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Translated:20140811 Echo Command with Practical Examples.md
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Translating by GOLinux ...
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Echo Command with Practical Examples
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Echo命令实例
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================================================================================
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echo command is built in **shell command** , which is used to display the value of a **variable** or **print a line of text**.
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Echo command plays a important role in building a shell script.
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echo命令是内建的**shell命令**，用于显示**变量**的值或者**打印一行文本**。
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echo命令在构建shell脚本时扮演着重要的角色。
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### Synatx : ###
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### 语法： ###
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# echo [Options] [String]
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The items in square brackets are optional. A string can be defined as finite sequence of characters (like letters, numerals, symbols punctuation marks).
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方括号中的项目是可选的。字符串可以定义为字符的有限序列（如字母，数字，符号，标点符号）。
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When echo command is used without any options or strings, echo returns a blank line on the display screen followed by the command prompt on the subsequent line. This is because pressing the ENTER key is a signal to the system to start a new line, and thus echo repeats this signal.
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当echo命令不带任何选项或字符串使用时，它会在显示屏上返回一个空白行，后面换一行跟上命令提示符。这是因为按下回车键就是发送一个信号给系统以开始一个新行，而echo重复了该信号。
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### Options : ###
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### 选项： ###
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- -n do not output the trailing newline
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- -e enable interpretation of backslash escapes
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- -E disable interpretation of backslash escapes (default)
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- -n 不要输出衍生的新行
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- -e 启用反斜线转义解释
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- -E 禁用反斜线转义解释（默认）
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If -e is in effect, the following sequences are recognized:
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- \\ backslash
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- \a alert (BEL)
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- \b backspace
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- \c produce no further output
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- \e escape
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- \f form feed
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- \n new line
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- \r carriage return
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- \t horizontal tab
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- \v vertical tab
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- \0NNN byte with octal value NNN (1 to 3 digits)
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- \xHH byte with hexadecimal value HH (1 to 2 digits)
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如果-e生效，下列序列被识别：
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### Example :1 Display the value of System Defined Variables ###
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- \\ 反斜线
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- \a 警告（BEL）
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- \b 反斜线
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- \c 不产生进一步输出
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- \e 转义
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- \f 换页
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- \n 新行
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- \r 换行字符
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- \t 水平制表
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- \v 垂直制表
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- \0NNN 八进制值表示的字节NNN（1到3个数字）
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- \xHH 十六进制值表示的字节NNN（1到2个数字）
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Using the set command , we can list the system define variables and to print the vaule of these variables we can use echo command :
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### 样例：1 显示系统定义的变量的值 ###
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使用set命令，我们可以列出系统定义的变量。而要打印这些变量的值，我们可以使用echo命令：
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jack@localhost:~$ echo $USER
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jack
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jack@localhost:~$ echo $HOME
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/home/jack
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### Example:2 Display the value of User defined Variables : ###
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### 样例：2 显示用户定义的变量的值 ###
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jack@nextstep4it:~$ var1=`date`
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jack@nextstep4it:~$ echo "Today's date time is : $var1"
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Today's date time is : Mon Jul 28 13:11:37 IST 2014
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### Example:3 Display the text String ###
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### 样例：3 显示文本字符串 ###
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jack@nextstep4it:~$ echo " Hi this echo command testing"
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Hi this echo command testing
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### Example:4 Use of backspace in echo command ###
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### 样例：4 在echo命令中使用反斜线 ###
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jack@nextstep4it:~$ echo -e "Ubuntu \bis \bthe \bbest \bDesktop \bOS"
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Above Command will Print :
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上述命令将打印：
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UbuntuisthebestDesktopOS
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### Example:5 Use of tab space in echo command ###
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### 样例：5 在echo命令中使用制表符空格 ###
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nextstep4it@nextstep4it:~$ echo -e "Ubuntu \tis \tthe \tbest \tDesktop \tOS"
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Above command will show below output :
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上述命令将显示如下输出：
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Ubuntu is the best Desktop OS
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### Example:6 Use of Vertical tab in echo Command ###
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### 样例：6 在echo命令中使用垂直制表符 ###
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jack@nextstep4it:~$ echo -e "Ubuntu \vis \vthe \vbest \vDesktop \vOS"
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Ubuntu
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@ -81,9 +82,9 @@ Ubuntu is the best Desktop OS
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Desktop
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OS
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### Example:7 Colored output of echo command ###
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### 样例：7 设置echo命令彩色输出 ###
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echo command can change the font style, background color of fonts and font colors. Escape sequence \033 can be used to alter font properties. -e option has to be used in order to the escape sequence be in effect. Some of escape codes are listed below :
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echo命令可以修改字体类型，字体背景色以及字体颜色，转义序列\033可以用于改变字体属性。要使转义序列生效，必须使用-e选项。下面列出了部分转义代码：
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- [0m: Normal
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- [1m: Bold fonts
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@ -110,12 +111,12 @@ echo command can change the font style, background color of fonts and font color
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- [46m: Background color changes to Sky Blue
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- [47m: Background color changes to Light Grey
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Below command will print the output in red color.
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下面的命令将用红色打印输出。
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jack@nextstep4it:~$ echo -e "\033[31mMagic of Linux\033[0m"
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Magic of Linux
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Below Command will print “Magic of Linux” in bold style and red background color.
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下面的命令将以粗体以及红色背景打印出“Magic of Linux”。
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nextstep4it@nextstep4it:~$ echo -e "\033[1m\033[41mMagic of Linux\033[0m"
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Magic of Linux
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@ -124,7 +125,7 @@ Below Command will print “Magic of Linux” in bold style and red background c
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via: http://www.nextstep4it.com/categories/unix-command/echo-command/
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译者：[译者ID](https://github.com/译者ID)
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译者：[GOLinux](https://github.com/GOLinux)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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