30 Jan
2023
30 Jan
'23
2:25 a.m.
On Sun, Jan 29, 2023, 12:21 PM Ron Natalie <ron(a)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