Saturday, November 12, 2016

Automating small tasks

Doughnut Script
In life we do small tasks over and over, thinking, this is too small to automate. After all, it may take 10 minutes to automate it, and it only takes 10 seconds to do it.

Recently, I have been doing some testing on systemd, software for Linux. And I have been logging into the a DUT (Device Under Test) on a console cable. Using the console allows one to bring up and down the network interfaces, and still remain connected to the DUT.

It didn't take long to log in via the console, start screen, log into the DUT, then su to root, about 10 seconds total. Then, type the commands to run the test, log out, and quit screen.

I have been doing this for a couple of months, when I thought, hey, maybe I should sit down and automate this. Not because I was tired of logging in manually, but because I wanted to write a larger regression script for bugs I had raised against systemd.

Creating a doughnut script

So I spent 10 minutes writing and debugging a console login doughnut script*. Then I copied the script, and started adding my regression lines (in the middle). Since this is systemd, the regression test doesn't ever seem to pass, but at least I can quickly determine what is broken.

Because I am never sure the state of the DUT, the serial login script does prompt detection to determine the next step in logging in. It does this with:
# set user prompt
*/.*: /
# detect prompt
+$prompt1=\n.*(\$ |login:|word:)

It determines prompts they same way you would with your eyes, presses <return> and "sees" what is returned. If it returns a prompt ($), then we are already logged in. If it asks for a login, then the script logs in.

Code Reuse

By setting the actual serial login in an include file, it is easily added to any script going forward. Suddenly the 10 minute time investment is paying off. But save yourself 10 minutes, and get the scripts from my github examples directory (look for serial_login.elt,, and

I find myself using the serial console script all the time, and it takes less than a second to log in. Automating little repetitive tasks can make life easier and faster, truly automation for the rest of us.

* a doughnut script is a script that sets things up, pauses (with *INTERACT), then breaks things down and cleans up.
** doughnut image by Evan-Amos - Own work, Public Domain, Link

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