On Sun, Jan 29, 2023, 12:21 PM Ron Natalie <ron@ronnatalie.com> wrote:

>
>
>
> "The main loop of the shell went as follows:
> 1) The shell closed all its open files, then opened the terminal special
> file for standard input and output (file descriptors 0 and 1).
>
> Unfortunately, the source code says otherwise.   None of shells V6, PWB,
> V7 do anything like is mentioned above.   They assume 0 and 1 (and 2) are
> already open.
> The only fd redirection they do is when you do pipes or redirection on the
> command line.
>

This was in reference to the pdp-7 unix implementation. I didn't check the
pdp7 version though. So what you said is true about the later versions for
sure, starting with v5.

Where this is done is, as I posted earlier, in /etc/init.    Init opens the
> tty device and dups it to 1 and then invokes either the shell (if we're in
> single user mode) or getty for interactive mode.
> This was done in V6 and PWB (1).   In V7, init added a second dup for file
> descriptor 2.
>


Yes. I quite enjoyed that.

My surprise was Dennis' paper didn't mention the innovation since it was
otherwise quote detailed.

Warner

>