Hello,
I was looking at open file descriptors of /bin/sh
under procfs:
$ ls -li /proc/$$/fd/
total 0
5 crw--w---- 1 jschauma tty 5, 1 Sep 14 02:47 0
5 crw--w---- 1 jschauma tty 5, 1 Sep 14 02:47 1
1090579 crw-rw-rw- 1 root wheel 1, 0 Sep 14 02:19 12
5 crw--w---- 1 jschauma tty 5, 1 Sep 14 02:47 2
$ ls -li /dev/tty
1090579 crw-rw-rw- 1 root wheel 1, 0 Sep 14 02:47 /dev/tty
$
0, 1, and 2 are obvious, but fd 12 did not seem
obvious to me.
Descriptor 12 being open to the current terminal means
I can do this:
$ echo foo >&12
foo
$
But I can also:
$ echo foo >&13
foo
$
even though fd 13 did not show up under /proc/$$/fd/.
Where does that fd come from, and why is not shown
under /proc/$$/fd? And what's the purpose of fds 12
and 13?
When using /bin/ksh, I see a different extraneous fd,
fd 10, but I can't write to it:
$ ls -li /proc/$$/fd/
total 0
5 crw--w---- 1 jschauma tty 5, 1 Sep 14 02:52 0
5 crw--w---- 1 jschauma tty 5, 1 Sep 14 02:52 1
1090579 crw-rw-rw- 1 root wheel 1, 0 Sep 14 02:51 10
5 crw--w---- 1 jschauma tty 5, 1 Sep 14 02:52 2
$ echo foo >&10
/bin/ksh: >&10 : illegal file descriptor name
$
bash creates /proc/$$/fd/255 with inode 5, it seems...
Is this documented anywhere?
-Jan
