深入学习Linux shell编程指南：Advanced Bash Scripting

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"Advanced Bash Scripts Guide 是一本深入探讨Linux shell编程艺术的手册，由 Mendel Cooper 编写，电子书的最新修订版发布于2011年8月30日，被称为 'VORTEXBERRY' 版本。这本书旨在为初学者提供基础知识，但其内容迅速提升到中级至高级水平，同时融入丰富的UNIX®技巧和知识。作者鼓励读者通过编写实际脚本来学习，认为这是掌握shell编程技巧的关键。该手册涵盖了广泛的范围，不假设读者有编程背景。它既是教材，自学者的指南，也是关于shell编程技术的参考书。书中包括详细的章节，如第1章介绍Shell编程基础，让读者了解脚本语言的基本概念；第2章则从一个简单的 'SHA-BANG' 开始，引导读者如何启动脚本，以及一系列初步的练习来帮助入门。作者强调了实践的重要性，提供了大量的练习和带有详尽注释的示例，让读者在互动中学习和成长。这本书适合作为课堂上教授编程理念的通用入门教程，也适合个人自我学习者深入研究和提升shell编程技能。此外，书中还包含了一个目录，列出了后续章节，如章节2.1介绍了如何调用脚本，以及预先安排的习题，帮助读者逐步掌握脚本的编写、执行和调试。Advanced Bash Scripts Guide 是一个系统且实用的学习资源，对于希望提升Linux系统管理能力的读者来说，是一本不可或缺的参考资料。"

bash$ cp /home/bozo/current_work/junk/* .

Copy all the "junk" files to $PWD.

"dot" character match. When matching characters, as part of a regular expression, a "dot" matches a

single character.

partial quoting [double quote]. "STRING" preserves (from interpretation) most of the special

characters within STRING. See Chapter 5.

full quoting [single quote]. 'STRING' preserves all special characters within STRING. This is a

stronger form of quoting than "STRING". See Chapter 5.

comma operator. The comma operator [16] links together a series of arithmetic operations. All are

evaluated, but only the last one is returned.

let "t2 = ((a = 9, 15 / 3))"

# Set "a = 9" and "t2 = 15 / 3"

The comma operator can also concatenate strings.

for file in /{,usr/}bin/*calc

# ^ Find all executable files ending in "calc"

#+ in /bin and /usr/bin directories.

if [ -x "$file" ]

then

echo $file

done

# /bin/ipcalc

# /usr/bin/kcalc

# /usr/bin/oidcalc

# /usr/bin/oocalc

# Thank you, Rory Winston, for pointing this out.

,, ,

Lowercase conversion in parameter substitution (added in version 4 of Bash).

escape [backslash]. A quoting mechanism for single characters.

\X escapes the character X. This has the effect of "quoting" X, equivalent to 'X'. The \ may be used to

quote " and ', so they are expressed literally.

See Chapter 5 for an in-depth explanation of escaped characters.

Filename path separator [forward slash]. Separates the components of a filename (as in

/home/bozo/projects/Makefile).

This is also the division arithmetic operator.

command substitution. The `command` construct makes available the output of command for

assignment to a variable. This is also known as backquotes or backticks.

Advanced Bash-Scripting Guide

Chapter 3. Special Characters 10

In combination with the >> redirection operator, has no effect on a pre-existing target file (: >>

target_file). If the file did not previously exist, creates it.

This applies to regular files, not pipes, symlinks, and certain special files.

May be used to begin a comment line, although this is not recommended. Using # for a comment

turns off error checking for the remainder of that line, so almost anything may appear in a comment.

However, this is not the case with :.

: This is a comment that generates an error, ( if [ $x -eq 3] ).

The ":" serves as a field separator, in /etc/passwd, and in the $PATH variable.

bash$ echo $PATH

/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:/sbin:/usr/sbin:/usr/games

A colon is acceptable as a function name.

:()

{

echo "The name of this function is "$FUNCNAME"

# Why use a colon as a function name?

# It's a way of obfuscating your code.

}

# The name of this function is :

This is not portable behavior, and therefore not a recommended practice.

reverse (or negate) the sense of a test or exit status [bang]. The ! operator inverts the exit status of

the command to which it is applied (see Example 6-2). It also inverts the meaning of a test operator.

This can, for example, change the sense of equal ( = ) to not-equal ( != ). The ! operator is a Bash

keyword.

In a different context, the ! also appears in indirect variable references.

In yet another context, from the command line, the ! invokes the Bash history mechanism (see

Appendix K). Note that within a script, the history mechanism is disabled.

wild card [asterisk]. The * character serves as a "wild card" for filename expansion in globbing. By

itself, it matches every filename in a given directory.

bash$ echo *

abs-book.sgml add-drive.sh agram.sh alias.sh

The * also represents any number (or zero) characters in a regular expression.

arithmetic operator. In the context of arithmetic operations, the * denotes multiplication.

** A double asterisk can represent the exponentiation operator or extended file-match globbing.

test operator. Within certain expressions, the ? indicates a test for a condition.

Advanced Bash-Scripting Guide

Chapter 3. Special Characters 12

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