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sources/tech/awk/Part3 - How to Use Awk to Filter Text or Strings Using Pattern Specific Actions.md

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+How to Use Awk to Filter Text or Strings Using Pattern Specific Actions
+=========================================================================
+
+![](http://www.tecmint.com/wp-content/uploads/2016/04/Use-Awk-to-Filter-Text-or-Strings-Using-Pattern.png)
+
+In the third part of the Awk command series, we shall take a look at filtering text or strings based on specific patterns that a user can define.
+
+Sometimes, when filtering text, you want to indicate certain lines from an input file or lines of strings based on a given condition or using a specific pattern that can be matched. Doing this with Awk is very easy, it is one of the great features of Awk that you will find helpful.
+
+Let us take a look at an example below, say you have a shopping list for food items that you want to buy, called food_prices.list. It has the following list of food items and their prices.
+
+```
+$ cat food_prices.list 
+No	Item_Name		Quantity	Price
+1	Mangoes			   10		$2.45
+2	Apples			   20		$1.50
+3	Bananas			   5		$0.90
+4	Pineapples		   10		$3.46
+5	Oranges			   10		$0.78
+6	Tomatoes		   5		$0.55
+7	Onions			   5            $0.45
+```
+
+And then, you want to indicate a `(*)` sign on food items whose price is greater than $2, this can be done by running the following command:
+
+```
+$ awk '/ *\$[2-9]\.[0-9][0-9] */ { print $1, $2, $3, $4, "*" ; } / *\$[0-1]\.[0-9][0-9] */ { print ; }' food_prices.list
+```
+
+![](http://www.tecmint.com/wp-content/uploads/2016/04/Filter-and-Print-Text-Using-Awk.gif)
+>Print Items Whose Price is Greater Than $2
+
+From the output above, you can see that the there is a `(*)` sign at the end of the lines having food items, mangoes and pineapples. If you check their prices, they are above $2.
+
+In this example, we have used used two patterns:
+
+- the first: `/ *\$[2-9]\.[0-9][0-9] */` gets the lines that have food item price greater than $2 and
+- the second: `/*\$[0-1]\.[0-9][0-9] */` looks for lines with food item price less than $2.
+
+This is what happens, there are four fields in the file, when pattern one encounters a line with food item price greater than $2, it prints all the four fields and a `(*)` sign at the end of the line as a flag.
+
+The second pattern simply prints the other lines with food price less than $2 as they appear in the input file, food_prices.list.
+
+This way you can use pattern specific actions to filter out food items that are priced above $2, though there is a problem with the output, the lines that have the `(*)` sign are not formatted out like the rest of the lines making the output not clear enough.
+
+We saw the same problem in Part 2 of the awk series, but we can solve it in two ways:
+
+1. Using printf command which is a long and boring way using the command below:
+
+```
+$ awk '/ *\$[2-9]\.[0-9][0-9] */ { printf "%-10s %-10s %-10s %-10s\n", $1, $2, $3, $4 "*" ; } / *\$[0-1]\.[0-9][0-9] */ { printf "%-10s %-10s %-10s %-10s\n", $1, $2, $3, $4; }' food_prices.list 
+```
+
+![](http://www.tecmint.com/wp-content/uploads/2016/04/Filter-and-Print-Items-Using-Awk-and-Printf.gif)
+>Filter and Print Items Using Awk and Printf
+
+2. Using $0 field. Awk uses the variable 0 to store the whole input line. This is handy for solving the problem above and it is simple and fast as follows:
+
+```
+$ awk '/ *\$[2-9]\.[0-9][0-9] */ { print $0 "*" ; } / *\$[0-1]\.[0-9][0-9] */ { print ; }' food_prices.list 
+```
+
+![](http://www.tecmint.com/wp-content/uploads/2016/04/Filter-and-Print-Items-Using-Awk-and-Variable.gif)
+>Filter and Print Items Using Awk and Variable
+
+Conclusion
+That’s it for now and these are simple ways of filtering text using pattern specific action that can help in flagging lines of text or strings in a file using Awk command.
+
+Hope you find this article helpful and remember to read the next part of the series which will focus on using comparison operators using awk tool.
+
+
+--------------------------------------------------------------------------------
+
+via: http://www.tecmint.com/awk-filter-text-or-string-using-patterns/
+
+作者：[Aaron Kili][a]
+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]: http://www.tecmint.com/author/aaronkili/
+