经典Shell脚本编程入门指南

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"ClassicShellScripting-English - 一本适合初学者的基础shell脚本编写书籍" 在信息技术领域，Shell脚本是一种强大的工具，特别是在系统管理和自动化任务执行方面。本书"Classic Shell Scripting"由Arnold Robbins和Nelson H.F. Beebe共同撰写，旨在帮助初学者理解和掌握Shell脚本的基本概念和技巧。这本书对于那些刚刚接触或希望深化对Shell编程理解的人来说，是一份宝贵的资源。 Shell脚本是基于Unix/Linux操作系统中的命令行接口，它允许用户通过编写一系列命令来执行自动化任务。通过学习Shell脚本，你可以创建自己的程序来处理日常的系统管理任务，如文件操作、系统监控、数据处理等。本书的内容可能涵盖以下关键知识点： 1. **Shell介绍**：首先，书会介绍什么是Shell，它的功能以及不同类型的Shell，如Bash（Bourne-Again SHell）、KSH（Korn Shell）和C Shell等。 2. **基本语法**：讲解如何创建和运行脚本，包括变量的声明与使用、条件语句（if-else）、循环结构（for, while）、函数定义等。 3. **命令行参数和I/O重定向**：如何处理命令行传递的参数，以及如何重定向输入和输出，这是实现脚本交互性和非交互性功能的关键。 4. **正则表达式和模式匹配**：正则表达式是文本处理的强大工具，书会教读者如何在脚本中使用它们进行数据匹配和提取。 5. **文件和目录操作**：如何在脚本中创建、删除、移动和修改文件及目录，这对于系统维护至关重要。 6. **错误处理和调试**：介绍如何捕获和处理脚本运行时的错误，以及如何调试脚本以找出问题。 7. **脚本案例分析**：书中可能会包含实际的脚本示例，让读者了解在实际场景中如何应用所学知识。 8. **高级特性**：更深入的主题，如进程控制、信号处理、函数库的使用等，有助于提升脚本的复杂性和效率。 9. **Shell脚本的最佳实践**：指导如何编写可读性强、易于维护的脚本，遵循良好的编程习惯。通过阅读"Classic Shell Scripting"，读者不仅可以学习到Shell脚本的基础知识，还能了解到如何编写高效且可靠的脚本。这本书适合个人自学，也适合作为教学材料，帮助初学者快速上手Shell编程，并为他们未来在系统管理、自动化和脚本开发领域打下坚实的基础。

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.

This is the Title of the Book, eMatter Edition

xvi

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.

This is the Title of the Book, eMatter Edition

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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