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[#]: collector: (lujun9972)
[#]: translator: (geekpi)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Getting started with awk, a powerful text-parsing tool)
[#]: via: (https://opensource.com/article/19/10/intro-awk)
[#]: author: (Seth Kenlon https://opensource.com/users/seth)
Getting started with awk, a powerful text-parsing tool
======
Let's jump in and start using it.
![Woman programming][1]
Awk is a powerful text-parsing tool for Unix and Unix-like systems, but because it has programmed functions that you can use to perform common parsing tasks, it's also considered a programming language. You probably won't be developing your next GUI application with awk, and it likely won't take the place of your default scripting language, but it's a powerful utility for specific tasks.
What those tasks may be is surprisingly diverse. The best way to discover which of your problems might be best solved by awk is to learn awk; you'll be surprised at how awk can help you get more done but with a lot less effort.
Awk's basic syntax is:
```
`awk [options] 'pattern {action}' file`
```
To get started, create this sample file and save it as **colours.txt**
```
name       color  amount
apple      red    4
banana     yellow 6
strawberry red    3
grape      purple 10
apple      green  8
plum       purple 2
kiwi       brown  4
potato     brown  9
pineapple  yellow 5
```
This data is separated into columns by one or more spaces. It's common for data that you are analyzing to be organized in some way. It may not always be columns separated by whitespace, or even a comma or semicolon, but especially in log files or data dumps, there's generally a predictable pattern. You can use patterns of data to help awk extract and process the data that you want to focus on.
### Printing a column
In awk, the **print** function displays whatever you specify. There are many predefined variables you can use, but some of the most common are integers designating columns in a text file. Try it out:
```
$ awk '{print $2;}' colours.txt
color
red
yellow
red
purple
green
purple
brown
brown
yellow
```
In this case, awk displays the second column, denoted by **$2**. This is relatively intuitive, so you can probably guess that **print $1** displays the first column, and **print $3** displays the third, and so on.
To display _all_ columns, use **$0**.
The number after the dollar sign (**$**) is an _expression_, so **$2** and **$(1+1)** mean the same thing.
### Conditionally selecting columns
The example file you're using is very structured. It has a row that serves as a header, and the columns relate directly to one another. By defining _conditional_ requirements, you can qualify what you want awk to return when looking at this data. For instance, to view items in column 2 that match "yellow" and print the contents of column 1:
```
awk '$2=="yellow"{print $1}' file1.txt
banana
pineapple
```
Regular expressions work as well. This conditional looks at **$2** for approximate matches to the letter **p** followed by any number of (one or more) characters, which are in turn followed by the letter **p**:
```
$ awk '$2 ~ /p.+p/ {print $0}' colours.txt
grape   purple  10
plum    purple  2
```
Numbers are interpreted naturally by awk. For instance, to print any row with a third column containing an integer greater than 5:
```
awk '$3>5 {print $1, $2}' colours.txt
name    color
banana  yellow
grape   purple
apple   green
potato  brown
```
### Field separator
By default, awk uses whitespace as the field separator. Not all text files use whitespace to define fields, though. For example, create a file called **colours.csv** with this content:
```
name,color,amount
apple,red,4
banana,yellow,6
strawberry,red,3
grape,purple,10
apple,green,8
plum,purple,2
kiwi,brown,4
potato,brown,9
pineapple,yellow,5
```
Awk can treat the data in exactly the same way, as long as you specify which character it should use as the field separator in your command. Use the **\--field-separator** (or just **-F** for short) option to define the delimiter:
```
$ awk -F"," '$2=="yellow" {print $1}' file1.csv
banana
pineapple
```
### Saving output
Using output redirection, you can write your results to a file. For example:
```
`$ awk -F, '$3>5 {print $1, $2} colours.csv > output.txt`
```
This creates a file with the contents of your awk query.
You can also split a file into multiple files grouped by column data. For example, if you want to split colours.txt into multiple files according to what color appears in each row, you can cause awk to redirect _per query_ by including the redirection in your awk statement:
```
`$ awk '{print > $2".txt"}' colours.txt`
```
This produces files named **yellow.txt**, **red.txt**, and so on.
In the next article, you'll learn more about fields, records, and some powerful awk variables.
* * *
This article is adapted from an episode of [Hacker Public Radio][2], a community technology podcast.
--------------------------------------------------------------------------------
via: https://opensource.com/article/19/10/intro-awk
作者：[Seth Kenlon][a]
选题：[lujun9972][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://opensource.com/users/seth
[b]: https://github.com/lujun9972
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/programming-code-keyboard-laptop-music-headphones.png?itok=EQZ2WKzy (Woman programming)
[2]: http://hackerpublicradio.org/eps.php?id=2114

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[#]: collector: (lujun9972)
[#]: translator: (geekpi)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Getting started with awk, a powerful text-parsing tool)
[#]: via: (https://opensource.com/article/19/10/intro-awk)
[#]: author: (Seth Kenlon https://opensource.com/users/seth)
awk 入门，强大的文本分析工具
======
让我们开始使用它。
![Woman programming][1]
awk 是用于 Unix 和类 Unix 系统的强大文本解析工具，但是由于它有可编程函数，因此你可以用它来执行常规解析任务，因此它也被视为一种编程语言。你可能不会使用 awk 开发下一个 GUI 应用，并且它可能不会代替你的默认脚本语言，但是它是用于特定任务的强大程序。
这些任务或许是惊人的多样化。了解 awk 可以很好解决你的哪些问题的最好方法是学习 awk。你会惊讶于 awk 如何帮助你完成更多工作，却花费更少的精力。
awk 的基本语法是：
```
`awk [options] 'pattern {action}' file`
```
首先，创建此示例文件并将其保存为 **colours.txt**
```
name       color  amount
apple      red    4
banana     yellow 6
strawberry red    3
grape      purple 10
apple      green  8
plum       purple 2
kiwi       brown  4
potato     brown  9
pineapple  yellow 5
```
数据被一个或多个空格分隔为列。以某种方式组织要分析的数据是很常见的。它不一定总是由空格分隔的列，甚至不是逗号或分号，但尤其是在日志文件或数据转储中，通常有一个可预测的格式。你可以使用数据格式来帮助 awk 提取和处理你关注的数据。
### 打印列
在 awk 中，**print** 函数显示你指定的内容。你可以使用许多预定义的变量，但是最常见的是文本文件中指定的列数。试试看：
```
$ awk '{print $2;}' colours.txt
color
red
yellow
red
purple
green
purple
brown
brown
yellow
```
在这里，awk 显示第二列，用 **$2** 表示。这是相对直观的，因此你可能会猜测 **print $1** 显示第一列，而 **print $3** 显示第三列，依此类推。
要显示_全部_列，请使用 **$0**。
美元符号（**$**）后的数字是_表达式_，因此 **$2**和 **$(1+1)** 是同一意思。
### 有条件地选择列
你使用的示例文件非常结构化。它有一行充当标题，并且各列直接相互关联。通过定义_条件_，你可以限定 awk 在找到此数据时返回的内容。例如，要查看第 2 列中与 “yellow” 匹配的项并打印第 1 列的内容：
```
awk '$2=="yellow"{print $1}' file1.txt
banana
pineapple
```
正则表达式也可以工作。此表达式近似匹配 **$2** 中以 **p** 开头跟上任意数量（一个或多个）字符后继续跟上 **p** 的值：
```
$ awk '$2 ~ /p.+p/ {print $0}' colours.txt
grape   purple  10
plum    purple  2
```
数字能被 awk 自然解释。例如，要打印第三列包含大于 5 的整数的行：
```
awk '$3>5 {print $1, $2}' colours.txt
name    color
banana  yellow
grape   purple
apple   green
potato  brown
```
### 字段分隔符
默认情况下，awk 使用空格作为字段分隔符。但是，并非所有文本文件都使用空格来定义字段。例如，用以下内容创建一个名为 **colours.csv** 的文件：
```
name,color,amount
apple,red,4
banana,yellow,6
strawberry,red,3
grape,purple,10
apple,green,8
plum,purple,2
kiwi,brown,4
potato,brown,9
pineapple,yellow,5
```
只要你指定将哪个字符用作命令中的字段分隔符，awk 就能以完全相同的方式处理数据。使用 **\--field-separator**（或简称为 **-F**）选项来定义分隔符：
```
$ awk -F"," '$2=="yellow" {print $1}' file1.csv
banana
pineapple
```
### 保存输出
使用输出重定向，你可以将结果写入文件。例如：
```
`$ awk -F, '$3>5 {print $1, $2} colours.csv > output.txt`
```
这将创建一个包含 awk 查询内容的文件。
你还可以将文件拆分为按列数据分组的多个文件。例如，如果要根据每行显示的颜色将 colours.txt 拆分为多个文件，你可以在 awk 中包含重定向语句来重定向_每条查询_：
```
`$ awk '{print > $2".txt"}' colours.txt`
```
这将生成名为 **yellow.txt**，**red.txt** 等文件。
在下一篇文章中，你将了解有关字段，记录和一些强大的 awk 变量的更多信息。
* * *
本文改编自社区技术播客 [Hacker Public Radio][2]。
--------------------------------------------------------------------------------
via: https://opensource.com/article/19/10/intro-awk
作者：[Seth Kenlon][a]
选题：[lujun9972][b]
译者：[geekpi](https://github.com/geekpi)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://opensource.com/users/seth
[b]: https://github.com/lujun9972
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/programming-code-keyboard-laptop-music-headphones.png?itok=EQZ2WKzy (Woman programming)
[2]: http://hackerpublicradio.org/eps.php?id=2114