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[Cathon is translating]
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How to Use Awk to Print Fields and Columns in File
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======================================================
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In this part of our Linux Awk command series, we shall have a look at one of the most important features of Awk, which is field editing.
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It is good to know that Awk automatically divides input lines provided to it into fields, and a field can be defined as a set of characters that are separated from other fields by an internal field separator.
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>Awk Print Fields and Columns
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If you are familiar with the Unix/Linux or do [bash shell programming][1], then you should know what internal field separator (IFS) variable is. The default IFS in Awk are tab and space.
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This is how the idea of field separation works in Awk: when it encounters an input line, according to the IFS defined, the first set of characters is field one, which is accessed using $1, the second set of characters is field two, which is accessed using $2, the third set of characters is field three, which is accessed using $3 and so forth till the last set of character(s).
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To understand this Awk field editing better, let us take a look at the examples below:
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**Example 1**: I have created a text file called tecmintinfo.txt.
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```
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# vi tecmintinfo.txt
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# cat tecmintinfo.txt
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```
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>Create File in Linux
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Then from the command line, I try to print the first, second and third fields from the file tecmintinfo.txt using the command below:
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```
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$ awk '//{print $1 $2 $3 }' tecmintinfo.txt
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TecMint.comisthe
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```
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From the output above, you can see that the characters from the first three fields are printed based on the IFS defined which is space:
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- Field one which is “TecMint.com” is accessed using `$1`.
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- Field two which is “is” is accessed using `$2`.
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- Field three which is “the” is accessed using `$3`.
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If you have noticed in the printed output, the field values are not separated and this is how print behaves by default.
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To view the output clearly with space between the field values, you need to add (,) operator as follows:
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```
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$ awk '//{print $1, $2, $3; }' tecmintinfo.txt
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TecMint.com is the
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```
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One important thing to note and always remember is that the use of `($)` in Awk is different from its use in shell scripting.
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Under shell scripting `($)` is used to access the value of variables while in Awk `($)` it is used only when accessing the contents of a field but not for accessing the value of variables.
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**Example 2**: Let us take a look at one other example using a file which contains multiple lines called my_shoping.list.
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```
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No Item_Name Unit_Price Quantity Price
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1 Mouse #20,000 1 #20,000
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2 Monitor #500,000 1 #500,000
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3 RAM_Chips #150,000 2 #300,000
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4 Ethernet_Cables #30,000 4 #120,000
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```
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Say you wanted to only print `Unit_Price` of each item on the shopping list, you will need to run the command below:
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```
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$ awk '//{print $2, $3 }' my_shopping.txt
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Item_Name Unit_Price
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Mouse #20,000
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Monitor #500,000
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RAM_Chips #150,000
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Ethernet_Cables #30,000
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```
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Awk also has a `printf` command that helps you to format your output is a nice way as you can see the above output is not clear enough.
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Using `printf` to format output of the Item_Name and Unit_Price:
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```
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$ awk '//{printf "%-10s %s\n",$2, $3 }' my_shopping.txt
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Item_Name Unit_Price
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Mouse #20,000
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Monitor #500,000
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RAM_Chips #150,000
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Ethernet_Cables #30,000
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```
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### Summary
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Field editing is very important when using Awk to filter text or strings, it helps you get particular data in columns in a list. And always remember that the use of `($)` operator in Awk is different from that in shell scripting.
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I hope the article was helpful to you and for any additional information required or questions, you can post a comment in the comment section.
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/awk-print-fields-columns-with-space-separator/
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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/category/bash-shell/
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@ -0,0 +1,106 @@
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如何使用 Awk 输出文本中的字段和列
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======================================================
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在 Awk 系列的这一节中，我们将看到 Awk 最重要的特性之一，字段编辑。
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需要知道的是，Awk 能够自动将输入的行，分隔为若干字段。每一个字段就是一组字符，它们和其他的字段由一个内部字段分隔符分隔开来。
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>Awk Print Fields and Columns
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如果你熟悉 Unix/Linux 或者使用 [bash 脚本][1]编过程，那么你应该知道什么是内部字段分隔符（IFS）变量。Awk 中默认的 IFS 是制表符和空格。
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Awk 中的字段分隔符的工作流程如下：当读到一行输入时，将它按照指定的 IFS 分割为不同字段，第一组字符就是字段一，可以通过 $1 来访问，第二组字符就是字段二，可以通过 $2 来访问，第三组字符就是字段三，可以通过 $3 来访问，以此类推，直到最后一组字符。
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为了更好地理解 Awk 的字段编辑，让我们看一个下面的例子：
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**例 1**：我创建了一个名为 tecmintinfo.txt 的文本文件。
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```
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# vi tecmintinfo.txt
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# cat tecmintinfo.txt
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```
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>在 Linux 上创建一个文件
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然后在命令行中，我试着使用下面的命令从文本 tecmintinfo.txt 中输出第一个，第二个，以及第三个字段。
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```
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$ awk '//{print $1 $2 $3 }' tecmintinfo.txt
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TecMint.comisthe
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```
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从上面的输出中你可以看到，前三个字段的字符是以空格为分隔符输出的：
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- 字段一是 “TecMint.com”，可以通过 `$1` 来访问。
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- 字段二是 “is”，可以通过 `$2` 来访问。
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- 字段三是 “the”，可以通过 `$3` 来访问。
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如果你注意观察输出的话可以发现，输出的字段值并没有被分隔开，这是 print 函数默认的行为。
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为了使输出看得更清楚，输出的字段值之间使用空格分开，你需要添加 (,) 操作符。
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```
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$ awk '//{print $1, $2, $3; }' tecmintinfo.txt
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TecMint.com is the
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```
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需要记住而且非常重要的是，`($)` 在 Awk 和在 shell 脚本中的使用是截然不同的！
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在 shell 脚本中，`($)` 被用来获取变量的值。而在 Awk 中，`($)` 只有在获取字段的值时才会用到，不能用于获取变量的值。
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**例 2**：让我们再看一个例子，用到了一个名为 my_shoping.list 的包含多行的文件。
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```
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No Item_Name Unit_Price Quantity Price
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1 Mouse #20,000 1 #20,000
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2 Monitor #500,000 1 #500,000
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3 RAM_Chips #150,000 2 #300,000
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4 Ethernet_Cables #30,000 4 #120,000
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```
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如果你只想输出购物清单上每一个物品的`单价`，你只需运行下面的命令：
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```
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$ awk '//{print $2, $3 }' my_shopping.txt
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Item_Name Unit_Price
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Mouse #20,000
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Monitor #500,000
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RAM_Chips #150,000
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Ethernet_Cables #30,000
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```
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可以看到上面的输出不够清晰，Awk 还有一个 `printf` 的命令，可以帮助你将输出格式化。
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使用 `printf` 来格式化 Item_Name 和 Unit_Price 的输出：
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```
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$ awk '//{printf "%-10s %s\n",$2, $3 }' my_shopping.txt
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Item_Name Unit_Price
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Mouse #20,000
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Monitor #500,000
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RAM_Chips #150,000
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Ethernet_Cables #30,000
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```
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### 总结
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使用 Awk 过滤文本或字符串时，字段编辑的功能是非常重要的。它能够帮助你从一个表的数据中得到特定的列。一定要记住的是，Awk 中 `($)` 操作符的用法与其在 shell 脚本中的用法是不同的！
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希望这篇文章对您有所帮助。如有任何疑问，可以在评论区域发表评论。
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/awk-print-fields-columns-with-space-separator/
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作者：[Aaron Kili][a]
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译者：[Cathon](https://github.com/Cathon)
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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/category/bash-shell/
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