automating telnet session using bash scripts

Question

I am working on automating some telnet related tasks  using Bash scripts  Once automated there will be no interaction of the user with telnet   that is it will be totally automated  the scripts looks something like this    execute some commands on the local system   access a remote system with an IP address  10 1 1 1  for example   telnet 10 1 1 1    execute some commands on the remote system   log all the activity  in a file  on the Local system   exit telnet   continue on with executing the rest of the script   There are 2 problems I am facing here   How to execute the commands on the remote system from the script  without human interaction   From my experience with some test codes  I was able to deduce that when the telnet 10 1 1 1 is executed  telnet goes into an interactive session and the subsequent lines of code in the script are executed on the local system  How can I run the lines of code on the remote system rather than the local one   I am unable to get a log file for the activity in the telnet session on the local system  The stdout redirect I used makes a copy on the remote system  I do not want to perform a copy operation to copy the log to the local system   How can I achieve this functionality

User · Answer

You can use expect scripts instaed of bash  Below example show how to telnex into an embedded board having no password     usr bin expect  set ip   lt ip gt    spawn   bin bash  send  telnet  ip r  expect         send   r  expect     sleep 2  send  ls r  expect      sleep 2 send --     r  expect  telnet gt   send   quit r  expect eof

User · Answer

While I d suggest using expect  too  for non-interactive use the normal shell commands might suffice  Telnet accepts its command on stdin  so you just need to pipe or write the commands into it   telnet 10 1 1 1  lt  lt EOF remotecommand 1 remotecommand 2 EOF    Edit  Judging from the comments  the remote command needs some time to process the inputs or the early SIGHUP is not taken gracefully by the telnet  In these cases  you might try a short sleep on the input      echo  remotecommand 1   echo  remotecommand 2   sleep 1      telnet 10 1 1 1   In any case  if it s getting interactive or anything  use expect

User · Answer

Play with tcpdump or wireshark and see what commands are sent to the server itself  Try this  printf  printf   username r n password r nwhoami r nexit r n     ncat  target 23   Some servers require a delay with the password as it does not hold lines on the stack  printf  printf   username r n  sleep 1 printf   password r nwhoami r nexit r n     ncat  target 23

User · Answer

Use ssh for that purpose  Generate keys without using a password and place it to  authorized keys at the remote machine  Create the script to be run remotely  copy it to the other machine and then just run it remotely using ssh   I used this approach many times with a big success  Also note that it is much more secure than telnet

User · Answer

Here is how to use telnet in bash shell expect       usr bin expect   just do a chmod 755 one the script     YOUR SCRIPT NAME sh  YOUHOST  PORT   if you get  Escape character is       as the output it means got connected otherwise it has failed  set ip  lindex  argv 0  set port  lindex  argv 1   set timeout 5 spawn telnet  ip  port expect

User · Answer

Following is working for me    put all of your IPs you want to telnet in IP sheet txt  while true read a do       sleep 3     echo df -kh     sleep 3     echo exit     telnet  a done lt IP sheet txt

User · Answer

bin bash ping count  4  avg max limit  1500  router  sagemcom-fast-2804-v2  adress  192 168 1 1  user  admin  pass  admin   VAR    expect -c            set timeout 3         spawn telnet   adress          expect   Login             send    user n           expect   Password            send    pass n           expect   commands            send   ping ya ru -c  ping count n           set timeout 9         expect   transmitted           send   exit               count ping   echo   VAR    grep packets   cut -c 1  avg ms   echo   VAR    grep round-trip   cut -d     -f 4   cut -d     -f 1   echo  1     ping    count ping        avg ms  echo   VAR

User · Answer

Write an expect script   Here is an example      usr bin expect   If it all goes pear shaped the script will timeout after 20 seconds  set timeout 20  First argument is assigned to the variable name set name  lindex  argv 0   Second argument is assigned to the variable user set user  lindex  argv 1   Third argument is assigned to the variable password set password  lindex  argv 2   This spawns the telnet program and connects it to the variable name spawn telnet  name   The script expects login expect  login     The script sends the user variable send   user    The script expects Password expect  Password    The script sends the password variable send   password    This hands control of the keyboard over to you  Nice expect feature   interact   To run     myscript expect name user password

User · Answer

This worked for me     I was trying to automate multiple telnet logins which require a username and password  The telnet session needs to run in the background indefinitely since I am saving logs from different servers to my machine   telnet sh automates telnet login using the  expect  command  More info can be found here  http   osix net modules article  id 30  telnet sh     usr bin expect set timeout 20 set hostName  lindex  argv 0  set userName  lindex  argv 1  set password  lindex  argv 2   spawn telnet  hostName  expect  User Access Verification  expect  Username   send   userName r  expect  Password   send   password r   interact   sample script sh is used to create a background process for each of the telnet sessions by running telnet sh  More information can be found in the comments section of the code   sample script sh     bin bash  start screen in detached mode with session-name  default session   screen -dmS default session -t screen name   save the generated logs in a log file  abc log   screen -S default session -p screen name -X stuff  script -f  tmp abc log   printf   r    start the telnet session and generate logs screen -S default session -p screen name -X stuff  expect telnet sh hostname username password   printf   r      Make sure there is no screen running in the backgroud by using the command  screen -ls    Read http   www gnu org software screen manual screen html Stuff to read more about screen and its options    -p  option in sample script sh preselects and reattaches to a specific window to send a command via the    -X    option otherwise you get a  No screen session found  error

User · Answer

Script for obtain version of CISCO-servers      bin sh  servers   192 168 34 1 192 168 34 3 192 168 34 2 192 168 34 3   user  cisco login  pass  cisco password   show version     host  1 expect  lt  lt  EOF set timeout 20 set host  host set user  user set pass  pass spawn telnet  host expect  Username   send   user r  expect  Password   send   pass r  expect -re       send  show version r  expect -re    -More-    send     expect -re       send  exit r  EOF    for ip in  servers  do   echo  ---------------------------------------------    echo   ip    show version  ip   grep -A3  SW Version  done

User · Answer

Telnet is often used when you learn HTTP protocol  I used to use that script as a part of my web-scraper   echo  open www example com 80   sleep 2  echo  GET  index html HTTP 1 1   echo  Host  www example com   echo  echo  sleep 2   let s say the name of the script is get-page sh then   get-page sh   telnet   will give you a html document   Hope it will be helpful to someone

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