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Expect Script SSH Example Tutorial

Published on August 3, 2022
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By Pankaj
Developer and author at DigitalOcean.
Expect Script SSH Example Tutorial

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Expect script is a great linux/unix utility. I have to deal with a lot of unix servers in my daily life, whether it’s at work or it’s my hosting server. So I need to remember a lot of SSH users, their passwords and then SU users and passwords. It’s kind of messy when the number of servers are huge. So I thought of writing a script that will automatically login me to the server. When I first started working on this, I got stuck as how to enter the SSH password because normal unix shells don’t have any way to send the password when it gets prompted for login. Then I come to know about expect script that allows to automate the interaction with programs that opens a terminal for input.

Expect Script

expect script, expect script ssh, expect script tutorial Expect Script is very easy to learn and as the name suggests it works by parsing the output of the command and when it matches the specified regular expression, it processes the specified instruction.

Expect Script SSH Example

Here is the script I created for automatically login to the SSH server and then login with super user and then run a simple command. sshsudologin.expect


#Usage sshsudologin.expect <host> <ssh user> <ssh password> <su user> <su password>

set timeout 60

spawn ssh [lindex $argv 1]@[lindex $argv 0]

expect "yes/no" { 
	send "yes\r"
	expect "*?assword" { send "[lindex $argv 2]\r" }
	} "*?assword" { send "[lindex $argv 2]\r" }

expect "# " { send "su - [lindex $argv 3]\r" }
expect ": " { send "[lindex $argv 4]\r" }
expect "# " { send "ls -ltr\r" }

Important Points about Expect Script

  1. Notice the first line that specifies that expect script will be used as interpreter.
  2. Expect script default timeout is 10 seconds, so I have set the timeout to 60 seconds to avoid any timeout issues if the login prompt takes time to come.
  3. Notice the expect command followed by the regular expression and then what should be send as a response. The first Yes/No choice is added to make sure that it doesn’t fail if remote server key is not already imported.
  4. The other expect regular expressions varies across the servers, for my server it ends with “#” but for some other servers it might end with “$”, so you may need to edit it accordingly. The only thing to check is that the regular expression for the expect command should matches, so that it will send the corresponding command or password.
  5. The last expect command just shows that we can send commands also once we are logged into the server.

Here is the output when I run the above expect script with correct parameters.

pankaj@Pankajs-MacBook-Pro:~$/Users/pankaj/scripts/sshloginsudo.expect 'journaldev.com' 'pankaj' 'ssh_pwd' 'su_user' 'su_pwd'
spawn ssh pankaj@journaldev.com
pankaj@journaldev.com's password: 
Last login: Sun Jun  9 19:54:17 2013 from c-67-161-57-160.hsd1.ca.comcast.net
pankaj@journal [~]# su - su_user
su_user@journal [~]# ls -ltr
total 708

Extra Tips on expect script

  1. The expect script can be reused since all the information is passed as arguments, so it’s best to create alias for each one of them for quick login and save your time in typing all the parameters. For example, alias journal="/Users/pankaj/scripts/sshloginsudo.expect 'journaldev.com' 'pankaj' 'ssh_pwd' 'su_user' 'su_pwd'"
  2. It’s always best to use single quotes to pass the arguments, since most of the time passwords contains special characters that can cause funny results if they are not quoted.

NOTE: The above script is tested on Mac OS and Linux systems. Reference: SourceForge Page

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About the authors
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Developer and author at DigitalOcean.

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take a look at https://github.com/clarkwang/sexpect . you can write expect scripts with shells only.

- clarkw

    I want an expect script to connect to a website, fill out a form and get back the response of server. Is it possible?

    - Pramod

      27.000000\t\tC1[175] i want to mach this expression , this is the value i get while printing it in command line , i am usng expect “27.000000\t\tC1\[175]”; but it not matching and giving timed out as output . its inerpretating the words correclty as i am able to see by issuing exp_internal 1 command… Any solutions

      - shyam

        Hi Pankaj, my requirement is file transfer from Windows server(Cygwin exe is installed for SFTP) to Unix Server and vice versa. I need java code for this. do you have any idea about that ?

        - Adhiran

          Hi Pankaj, I was trying almost the same example. I am trying to execute a script in server B from server A. My problem is the script is not exiting from SSH session.How can I get control back to script in server A and print some message saying the script is done. #Shell script in Server A #!/usr/bin/expect -f set timeout -1 set Username “” set password “” set ipaddress “” set script “” spawn $env(SHELL) send “ssh $Username@$ipaddress $script\r && exit” expect { “(yes/no)?” {send “yes\r”;exp_continue} “password:” {send “$password\r”;interact;} }

          - Riya

            How can I ssh to one more session through an existing ssh session?

            - Vamshi

              Awesome :) now I can have up to six consoles open on a remote machine and monitor its logs with a single key combination Ctrl-Alt-m, want to learn how I did ? https://ychaouche.informatick.net/kde

              - yassine

                Hi there, I have a problem when trying to ssh to a solaris box using groovy script and expect To give you some background, I can ssh to the solaris box with no problem from command line using putty, I can also execute my groovy and expect script from Eclipse and I am able to connect. However when I try to do the same from a web server that is deployed on weblogic I get the following error: Error: java.lang. IllegalArgumentException: No Configuration was registered that can handle the configuration named com.sun.security.jgss.krb5.initiate This happens when I use def shell = ex.spawn(‘solarisBox’, 22, user,password) ex is an instantiated object of ExpectJ… a Java wrapper for expect if I try to use def shell = ex.spawn(“ssh user@solarisBox”) in my script shell.expect(prompt) shell.send(pass) I get Java.IOException broken pipe using groovy 1.5.5 and I believe the expect version is 2.0.7 Please help, thank you so much in advance.

                - Samir

                  Could you please share the packages for send and intreact commands, as while running command getting command not found error. The operating system am using was RHEL 6.5 .

                  - MOHAN

                    Hi Pankaj I have gone through this web page. It was very helpful to learn about expect scripts. I need one help from you. I wrote same script which you have mentioned in this page to login to remote server. After login I am going to particular path and call shell script inside expect script. Its is executing properly in terminal( I am using Linux server). When I am calling that script on jenkins. Its not excuting properly. Please help me out its very urgent. If you need some information please let me know. Thanks pawar

                    - Gowtham