README
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Command-Line Interface (CLI) Programming
The command-line is a versatile, efficient, and portable interface that has seen continuous, ubiquitous use since the mainframe computing era. To this day, it remains the primary interface for managing server and other production systems, and is regularly used by computer professionals to complete both simple and complex tasks with ease.
The capabilities of command-line systems have evolved over time, but the underlying principles have remained much the same: a command line program accepts program arguments, inherits an environment, and operates on input and output text streams.
The Command Shell
A program that interprets command descriptions and accordingly arranges for programs to run is known as a shell. It is so named because it encapsulates the lower level operating system kernel; the software that directly manages system hardware, process invocation and scheduling, and other critical tasks, but which, unlike a shell, does not any direct user interface.
Shells vary in the syntax they accept and the features they provide, but typically provide at least: command pipelining, stream redirection, conditional control flow, pattern matching, job control, and, for interactive shells, command history.
The Bourne Shell, released by Bell Labs in 1977, was the first Unix shell with excellent programming features; it set the standard in shell syntax and capabilities, and has left a strong legacy of similar shells that are referred to as "Bourne shell compatible" (or "sh compatible" for short, after the shell's command name). The following sections are described in terms of Bourne shell compatible semantics and syntax.
All material is licensed under the Apache License Version 2.0, January 2004.
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