Re: read with redirected stdin

[Pier Paolo Grassi <pierpaolog@gmail.com>]

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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


Il giorno sab 7 gen 2023 alle ore 14:44 Roman Perepelitsa <
roman.perepelitsa@gmail.com> ha scritto:

> On Sat, Jan 7, 2023 at 2:32 PM Pier Paolo Grassi <pierpaolog@gmail.com>
> wrote:
> >
> > Hello, I have a script that asks to create a target dir if it doesn't
> exist.
> > to that extend I inserted an
> > read -k1
> > in the script.
> > To be able to ask the user for confirm even when the script stdin is
> connected to a pipe I did
> > read -k1 < /dev/tty
>
> Note that this redirect doesn't affect `read -k1`. It'll read from the
> terminal either way.
>
> You can do something like this in your script:
>
>   if [[ -r $TTY ]]; then
>     read -k1
>   else
>     read -k1 -u0
>   fi
>
> There is a corner case when you log in as root and then su to a
> non-privileged user. $TTY won't be readable even though the process
> has a TTY. Since you are redirecting stdin anyway, this corner case
> shouldn't affect you.
>
> Roman.
>

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