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Learn is a Computer-Based Teaching tool that gives basic training in using UNIX and Linux. (Linux is a version of UNIX.)
The UNIX operating system was developed by computer science researchers at Bell Laboratories in the 1970s and became available outside Bell in the 1980s. Within Bell it was used by all sorts of people. This was before the advent of personal computers and some of the users had little or no experience of computers. Mike Lesk and Brian Kernighan created the learn system to explain how to use computers in general and UNIX in particular.
The lessons in learn reflect the state of computing in the late 1970's, in particular the command-line interface that was used in those days. You see a prompt, you type a command, it runs and produces a result, you see another prompt, and so on. These days we all use very powerful desktop or laptop computers. Point and click window-based operating systems such as Microsoft Windows have replaced the old command-line interfaces and interactive screen-based word processors have replaced the very primitive text editors of the 1970's. The learn system became redundant and fell out of use. Later versions of UNIX didn't even include it.
The learn software is not strictly open-source in the conventional sense. The material is copyright AT&T, but a note in the source code gives permission for fairly free use. For the precise conditions, see the file LICENSE or any of the C source files.
Early versions of UNIX needed a fairly expensive computer to run and it was licensed - companies using it had to pay a license fee to use it. Then, personal computers became powerful enough to run UNIX and free versions emerged, notably Linux.
The learn software was originally included in version 7 UNIX which was released in 1978. The software and the lessons were not reworked as UNIX developed and they became increasingly out of date. Later versions of UNIX didn't even include the learn software. The C source code was preserved by the OpenBSD group, but C itself had changed and the learn system no longer even compiled.
In 2002 I applied some simple changes to make learn work again and later released the result on Github, but there was still a chicken and egg problem. Learn is aimed at people who don't know anything about UNIX, but they needed to know enough to build and install learn, and they needed a computer running UNIX to run it on. That was OK if they owned an Apple Mac, but the majority only had a machine running Microsoft Windows. In any case, Linux also now offered a point-and-click windowing interface, so you could use it without knowing anything about the command-line interface.
With the growth of Virtual Private Server (VPS) systems AKA cloud computing, the situation has changed again. A large computer system can now be made up of hundreds or even thousands of low-powered virtual computers. (Virtual meaning that one very powerful computer simulates (pretends to be) many small computers.) Typically these virtual computers exist in some remote data Centre and are used as servers (computers providing some service over a network). The companies that use them rent them by the month or sometimes by the second, controlling them via the Internet. I run my web server on a virtual server rented from Digital Ocean and it costs me $5 per month.
If you build your system out of a few hundred virtual computers, you don't want to pay for a few hundred operating system licences. Being free, Linux has become one of the operating system of choice for cloud computing.
We use cloud servers because they are cheap, and the cheapest way to access them is via a command-line interface rather than a point-and-click windowing system. So we are now back where we were in the late 1970's, controlling a low-powered computer by typing a command, waiting for it to finish and then typing another. Generations of techies who are used to running Microsoft Windows systems via a nice point-and-click interface now have to get their heads around running cloud-based Linux systems via a command-line interface.
Hmm. We used to have a piece of software that helped people do that. It was called "learn". Trouble is, it's not included by default in Linux systems anymore, and in any case, most of the people who could benefit from it only know how to use Microsoft Windows, so ideally learn should run under that.
The solution is, again, virtual computing. From Windows version 10 onwards a laptop running Windows Home can also simulate several virtual computers using the Docker software which offers containerisation. It allows you to package up a complete computer system - operating system and application software - and run the whole thing in a virtual computer within a Microsoft Windows system. So, I can provide a complete ready-made Linux system with the learn software installed that you can run on your Windows machine in a Docker container. Once you've used learn to teach you the basics you can use the same Linux container to experiment and go further.
Now over forty years old, the learn software looks a little clunky compared to modern computer-based training systems. Its power as a teaching tools comes from the fact that it drives the user through a series of exercises using UNIX commands on a real UNIX system.
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