I thought it was worth mentioning this collaborative book on Data Science, which is gradually taking shape on Wikibooks. From time to time I have a look and new sections are completed with a very accessible language:

Data Science: An Introduction – Wikibooks, open books for an open world.

Grep a string-digit-string pattern where the numerical value must have more than one digit and output it to a text file:

A very good introductory video from BlazeMeter, a performance & load testing cloud platform. I have been involved in some load testing for a multiple frond ends web application and I needed to use a free tool. Jmeter was recommended to me by a Java programmer I know at work and it turned out to be an excellent product. Although many people think its interface is not particularly user friendly, once you learn the basics and you are familiarised with the concept of Thread Group, Timer, Controller, Listener, etc, it is a great help in your testing. Furthermore, you can automatically record scripts either via HTTP Test Script Recorder option or by exporting the .jmx file created with the chrome plugin 

Jmeter home page and various resources to get started:

https://jmeter.apache.org/

https://jmeter.apache.org/usermanual/index.html

http://blazemeter.com/jmeter

http://jmeter-plugins.org/

The video itself (finally!):