Expect – For more remote work, automation, & CI

If you ever have a situation were you want to run scripts automatically this will help.
You can even time the events through cron or CI (continual integration) software like Hudson/Jenkins.
Let me introduce you to a new command I was not aware of until this year.

It is called Expect.expect

Expect can be installed like any other package in a Linux environment.

  • $ sudo yum install expect
  • $ sudo apt-get install expect

Here is an example of what created inside Jenkins to run after a build as an shell script.

Instead of #!/usr/bin/bash

Use:hudson

#!/usr/bin/expect
set prompt "$ "
spawn ssh -t user@remote.server
set timeout 30
expect {
timeout {
puts "Connection timed out"
exit 1
}
"yes/no" {
send "yes\r"
exp_continue
}
"assword:" {
send -- "job00ibm\r"
exp_continue
}
"$prompt" {
send "cd ~/test/\r"
}
}

Now, as long as you have Internet, the correct username, remote server, and password. You should of just created a script the will SSH into a remote server and accept the RSA fingerprint. Or you just created a script that tells you the connection timed out.
Don’t alter this part of the script much because you want to be able to re-use and if there is not a yes/no at the prompt it will continue to expect assword:.
You can get change the last command to anything you want. I added that part because you remotes into a server for no reason?

Add this to the script and it will send the command to find anything with a certain name in it to be removed from the current directory.
expect {
"$prompt" {
send "find . -name '*filename*' -type f -print0 |xargs -0 rm -f\r"
}
}

Add this to the script to find files of a certain name and copy to a new location. You should be able to use modified times in the find switch if that helps.
expect {
"$prompt" {
send "find . -name 'coke*' -type f | xargs -n1 -i cp {} /data02/home/ibmcorp/12180-us-mcrtest1/upload/\r"
}
}

Add this to the script to run a script in the current directory.
expect {
"$prompt" {
send ". name.sh\r"
}

Does your script prompt for anything? Expect can enter the reply for you.
}
expect {
"the expected promt" {
send -- "the reply\r"
}
}

Some things need to e escaped like these ampersands. It is not way to find out what all needs to be escaped but you can figure that through trial and error, intuition, or because of how smart you are.
expect {
":" {
send "me\@a-erickson.com\r"
}
}

That’s my real address if you want to reach me.

All done running your script? Don’t forget to exit your connection.
expect {
"$ " {
send "exit\r"
}
}remote

  Have fun work remotely 🙂

About Adam M. Erickson

Geek, Dad, Life-Student, Biker & DIY Enthusiast Application Developer Attended Ferris State University Lives in Muskegon, MI
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