Let us define a function that will take a user's login credentials from the Command Prompt and connect to a telnet server.

Upon successful connection, it will send the Unix 'ls' command. Then, it will display the output of the command, for example, listing the contents of a directory.

Listing 6.1 shows the code for a telnet session that executes a Unix command remotely as follows:

#!/usr/bin/env python 
# Python Network Programming Cookbook, Second Edition -- Chapter - 6 
# This program is optimized for Python 3.5.2. 
# It may run on any other version with/without modifications. 
# To make it run on Python 2.7.x, needs some changes due to API differences. 
# Follow the comments inline to make the program work with Python 2. 
 
 
import getpass 
import sys 
import telnetlib 
 
HOST = "localhost" 
 
def run_telnet_session(): 
 
    user = input("Enter your remote account: ") 
    # Comment out the above line and uncomment 
      the below line for Python 2.7. 
    # user = raw_input("Enter your remote account: ") 
 
    password = getpass.getpass() 
     
    session = telnetlib.Telnet(HOST) 
     
    session.read_until(b"login: ") 
    session.write(user.encode('ascii') + b"
") 
    if password: 
        session.read_until(b"Password: ") 
        session.write(password.encode('ascii') + b"
") 
     
    session.write(b"ls
") 
    session.write(b"exit
") 
     
    print (session.read_all()) 
 
if __name__ == '__main__': 
    run_telnet_session() 

If you run a telnet server on your local machine and run this code, it will ask you for your remote user account and password. The following output shows a telnet session executed on an Ubuntu machine:

$ python 6_1_execute_remote_telnet_cmd.py 
Enter your remote account: pradeeban
Password: 
    
ls
exit
Last login: Tue Jun  6 22:39:44 CEST 2017 from localhost on pts/20
Welcome to Ubuntu 16.04.2 LTS (GNU/Linux 4.8.0-53-generic x86_64)
    
* Documentation:  https://help.ubuntu.com
* Management:     https://landscape.canonical.com
* Support:        https://ubuntu.com/advantage
    
89 packages can be updated.
3 updates are security updates.
    
pradeeban@llovizna:~$ ls
INESC-ID GSD     openflow
Desktop                    MEOCloud         software
Documents               Downloads       Dropbox                    
Obidos           floodlight                 OpenDaylight 
pradeeban@llovizna:~$ exit
logout