Design Goals

 

One of the design goals of the UNIX developers was simplicity: to leave complexity to the application developers. This has continued until today, where the development of the Linux kernel is still funneled through a single person. (Many people help kernel development, but it is all overseen by a single person.)

One of the results of this simplicity is a relatively good level of security. Another is that it is relatively easy to construct larger programs by piecing together smaller programs. A great deal of this relative ease comes from the ideas that:

• by default programs read from STDIN,
• by default, normal output is written to STDOUT,
• by default, normal errors are written to STDERR,
• that the shell can redirect STDIN, STDOUT, and STDERR.

These ideas, coupled with the idea that programs should do one task only, and do it well; is something which pervades much of modern computer science. It allows the development of ``libraries'' of routines for a person to use to accomplish some task. (The shell programmer, and in some cases the user, uses UNIX utilities the way a programmer would use library functions.) In the case of the average UNIX user, the library tends to be the contents of the /bin, /usr/bin and /usr/local/bin directories.