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Top Forums Shell Programming and Scripting Bash: capturing *Anything* which showed on screen Post 302490703 by Corona688 on Tuesday 25th of January 2011 02:01:02 PM
Old 01-25-2011
Certain things like ssh (and many other authentication systems) don't use stdin/stdout/stderr but directly open the controlling terminal, often /dev/tty (which on linux at least is kind of 'magic' in that /dev/tty is always your own terminal, no matter what that may be.) This happens after the shell runs the program, and can't be redirected.

You'd need to create your own virtual terminal device to intercept traffic at this level. The virtual terminal would be the controlling terminal and ssh would open and interact with it. This is how the expect language is able to interact with programs that demand a terminal device.
 

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PTY(4)							   BSD Kernel Interfaces Manual 						    PTY(4)

NAME
pty -- BSD-style compatibility pseudo-terminal driver SYNOPSIS
device pty DESCRIPTION
The pty driver provides support for the traditional BSD naming scheme that was used for accessing pseudo-terminals. When the device /dev/ptyXX is being opened, a new terminal shall be created with the pts(4) driver. A device node for this terminal shall be created, which has the name /dev/ttyXX. New code should not try to allocate pseudo-terminals using this interface. It is only provided for compatibility with older C libraries that tried to open such devices when posix_openpt(2) was being called. FILES
The BSD-style compatibility pseudo-terminal driver uses the following device names: /dev/pty[l-sL-S][0-9a-v] Pseudo-terminal master devices. /dev/tty[l-sL-S][0-9a-v] Pseudo-terminal slave devices. DIAGNOSTICS
None. SEE ALSO
posix_openpt(2), pts(4), tty(4) HISTORY
A pseudo-terminal driver appeared in 4.2BSD. BUGS
Unlike previous implementations, the master slave device nodes are destroyed when the PTY becomes unused. A call to stat(2) on a nonexistent master device will already cause a new master device node to be created. The master device can only be destroyed by opening and closing it. The pty driver cannot be unloaded, because it cannot determine if it is being used. BSD
August 20, 2008 BSD
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