Linux System Administration: A User's Guide
Now that you have had your introduction to scripting with expect, I am going to make the process almost impossibly easy. Rather than manually creating an expect script, how about letting a program do that for you, too? When you install expect, you will also install a cool little program called autoexpect. Simply put, autoexpect will watch whatever you are doing in an interactive session and create the expect script for you. Here is the format of the command:
autoexpect -f script_outputfile command_string
For instance, let's imagine that we wanted to log in to a remote system that is behind a firewall, essentially a two-step login process. After we log in to the firewall, we then execute a login (telnet, ssh, etc.) to yet another system on the internal network, then execute a standard menu program. We would like to have this whole process of logging in twice and starting this menu automated for us. From the command prompt, we would then type this command:
autoexpect -f superlogin.script telnet firewall.mycompany.comWhen you have finished your login, you can exit the menu and log out. autoexpect will have captured the entire session for you. Before running your new script, you will probably want to do some editing to clean things up a bit. autoexpect's output is probably a little wordier than you want. Furthermore, you will want to remove the lines that exit from your menu and log out, but the basics of the script and all the prompts are captured there for you. Make the script executable and you are almost done.
There is still one other thing you will want to add. At the end of your new expect script, add this command: interact
This tells expect to return control to you after it has done its work. Without it, expect closes the spawned process, and all you've managed to do is log in and log out very quickly.
In no way do I intend this to be the definitive reference on expect. I do, however, hope that this little introduction (indeed, this whole chapter) will serve to whet your appetite and inspire your imagination to explore other ways of developing constructive laziness. After all, we all have other work to do.
What's all this on your screen about a magic cloak?
Free DevOps eBooks, Videos, and more!
Regardless of where you are in your DevOps process, Linux Journal can help!
We offer here the DEFINITIVE DevOps for Dummies, a mobile Application Development Primer, and advice & help from the expert sources like:
- Linux Journal
- Android Candy: Google Keep
- Readers' Choice Awards 2014
- Handling the workloads of the Future
- How Can We Get Business to Care about Freedom, Openness and Interoperability?
- Days Between Dates?
- diff -u: What's New in Kernel Development
- Synchronize Your Life with ownCloud
- Computing without a Computer
- Non-Linux FOSS: Don't Type All Those Words!