What are UNIX® and Unix?

"You need Unix-level performance and reliability. You don't have a Unix-level budget."
— Microsoft advertisement (2003)

Unix is one of the oldest operating systems, originally coded in assembly in 1969 by Dennis Ritchie (right) and Ken Thompson (left) at Bell Labs (pictured below).

By Unknown author — http://catb.org/~esr/jargon/html/U/Unix.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=31308

In 1972, Unix was coded again in C (its native language) for portability. Unix is the most portable and reliable OS.

By the way, UNIX® is not the same as Unix. UNIX® (in upper case letters and often presented with the copyright symbol) is a trademark while Unix (in proper case, proper name) is a philosophy and an IEEE standard — Portable Operating System Interface (POSIX). The open standard (as well as the trademark) is currently owned and managed by The Open Group.

The current version is V7, which is "aligned with the Single UNIX Specification Version 4, 2018 Edition" (The Open Group, 08/2022). The latter unites specifications, product, trade mark and technology under a single mark (name) rather than having entities within UNIX® (The Open Group, 08/2022, published in 2020).

Several vendors have registered versions of UNIX®. They are Tru64 Unix, IBM AIX, UnixWare, IRIX and Sun Solaris.

There are also several clones such Linux. This means that these are not UNIX®. They UNIX® clones, but nonetheless they are considered Unix. If you are confused, you are not alone.

About 90% of the internet relies on a variation of Unix (normally either Linux or BSD), with Apache Software Foundation (ASF) or related technology.

If you are interested in learning Unix as well as its clones or other derivatives, you should learn how to use, at least, one shell.

Installing Unix (or Unix Clones):

Unfortunately, I have no experience installing or using Tru64 Unix, IBM AIX, UnixWare, IRIX or Sun Solaris.

I have experience installing BSD and Linux though. In the latter case, in most cases, installing the OS is as simple as following the instructions from the installer. Some are more technical where you need to know the hardware in detail and select the proper packages.

Shells

Because there many distros in the market (mostly based on a parent distro — for example, Linux Mint based on Ubuntu, which is based on Debian — learning Linux is not necessarily learning how to use the GUI installed in the distro of your choice. Learning Linux is learning how to operate the command language interpreter or shell. Just like the number of distros, there are several shells available for UNIX® and Unix-like OSs.

Bourne Shell (sh) was developed by Stephen Bourne for Bell Labs in 1979 for Version 7 Unix. The prompt is $ in user mode (user@foobar:~$) and # as root using sudo -i (root@foobar:~#).
- Bourne Again Shell (bash) was developed by Brian Fox for the GNU Project in 1989 as a replacement of the 1979 Bourne Shell. It "incorporates useful features from the Korn Shell (ksh) and the C Shell (csh)" (GNU Project, 09/2020). Bash is the most used and most commonly pre-installed in many Linux distributions. This is the shell that I have used most and therefore I am most comfortable with.
- KornShell (ksh) was developed by David Korn for Bell Labs in 1983. It is backward compatible with bash and partially compatible with C shell.
- Almquist Shell (ash) was developed by Kenneth Almquist in 1989 as a replacement for the Bourne Shell in System V4 (BSD).
  - Debian Almquist Shell (dash) is the Debian version of ash developed by Herbert Xu in 1997. dash became the default shell in Debian GNU/Linux and Debian-based distributions like Ubuntu for boot sequence.
C shell (csh) was developed by Bill Joy in 1978 for 2BSD. The prompt is % in user mode.
- TENEX/TOPS C shell (tcsh, pronounced tish) was developed by Ken Greer at Carnegie Mellon University in 1975 and merged tcsh into csh in 1981. Mike Ellis at Fairchild A.I. Labs expanded tcsh with command competition in 1983. Other key developers include Paul Placeway and Christos Zoulas. It is backward compatible with csh.
- Z shell (zsh) was written by Paul Falstad in 1990 while studying at Princeton University. It is named after then-Princeton professor Zhong Shao. In 2019, Zsh became the default shell in macOS.

Unix Emulators:

Cygwin is an open source "Linux-like environment for Windows [4.x and up]" (emulator) originally developed by Cygnus Solutions and then acquired by Red Hat.

Similar to other Unix distributions regardless of OS or vendor, Cygwin has its own package manager — apt-cyg, which does not come installed by default. You would need to run the following commands to get the package from the specific website (wget) as shown below.

              
              wget https://raw.githubusercontent.com/transcode-open/apt-cyg/master/apt-cyg

Then you need to change the mode (chmod) of apt-cyg package to executable (+x).

              
              chmod +x apt-cyg

As the last step, you need to move (mv) the apt-cyg package to /usr/local/bin so it can be accessible — included in the path system variable.

              
              mv apt-cyg /usr/local/bin

Now that apt-cyg has been installed, made into an executable and made accessible in the path system variable, you can use it as any other apt package manager similar to apt-get as in Debian and its derivatives.

              
              apt-cyg install gcc-core  # compiler collection from GNU
              apt-cyg install git       # version control system
              apt-cyg install lynx      # text-only web browser
              apt-cyg install nano      # text editor
              apt-cyg install nasm      # assembly language
              apt-cyg install pip       # package installer for Python
              apt-cyg install python3   # language we all must to learn
              apt-cyg install sqlite3   # relational database
              apt-cyg install tidy      # utility to clean up HTML code

By User:Cljk — Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=186257

Git for Windows offers a limited open source Bash emulator for Windows in order to access the Git version control system based on the MinGW-w64 (MINGW64) project. This emulator is often the choice of open source developers using Windows. As of 2018, GitHub including the Octocat (its mascot) became part of Microsoft.

I have not found a package manager for MINGW64. I guess installing apt-cyg, but I have not tried it. As a purist, I would not do it.
Termux< is an open source emulator and Linux environment for Android with its own package manager (pkg) Similar to apt-get (Linux), brew (macOS, also used in Linux) and other package managers, you can update the list of available packages in the pkg repository and upgrade the packages currently installed in the Termux instance (guest) running on Android (host). I would recommend doing this before installing any new package and to make sure that your packages are up-to-date.
```
          
          pkg update &&
          pkg upgrade
        
```
The latter runs two commands in order — one after another using the && (and) operator.

You can also install packages in the Termux instance using pkg calling the correct package name.
```
          
          pkg install [package_name]
        
```