Re: "builtin jobs" does not output to stdout.

[Koichi Murase]

2023年2月15日(水) 0:51 Chet Ramey <chet.ramey@case.edu>:
> On 2/11/23 11:14 AM, Koichi Murase wrote:
> > 2023年2月12日(日) 0:42 Robert Elz <kre@munnari.oz.au>:
> >> Why would you want to ever say "builtin jobs" though?
> >> The jobs command has to be buikt in to work.
> >
> > `jobs' can be overwritten by a shell function. For example, when a
> > user wants to modify the behavior of `jobs' for interactive uses, a
> > typical solution is to override `jobs' with a shell function and call
> > `builtin jobs' in the overriding function.
> >
> > I guessed you have asked this because `jobs' would be specified as a
> > special built-in utility [XCU 2.14], which cannot be hidden by a
> > shell-function name, but it doesn't seem to be the case actually;
>
> There's no way `jobs' would ever be a special builtin. It's always been
> UPE shaded (User Portability). Job control wasn't even mandatory in
> POSIX until Issue 6 (2004), and the specification that jobs can be run
> when job control isn't enabled came well after that.

Thank you for the information. I find it interesting to hear about the
historical background.

The statement about the special built-in was just my initial guess for
the reason why kre seemed to claim that `builtin jobs' is equivalent
to `jobs', but I just checked the standard and immediately knew my
guess was incorrect. I still don't think `builtin jobs' is equivalent
to `jobs' because `jobs' can pick up a shell function.

> > I naively think that it is a valid request that `builtin jobs' would
> > behave in the same way as `jobs' in this context. POSIX also states
> > that the results are unspecified when the command name matches
> > `builtin' according to [XCU 2.9.1 / Command Search and Execution /
> > rule 1b].
>
> Whether or not `builtin' is specified by POSIX isn't really relevant. That
> list just means that some shells have implemented `builtin' as a builtin
> command, so portable applications should take care with it.

I just meant that even if Bash treats `builtin jobs' the same as
`jobs' in these particular subshell contexts, it doesn't conflict with
POSIX. So, POSIX seems to be irrelevant when we think about the
behavior when `builtin' is involved.