On 07Apr2015 20:38, Chris Angelico <ros...@gmail.com> wrote:
On Tue, Apr 7, 2015 at 3:48 PM, Cameron Simpson <c...@zip.com.au> wrote:
The operating system arranges the commection of the shell to the terminal.
Your usual program has by default a stdin, stdout and stderr. These are
_all_ the same file handle, duplicated to each of the three file descriptors
0, 1 and 2 respectively. On the operating system side, the OS has performed
_one_ open() call on the terminal device and handed the caller a single file
descriptor. The caller then calls dup() (or modernly, dup2()) to present the
open terminal as stdin, stdout and stderr.
Really? I can believe that stdout and stderr are initially duplicates,
but stdin as well? Isn't stdin opened for reading only, and
stdout/stderr for writing only?
No. Have a look with lsof:
lsof -p $$
in a terminal.
I grew up on DOS and OS/2, not on Unix, so maybe there's a massive
simplification here that I'm not aware of. That'd be pretty clean and
tidy if what you say is the case!
The setup is very simple: open the tty for read/write, close everything else,
dup the tty to fds 0, 1 and 2, make the tty the child's controlling terminal.
There's a little housekeeping like setting tty modes (erase and kill
characters, so forth) and putting the child in its own process group, but the
basics are as stated.
Cheers,
Cameron Simpson <c...@zip.com.au>
TeX: When you pronounce it correctly to your computer, the terminal may
become slightly moist. - D. E. Knuth.
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