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[Translated] How To Assign Output of a Linux Command to a Variable
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GHLandy Translating
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How To Assign Output of a Linux Command to a Variable
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============================================================
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When you run a command, it produces some kind of output: either the result of a program is suppose to produce or status/error messages of the program execution details. Sometimes, you may want to store the output of a command in a variable to be used in a later operation.
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In this post, we will review the different ways of assigning the output of a shell command to a variable, specifically useful for shell scripting purpose.
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To store the output of a command in a variable, you can use the shell command substitution feature in the forms below:
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```
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variable_name=$(command)
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variable_name=$(command [option ...] arg1 arg2 ...)
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OR
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variable_name='command'
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variable_name='command [option ...] arg1 arg2 ...'
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```
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Below are a few examples of using command substitution.
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In this first example, we will store the value of `who` (which shows who is logged on the system) command in the variable `CURRENT_USERS` user:
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```
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$ CURRENT_USERS=$(who)
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```
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Then we can use the variable in a sentence displayed using the [echo command][1] like so:
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```
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$ echo -e "The following users are logged on the system:\n\n $CURRENT_USERS"
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```
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In the command above: the flag `-e` means interpret any escape sequences ( such as `\n` for newline) used. To avoid wasting time as well as memory, simply perform the command substitution within the [echo command][2] as follows:
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```
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$ echo -e "The following users are logged on the system:\n\n $(who)"
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```
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[
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][3]
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Shows Current Logged Users in Linux
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Next, to demonstrate the concept using the second form; we can store the total number of files in the current working directory in a variable called `FILES` and echo it later as follows:
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```
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$ FILES=`sudo find . -type f -print | wc -l`
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$ echo "There are $FILES in the current working directory."
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```
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[
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][4]
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Show Number of Files in Directory
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That’s it for now, in this article, we explained the methods of assigning the output of a shell command to a variable. You can add your thoughts to this post via the feedback section below.
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--------------------------------------------------------------------------------
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作者简介：
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Aaron Kili is a Linux and F.O.S.S enthusiast, an upcoming Linux SysAdmin, web developer, and currently a content creator for TecMint who loves working with computers and strongly believes in sharing knowledge.
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/assign-linux-command-output-to-variable/
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作者：[Aaron Kili][a]
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译者：[译者ID](https://github.com/译者ID)
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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) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:http://www.tecmint.com/author/aaronkili/
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[1]:http://www.tecmint.com/echo-command-in-linux/
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[2]:http://www.tecmint.com/echo-command-in-linux/
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[3]:http://www.tecmint.com/wp-content/uploads/2017/01/Shows-Current-Logged-Users-in-Linux.png
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[4]:http://www.tecmint.com/wp-content/uploads/2017/01/Show-Number-of-Files-in-Directory.png
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如何将 Linux 命令的输出赋值给变量
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==================================
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每当你运行一个命令，它都出在屏幕上输出一些内容：该命令的期望结果或者该命令执行细节的状态/错误消息。有些时候，你可能想要将某个命令的输出内容存储在一个变量中，以待在后续操作中取出来使用。
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本文将介绍将 shell 命令赋值给变量的不同方法，这对于 shell 脚本编程是特别有用的。
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你可以使用如下的 shell 命令置换特性来将命令的输出存储到变量中：
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```
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变量名=$(命令)
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变量名=$(命令 [命令选项 ...] 参数1 参数2 ...)
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或者:
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变量名='命令'
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变量名='命令 [命令选项 ...] 参数1 参数2 ...'
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```
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以下是使用命令置换特性的示例：
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本例，我们将 `who` (显示当前登录系统的用户) 的输出值存储到 `CURRENT_USERS` 变量中：
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```
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$ CURRENT_USERS=$(who)
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```
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然后，我们可以使用 [echo 命令][1] 来使用上述变量，如下：
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```
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$ echo -e "以下为登录到系统中的用户：\n\n $CURRENT_USERS"
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```
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上面的命令中：`-e` 标记表示解释所有的转义序列 (如 `\n` 为换行)。为节约时间和内存，通常在 [echo 命令][2] 中使用命令置换特性，如下：
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```
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$ echo -e "以下为登录到系统中的用户：\n\n $(who)"
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```
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[][3]
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在 Linux 中显示当前登录系统的用户
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接下来，为了演示刚刚的第二种形式，我们以把当前工作目录下文件数存储到变量 `FILES` 为了，然后使用 echo 来输出，如下：
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```
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$ FILES=`sudo find . -type f -print | wc -l`
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$ echo "当前目录有 $FILES 个文件。"
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```
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[][4]
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显示目中包含文件的数量
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至此，文毕。我们展示了将 shell 命令的输出赋值给变量的方法。你可以在下边的评论反馈区留下你的想法。
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---------------------------------------------------------
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作者简介：
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Aaron Kili 是一名 Linux 和 F.O.S.S 忠实拥护者、高级 Linux 系统管理员、Web 开发者，目前在 TecMint 是一名活跃的博主，热衷于计算机并有着强烈的只是分享意愿。
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译者简介：
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[GHLandy](http://GHLandy.com) —— 欲得之，则为之奋斗 (If you want it, work for it.)。
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------------------------------------------------
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via: http://www.tecmint.com/assign-linux-command-output-to-variable/
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作者：[Aaron Kili][a]
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译者：[GHLandy](https://github.com/GHLandy)
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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) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:http://www.tecmint.com/author/aaronkili/
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[1]:http://www.tecmint.com/echo-command-in-linux/
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[2]:http://www.tecmint.com/echo-command-in-linux/
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[3]:http://www.tecmint.com/wp-content/uploads/2017/01/Shows-Current-Logged-Users-in-Linux.png
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[4]:http://www.tecmint.com/wp-content/uploads/2017/01/Show-Number-of-Files-in-Directory.png
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