经典Shell编程入门指南

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经典Shell编程是一本由Arnold Robbins和Nelson H.F. Beebe合著的专业书籍，专为初学者设计，尽管其英文版为主，但凭借其深入浅出的讲解和实用性，使得它成为学习Shell编程的理想入门教材。该书版权属于2005年的O'Reilly Media，享有所有权利，适用于教育、商业或销售推广用途，电子版也在其网站Safari.O'Reilly.com上提供。本书的编辑团队包括Tatiana Apandi和Allison Randal，他们的专业指导确保了内容的质量。生产编辑Adam Witwer的细致工作确保了书籍制作的流畅性，而Cover Designer Emma Colby和Interior Designer David Futato则负责了吸引人的封面设计和内部版面布局。《经典Shell Scripting》在2005年首次出版，标志着第一版的诞生。书中包含了一系列精心编排的知识点，如Nutshell Handbook、Nutshell Handbook logo、O'Reilly logo等，都是O'Reilly Media的注册商标。此外，书中还使用了一些制造商和卖家使用的特定设计标志，如非洲龟图案，这些都与O'Reilly的品牌形象紧密相连。内容涵盖的核心知识点包括但不限于： 1. Shell基础知识：介绍Shell语言的基本概念，如bash shell（最常用的Unix/Linux shell），shell的工作原理，以及命令行操作基础。 2. 变量与命令：讲解如何声明和使用变量，如何执行基本的文件操作，如复制、移动、删除以及查找文件。 3. 流程控制：介绍条件语句（if-else）、循环（for、while）和函数的使用，帮助读者理解如何组织代码逻辑。 4. 管道和进程管理：通过实例演示如何利用管道（pipe）连接多个命令，以及如何使用子进程（subprocesses）进行更复杂的任务处理。 5. 脚本编写技巧：探讨如何编写可读性强、可维护的Shell脚本，包括变量替换、命令替换、通配符的使用等高级特性。 6. 错误处理与调试：提供如何识别和处理Shell脚本中的错误，以及如何使用调试工具进行问题排查的方法。 7. 环境配置与系统管理：涉及环境变量、路径设置、用户权限以及如何利用Shell脚本进行系统监控和自动化任务。《经典Shell Scripting》作为一本经典教材，不仅适合初次接触Shell的新手，也为有经验的开发者提供了深入理解和实践的机会。通过阅读这本书，读者能够建立起坚实的Shell编程基础，并逐步提升自己的技能。无论是为了日常运维，还是进一步开发自动化工具，这都是一本不可或缺的参考书籍。

This is the Title of the Book, eMatter Edition

xiv

Preface

program, we tell you which options are the most useful. In fact, we typically do

not cover all the options that individual programs have, leaving that task to the

program’s manual page, or to other reference books, such as Unix in a Nutshell

(O’Reilly) and Linux in a Nutshell (O’Reilly).

By the time you’ve finished this book, you should not only understand the Unix

toolset, but also have internalized the Unix mindset and the Software Tools

philosophy.

What You Should Already Know

You should already know the following things:

• How to log in to your Unix system

• How to run programs at the command line

• How to make simple pipelines of commands and use simple I/O redirectors,

such as

and

• How to put jobs in the background with

• How to create and edit files

• How to make scripts executable, using

chmod

Furthermore, if you’re trying to work the examples here by typing commands at your

terminal (or, more likely, terminal emulator) we recommend the use of a POSIX-

compliant shell such as a recent version of

ksh93

, or the current version of

bash

.In

particular,

/bin/sh

on commercial Unix systems may not be fully POSIX-compliant.

Chapter 14 provides Internet download URLs for

ksh93

bash

, and

zsh

Chapter Summary

We recommend reading the book in order, as each chapter builds upon the concepts

and material covered in the chapters preceding it. Here is a chapter-by-chapter sum-

mary:

Chapter 1, Background

Here we provide a brief history of Unix. In particular, the computing environ-

ment at Bell Labs where Unix was developed motivated much of the Software

Tools philosophy. This chapter also presents the principles for good Software

Tools that are then expanded upon throughout the rest of the book.

Chapter 2, Getting Started

This chapter starts off the discussion. It begins by describing compiled lan-

guages and scripting languages, and the tradeoffs between them. Then it moves

on, covering the very basics of shell scripting with two simple but useful shell

scripts. The coverage includes commands, options, arguments, shell variables,

This is the Title of the Book, eMatter Edition

Preface

output with

echo

and

printf

, basic I/O redirection, command searching, access-

ing arguments from within a script, and execution tracing. It closes with a look

at internationalization and localization; issues that are increasingly important in

today’s “global village.”

Chapter 3, Searching and Substitutions

Here we introduce text searching (or “matching”) with regular expressions. We

also cover making changes and extracting text. These are fundamental opera-

tions that form the basis of much shell scripting.

Chapter 4, Text Processing Tools

In this chapter we describe a number of the text processing software tools that

are used over and over again when shell scripting. Two of the most important

tools presented here are

sort

and

uniq

, which serve as powerful ways to orga-

nize and reduce data. This chapter also looks at reformatting paragraphs, count-

ing text units, printing files, and retrieving the first or last lines of a file.

Chapter 5, Pipelines Can Do Amazing Things

This chapter shows several small scripts that demonstrate combining simple

Unix utilities to make more powerful, and importantly, more flexible tools. This

chapter is largely a cookbook of problem statements and solutions, whose com-

mon theme is that all the solutions are composed of linear pipelines.

Chapter 6, Variables, Making Decisions, and Repeating Actions

This is the first of two chapters that cover the rest of the essentials of the shell

language. This chapter looks at shell variables and arithmetic, the important

concept of an exit status, and how decision making and loops are done in the

shell. It rounds off with a discussion of shell functions.

Chapter 7, Input and Output, Files, and Command Evaluation

This chapter completes the description of the shell, focusing on input/output,

the various substitutions that the shell performs, quoting, command-line evalua-

tion order, and shell built-in commands.

Chapter 8, Production Scripts

Here we demonstrate combinations of Unix tools to carry out more complex

text processing jobs. The programs in this chapter are larger than those in

Chapter 5, but they are still short enough to digest in a few minutes. Yet they

accomplish tasks that are quite hard to do in conventional programming lan-

guages such as C, C++, or Java™.

Chapter 9, Enough awk to Be Dangerous

This chapter describes the essentials of the

awk language. awk is a powerful lan-

guage in its own right. However, simple, and sometimes, not so simple,

awk

pro-

grams can be used with other programs in the software toolbox for easy data

extraction, manipulation, and formatting.

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Preface

Chapter 10, Working with Files

This chapter introduces the primary tools for working with files. It covers listing

files, making temporary files, and the all-important

find

command for finding

files that meet specific criteria. It looks at two important commands for dealing

with disk space utilization, and then discusses different programs for comparing

files.

Chapter 11, Extended Example: Merging User Databases

Here we tie things together by solving an interesting and moderately challenging

task.

Chapter 12, Spellchecking

This chapter uses the problem of doing spellchecking to show how it can be

solved in different ways. It presents the original Unix shell script pipeline, as well

as two small scripts to make the freely available

ispell

and

aspell

commands

more usable for batch spellchecking. It closes off with a reasonably sized yet

powerful spellchecking program written in

awk

, which nicely demonstrates the

elegance of that language.

Chapter 13, Processes

This chapter moves out of the realm of text processing and into the realm of job

and system management. There are a small number of essential utilities for man-

aging processes. In addition, this chapter covers the

sleep

command, which is

useful in scripts for waiting for something to happen, as well as other standard

tools for delayed or fixed-time-of-day command processing. Importantly, the

chapter also covers the

trap

command, which gives shell scripts control over

Unix signals.

Chapter 14, Shell Portability Issues and Extensions

Here we describe some of the more useful extensions available in both ksh and

bash

that aren’t in POSIX. In many cases, you can safely use these extensions in

your scripts. The chapter also looks at a number of “gotchas” waiting to trap the

unwary shell script author. It covers issues involved when writing scripts, and

possible implementation variances. Furthermore, it covers download and build

information for

ksh

and

bash

. It finishes up by discussing shell initialization and

termination, which differ among different shell implementations.

Chapter 15, Secure Shell Scripts: Getting Started

In this chapter we provide a cursory introduction to shell scripting security

issues.

Appendix A, Writing Manual Pages

This chapter describes how to write a manual page. This necessary skill is usu-

ally neglected in typical Unix books.

Appendix B, Files and Filesystems

Here we describe the Unix byte-stream filesystem model, contrasting it with

more complex historical filesystems and explaining why this simplicity is a

virtue.

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Preface

xvii

Appendix C, Important Unix Commands

This chapter provides several lists of Unix commands. We recommend that you

learn these commands and what they do to improve your skills as a Unix developer.

Bibliography

Here we list further sources of information about shell scripting with Unix.

Glossary

The Glossary provides definitions for the important terms and concepts intro-

duced in this book.

Conventions Used in This Book

We leave it as understood that, when you enter a shell command, you press Enter at

the end. Enter is labeled Return on some keyboards.

Characters called Ctrl-X, where X is any letter, are entered by holding down the Ctrl

(or Ctl, or Control) key and then pressing that letter. Although we give the letter in

uppercase, you can press the letter without the Shift key.

Other special characters are newline (which is the same as Ctrl-J), Backspace (the

same as Ctrl-H), Esc, Tab, and Del (sometimes labeled Delete or Rubout).

This book uses the following font conventions:

Italic

Italic is used in the text for emphasis, to highlight special terms the first time

they are defined, for electronic mail addresses and Internet URLs, and in man-

ual page citations. It is also used when discussing dummy parameters that

should be replaced with an actual value, and to provide commentary in

examples.

Constant Width

This is used when discussing Unix filenames, external and built-in commands,

and command options. It is also used for variable names and shell keywords,

options, and functions; for filename suffixes; and in examples to show the con-

tents of files or the output from commands, as well as for command lines or

sample input when they are within regular text. In short, anything related to

computer usage is in this font.

Constant Width Bold

This is used in the text to distinguish regular expressions and shell wildcard pat-

terns from the text to be matched. It is also used in examples to show interaction

between the user and the shell; any text the user types in is shown in

Constant

Width Bold

. For example:

$ pwd User typed this

/home/tolstoy/novels/w+p System printed this

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