深入探索Linux命令行接口

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"《Linux命令行》是一本由William E. Shotts, Jr.编写的书籍，它全面探讨了Linux命令行接口，不仅限于特定的shell程序如bash，而是覆盖了更广泛的命令行工具和实践。这本书旨在帮助读者理解命令行如何工作，能执行哪些任务，以及最佳的操作方法。该书遵循Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License，是LinuxCommand.org项目的一部分，旨在帮助那些使用旧操作系统的人迁移到Linux环境。印刷版可在lulu.com购买。" 在Linux操作系统中，命令行接口（CLI）是一种强大的工具，它允许用户通过文本命令与系统交互，执行各种任务，包括文件管理、系统管理、网络通信等。本书深入浅出地介绍了以下关键知识点： 1. **命令行基础**：讲解了如何启动终端，基本的命令行操作，如导航目录（`cd`）、查看当前目录（`pwd`）、列出目录内容（`ls`）等。 2. **文本编辑器**：介绍Vim和Emacs等常用文本编辑器的使用，这对于编写脚本或修改配置文件至关重要。 3. **文件和目录管理**：涵盖文件的创建、复制、移动、删除等操作，以及权限和所有权的概念。 4. **管道和重定向**：解释如何使用管道（`|`）将一个命令的输出作为另一个命令的输入，以及重定向（`>`和`<`）输入和输出到文件。 5. **正则表达式**：教授如何使用正则表达式进行文本匹配和搜索，这对于数据处理和脚本编程非常有用。 6. **Shell脚本编程**：详述bash shell的基础知识，包括变量、条件语句、循环结构，以及编写自定义脚本的方法。 7. **软件包管理和更新**：介绍如何使用包管理器如apt（Debian/Ubuntu）或yum（CentOS/RHEL）安装、升级和卸载软件。 8. **进程管理**：讲解如何控制进程，如启动、停止、挂起和恢复进程，以及查看系统资源使用情况。 9. **网络命令**：讨论ping、traceroute、ssh、scp等网络相关命令，帮助用户诊断和管理网络连接。 10. **系统和性能监控**：介绍如何使用top、vmstat、iostat等工具监控系统性能和资源使用。本书通过实际案例和练习，让读者能够掌握这些命令行工具的用法，提升在Linux环境中的工作效率。对于初学者和有一定经验的用户来说，都是极好的学习资源。通过阅读本书，不仅可以深化对Linux操作系统的理解，还能培养解决问题和自动化任务的能力。

1 – Introduction

I want to tell you a story.

No, not the story of how, in 1991, Linus Torvalds wrote the first version of the Linux

kernel. You can read that story in lots of Linux books. Nor am I going to tell you the

story of how, some years earlier, Richard Stallman began the GNU Project to create a free

Unix-like operating system. That's an important story too, but most other Linux books

have that one, as well.

No, I want to tell you the story of how you can take back control of your computer.

When I began working with computers as a college student in the late 1970s, there was a

revolution going on. The invention of the microprocessor had made it possible for

ordinary people like you and me to actually own a computer. It's hard for many people

today to imagine what the world was like when only big business and big government ran

all the computers. Let's just say, you couldn't get much done.

Today, the world is very different. Computers are everywhere, from tiny wristwatches to

giant data centers to everything in between. In addition to ubiquitous computers, we also

have a ubiquitous network connecting them together. This has created a wondrous new

age of personal empowerment and creative freedom, but over the last couple of decades

something else has been happening. A single giant corporation has been imposing its

control over most of the world's computers and deciding what you can and cannot do

with them. Fortunately, people from all over the world are doing something about it.

They are fighting to maintain control of their computers by writing their own software.

They are building Linux.

Many people speak of “freedom” with regard to Linux, but I don't think most people

know what this freedom really means. Freedom is the power to decide what your

computer does, and the only way to have this freedom is to know what your computer is

doing. Freedom is a computer that is without secrets, one where everything can be

known if you care enough to find out.

Why Use The Command Line?

Have you ever noticed in the movies when the “super hacker,”— you know, the guy who

can break into the ultra-secure military computer in under thirty seconds—sits down at

Why Use The Command Line?

the computer, he never touches a mouse? It's because movie makers realize that we, as

human beings, instinctively know the only way to really get anything done on a computer

is by typing on a keyboard.

Most computer users today are only familiar with the graphical user interface (GUI) and

have been taught by vendors and pundits that the command line interface (CLI) is a

terrifying thing of the past. This is unfortunate, because a good command line interface is

a marvelously expressive way of communicating with a computer in much the same way

the written word is for human beings. It's been said that “graphical user interfaces make

easy tasks easy, while command line interfaces make difficult tasks possible” and this is

still very true today.

Since Linux is modeled after the Unix family of operating systems, it shares the same

rich heritage of command line tools as Unix. Unix came into prominence during the

early 1980s (although it was first developed a decade earlier), before the widespread

adoption of the graphical user interface and, as a result, developed an extensive command

line interface instead. In fact, one of the strongest reasons early adopters of Linux chose it

over, say, Windows NT was the powerful command line interface which made the

“difficult tasks possible.”

What This Book Is About

This book is a broad overview of “living” on the Linux command line. Unlike some

books that concentrate on just a single program, such as the shell program, bash, this

book will try to convey how to get along with the command line interface in a larger

sense. How does it all work? What can it do? What's the best way to use it?

This is not a book about Linux system administration. While any serious discussion

of the command line will invariably lead to system administration topics, this book only

touches on a few administration issues. It will, however, prepare the reader for

additional study by providing a solid foundation in the use of the command line, an

essential tool for any serious system administration task.

This book is very Linux-centric. Many other books try to broaden their appeal by

including other platforms such as generic Unix and MacOS X. In doing so, they “water

down” their content to feature only general topics. This book, on the other hand, only

covers contemporary Linux distributions. Ninety-five percent of the content is useful for

users of other Unix-like systems, but this book is highly targeted at the modern Linux

command line user.

Who Should Read This Book

This book is for new Linux users who have migrated from other platforms. Most likely

you are a “power user” of some version of Microsoft Windows. Perhaps your boss has

told you to administer a Linux server, or maybe you're just a desktop user who is tired of

1 – Introduction

all the security problems and want to give Linux a try. That's fine. All are welcome

here.

That being said, there is no shortcut to Linux enlightenment. Learning the command line

is challenging and takes real effort. It's not that it's so hard, but rather it's so vast. The

average Linux system has literally thousands of programs you can employ on the

command line. Consider yourself warned; learning the command line is not a casual

endeavor.

On the other hand, learning the Linux command line is extremely rewarding. If you think

you're a “power user” now, just wait. You don't know what real power is— yet. And,

unlike many other computer skills, knowledge of the command line is long lasting. The

skills learned today will still be useful ten years from now. The command line has

survived the test of time.

It is also assumed that you have no programming experience, but not to worry, we'll start

you down that path as well.

What's In This Book

This material is presented in a carefully chosen sequence, much like a tutor sitting next to

you guiding you along. Many authors treat this material in a “systematic” fashion, which

makes sense from a writer’s perspective, but can be very confusing to new users.

Another goal is to acquaint you with the Unix way of thinking, which is different from

the Windows way of thinking. Along the way, we'll go on a few side trips to help you

understand why certain things work the way they do and how they got that way. Linux

is not just a piece of software, it's also a small part of the larger Unix culture, which has

its own language and history. I might throw in a rant or two, as well.

This book is divided into five parts, each covering some aspect of the command line

experience. Besides the first part, which you are reading now, this book contains:

● Part 2 – Learning The Shell starts our exploration of the basic language of the

command line including such things as the structure of commands, file system

navigation, command line editing, and finding help and documentation for

commands.

● Part 3 – Configuration And The Environment covers editing configuration

files that control the computer's operation from the command line.

● Part 4 – Common Tasks And Essential Tools explores many of the ordinary

tasks that are commonly performed from the command line. Unix-like operating

systems, such as Linux, contain many “classic” command line programs that are

used to perform powerful operations on data.

● Part 5 – Writing Shell Scripts introduces shell programming, an admittedly

What's In This Book

rudimentary, but easy to learn, technique for automating many common

computing tasks. By learning shell programming, you will become familiar with

concepts that can be applied to many other programming languages.

How To Read This Book

Start at the beginning of the book and follow it to the end. It isn’t written as a reference

work, it's really more like a story with a beginning, middle, and an end.

Prerequisites

To use this book, all you will need is a working Linux installation. You can get this in

one of two ways:

1. Install Linux on a (not so new) computer. It doesn't matter which distribution

you choose, though most people today start out with either Ubuntu, Fedora, or

OpenSUSE. If in doubt, try Ubuntu first. Installing a modern Linux distribution

can be ridiculously easy or ridiculously difficult depending on your hardware. I

suggest a desktop computer that is a couple of years old and has at least 256

megabytes of RAM and 6 gigabytes of free hard disk space. Avoid laptops and

wireless networks if at all possible, as these are often more difficult to get

working.

2. Use a “Live CD.” One of the cool things you can do with many Linux

distributions is run them directly from a CDROM without installing them at all.

Just go into your BIOS setup and set your computer to “Boot from CDROM,”

insert the live CD, and reboot. Using a live CD is a great way to test a computer

for Linux compatibility prior to installation. The disadvantage of using a live CD

is that it may be very slow compared to having Linux installed on your hard drive.

Both Ubuntu and Fedora (among others) have live CD versions.

Regardless of how you install Linux, you will need to have occasional superuser (i.e.,

administrative) privileges to carry out the lessons in this book.

After you have a working installation, start reading and follow along with your own

computer. Most of the material in this book is “hands on,” so sit down and get typing!

Why I Don't Call It “GNU/Linux”

In some quarters, it's politically correct to call the Linux operating system the

“GNU/Linux operating system.” The problem with “Linux” is that there is no

completely correct way to name it because it was written by many different

1 – Introduction

people in a vast, distributed development effort. Technically speaking, Linux is

the name of the operating system's kernel, nothing more. The kernel is very

important of course, since it makes the operating system go, but it's not enough to

form a complete operating system.

Enter Richard Stallman, the genius-philosopher who founded the Free Software

movement, started the Free Software Foundation, formed the GNU Project, wrote

the first version of the GNU C Compiler (gcc), created the GNU General Public

License (the GPL), etc., etc., etc. He insists that you call it “GNU/Linux” to

properly reflect the contributions of the GNU Project. While the GNU Project

predates the Linux kernel, and the project's contributions are extremely deserving

of recognition, placing them in the name is unfair to everyone else who made

significant contributions. Besides, I think “Linux/GNU” would be more

technically accurate since the kernel boots first and everything else runs on top of

it.

In popular usage, “Linux” refers to the kernel and all the other free and open

source software found in the typical Linux distribution; that is, the entire Linux

ecosystem, not just the GNU components. The operating system marketplace

seems to prefer one-word names such as DOS, Windows, MacOS, Solaris, Irix,

AIX. I have chosen to use the popular format. If, however, you prefer to use

“GNU/Linux” instead, please perform a mental search and replace while reading

this book. I won't mind.

Acknowledgments

I want to thank the following people, who helped make this book possible:

Jenny Watson, Acquisitions Editor at Wiley Publishing who originally suggested that I

write a shell scripting book.

John C. Dvorak, noted columnist and pundit. In an episode of his video podcast, “Cranky

Geeks,” Mr. Dvorak described the process of writing: “Hell. Write 200 words a day and

in a year, you have a novel.” This advice led me to write a page a day until I had a book.

Dmitri Popov wrote an article in Free Software Magazine titled, “Creating a book

template with Writer,” which inspired me to use OpenOffice.org Writer for composing

the text. As it turned out, it worked wonderfully.

Mark Polesky performed an extraordinary review and test of the text.

Jesse Becker, Tomasz Chrzczonowicz, Michael Levin, Spence Miner also tested and

reviewed portions of the text.

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