LinuxQuestions.org - [SOLVED] another script for telnet connection

- Linux - Newbie (https://www.linuxquestions.org/questions/linux-newbie-8/)

- - another script for telnet connection (https://www.linuxquestions.org/questions/linux-newbie-8/another-script-for-telnet-connection-4175474897/)

another script for telnet connection

first thing i have to say, i cannot use the following:

expect
netcat
nmap

this has to be in bash and has to be in telnet.

my senior admin asked me to come up with a script to telnet to a server on port 110, actually log in, be able to list, and then log out.

if i am able to do those things, then awesome, no action needed.

if, however, i am unable to establish a connection, i need to be notified via email no connection established.

i have the log in portion of the script developed and it works, but i do not know how to finish the script if the connection cannot be established.

any input and help is appreciated.

here is the first part of my script

PHP Code:




#!/bin/bash 
 
( 
echo open 123.123.123.123 110 
sleep 2 
echo "user username" 
sleep 1 
echo "pass password" 
sleep 4 
echo "list" 
sleep 4 
echo "quit" 
sleep 1 
) | telnet

You could make a seperate check, before going on with the log in, such as:

Code:

telnet 127.0.0.1 > /dev/null 2>&1 || echo "connection refused, so i wont bother logging in"

reason being, is that in your script, you are calling interactive telnet and it is working. the exit code says 'yep, i opened telnet and closed telnet correctly.' It doesn't care that a command inside of it didn't work. just as if you called interactive python and typed 'woijeoijewe;fwojoa;wejfoijeijei' then exited, python would exit with a clean code, because what you did in the interpreter doesn't matter.

Expect is built for this and can handle the input/output plus timeouts etc....sys admin , is your school teacher?

no, sys admin is not my school teacher, i work with him and i'm not sure if he's giving me this to help me with scripting or if there is another reason.

I've given you a simple example and explanation of how to do this. Is there a problem?

Of course you can go that way, but that script is very weak. If you are not going to automate a lot of things using telnet is the way to go.

Now if you want something more powerful, Perl has a nice Telnet Module.

http://search.cpan.org/~jrogers/Net-.../Net/Telnet.pm

Quote:

Originally Posted by szboardstretcher (Post 5017022)

I've given you a simple example and explanation of how to do this. Is there a problem?

not yet ... i'm working on it right now to fully understand it, which right now i don't.

and how to implement it in a non interactive script.

In general, using telent to handle passwords is NOT secure. There is no encryption used so anyone sniffing the network has the password...

ssh (with RSA authentication) can do this without a problem, without even needing a password, and be more secure at the same time.

Quote:

Originally Posted by szboardstretcher (Post 5016947)

You could make a seperate check, before going on with the log in, such as:

Code:

telnet 127.0.0.1 > /dev/null 2>&1 || echo "connection refused, so i wont bother logging in"

thanks for the help on this. and i now see what you mean about what the exit code is reporting ... it only cares if i open telnet IP PORT and does not care if i can log in and run a command. i started my script basing on the exit code which is not going to give me what i want.

i am now going to focus on this method and i think it will give me what i need:

Initiates the login session to port 110, using netcat and an input file that will have the log in credentials
Capture the output to a file
Grep the output file for Authentication failed
IF
Authentication failed exists = notify
Authentication does not exist = no action needed

once i get it developed and working i'll post it up for your input.

seems so simple now but man this hurt my head.

Code:

#!/bin/bash



nc 123.123.123.123 110 < credentials.txt >> output.txt





grep "Authentication fail" output.txt

if [ $? = 0 ]

then

echo -e "Unable to netcat to 123.123.123.123 from $HOSTNAME" | mail -s "Authentication error on $HOSTNAME" whomever@wherever.com



rm -rf output.txt

fi