1. Unix was developed in Bell Labs, a research-oriented environment. Users are mainly computer scientist in Bell Labs. All those stuff make unix very elegant, not chatty system.
2. Since every one in Bell Labs can change the system by themselves, which brings a lot of inconsistencies for many tools. A standard was formed in the end: POSIX.
All modern unix-like operating system, including GNU/Linux, BSD derived systems, they are all POSIX compliant.
3. Unix Principals:
1) Focus on one thing: each program or tool focus on one thing, making it easy to maintain, document, efficient.
2) Process Lines of Text not binary. Text is the main content for most unix tool to deal with, making lines of text universal language in Unix world.
3) Use regular expressions. Unix use most of the power of regular expressions. It tries to use 2 kinds of regular expressions: grep(Basic Regular Expressions or BREs per POSIX standard), egrep(Extended Regular Expressions or EREs per POSIX standard)
4) Default to standard I/O.If not providing the specific input/output, unix will read from standard input and output to standard output by default.
5) Elegant and not chatty. Since unix is built for well-educated computer scientists or engineers, it should always assume the user knows a lot, and all solutions it provides is very elegant and not chatty.
6) Reuse existing tools. If there is existing tool to solve a problem, it always use existing ones. If we need another specialized tool, the user need to build the tool from "a general picture", trying to make it be reused in the future.
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