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Re: TTY management
- X-seq: zsh-workers 44095
- From: Sebastian Gniazdowski <sgniazdowski@xxxxxxxxx>
- To: Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>
- Subject: Re: TTY management
- Date: Thu, 28 Feb 2019 15:35:06 +0100
- Cc: Zsh hackers list <zsh-workers@xxxxxxx>
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On Fri, 8 Feb 2019 at 01:16, Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> wrote:
> First let's talk about "vim | cat". Programs that expect to use
> capabilities of an interactive terminal nearly always make their own
> determination of whether they can do so, but how this is done varies a
> lot. Vim in particular works very hard to find a terminal - it will
> look at both stdin and stdout, and if either of those is a terminal it
> will try to interact with that (assuming the descriptor is open for
> both reading and writing).
I think this works differently, and I have proof for this:
% vim | cat > file
doesn't yield a working vim like the `vim | cat' does. This means that
vim doesn't look for a terminal on stderr or /dev/tty, but that
instead it just streams its terminal-codes to the redirected stdout.
If the redirected output is still a terminal, then things work, if not
(e.g. the >file above), then things don't work.
That's why I wanted to just make the isatty() test pass with True.
> Regarding isatty() -- as has been explained, this is a system call.
> It examines an ioctl that is restricted to terminal devices.
> Terminal devices operate
> using (what to the OS appear to be) hardware-level drivers to mediate
> the bidirectional data flow.
Ahso, pity then this would mean that one cannot simply pretend that a
descriptor is a tty.
> There are actually security-related reasons for this -- think 1980/90s
> technology -- you don't want a man-in-the-middle attack capturing a
> login exchange from a physical terminal in a computer lab, for
> example. Virtual terminal devices came along later and have to
> address this differently.
> The upshot of this is that, as PWS said, the core shell is not the
> place to handle this. If someone wants to find open-source of the
> "script" command and turn it into a module, though, that might be
> worth considering.
What exactly would this module do?
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