深入学习Linux Shell编程教程

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"《高级Bash脚本指南》(AdvancedBash-ScriptingGuide)是一本深入探讨shell脚本艺术的实用手册，由Mendel Cooper编写，邮箱地址为<the_grendel.abs@gmail.com>。该书适用于Linux操作系统下的shell编程新手，但随着内容的推进，它将引导读者快速达到中级到高级的水平。作者在书中巧妙地融入了Unix®的智慧和传统，使学习过程充满启发。这本书的特点在于，它不仅是入门教程，也是一本自学教材和关于shell脚本技术的参考资源。作者鼓励读者积极参与，通过实践来真正掌握脚本编写，强调“唯一能真正学会编程的方式就是编写脚本”。书中包含丰富的练习和详尽注释的例子，适合用作课堂上的编程概念入门课程。第一章“Shell编程！”是整个学习旅程的起点，介绍了shell编程的基础概念和原则。从第一章的章节标题和描述来看，读者可以期待在这一章学习如何入门shell编程，了解基本语法和环境设置。第二章“以一个Sha-Bang开始”则可能涵盖了启动shell脚本的基本步骤、命令行环境的介绍以及首个脚本示例的展示。这个章节可能是对新接触者来说至关重要的一章，因为它奠定了后续章节深入学习的基础。《高级Bash脚本指南》是一本实用且富有深度的资源，无论是初学者还是有一定基础的shell用户，都能从中收获丰富的知识和技能，进一步提升自己的Linux系统管理能力。通过跟随作者的指导，读者不仅能掌握shell脚本，还能培养出解决问题和自动化任务的高效技能。"

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 [15] 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

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 ":" also 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

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 J). 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.

In a double-parentheses construct, the ? can serve as an element of a C-style trinary operator, ?:.

(( var0 = var1<98?9:21 ))

# ^ ^

# if [ "$var1" -lt 98 ]

# then

# var0=9

# else

# var0=21

# fi

In a parameter substitution expression, the ? tests whether a variable has been set.

wild card. The ? character serves as a single-character "wild card" for filename expansion in

globbing, as well as representing one character in an extended regular expression.

Advanced Bash-Scripting Guide

Chapter 3. Special Characters 12

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