Linux® Desk Reference, Second Edition

Introduction

The concept of a standard input and a standard output is one of the most useful features of UNIX-like operating systems. The idea is that every program, no matter how diverse, should be reading input and generating output in a uniform, clearly understood way. Once you have that, it makes it much easier for programs to talk to one another directly. It is also possible to write generic programs that bridge the input and output of any two programs, which is an amazingly handy ability to have.

To put it another way, for the most part, standard input and standard output are nothing more than the keyboard and the monitor, respectively. But if you want to, you can redirect the output that would have gone to your monitor to somewhere more ...