[scripting] Creating a script for a Telnet session?

Does anyone know of an easy way to create a script that can connect to a telnet server, do some usual telnet stuff, and then log off? I am dealing with users who are not familiar with telnet and the commands they will need to run. All I want is for them to double-click on a script, and have that script automatically execute the commands for them.

You're probably wondering, "What platform are the users on?" They will be on both Windows and Linux. Implementations in languages like Perl, Java, or Python are acceptable. I see that Perl has a Net:: Telnet module. Has anyone used that?

My ideal solution would be to create two script files. a BAT file for windows, and a shell script for Linux. While this would make dual maintenance an issue, it would mean I wouldn't have to install Perl/Java/Python/etc... on every machine. Unfortunately, I have not seen any way to automate a telnet session with batch files or shell scripts.

Thanks.

I've used various methods for scripting telnet sessions under unix, but the simplest one is probably a sequence of echo and sleep commands, with their output piped into telnet. Piping the output into another command is also a possibility.

Silly example

(echo password; echo "show ip route"; sleep 1; echo "quit" ) | telnet myrouter

This (basicallly) retrieves the routing table of a Cisco router.

Write the telnet session inside a BAT Dos file and execute.

Another method is to use netcat (or nc, dependent upon which posix) in the same format as vatine shows or you can create a text file that contains each command on it's own line.

I have found that some posix' telnets do not handle redirect correctly (which is why I suggest netcat)

Check for the SendCommand tool.

You can use it as follows:

perl sendcommand.pl -i login.txt -t cisco -c "show ip route"

I like the example given by Active State using python. Here is the full link. I added the simple log in part from the link but you can get the gist of what you could do.

import telnetlib

prdLogBox='142.178.1.3'
uid = 'uid'
pwd = 'yourpassword'

tn = telnetlib.Telnet(prdLogBox)
tn.read_until("login: ")
tn.write(uid + "\n")
tn.read_until("Password:")
tn.write(pwd + "\n")
tn.write("exit\n")
tn.close()

Couple of questions:

1. Can you put stuff on the device that you're telnetting into?
2. Are the commands executed by the script the same or do they vary by machine/user?
3. Do you want the person clicking the icon to have to provide a userid and/or password?

That said, I wrote some Java a while ago to talk to a couple of IP-enabled power strips (BayTech RPC3s) which might be of use to you. If you're interested I'll see if I can dig it up and post it someplace.

This vbs script reloads a cisco switch, make sure telnet is installed on windows.

Option explicit
Dim oShell
set oShell= Wscript.CreateObject("WScript.Shell")
oShell.Run "telnet"
WScript.Sleep 1000
oShell.Sendkeys "open 172.25.15.9~"
WScript.Sleep 1000
oShell.Sendkeys "password~"
WScript.Sleep 1000
oShell.Sendkeys "en~"
WScript.Sleep 1000
oShell.Sendkeys "password~"
WScript.Sleep 1000
oShell.Sendkeys "reload~"
WScript.Sleep 1000
oShell.Sendkeys "~"
Wscript.Quit

Bash shell supports this out-of-box, e.g.

exec {stream}<>/dev/tcp/example.com/80
printf "GET / HTTP/1.1\nHost: example.com\nConnection: close\n\n" >&${stream}
cat <&${stream}

To filter and only show some lines, run: grep Example <&${stream}.

import telnetlib

user = "admin"
password = "\r"

def connect(A):
    tnA = telnetlib.Telnet(A)
    tnA.read_until('username: ', 3)
    tnA.write(user + '\n')
    tnA.read_until('password: ', 3)
    tnA.write(password + '\n')
    return tnA
def quit_telnet(tn)
    tn.write("bye\n")
    tn.write("quit\n")

It may not sound a good idea but i used java and used simple TCP/IP socket programming to connect to a telnet server and exchange communication. ANd it works perfectly if you know the protocol implemented. For SSH etc, it might be tough unless you know how to do the handshake etc, but simple telnet works like a treat.

Another way i tried, was using external process in java System.exec() etc, and then let the windows built in telnet do the job for you and you just send and receive data to the local system process.