Re: read with redirected stdin

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

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I think I got something wrong in my code to reproduce the cron problem:

true | setsid zsh -c 'ps -o tty $$; read -k1 && echo 1'

ps does not shows a tty, but read works correctly...

Pier Paolo Grassi


Il giorno sab 7 gen 2023 alle ore 18:21 Pier Paolo Grassi <
pierpaolog@gmail.com> ha scritto:

> 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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