使用Popen的Python中的持久ssh会话

Question

I am creating a movie controller (Pause/Stop...) using python where I ssh into a remote computer, and issue commands into a named pipe like so

echo -n q > ~/pipes/pipename

I know this works if I ssh via the terminal and do it myself, so there is no problem with the setup of the named pipe redirection. My problem is that setting up an ssh session takes time (1-3 seconds), whereas I want the pause command to be instantaneous. Therefore, I thought of setting up a persistent pipe like so:

controller = subprocess.Popen ( "ssh -T -x <hostname>", shell = True, close_fds = True, stdin=subprocess.PIPE, stderr=subprocess.PIPE, stdout=subprocess.PIPE )

Then issue commands to it like so

controller.stdin.write ( 'echo -n q > ~/pipes/pipename' )

I think the problem is that ssh is interactive so it expects a carriage return. This is where my problems begin, as nearly everyone who has asked this question has been told to use an existing module:

• Vivek's answer
• Chakib's Answer
• shx2's Answer
• Crafty Thumber's Answer
• Artyom's Answer
• Jon W's Answer

Which is fine, but I am so close. I just need to know how to include the carriage return, otherwise, I have to go learn all these other modules, which mind you is not trivial (for example, right now I can't figure out how pexpect uses either my /etc/hosts file or my ssh keyless authentications).

Answer 1

I'm not sure why it's not working the way you have it set up, but I'll take a stab at this. I think what I would do is change the Popen call to:

controller = subprocess.Popen("ssh -T -x <hostname> \"sh -c 'cat > ~/pipes/pipename'\"", ...

And then simply controller.stdin.write('q') .

Answer 2

To add a newline to the command, you will need to add a newline to the string:

controller.stdin.write('\n')

You may also need to flush the pipe:

controller.stdin.flush()

And of course the controller has to be ready to receive new data, or you could block forever trying to send it data. (And if the reason it's not ready is that it's blocking forever waiting for you to read from its stdout, which is possible on some platforms, you're deadlocked unrecoverably.)