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Awk is a powerful text parsing tool for Unix and Unix-like systems, but because it has programmable functions, you can use it to perform regular parsing tasks, so it is also considered a programming language. You may not use awk to develop the next GUI application, and it may not replace your default scripting language, but it is a powerful program for specific tasks.

These tasks may be surprisingly diverse. The best way to find out which problems awk can solve is to learn awk. You'll be amazed at how awk helps you get more work done with less effort.

The basic syntax of awk is:

Awk [options] 'pattern {action}' file

First, create the sample file and save it as colours.txt.

Name color amountapple red 4banana yellow 6strawberry red 3grape purple 10apple green 8plum purple 2kiwi brown 4potato brown 9pineapple yellow 5

The data is separated into columns by one or more spaces. It is common to organize the data to be analyzed in some way. It is not always a column separated by spaces, or even not a comma or semicolon, but especially in log files or data dumps, there is usually a predictable format. You can use data formats to help awk extract and process the data you care about.

Print column

In awk, the print function displays what you specify. You can use many predefined variables, but the most common are columns named with integers in a text file. Try it:

$awk'{print $2;} 'colours.txtcolorredyellowredpurplegreenpurplebrownbrownyellow

Here, awk displays the second column, represented by $2. This is relatively straightforward, so you might guess that print $1 displays the first column, print $3 shows the third column, and so on.

To display all columns, use $0.

The number after the dollar sign ($) is an expression, so $2 and $(1x 1) have the same meaning.

Conditionally select columns

The sample file you use is very structured. It has a row that acts as a title, and the columns are directly related to each other. By defining conditions, you can define what awk returns when it finds this data. For example, to view the items in the second column that match yellow and print the contents of the first column:

Awk'$2 file1.txtbananapineapple = "yellow" {print $1} 'file1.txtbananapineapple

Regular expressions also work. This expression approximately matches the value of p starting with p in $2 followed by any number of (one or more) characters:

$awk'$2 ~ / p.+p/ {print $0} 'colours.txtgrape purple 10plum purple 2

Numbers can be interpreted naturally by awk. For example, to print a row in the third column that contains integers greater than 5:

Awk'$3 > 5 {print $1, $2} 'colours.txtname colorbanana yellowgrape purpleapple greenpotato brown field delimiter

By default, awk uses spaces as the field delimiter. However, not all text files use spaces to define fields. For example, create a file called colours.csv with the following:

Name,color,amountapple,red,4banana,yellow,6strawberry,red,3grape,purple,10apple,green,8plum,purple,2kiwi,brown,4potato,brown,9pineapple,yellow,5

As long as you specify which character to use as the field delimiter in the command, awk can process the data in exactly the same way. Use the-- field-separator (or-F for short) option to define the delimiter:

$awk-F ","'$2percent = "yellow" {print $1} 'file1.csvbananapineapple saves the output

Using output redirection, you can write the results to a file. For example:

$awk-F,'$3 > 5 {print $1, $2} colours.csv > output.txt

This creates a file that contains the contents of the awk query.

You can also split files into multiple files grouped by column data. For example, if you want to split the colours.txt into multiple files based on the color displayed in each row, you can include a redirect statement in the awk to redirect each query:

$awk'{print > $2 ".txt"} 'colours.txt

This generates files named yellow.txt, red.txt, and so on.

Thank you for reading! This is the end of this article on "how to use awk in linux". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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