After connecting via ssh contrib command, execute multiple commands in the same session

[sla-te]

As of now, what I understood when using ssh is the following

my_server = sh.ssh.bake("-i", "priv_key", "[email protected]")
print(my_server("ifconfig"))
print(my_server("whoami"))

This though will open two separate sessions for execution of each command, which makes it difficult to run a chain of commands within the same session. What would be the correct way to run multiple commands in the same session?

[amoffat]

Long running ssh sessions is not really what sh is designed for, though it can be done, with significant effort. You're better off using something like https://github.com/fabric/fabric

[sla-te]

Thank you for the suggestion, the amount of open issues in this repo scares me, what about using a context manager as suggested here: #592?

[amoffat]

I had forgotten about that solution. It sounds like that could work. Try it out and share your results here and we can mark that as the answer if it works.

[sla-te]

In his explanation he describes to "keep the ssh session master alive" but as far as I understand sh syntax, there is only _bg=True which exits after the command is completed and sh.sshexecuted with without any command in addition to perform on the server would exit right after connecting, would you by any chance have an elegant idea to handle this cleanly?

With my limited knowledge about sh my only idea would be to provide a _out=interact which does something like:

while self.keep_alive:
    sleep(1)

and in __exit__ setting self.keep_alive to False followed by .wait() on the process/command running in the background.

[sla-te]

This is what I ultimately came up with:

from dataclasses import dataclass, field
from time import sleep
from typing import Any

import sh

@dataclass(slots=True)
class MasterSlaveSsh:
    master: Any = field(
        init=False,
        default_factory=lambda: sh.ssh.bake(
            "-o", "ControlMaster=yes", "-o", "ControlPath=~/.ssh/control-10.0.0.1_root", "-i", "priv_key", "[email protected]"
        ),
    )
    slave: Any = field(
        init=False,
        default_factory=lambda: sh.ssh.bake("-o", "ControlPath=~/.ssh/control-10.0.0.1_root", "-i", "priv_key", "[email protected]"),
    )

    def __enter__(self) -> slave:
        is_connected: bool = False

        def assert_connected(line):
            nonlocal is_connected

            if line.strip() == "sleeping...":
                is_connected = True

        self.master = self.master(
            'touch /root/heartbeat; while [ -f "/root/heartbeat" ]; do echo "sleeping..."; sleep 3; done;', _bg=True, _out=assert_connected
        )
        while not is_connected:
            sleep(1)

        print("Connected")

        return self.slave

    def __exit__(self, exc_type, exc_val, exc_tb):
        print(self.slave.rm("-v", "/root/heartbeat"))
        self.master.wait()


with MasterSlaveSsh() as ssh:
    print(ssh("echo 1 Doing work; sleep 3;"))
    print(ssh("echo 2 Doing work; sleep 3;"))
    print(ssh("echo 3 Doing work; sleep 3;"))

If you have any better ideas, do let me know, this way at least it uses the same connection - the shell/environment is still not the same per session though, maybe using screen would be most elegant for fixing that.

[amoffat]

Cool, thanks for sharing, this will be helpful to other users. If this solves your problem, go ahead and mark it as the answer 👍