深入学习高级shell编程：经典教程

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"《高级shell编程指南》是一本深入探索shell脚本艺术的权威著作，由Mendel Cooper撰写，电子邮箱地址为<the_grendel.abs@gmail.com>。该指南旨在为读者提供一个从零基础到中级/高级水平的系统教学，即使对编程一无所知的人也能快速上手。书中融入了大量的Unix®智慧和经验，不仅作为教材供个人学习，还是shell编程技术的宝典，强调通过实践写作来真正掌握脚本。作者Mc在2014年3月10日进行了第10次修订，将此作品置于公共领域，确保了知识的无版权共享。此书特别适合用作课堂上的编程入门教程，通过精心设计的大量练习和详尽注释的实例，鼓励读者积极参与，通过编写实际的脚本来提升技能。章节内容广泛，包括： 1. 第一章 - Shell编程基础，探讨shell语言的核心概念，如变量、控制结构、函数等，并介绍如何创建和执行简单的脚本。 2. 开始篇 - 从基础操作开始，逐步引导读者了解如何使用shell命令行工具，以及如何组织和管理脚本结构。随着读者深入学习，他们将掌握诸如参数处理、错误处理、脚本调试、文件I/O操作、正则表达式等高级主题，这些都是构建高效和可维护shell脚本的关键要素。本书不仅提供了理论知识，还为那些希望在实际环境中应用shell脚本的专业人士提供了实用的工具和策略。《高级shell编程指南》是一部不可或缺的参考资料，无论是初学者还是经验丰富的shell开发者，都能从中获得宝贵的知识和实践指导，助力他们在shell编程的道路上不断进步。"

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. In fact, more recent releases

of Bash do not permit this usage. An underscore _ works, though.

A colon can serve as a placeholder in an otherwise empty function.

not_empty ()

{

} # Contains a : (null command), and so is not empty.

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 L). 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

Advanced Bash-Scripting Guide

Chapter 3. Special Characters 12

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