On 6/30/20 4:37 PM, Dmitry Alexandrov wrote: > Chet Ramey <chet.ra...@case.edu> wrote: >> On 6/29/20 4:33 PM, Dmitry Alexandrov wrote: >>> 1) unexpected, as (a) it does not seem to be documented, (b) itʼs >>> counter-intuitive and (c) other bourne-like shells (busybox ash, dash, >>> ksh93, mksh, zsh) does not do that; >> >> It's an opportunity for optimization, not a bug > > I am not saying that this is a bug, only that it is inconsistent with almost > any other bourne-like shell.
And I understood Chet's point to be that you shouldn't have "expected"
something which isn't guaranteed. Just because it works out that way,
doesn't mean it has to; it's not like other shells document this behavior.
Relying on undocumented behavior isn't the greatest. :p
>>> 2) inconvenient, as in some cases PID of the parent shell is not an
>>> appropriate substitute for the PID of the real process.
>
>> since the results are correct.
>
> The results are _different_ across shell and, unfortunately, results provided
> by Bash are the least useful. Consider:
>
> $ command … &
> [1] 30737
> $ strace -p $!
> strace: Process 30737 attached
> wait4(-1,
>
> :-/
Useful replacements:
You could decline to use "command", and it doesn't involve a shell process.
$ cat &
[1] 2092238
$ ps --pid $! --ppid $!
PID TTY TIME CMD
2092238 pts/42 00:00:00 cat
[1]+ Stopped cat
If you need to ensure a disk executable is used,
$ "$(type -P cat)" &
[1] 2092352
$ ps --pid $! --ppid $!
PID TTY TIME CMD
2092352 pts/42 00:00:00 cat
[1]+ Stopped "$(type -P cat)"
Anyway, Chet didn't say it won't be changed to do what you expected;
after all, it's acknowledged as an opportunity for optimization, and
optimization is good..
--
Eli Schwartz
Arch Linux Bug Wrangler and Trusted User
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