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* âFinish tranlating awk series part4 * Update Part 4 - How to Use Comparison Operators with Awk in Linux.md
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How to Use Comparison Operators with Awk in Linux
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===================================================
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When dealing with numerical or string values in a line of text, filtering text or strings using comparison operators comes in handy for Awk command users.
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In this part of the Awk series, we shall take a look at how you can filter text or strings using comparison operators. If you are a programmer then you must already be familiar with comparison operators but those who are not, let me explain in the section below.
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### What are Comparison operators in Awk?
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Comparison operators in Awk are used to compare the value of numbers or strings and they include the following:
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- `>` – greater than
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- `<` – less than
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- `>=` – greater than or equal to
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- `<=` – less than or equal to
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- `==` – equal to
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- `!=` – not equal to
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- `some_value ~ / pattern/` – true if some_value matches pattern
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- `some_value !~ / pattern/` – true if some_value does not match pattern
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Now that we have looked at the various comparison operators in Awk, let us understand them better using an example.
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In this example, we have a file named food_list.txt which is a shopping list for different food items and I would like to flag food items whose quantity is less than or equal 20 by adding `(**)` at the end of each line.
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```
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File – food_list.txt
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No Item_Name Quantity Price
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1 Mangoes 45 $3.45
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2 Apples 25 $2.45
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3 Pineapples 5 $4.45
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4 Tomatoes 25 $3.45
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5 Onions 15 $1.45
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6 Bananas 30 $3.45
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```
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The general syntax for using comparison operators in Awk is:
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```
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# expression { actions; }
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```
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To achieve the above goal, I will have to run the command below:
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```
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# awk '$3 <= 30 { printf "%s\t%s\n", $0,"**" ; } $3 > 30 { print $0 ;}' food_list.txt
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No Item_Name` Quantity Price
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1 Mangoes 45 $3.45
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2 Apples 25 $2.45 **
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3 Pineapples 5 $4.45 **
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4 Tomatoes 25 $3.45 **
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5 Onions 15 $1.45 **
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6 Bananas 30 $3.45 **
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```
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In the above example, there are two important things that happen:
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- The first expression `{ action ; }` combination, `$3 <= 30 { printf “%s\t%s\n”, $0,”**” ; }` prints out lines with quantity less than or equal to 30 and adds a `(**)` at the end of each line. The value of quantity is accessed using `$3` field variable.
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- The second expression `{ action ; }` combination, `$3 > 30 { print $0 ;}` prints out lines unchanged since their quantity is greater then `30`.
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One more example:
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```
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# awk '$3 <= 20 { printf "%s\t%s\n", $0,"TRUE" ; } $3 > 20 { print $0 ;} ' food_list.txt
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No Item_Name Quantity Price
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1 Mangoes 45 $3.45
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2 Apples 25 $2.45
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3 Pineapples 5 $4.45 TRUE
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4 Tomatoes 25 $3.45
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5 Onions 15 $1.45 TRUE
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6 Bananas 30 $3.45
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```
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In this example, we want to indicate lines with quantity less or equal to 20 with the word (TRUE) at the end.
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### Summary
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This is an introductory tutorial to comparison operators in Awk, therefore you need to try out many other options and discover more.
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In case of any problems you face or any additions that you have in mind, then drop a comment in the comment section below. Remember to read the next part of the Awk series where I will take you through compound expressions.
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/comparison-operators-in-awk/
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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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@ -0,0 +1,95 @@
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在 Linux 下如何使用 Awk 比较操作符
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===================================================
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对于 Awk 命令的用户来说，处理一行文本中的数字或者字符串时，使用比较运算符来过滤文本和字符串是十分方便的。
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在 Awk 系列的此部分中，我们将探讨一下如何使用比较运算符来过滤文本或者字符串。如果你是程序员，那么你应该已经熟悉比较运算符；对于其它人，下面的部分将介绍比较运算符。
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### Awk 中的比较运算符是什么？
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Awk 中的比较运算符用于比较字符串和或者数值，包括以下类型：
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- `>` – 大于
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- `<` – 小于
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- `>=` – 大于等于
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- `<=` – 小于等于
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- `==` – 等于
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- `!=` – 不等于
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- `some_value ~ / pattern/` – 如果some_value匹配模式pattern，则返回true
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- `some_value !~ / pattern/` – 如果some_value不匹配模式pattern，则返回true
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现在我们通过例子来熟悉 Awk 中各种不同的比较运算符。
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在这个例子中，我们有一个文件名为 food_list.txt 的文件，里面包括不同食物的购买列表。我想给食物数量小于或等于30的物品所在行的后面加上`(**)`
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```
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File – food_list.txt
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No Item_Name Quantity Price
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1 Mangoes 45 $3.45
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2 Apples 25 $2.45
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3 Pineapples 5 $4.45
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4 Tomatoes 25 $3.45
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5 Onions 15 $1.45
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6 Bananas 30 $3.45
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```
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Awk 中使用比较运算符的通用语法如下：
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```
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# expression { actions; }
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```
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为了实现刚才的目的，执行下面的命令：
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```
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# awk '$3 <= 30 { printf "%s\t%s\n", $0,"**" ; } $3 > 30 { print $0 ;}' food_list.txt
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No Item_Name` Quantity Price
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1 Mangoes 45 $3.45
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2 Apples 25 $2.45 **
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3 Pineapples 5 $4.45 **
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4 Tomatoes 25 $3.45 **
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5 Onions 15 $1.45 **
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6 Bananas 30 $3.45 **
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```
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在刚才的例子中，发生如下两件重要的事情：
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- 第一个表达式 `{ action ; }` 组合， `$3 <= 30 { printf “%s\t%s\n”, $0,”**” ; }` 打印出数量小于等于30的行，并且在后面增加`(**)`。物品的数量是通过 `$3`这个域变量获得的。
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- 第二个表达式 `{ action ; }` 组合, `$3 > 30 { print $0 ;}` 原样输出数量小于等于 `30` 的行。
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再举一个例子：
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```
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# awk '$3 <= 20 { printf "%s\t%s\n", $0,"TRUE" ; } $3 > 20 { print $0 ;} ' food_list.txt
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No Item_Name Quantity Price
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1 Mangoes 45 $3.45
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2 Apples 25 $2.45
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3 Pineapples 5 $4.45 TRUE
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4 Tomatoes 25 $3.45
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5 Onions 15 $1.45 TRUE
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6 Bananas 30 $3.45
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```
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在这个例子中，我们想通过在行的末尾增加 (TRUE) 来标记数量小于等于20的行。
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### 总结
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这是一篇对 Awk 中的比较运算符介绍性的指引，因此你需要尝试其他选项，发现更多使用方法。
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如果你遇到或者想到任何问题，请在下面评论区留下评论。请记得阅读 Awk 系列下一部分的文章，那里我将介绍组合表达式。
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/comparison-operators-in-awk/
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作者：[Aaron Kili][a]
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译者：[chunyang-wen](https://github.com/chunyang-wen)
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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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