3 35465 stopped sleep 90 &
2 35464 stopped sleep 50 &
1 35463 stopped sleep 30 &
For whatever reason, I decide to background them all with manually-specified PGIDs. Unfortunately, I fat-finger one of the PGIDs. What is the difference between these commands?
> bg 35463 a35464 35465
> bg 35465 a35464 35463
If you said each one only backgrounds one process, and it's different between the two, you are correct!
I don't think this is sensible. Either all valid PGIDs should be backgrounded, or none should. Order should not matter.
(The new disown builtin disowns all valid PGIDs, but returns an error if any of the PGIDs are invalid.)