On Sat, Jan 7, 2023 at 11:23 AM Pier Paolo Grassi <pierpaolog@gmail.com>
wrote:

> Thanks, but i don't _always_ redirect stdin.
> i wonder how is ps getting the tty (it displays an ? when there is no tty
> for the process)
> I suppose it uses /proc, but couldn't find a reference or the info
> exploring the /proc fs by myself.
> for now I am asking directly ps:
> [[ "$(ps h -o tty $$)" != "?" ]] && ...
>
> Pier Paolo Grassi
>
> Hi,

Don't really have an answer how ps gets its info but the attached script is
something
I have been working on. It uses the /proc file system directly to get info.
It uses zstat
to look for the tty info.  If nothing is returned it substitutes '?".  Some
processes point to
/dev/null. The script is still a work in progress. I was trying to get the
same results as
"ps -eHo uid=,pid=,ppid=,tty=,comm=" via a zsh script.

This doesn't answer your original question, but may give you some insight
into the
/proc file system.

Hope the script is helpful.

Regards,

Jim Murphy