Re: $PPID not updated when the PPID changes (parent killed)

[Vincent Lefevre <vincent@vinc17.net>]

On 2021-05-17 16:15:24 -0700, Bart Schaefer wrote:
> On Mon, May 17, 2021 at 3:27 PM Phil Pennock
> <zsh-workers+phil.pennock@spodhuis.org> wrote:
> >
> >   The initial parent process ID; that is, the process ID of the process
> >   which created this shell process, at the time that it did so.
> 
> This is pretty close to what I was thinking.  Does "at the time"
> really add anything?

It would be better without it.

> >   Just as for $$, the value is only set for the original shell and does
> >   not dynamically change for implicit subshells (as created for (list)
> >   and for pipelines).
> 
> Except (list) is an explicit subshell, isn't it?
> 
> > It's an attempt to be clearer that "if you run zsh within zsh,
> > that's not a subshell, sure _that_ gets $$ and $PPID reset".
> 
> Indeed.  I'm tempted to say
> 
>   Just as with $$, the value is updated only within a new shell
>   that increases $SHLVL, and not in other subshells.
> 
> And then clarify "a new shell" under SHLVL if necessary, but I hope it isn't.

The zsh man pages use "subshell" at various places. They should be
consistent on what a subshell is, perhaps have a clear definition
at one place, and say what happens when a subshell is created.

Note also that the following in the zshmodules(1) man page should be
updated too:

  sysparams
      A readonly associative array.  The keys are:
[...]
      ppid   Returns  the  process  ID  of  the  parent of the current
             process, even in subshells.  Compare $PPID, which returns
             the process ID of the parent of the main shell process.

This is even more confusing, because there are actually 2 differences
between $sysparams[ppid] and $PPID:

1. The fact that $sysparams[ppid] takes a new value in subshells, but
   not $PPID.

2. The fact that $sysparams[ppid] is updated when the parent process
   terminates, but not $PPID.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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