Automating telnet session using bash scripts

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 through heredoc:

telnet 10.1.1.1 <<EOFremotecommand 1remotecommand 2EOF

(Edit: Judging from the comments, the remote command needs some time to process the inputs or the early SIGHUP is not taken gracefully by 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.

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 nameset name [lindex $argv 0]#Second argument is assigned to the variable userset user [lindex $argv 1]#Third argument is assigned to the variable passwordset password [lindex $argv 2]#This spawns the telnet program and connects it to the variable namespawn telnet $name #The script expects loginexpect "login:" #The script sends the user variablesend "$user "#The script expects Passwordexpect "Password:"#The script sends the password variablesend "$password "#This hands control of the keyboard over to you (Nice expect feature!)interact

To run:

./myscript.expect name user password

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 ;)