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When filtering text, sometimes you may want to mark lines in a file or line string based on a given condition or with a specific pattern that can be matched. Using awk to accomplish this task is very easy, and this is one of several features in awk that may help you.

Let's take a look at the following example. For example, you have a shopping list of the food you want to buy, which is called food_prices.list. The name of the food and the corresponding price are as follows:

$cat food_prices.listNo Item_Name Quantity Price1 Mangoes 10 $2.452 Apples 20 $1.503 Bananas 5 $0.904 Pineapples 10 $3.465 Oranges 10 $0.786 Tomatoes 5 $0.557 Onions 5 $0.45

Then, if you want to use a (*) symbol to mark foods with a unit price greater than $2, you can do so 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

Print out items with a unit price greater than $2

From the output above, you can see that there is already a (*) mark at the end of the line containing mango and pineapple. If you check their unit price, you can see that their unit price is indeed over $2.

In this example, we have used two modes: the first mode: / * / $[2-9] /. 0-9 * / will get rows that contain food with a unit price greater than that. The second mode [0-1] /. 0-9 * / will find those lines where the unit price of food is less than $2.

What exactly does the above command do? This file has four fields, and when the pattern matches to a line with a unit price of food greater than $2, it outputs all four fields and adds a (*) symbol at the end of the line as a tag.

The second mode simply outputs other lines that contain food with a unit price of less than $2, as they appear in the input file food_prices.list.

This allows you to use patterns to filter out food items that cost more than $2, although there are some problems with the above output, and the lines with the (*) symbol are not formatted like other lines, which makes the output less clear.

We saw the same problem in part 2 of the awk series, but we can solve it in two ways:

1. You can use the printf command as follows, but it is long and boring:

$awk'/ * / $[2-9] /. [0-9] [0-9] * / {printf "%-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

Use Awk and Printf to filter and output projects

2. Use the $0 field. Awk uses the variable 0 to store the entire input line. For the above questions, this approach is very convenient, and it is also simple and fast:

$awk'/ * / $[2-9] /. [0-9] [0-9] * / {print $0 "*";} / * / $[0-1] /. [0-9] [0-9] * / {print;} 'food_prices.list

Use Awk and variables to filter and output projects

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