Send password to sftp subprocess in Python

Question

import subprocess

password= "xyz"

p = subprocess.Popen(["sudo", "-S", "whoami"], stdin=subprocess.PIPE, stdout=subprocess.PIPE)

print (p.communicate((password+"\n").encode())) 


ps = subprocess.Popen(["sftp", "user@sftphost"], stdin=subprocess.PIPE, stdout=subprocess.PIPE)

print (ps.communicate((password+"\n").encode())) # without print as well I get prompted for password

First command (sudo -S whoami) is successful through subprocess taking the password correctly. However, the password is not accepted for sftp command – I am still getting prompted to enter password.

I have the same question as Use subprocess to send a password. However, I do not want to use the solution like Pexpect or expect. I have tried rest of the solutions.

Want to know why this fails for sftp and is there any other way?

Answer 1

OpenSSH sftp always reads the password from the terminal (it does not have an equivalent of sudo -S switch).

There does not seem to be a readily available way to emulate a terminal with subprocess.Popen, see: How to call an ncurses based application using subprocess module in PyCharm IDE?

---

You can use all the hacks that are commonly used to automate password authentication with OpenSSH sftp, like sshpass or Expect:
How to run the sftp command with a password from Bash script?

Or use a public key authentication.

---

Though even better is to use a native Python SFTP module like Paramiko or pysftp.

With them, you won't have these kinds of problems.