linux - 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:

1. 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?

2. 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?

Answer 1

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 <<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 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.