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首页深入掌握Bash shell编程指南(第2版)

深入掌握Bash shell编程指南(第2版)

Bash

Pocket

Reference

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"《Bash Pocket Reference》第二版(2016年)是一本针对Mac OS X、Linux和Unix-like系统用户的实用指南，主要讲解Bashshell的基础知识和高级技巧。作者Arnold Robbins专为那些希望深入理解和操作这些系统的Power Users和Sysadmins编写，旨在提供快速查阅和解决问题的便利。本书覆盖了大量关键主题，包括但不限于： 1. **启动shell**：学习如何正确启动和配置Bash shell，包括各种启动选项。 2. **语法**：详细解析Bash的命令行语法结构，以及如何编写清晰易懂的脚本。 3. **函数和变量**：介绍变量的命名规则、赋值方法以及如何使用条件语句和循环控制结构。 4. **算术表达式**：理解如何在脚本中执行数学运算和逻辑运算。 5. **命令历史**：如何利用命令历史功能进行高效导航和重用。 6. **程序化完成**：掌握自动补全功能，提升输入效率。 7. **作业控制**：学习如何管理和监控后台任务，以及如何中断和调度任务。 8. **Shell选项**：了解并使用各种可定制的Bash选项来优化shell行为。 9. **命令执行**：深入理解命令的执行过程和管道操作。 10. **子进程**：探讨如何创建和交互子进程，提高复杂任务的处理能力。 11. **受限shell**：了解安全模式和限制用户权限的使用场景。 12. **内置命令**：列举并解释Bash内建的常用命令，如`cd`、`echo`等。《Bash Pocket Reference》第二版针对Bash 4.4进行了更新，确保信息的时效性。它不仅适合初学者快速上手，也是经验丰富的用户查找答案和参考的宝贵工具。该书版权属于Arnold Robbins，并由O'Reilly Media出版，提供了在线版本供读者访问。整个指南结构清晰，便于查找，是系统管理员和编程爱好者的必备参考书籍。"

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Class Characters matched

lower

Lowercase characters

Printable characters

punct

Punctuation characters

space

Whitespace characters

upper

Uppercase characters

word [[:word:]] is the same as [[:alnum:]_] (not in POSIX)

xdigit

Hexadecimal digits

Tip

Bash reads scripts one line at a time. It parses each line com‐

pletely before beginning to execute any of the commands on

the line. This has two implications:

• You cannot define an alias and then use it on the same

line.

• You should place commands that affect parsing of the

script on lines by themselves, before the parts of the

script that are affected.

Similar concerns apply to functions; they are parsed all at once,

so you cannot turn on the extglob option inside a function

body expecting it to affect just that function. Thus, in order to

use the extended pattern matching facilities, you should put

this command on a line by itself at the beginning of your script:

shopt -s extglob # enable extended shell patterns

10 | The Bash Shell

Examples

ls new*

List new and new.1

cat ch?

Match ch9 but not ch10

gvim [D-R]*

Match les beginning with D through R

pr !(*.o|core) | lpr

Print non-object and non-core les

NOTE

On modern systems, ranges such as [D-R] are not portable;

the system’s locale may include more than just the upper‐

case letters from D to R in the range. However, see the

globasciiranges shell option for a way to control this.

Brace Expansion

Bash has long supported brace expansion, based on a similar

feature from the C shell. Unlike filename metacharacters, brace

expansion is purely textual; the words created by brace expan‐

sion do not have to match existing files. There are two forms:

pre{X,Y[,Z…]}post

Expands to preXpost, preYpost, and so on.

pre{start..end[..incr]}post

start and end are either integers or single letters. incr is an

integer. The shell expands this construct to the full range

between start and end, increasing by incr if supplied.

The prefix and postfix texts are not required for either form.

For numeric expansion, start or end or both may be prefixed

with one or more leading zeros. The results of expansion are

padded with zeros to the maximum of the widths of start and

end. Bash ignores leading zeros on incr, always treating it as a

decimal value.

Syntax | 11

Brace expansions may be nested, and the results are not sorted.

Brace expansion is performed before other expansions, and the

opening and closing braces must not be quoted for Bash to rec‐

ognize them. Bash skips over command substitutions within

brace expansions. To avoid conflict with parameter expansion,

${ cannot start a brace expansion.

Examples

# Expand textually; no sorting

$ echo hi{DDD,BBB,CCC,AAA}there

hiDDDthere hiBBBthere hiCCCthere hiAAAthere

# Expand, then match ch1, ch2, app1, app2

$ ls {ch,app}?

# Expands to mv info info.old

$ mv info{,.old}

# Simple numeric expansion

$ echo 1 to 10 is {1..10}

1 to 10 is 1 2 3 4 5 6 7 8 9 10

# Numeric expansion with increment

$ echo 1 to 10 by 2 is {1..10..2}

1 to 10 by 2 is 1 3 5 7 9

# Numeric expansion with zero padding

$ echo 1 to 10 with zeros is {01..10}

1 to 10 with zeros is 01 02 03 04 05 06 07 08 09 10

Escape Sequences

Bash recognizes and interprets special escape sequences in three

different contexts:

• The $'…' quoted string

• Arguments to echo -e and printf %b

• Format strings for printf

12 | The Bash Shell

The following table lists common escape sequences (those

accepted in all contexts) as well as the unique escape sequences

for each of the above contexts:

Sequence Availability Value

All ASCII BEL (visual or audible alert)

All Backspace

\c echo -e,

printf %b

Suppress the terminating newline (like

echo -n) and do not print any

following characters

\cX $'…'

Control character X

All Escape

All Formfeed

All Newline

All Carriage return

All Tab

\uHHHH

All Unicode character HHHH

\UHHHHHHHH

All Unicode character HHHHHHHH

All Vertical tab

\xHH

All Hexadecimal value HH

\nnn

$'…', printf

Octal value nnn

\0nnn echo -e,

printf %b

Octal value nnn

\’ $'…'

Single quote

\" $'…'

Double quote

\? $'…'

Question mark

All Backslash

Syntax | 13

Additionally, the shell interprets a slightly overlapping set of

escape sequences in the values of the PS0, PS1, PS2, and PS4

prompt strings. This is discussed in the section “Special Prompt

Strings” on page 46.

Quoting

Quoting disables a character’s special meaning and allows it to

be used literally. The following table displays characters that

have special meaning:

Character Meaning

;

Command separator

Background execution

()

Command grouping

Pipe

< > &

Redirection symbols

* ? [ ] ~ + - @ !

Filename metacharacters

" ' \

Used in quoting other characters

Command substitution

Variable substitution (or command or arithmetic

substitution)

Start a comment that continues to the end of the line

space tab newline

Word separators

14 | The Bash Shell

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深入掌握Bash shell编程指南(第2版)

Bash Pocket Reference, 2nd Edition(2016)

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