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How to Use Compound Expressions with Awk in Linux
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====================================================
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All along, we have been looking at simple expressions when checking whether a condition has been meet or not. What if you want to use more then one expression to check for a particular condition in?
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In this article, we shall take a look at the how you can combine multiple expressions referred to as compound expressions to check for a condition when filtering text or strings.
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In Awk, compound expressions are built using the `&&` referred to as `(and)` and the `||` referred to as `(or)` compound operators.
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The general syntax for compound expressions is:
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```
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( first_expression ) && ( second_expression )
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```
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Here, `first_expression` and `second_expression` must be true to make the whole expression true.
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```
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( first_expression ) || ( second_expression)
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```
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Here, one of the expressions either `first_expression` or `second_expression` must be true for the whole expression to be true.
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**Caution**: Remember to always include the parenthesis.
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The expressions can be built using the comparison operators that we looked at in Part 4 of the awk series.
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Let us now get a clear understanding using an example below:
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In this example, a have a text file named `tecmint_deals.txt`, which contains a list of some amazing random Tecmint deals, it includes the name of the deal, the price and type.
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```
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TecMint Deal List
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No Name Price Type
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1 Mac_OS_X_Cleanup_Suite $9.99 Software
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2 Basics_Notebook $14.99 Lifestyle
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3 Tactical_Pen $25.99 Lifestyle
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4 Scapple $19.00 Unknown
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5 Nano_Tool_Pack $11.99 Unknown
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6 Ditto_Bluetooth_Altering_Device $33.00 Tech
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7 Nano_Prowler_Mini_Drone $36.99 Tech
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```
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Say that we want only print and flag deals that are above $20 and of type “Tech” using the (**) sign at the end of each line.
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We shall need to run the command below.
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```
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# awk '($3 ~ /^\$[2-9][0-9]*\.[0-9][0-9]$/) && ($4=="Tech") { printf "%s\t%s\n",$0,"*"; } ' tecmint_deals.txt
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6 Ditto_Bluetooth_Altering_Device $33.00 Tech *
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7 Nano_Prowler_Mini_Drone $36.99 Tech *
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```
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In this example, we have used two expressions in a compound expression:
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- First expression, `($3 ~ /^\$[2-9][0-9]*\.[0-9][0-9]$/)` ; checks the for lines with deals with price above `$20`, and it is only true if the value of $3 which is the price matches the pattern `/^\$[2-9][0-9]*\.[0-9][0-9]$/`
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- And the second expression, `($4 == “Tech”)` ; checks whether the deal is of type “`Tech`” and it is only true if the value of `$4` equals to “`Tech`”.
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Remember, a line will only be flagged with the `(**)`, if first expression and second expression are true as states the principle of the `&&` operator.
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### Summary
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Some conditions always require building compound expressions for you to match exactly what you want. When you understand the use of comparison and compound expression operators then, filtering text or strings based on some difficult conditions will become easy.
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Hope you find this guide useful and for any questions or additions, always remember to leave a comment and your concern will be solved accordingly.
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/combine-multiple-expressions-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 +1,79 @@
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如何使用 Awk 复合表达式
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====================================================
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一直以来在查对条件是否匹配时，我们寻求的都是简单的表达式。那如果你想用超过一个表达式，来查对特定的条件呢？
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本文，我们将看看如何在过滤文本和字符串时，结合多个表达式，即复合表达式，用以查对条件。
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Awk 的复合表达式可由表示`与`的组合操作符 `&&` 和表示`或`的 `||` 构成。
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复合表达式的常规写法如下：
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```
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( first_expression ) && ( second_expression )
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```
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为了保证整个表达式的正确，在这里必须确保 `first_expression` 和 `second_expression` 是正确的。
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```
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( first_expression ) || ( second_expression)
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```
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为了保证整个表达式的正确，在这里必须确保 `first_expression` 或 `second_expression` 是正确的。
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**注意**：切记要加括号。
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表达式可以由比较操作符构成，具体可查看 awk 系列的第四部分。
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现在让我们通过一个例子来加深理解：
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此例中，有一个文本文件 `tecmint_deals.txt`，文本中包含着一张随机的 Tecmint 交易清单，其中包含了名称、价格和种类。
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```
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TecMint Deal List
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No Name Price Type
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1 Mac_OS_X_Cleanup_Suite $9.99 Software
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2 Basics_Notebook $14.99 Lifestyle
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3 Tactical_Pen $25.99 Lifestyle
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4 Scapple $19.00 Unknown
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5 Nano_Tool_Pack $11.99 Unknown
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6 Ditto_Bluetooth_Altering_Device $33.00 Tech
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7 Nano_Prowler_Mini_Drone $36.99 Tech
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```
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我们只想打印出价格超过 $20 的物品，并在其中种类为 “Tech” 的物品的行末用 (**) 打上标记。
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我们将要执行以下命令。
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```
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# awk '($3 ~ /^\$[2-9][0-9]*\.[0-9][0-9]$/) && ($4=="Tech") { printf "%s\t%s\n",$0,"*"; } ' tecmint_deals.txt
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6 Ditto_Bluetooth_Altering_Device $33.00 Tech *
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7 Nano_Prowler_Mini_Drone $36.99 Tech *
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```
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此例，在复合表达式中我们使用了两个表达式：
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- 表达式 1：`($3 ~ /^\$[2-9][0-9]*\.[0-9][0-9]$/)` ；查找交易价格超过 `$20` 的行，即只有当 `$3` 也就是价格满足 `/^\$[2-9][0-9]*\.[0-9][0-9]$/` 时值才为 true。
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- 表达式 2：`($4 == “Tech”)` ；查找是否有种类为 “`Tech`”的交易，即只有当 `$4` 等于 “`Tech`” 时值才为 true。
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切记，只有当 `&&` 操作符的两端状态，也就是两个表达式都是 true 的情况下，这一行才会被打上 `(**)` 标志。
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### 总结
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有些时候为了匹配你的真实想法，就不得不用到复合表达式。当你掌握了比较和复合表达式操作符的用法之后，在难的文本或字符串过滤条件也能轻松解决。
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希望本向导对你有所帮助，如果你有任何问题或者补充，可以在下方发表评论，你的问题将会得到相应的解释。
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--------------------------------------------------------------------------------
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via: http://www.tecmint.com/combine-multiple-expressions-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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