UNIX

Introduction

UNIX is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others.

In the 1990s, Unix and Unix-like systems grew in popularity and became the operating system of choice for over 90% of the world's top 500 fastest supercomputers, as BSD and Linux distributions were developed through collaboration by a worldwide network of programmers. In 2000, Apple released Darwin, also a Unix system, which became the core of the Mac OS X operating system, later renamed macOS.

The UNIX Philosophy

The Unix philosophy is a set of cultural norms and philosophical approaches to development of Unix-like and POSIX compatible systems. It is based on the experience of leading developers of the UNIX operating system. Early Unix developers were important in bringing the concepts of modularity and reusability into software engineering practices. Over time these norms became as important and influential as the technology itself.

The Unix Philosophy emphasizes building simple, compact, clear, modular, and extensible code that can be easily maintained and repurposed by developers other than its creators. The Unix Philosophy favors composability as opposed to monolithic design.

The Unix philosophy is documented by Doug McIlroy in the Bell System Technical Journal from 1978:

  1. Make each program do one thing well. To do a new job, build afresh rather than complicate old programs by adding new "features".
  2. Expect the output of every program to become the input to another, as yet unknown program. Don't clutter output with extraneous information. Avoid stringently columnar or binary input formats. Don't insist on interactive input.
  3. Design and build software, even operating systems, to be tried early, ideally within weeks. Don't hesitate to throw away the clumsy parts and rebuild them.
  4. Use tools in preference to unskilled help to lighten a programming task, even if you have to detour to build the tools and expect to throw some of them out after you've finished using them.

It was later summarized by Peter H. Salus in Basics of the Unix Philosophy:

Unix Influence on Software

Unix has had a massive influence on how operating systems and software tools are designed. Notably, two popular operating systems have come from UNIX and its design philosophies:

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