From: Stephane Chazelas <stephane@chazelas.org>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: Zsh hackers list <zsh-workers@zsh.org>
Subject: Re: $PPID not updated when the PPID changes (parent killed)
Date: Tue, 18 May 2021 19:06:01 +0100 [thread overview]
Message-ID: <20210518180601.4q6o3xpeva7uhyjo@chazelas.org> (raw)
In-Reply-To: <CAH+w=7bywj1X1fyPLgpmo_OoqBEN8PjEDxDeKP-tMR_O4g04tg@mail.gmail.com>
2021-05-17 16:15:24 -0700, Bart Schaefer:
[...]
> Indeed. I'm tempted to say
>
> Just as with $$, the value is updated only within a new shell
> that increases $SHLVL, and not in other subshells.
[...]
$ (SHLVL=0; zsh -c 'echo $SHLVL $$ $PPID; sleep 2; exec zsh -c "echo \$SHLVL \$$ \$PPID"' & sleep 1)
1 485756 485755
1 485756 302910
(where in that case 302910 is the pid of the systemd user's
session child subreaper, traditionally, one would get 1
instead).
$PPID, like $$ are set when the shell is initialised, just after
it had been executed.
In the example above, the same 485756 process executed zsh twice
and $$ and $PPID were set twice.
Because of the exec (and it would have been the same without
exec in a few contexts where zsh skips forks implicitly), $SHLVL
is not incremented (well it is decremented by the first zsh
before exec and incremented again by the second).
$SHLVL (a (t)csh thing IIRC, not handled by all shells) is the
number of shell *invocations* you need to exit before that logs
you out.
I would find it much clearer if we described $$/$PPID in
relation to shell invocation initialisation like POSIX does.
--
Stephane
next prev parent reply other threads:[~2021-05-18 18:06 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-16 15:24 Vincent Lefevre
2021-05-16 18:37 ` Bart Schaefer
2021-05-17 20:26 ` Vincent Lefevre
2021-05-17 21:00 ` Bart Schaefer
2021-05-17 22:27 ` Phil Pennock
2021-05-17 23:15 ` Bart Schaefer
2021-05-18 0:30 ` Phil Pennock
2021-05-18 1:14 ` Bart Schaefer
2021-05-18 8:28 ` Vincent Lefevre
2021-05-18 8:15 ` Vincent Lefevre
2021-05-18 14:53 ` Bart Schaefer
2021-05-19 4:25 ` Bart Schaefer
2021-07-18 23:10 ` Lawrence Velázquez
2021-05-18 15:18 ` Mikael Magnusson
2021-05-18 16:14 ` Peter Stephenson
2021-05-18 18:20 ` Bart Schaefer
2021-05-18 17:37 ` Martijn Dekker
2021-05-18 18:08 ` Bart Schaefer
2021-05-18 19:40 ` Martijn Dekker
2021-05-18 18:06 ` Stephane Chazelas [this message]
2021-05-18 18:12 ` Bart Schaefer
2021-05-18 18:50 ` $SHLVL origin (was: $PPID not updated when the PPID changes (parent killed)) Stephane Chazelas
2021-05-18 15:56 ` $PPID not updated when the PPID changes (parent killed) Stephane Chazelas
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210518180601.4q6o3xpeva7uhyjo@chazelas.org \
--to=stephane@chazelas.org \
--cc=schaefer@brasslantern.com \
--cc=zsh-workers@zsh.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/zsh/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).