eval vs &

eval vs &

[Scott Schwartz]

Consider this:

; x='sleep 3'
; eval $x &
16105
; x='sleep 3 &'
; eval $x
; # No pid?

/bin/sh would print the pid.

(Speaking of asynchronous processes, I kind of miss getting exit
notification and being able to find out what their exit status is ala
csh.  It's not as if rc isn't doing the wait() already.  Maybe when
file completion is done.... :-))

Re: eval vs &

[schwartz]

| re: eval and &. Well, input for eval is rescanned noninteractively,
| so interactive features get lost during an eval. This is perhaps
| bogomorphic. At the same time, however, you don't want rc to print
| prompts while it chugs through an eval.

I suppose.  But it surprised me while using ``--'', just now.

| re: wait(). rc does not trap SIGCLD, so it cannot notify you
| asynchronously of a child's death. This may be another bogomorphism,
| but so far I've been using Occam's razor, i.e., avoiding complexity
| in the design whenever possible.

Actually async notification is not really what I had in mind.  I was
thinking that when rc does happen to wait(), it could collect all the
statuses and put them in $astatus.  The the prompt function could print
them if you wanted them.   

Re: eval vs &

[Byron Rakitzis]

re: eval and &. Well, input for eval is rescanned noninteractively,
so interactive features get lost during an eval. This is perhaps
bogomorphic. At the same time, however, you don't want rc to print
prompts while it chugs through an eval.

re: wait(). rc does not trap SIGCLD, so it cannot notify you
asynchronously of a child's death. This may be another bogomorphism,
but so far I've been using Occam's razor, i.e., avoiding complexity
in the design whenever possible.