Unix Shell编程指南：提升操作系统效率

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"Unix Shell编程教程" 《Unix Shell编程》第三版是Stephen Ochan撰写的一本教程，由Sams Publishing出版，发布于2003年2月27日，共456页，旨在帮助Unix和Linux用户充分利用其操作系统，提高工作效率。这本书向读者展示了如何通过掌握Shell的力量来控制他们的系统，高效地工作，并解决常见的问题。本书主要涵盖了三种常用的Unix Shell：Kornshell、Bourne shell（如bash）及其变种。首先，它提供了一个通用的Unix和工具入门教程，然后深入到Shell编程的具体细节中。以下是书中涉及的主要话题： 1. **正则表达式**：这是Shell编程中用于文本匹配和模式查找的重要工具，读者将学习如何使用这些表达式进行数据处理和搜索。 2. **内核和工具**：讲解了Unix操作系统的内核基础，以及与之配合使用的各种命令行工具，这些工具在日常系统管理中非常关键。 3. **命令文件**：也称为shell脚本，是编写一系列命令以实现自动化任务的文件。读者将学习如何创建和执行这些脚本。 4. **参数**：理解并使用Shell中的参数是编程的基础，读者将学会如何传递参数给脚本，以及如何在脚本中处理这些参数。 5. **文本过滤器**：如grep、sed和awk等，它们用于对文本流进行操作，进行数据筛选、转换或格式化。掌握这些工具可以极大地提升文本处理能力。 6. **理解和调试Shell脚本**：编写脚本时，错误是难以避免的，读者将学习如何定位和修复脚本中的问题，以及如何进行有效的调试。 7. **变量的创建和利用**：在Shell编程中，变量是存储数据的关键，读者将了解如何声明、赋值和使用变量。 8. **进程和工具**：讲解如何控制和管理Unix环境中的进程，包括后台运行、进程间通信和信号处理。 9. **自定义Shell**：根据个人需求定制Shell环境，包括配置文件、别名和函数，使工作环境更符合个人习惯。通过这本书的学习，无论是初学者还是有经验的Unix用户，都能增强他们对Unix系统的掌控力，提升解决问题的能力，并能编写出高效、实用的Shell脚本来自动化日常任务。

? ?

Some Basic Commands

Displaying the Date and Time: The

date

Command

The

date

command tells the system to print the date and time:

$ date

Sat Jul 20 14:42:56 EDT 2002

date

prints the day of the week, month, day, time (24-hour clock, the system's time zone),

and year. Throughout this book, whenever we use

boldface type like this

, it's to indicate

what you, the user, types in.

Normal face type like this

is used to indicate what the

Unix system prints. Italic type is used for comments in interactive sequences.

Every Unix command is ended with the pressing of the Enter key. Enter says that you are

finished typing things in and are ready for the Unix system to do its thing.

Finding Out Who's Logged In: The

who

Command

The

who

command can be used to get information about all users currently logged in to the

system:

$ who

pat tty29 Jul 19 14:40

ruth tty37 Jul 19 10:54

steve tty25 Jul 19 15:52

Here, three users are logged in:

pat

ruth

, and

steve

. Along with each user id, the tty

number of that user and the day and time that user logged in is listed. The tty number is a

unique identification number the Unix system gives to each terminal or network device that a

user has logged into.

The

who

command also can be used to get information about yourself:

$ who am i

pat tty29 Jul 19 14:40

who

and

who am i

are actually the same command:

who

. In the latter case, the

and

are

arguments to the

who

command.

Echoing Characters: The

echo

Command

The

echo

command prints (or echoes) at the terminal whatever else you happen to type on

the line (there are some exceptions to this that you'll learn about later):

$ echo this is a test

this is a test

$ echo why not print out a longer line with echo?

why not print out a longer line with echo?

$ echo

A blank line is

displayed

$ echo one two three four five

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Working with Files

The Unix system recognizes only three basic types of files: ordinary files, directory files, and

special files. An ordinary file is just that: any file on the system that contains data, text,

program instructions, or just about anything else. Directories are described later in this

chapter. As its name implies, a special file has a special meaning to the Unix system and is

typically associated with some form of I/O.

A filename can be composed of just about any character directly available from the keyboard

(and even some that aren't) provided that the total number of characters contained in the

name is not greater than 255. If more than 255 characters are specified, the Unix system

simply ignores the extra characters.

[1]

Modern Unix and Microsoft Windows systems support long filenames; however, some older Unix and

Windows systems only allow much shorter filenames.

The Unix system provides many tools that make working with files easy. Here we'll review

many basic file manipulation commands.

Listing Files: The

Command

To see what files you have stored in your directory, you can type the

command:

$ ls

READ_ME

names

tmp

This output indicates that three files called

READ_ME

names

, and

tmp

are contained in the

current directory. (Note that the output of

may vary from system to system. For example,

on many Unix systems

produces multicolumn output when sending its output to a terminal;

on others, different colors may be used for different types of files. You can always force

single-column output with the

option.)

Displaying the Contents of a File: The

cat

Command

You can examine the contents of a file by using the

cat

command. The argument to

cat

the name of the file whose contents you want to examine.

$ cat names

Susan

Jeff

Henry

Allan

Ken

Counting the Number of Words in a File: The

Command

With the

command, you can get a count of the total number of lines, words, and

characters of information contained in a file. Once again, the name of the file is needed as the

argument to this command:

$ wc names

5 5 27 names

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The

command lists three numbers followed by the filename. The first number represents the

number of lines contained in the file (5), the second the number of words contained in the file

(in this case also 5), and the third the number of characters contained in the file (27).

Command Options

Most Unix commands allow the specification of options at the time a command is executed.

These options generally follow the same format:

letter

That is, a command option is a minus sign followed immediately by a single letter. For example,

to count just the number of lines contained in a file, the option

-l

(that's the letter l) is given

to the

command:

$ wc -l names

5 names

To count just the number of characters in a file, the

-c

option is specified:

$ wc -c names

27 names

Finally, the

-w

option can be used to count the number of words contained in the file:

$ wc -w names

5 names

Some commands require that the options be listed before the filename arguments. For

example,

sort names -r

is acceptable, whereas

wc names -l

is not. Let's generalize by

saying that command options should precede filenames on the command line.

Making a Copy of a File: The

Command

To make a copy of a file, the

command is used. The first argument to the command is the

name of the file to be copied (known as the source file), and the second argument is the

name of the file to place the copy into (known as the destination file). You can make a copy

of the file

names

and call it

saved_names

as follows:

$ cp names saved_names

Execution of this command causes the file named

names

to be copied into a file named

saved_names

. As with many Unix commands, the fact that a command prompt was displayed

after the

command was typed indicates that the command executed successfully.

Renaming a File: The

Command

A file can be renamed with the

command. The arguments to the

command follow the

same format as the

command. The first argument is the name of the file to be renamed,

and the second argument is the new name. So, to change the name of the file

saved_names

hold_it

, for example, the following command would do the trick:

$ mv saved_names hold_it

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Unix Shell编程指南：提升操作系统效率

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