Logging in to a Host Over SSH Using Expect

This post will go over how to log in to a remote system over ssh using expect.  While it would be a better option to use key-based authentication for non-interactive logins, this is not always an option.

Step 1:
Automatically accept the host fingerprint to known_hosts.  Here is an expect script that will accept the remote host's fingerprint to the known_hosts file, otherwise, you will need to accept the key manually.

#!/usr/bin/expect
set timeout 5
set ip [lindex $argv 0]
spawn ssh user@$ip

expect "(yes/no)?"
send "yes\n"

Step 2:
Create a script to log in and do whatever task needs to be automated.  For example, this script logs in to a host, grabs the uptime, and stores the session in the file log.txt.

#!/usr/bin/expect

set timeout 5
set ip [lindex $argv 0]
set password [lindex $argv 1]
set output [open "log.txt" "a+"]

spawn ssh user@$ip

expect "Password:"
send "$password\n"

expect "#"
send "uptime\n"

expect "#"
send "exit\n"

expect eof