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Expect is available in most Linux distributions. If it is not already installed in your system you install it in Debian as shown below.

<pre>
<code class="language-bash line-numbers normalize-whitespace">
apt-get update
apt-get install expect
</code>
</pre>


Here is a working expect script that reads all inputs from command line. I will break it down as we go on. Please note that lines beginning 

with ;# are comments.

<pre>
<code class="language-bash line-numbers normalize-whitespace">
#! /bin/expect

set timeout 20

;# -- command line arguments to our scripts
set user [lindex $argv 0]
set password [lindex $argv 1]
set host [lindex $argv 2]

;# shell prompt character
set prompt "$ "

;# -- main procecure 
proc dostuff {} {
 send -- "ls -lrt\r"
 return
}

;# script start running here

spawn /usr/bin/ssh $user@$host

;# loops forever until we get a shell prompt

while (1) {

 expect {
 ;# -- This is the prompt when you first use
 ;# -- ssh that says "Are you sure you want to continue ..."

 "no)? " {
 send -- "yes\r"
 }

 ;# -- the prompt for password
 "password: " {
 send -- "$password\r"
 }

 ;# -- and finally we got a shell prompt
 "$prompt" {
 dostuff
 break
 }
 }

}

;# -- exit
expect "$prompt"
send -- "exit\r"

expect eof
</code>
</pre>


The script is executed as below

<pre>
<code class="language-bash line-numbers normalize-whitespace">
expect {filename-of-the-script} user password host
</code>
</pre>

The script starts by executing ssh through spawn command. We go into a while loop until we get a shell prompt which signals that we 

have successfully logged in. We then call our main task the procedure dostuff. Our expect statement takes a switch form which 

executes a case that matches part of the ssh program prompt presented to our script. 


The "--" after the send statement means that its parameter should be treated as plain string. A send statement is terminated with a "\r" charater simulating a carraige return. The shell prompt character that we use is the $ sign. You may want to change that if you have different shell setup.




Below is the same script but now it reads hosts information from a text file. Entries to the text file is teminated by a return character. We are assuming that all hosts has a user with password that you specify from command line.


<pre>
<code class="language-bash line-numbers normalize-whitespace">
#! /bin/expect

set timeout 20
set user [lindex $argv 0]
set password [lindex $argv 1]
set prompt "$ "

;# -- main activity

proc dostuff { currenthost} {

 ;# do something with currenthost

 send -- "ls -lrt\r"
 return
}

;# -- start of task

set fd [open ./hostlist r]
set hosts [read -nonewline $fd]
close $fd


foreach host [split $hosts "\n" ] {

 spawn /usr/bin/ssh $user@$host

 while (1) {
 expect {

 "no)? " {
 send -- "yes\r"
 }
 
 "password: " {
 send -- "$password\r"
 }
 
 "$prompt" {
 dostuff { $host }
 break
 }
 }
 }

 expect "$prompt"
 send -- "exit\r"

}

expect eof
</code>
</pre>

The script is now executed as below

<pre>
<code class="language-bash line-numbers normalize-whitespace">
expect {filename-of-the-script} user password
</code>
</pre>

Our text is read into a buffer which is then split into a list in our for loop. Notice that our hostlist file should be in the folder as our script. Also notice that our dostuff procedure now takes a parameter. You may want to use this parameter to select a task you may require for that specific host.


That's it. Good luck.

Using Expect script to automate SSH logins and do routine tasks accross multiple hosts