Whoa...dont you mean

Code:

ls 1>ls.out 2>&1

...the order IS important.

I would be surprised if you couldn't capture this....have you tried something like "script" ? That seems to capture my ssh sessions fine...
If that captures it, then anything can (cos it doesnt run setuid)

BTW, There are oddities that you have to be aware of, for example if you have:

Code:

cat /tmp/foo | more

The "more" command throws up a prompt onto the users screen, and waits for the user to press a key. This obviously isnt from stdin (as it takes that from the cat /tmp/foo). Actually what the shell does is to pass the stderr to the "more" command and the more command checks to see if that is attached to a tty and then does its input/output through that....but thats another story)

Although its theoretically possible for programs to open /dev/tty, this is almost never done by useful applications. This is because the shell would normally be in control of the tty, and uses it for job control. If another program opened /dev/tty and started trying to do I/O through it, the shell would probably quit out or get arsey.

I hope this makes things a little clearer

---------- Post updated at 11:48 PM ---------- Previous update was at 11:35 PM ----------

Yep, looking at script, it allocates a new pseudoterminal (pty), which pretends to be the logged in users tty. This is the same as "expect", and indeed exactly the same method that sshd and telnetd use to emulate terminals. If you look at the code to expect or script (or indeed sshd) you will see their method of allocating pty's and from there you can do interactive I/O to any process, even the ones, like passwd, that insist on a controlling pty.

---------- Post updated 01-26-11 at 12:03 AM ---------- Previous update was 01-25-11 at 11:48 PM ----------

(BTW, I just noticed your original question contained the sentence "I have a simple question about I/O redirection. "....So, I apologise for my over complicated answer...I realise now that it probably wasn't what you were after...)