Simplest way to run an Expect script from Python

Question

I'm trying to instruct my Python installation to execute an Expect script "myexpect.sh":

#!/usr/bin/expect
spawn ssh usr@myip
expect "password:"
send "mypassword\n";
send "./mycommand1\r"
send "./mycommand2\r"
interact

I'm on Windows so re-writing the lines in the Expect script into Python are not an option. Any suggestions? Is there anything that can run it the way "./myexpect.sh" does from a bash shell?

---

I have had some success with the subprocess command:

subprocess.call("myexpect.sh",  shell=True)

I receive the error:

myexpect.sh is not a valid Win32 application.

How do I get around this?

Sagunto

...are you asking how to run a bash script on Windows without bash? I don't even see where Python comes in here. Furthermore, you probably should give .txt extensions to your shell scripts (.sh if anything) – Ampulla

@MateuszKowalczyk in a sense yes: I would like to automate running this script, from a .py file - when I run the .py file, the expect script will be called and run as part of the sequence of the .py file. – Sagunto

So it looks like you're not looking for a python-related solution at all (other than the fact that it's being controlled from Python). You simply want a program on Windows that will be able to read the expect script and execute it, right? – Halfwitted

@EricFinn I am looking for a python solution - the myexpect.sh runs fine if I execute it from a cygwin terminal, but that is not my final goal. What I would like to do is have my python script execute my .sh script whenever I run my .py file, so I don't have to execute it from a terminal by hand before I run my .py file. – Sagunto

@Sagunto But it looks like your question isn't really Python-specific; you're just telling the OS to run a file as a program, and a solution that will allow the OS to run said file (most likely through a Windows port of Expect) would work with any language, not just Python. Or would also reading in the script and interpreting it yourself in Python be acceptable? – Halfwitted

@EricFinn The best solution is something like pexpect functionality, where I can write the Expect lines right into my .py code. There is no pexpect library for windows (although winpexpect may prove fruitful), and subprocess is a gordian knot at my level of python expertise. I was hoping I was missing something obvious like "run myexpect.sh" but I don't think it's that simple. – Sagunto

Yeah, there isn't a program for running expect scripts packaged with Windows, and it doesn't really look like there's a Windows-compatible Python package to do it. – Halfwitted

it seems you want this: subprocess.call(r"c:\path\to\cygwin\expect.exe", "myexpect.sh"]). Your specific script could be implemented using fabric – Jacquetta

Answer 1

Use the pexpect library. This is the Python version for Expect functionality.

Example:

child = pexpect.spawn('Some command that requires password')
child.expect('Enter password:')
child.sendline('password')
child.expect(pexpect.EOF, timeout=None)
cmd_show_data = child.before
cmd_output = cmd_show_data.split('\r\n')
for data in cmd_output:
    print data

Pexpect comes with lots of examples to learn from. For use of interact(), check out script.py from examples:

• https://github.com/pexpect/pexpect/tree/master/examples

(For Windows, there is an alternative to pexpect.)

• Can I use Expect on Windows without installing Cygwin?

Gardol

pexpect is a brilliant solution if you're on a Linux platform, but there is no pexpect library available for Windows platforms. – Sagunto

@gortron: There was an SO discussion on pexpect equivalent for windows. I have added that to the answer. See if that helps. – Gardol

For posterity: winpexpect is a clean solution. – Sagunto

@gortron: Thanks! It has been long since I have been on windows platform. – Gardol

@gortron: there is no ssh command on Windows. I don't see how using winpexpect would help here. – Jacquetta

@Gardol i'm trying to setup a SSH tunnel with dual step authentication but unable to get the second prompt. I just wanted to sendline for the first prompt but want manual input for second prompt or may be third one as well, which is a value from MFA. Thanks in advance. – Agitate

License may be unwelcome in many companies – Folie

Answer 2

Since it is an .expect script, I think you should change the extend name of your script.

Instead of using

subprocess.call("myexpect.sh", shell=True)

you should use

subprocess.call("myexpect.expect", shell=True)

Eigenfunction

It's fine, bro. Since there is a shebang, it doesn't matter whatever the file extension is. – Natashianatassia

The system should not care but it is good to be explicit when possible. – Folie