Develop Reference

Using pexpect to send script process to the background

I'm trying to write a script to connect to VPN more easily. I want the script to use the user input and connect to a vpn endpoint via openvpn, print the process ID for the user, and then continue running in the background but return the user to the shell. I tried child.close(force=False), os.fork(), and a few other things without any luck. The code I'm using is below. Any advice is much appreciated!
import getpass
import os
import pexpect
import random
import subprocess
import sys
country = sys.argv[1] if len(sys.argv) > 1 else 'US'
print('Connecting to VPN through ' + country)
vpns=subprocess.run(['ls', '/etc/openvpn/'], capture_output=True).stdout.decode().split('\n')
matching_vpns=filter(lambda vpn: vpn[:2].lower() == country.lower(), vpns)
chosen_vpn = random.choice(list(matching_vpns))
print('Connecting to ' + chosen_vpn + '\n')
child = pexpect.spawnu('sudo openvpn /etc/openvpn/'+chosen_vpn)
child.expect('Enter Auth Username:')
username = input('Enter Auth Username: ')
child.sendline(username)
child.expect('Enter Auth Password:')
password = getpass.getpass('Enter Auth Password: ')
child.sendline(password)
child.logfile_read = sys.stdout
while True:
try:
child.expect('\n', timeout=None)
if 'Initialization Sequence Completed' in child.before:
print("\nSuccessfully connected to " + chosen_vpn)
print("To stop VPN, run 'sudo pkill -9 -P " + str(child.pid) + "'")
break
except pexpect.EOF:
break

How can i get telnet output printed line by line?

I have implemented a script that connects to a Cisco device and collects the show run output.
The script is:
import getpass
import telnetlib
import time
HOST = "10.62.149.9"
user = input("Enter your remote account: ")
password = getpass.getpass("User Password: ")
enable = getpass.getpass("Enable Password: ")
tn = telnetlib.Telnet(HOST)
tn.read_until(b"Username: ")
tn.write(user.encode('ascii') + b"\n")
if password:
tn.read_until(b"Password: ")
tn.write(password.encode('ascii') + b"\n")
tn.write(b"enable\n")
if enable:
tn.read_until(b"Password: ")
tn.write(enable.encode('ascii') + b"\n")
tn.write(b"term len 0\n")
tn.write(b"show run\n")
time.sleep(10)
s = tn.read_very_eager()
print (s)
tn.close()
The script output is:
\r\ninterface GigabitEthernet1/0/26\r\n!\r\ninterface GigabitEthernet1/0/27\r\n!\r\ninterface GigabitEthernet1/0/28\r\n!\r\ninterface GigabitEthernet1/0/29\r\n!\r\ninterface GigabitEthernet1/0/30\r\n!\r\ninterface GigabitEthernet1/0/31\r\n!\r\ninterface GigabitEthernet1/0/32\r\n!\r\ninterface GigabitEthernet1/0/33\r\n!\r\ninterface GigabitEthernet1/0/34\r\n!\r\ninterface GigabitEthernet1/0/35\r\n!\r\ninterface GigabitEthernet1/0/36\r\n!\r\ninterface GigabitEthernet1/0/37\r\n!\r\ninterface GigabitEthernet1/0/38\r\n!\r\ninterface GigabitEthernet1/0/39\r\n!\r\ninterface GigabitEthernet1/0/40\r\n!\r\ninterface GigabitEthernet1/0/41\r\n!\r\ninterface GigabitEthernet1/0/42\r\n!\r\ninterface GigabitEthernet1/0/43\r\n!\r\ninterface GigabitEthernet1/0/44\r\n!\r\ninterface GigabitEthernet1/0/45\r\n!\r\ninterface GigabitEthernet1/0/46\r\n!\r\ninterface GigabitEthernet1/0/47\r\n!\r\ninterface GigabitEthernet1/0/48\r\n no switchport\r\n ip address 10.62.149.9
255.255.255.128\r\n!\r\ninterface GigabitEthernet1/0/49\r\n!\r\ninterface GigabitEthernet1/0/50\r\n!\r\ninterface GigabitEthernet1/0/51\r\n!\r\ninterface GigabitEthernet1/0/52\r\n!\r\ninterface Vlan1\r\n no ip address\r\n shutdown\r\n!\r\ninterface Vlan10\r\n ip address 10.10.10.1
255.255.255.0\r\n!\r\ninterface Vlan199\r\n ip address 217.21.0.6 255.255.254.0\r\n no ip redirects\r\n ip ospf priority 100\r\n!\r\ninterface Vlan777\r\n ip address 7.7.7.1
Question
Is there a way to change the script so the output is presented line by line way?

The documentation for telnetlib isn't very clear about Telnet.read_very_eager, but it mentions that it reads and writes bytes for other methods. type(s) is probably bytes.
Use bytes.decode to get a string: print(s.decode('ascii')) (use the appropriate encoding)
Note: This is for Python 3.

You need to check the string with some common special character that separates the lines using python split() function and after that initiate a for loop with the length of variable and then print.

Telnet script does not work inside a function

Out of function, the script works, but inside the function, script does not work.
import telnetlib
import sys
def teltest():
host = "192.168.2.2"
user = "admin"
password = "admin"
tn = telnetlib.Telnet(host)
tn.read_until("Username:")
tn.write(user + "\n")
tn.read_until("Password:")
tn.write(password + "\n")
tn.write("enable\n")
tn.write("config t\n")
tn.write("interface eth 0/0/13\n")
tn.write("description TEST\n")
teltest()
Why and how can i fix it?

This is happening because of the function returns before properly terminating the connection leaving the other end of the device in a meta state. Adding a sleep at the end as mentioned in the comments would let room for cleaning up the connection thereby executing what was written onto the device.
Telnet.write(buffer) Write a string to the socket, doubling any IAC
characters. This can block if the connection is blocked. May raise
socket.error if the connection is closed.
import telnetlib
import sys
def teltest():
host = "192.168.2.2"
user = "admin"
password = "admin"
tn = telnetlib.Telnet(host)
tn.read_until("Username:")
tn.write(user + "\n")
tn.read_until("Password:")
tn.write(password + "\n")
tn.write("enable\n")
tn.write("config t\n")
tn.write("interface eth 0/0/13\n")
tn.write("description TEST\n")
time.sleep(1)
teltest()
Posting this as an answer for the benefit of the community despite the fact that the op received help from comments.

Python socket works as a telnet connection and requires double read

I'm connecting to the device using telnet. Once I connected, I need to enter user name admin, press enter \n and use blank password (enter again \n). After the described login process I should end up with the invitation (prompt) #. I'm reading from the socket after each write. The program is below:
import socket
s = socket.socket()
#Connecting using telnet
s.connect(('192.168.1.2',23))
a = s.recv(1000)
print 'a:', a
s.send('admin\n\n')
b = s.recv(1000)
print 'b:', b
c = s.recv(1000)
print 'c:', c
The output of the program is the following:
a: ��
b: �������� ��!��"��'����#��User:
c: admin
Password:
(prompt) #
QUESTION:
Why do I need to do double read to receive all the information (print b and print c) instead of just one read (print b)?

Instead of using raw sockets, you can use the telnetlib.
Typical usage:
import getpass
import sys
import telnetlib
HOST = "localhost"
user = raw_input("Enter your remote account: ")
password = getpass.getpass()
tn = telnetlib.Telnet(HOST)
tn.read_until("login: ")
tn.write(user + "\n")
if password:
tn.read_until("Password: ")
tn.write(password + "\n")
tn.write("ls\n")
tn.write("exit\n")
print tn.read_all()
This will ask for your username and password, then use the entered information to authenticate to the server as seen here:
tn.read_until("login: ")
tn.write(user + "\n")
if password:
tn.read_until("Password: ")
tn.write(password + "\n")
You can read the telnetlib documentation for python 2.x here.

Qustion regarding telnet to a switch on the network and sending in specific commands

I have written a python program to telnet to a switch on the network, login and enter specific commands. But I don't know what is wrong with my program as the program never gets passed through after login. I doubt the program is even taking in the password I gave at command line.
Here is my program:
import telnetlib
import getpass
import sys
Host = "10.210.1.2"
user = raw_input("hbommireddy")
password = getpass.getpass()
tn = telnetlib.Telnet(Host)
tn.read_until("Login: ")
tn.write(user + "\n")
if password:
tn.read_until("Password: ")
tn.write(password + "\n")
tn.read_until("SYSTEM-QA-S4810>")
tn.write("en\n")
tn.read_until("SYSTEM-QA-S4810#")
tn.write("show interface status\n")
print tn.read_all()