One of the simplifying assumptions that is built into this idea is that the input and output to the program are simple streams ( a file, a terminal ). Not surprisingly that makes things a lot less complex so you can focus on the programming.
Since a Raspberry Pi is only $35 or $50 with enough stuff to program it, that is one way to get started. Of course taking an older tossed of PC and installing Linux on it works too (which can often be done for free if there are businesses around)
You can download complete Linux VM images that just work from the net. VirtualBox is free and is installed in 5 minutes. It's hardly frustrating. Certainly less so than getting a RPi up and running, not to mention you end up with an odd, underpowered device secondary to your regular machine.
That's not to say the RPi isn't an interesting, rewarding experience on its own merits -- that's why I got one --, but I wouldn't recommend it to anybody interested primarily in getting a *nix environment for experimentation or programming.
As far as the Windows and Mac comment goes, there is no reason why you couldn't do this on either. In fact Mac OS X supports the same commands as linux. In Windows case, I see no reason why you couldn't do one of two things:
1. The first would be implementing your own linux commands so they work on Windows. You would probably want something like cygwin, a linux vm, or an actual linux box to test this stuff on though.
2. Pick Windows commands instead and implement them instead. It’s the same idea roughly. I haven't used a Windows machine in almost a decade, so I'm not sure what all would be involved, but seems possible that you could get them to work roughly similar.
As far as specific languages go, there’s no reason that almost any language couldn’t be used as long as it can take arguments from the command line.
The point is to copy the commands, you can copy them on any operating system. It just happens that Mac & Linux have them built in while Windows doesn't.
As for which languages, this actually seems like it would be useful for learning any language that has reasonable ways of interacting with IO streams. Off the top of my head:
I think, almost by definition, for a language to have any interest, it must be able to deal with I/O streams. I can't think of a language that wouldn't work (I'd be very interested if somebody knows one and why it wouldn't work).
What the scripting languages give you is simplicity. No need to muss with compilers.
On Windows you can install Linux in a virtual machine, or you can install Cygwin (which is basically an almost complete POSIX system on Windows).
You can use your preferred programming language to implement any of these tools: Ruby, Python, Perl, Scheme, Common Lisp, C, C++ ... The original Unix implementation of these tools was done in C.
Windows doesn't have many of the basic Unix tools, but you can still implement them using your programming language of choice (how great). No, you're not limited to these three languages. I only meant in the article that these three are probably the easier to copy Unix with, for their scripting nature.
For instance, what are your options on Windows or Mac? And are the languages you can do this with limited to Ruby, Python, or Javascript?