awk tutorial: Learn about awk variables with 3 practical examples

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awk tutorial: Learn about awk variables with 3 practical examples

Author：JIYIK Last Updated：2025/04/07 Views：

This article is a part of the ongoing series of Awk tutorials and examples. Like any other programming language, Awk also has user-defined variables and built-in variables.

In this article, let's review how to define and use awk variables.

Awk variables should start with a letter and can contain alphanumeric characters or underscores. Keywords cannot be used as awk variables. Awk does not support variable declaration like other programming languages. It is always better to initialize awk variables in the BEGIN section, which is executed only once at the beginning. There are no data types in awk. Whether an awk variable is treated as a number or a string depends on the context in which it is used. Now let us review a few simple examples to learn how to use user defined awk variables.

awk example 1: book billing

In this example, the input file bookdetails.txt contains records with fields - item number, book name, quantity, and price of each book.

$ cat bookdetails.txt

awk example bookdetail file content

Now the following Awk script reads and processes the above bookdetails.txt file and generates a report showing - the sales rate of each book, and the total amount of all the books sold.

So far, we have seen Awk read commands from the command line, but Awk can also read commands from a file using the -f option.

语法

$ awk -f script-filename inputfilename

Now our Awk script for book billing calculations looks like this.

$ cat book-calculation.awk
BEGIN {
    total=0;
}
{
    itemno=$1;
    book=$2;
    bookamount=$3*$4;
    total=total+bookamount;
    print itemno," ", book,"\t","$"bookamount;
}
END {
    print "Total Amount = $"total;
}

awk file

In the above script,

The awk BEGIN section initializes the variable total. itemno, total, book, bookamount are user-defined awk variables.
In the Awk Action section, Quantity*bookpricethis will be stored in a variable called bookamount. Each book amount will be added to the total.
Finally in the Awk END section, the total variable will have the total amount.

Now execute the book-calculation.awk script to generate a report showing each book rate and total amount as shown below.

$ awk -f book-calculation.awk bookdetails.txt

awk generates reports

awk example 2. Student score calculation

In this example, an input file "student-marks.txt" is created which contains the following contents - Student Name, Roll Number, Test1 Marks, Test2 Marks and Test3 Marks.

$ cat student-marks.txt

awk example 2 student-marks file content

Now, the following awk script will calculate and generate a report to show the average score of each student, the average of Test1, Test2 and Test3 scores.

student.awk

BEGIN {
    test1=0;
    test2=0;
    test3=0;
    print "Name\tRollNo\t Average Score";

}
{
    total=$3+$4+$5;
    test1=test1+$3;
    test2=test2+$4;
    test3=test3+$5;
    print $1"\t"$2"\t",total/3;
}
END{
    print "Average of Test1="test1/NR;
    print "Average of Test2="test2/NR;
    print "Average of Test3="test3/NR;

}

awk example 2 execution results

In the above awk script,

In the Awk BEGIN section, all awk variables are initialized to zero. test1, test2, test3, and total are user defined awk variables.
In the Awk ACTION section, $3, $4, $5 are the scores of Test1, Test2, and Test3 respectively. The total variable is the sum of the 3 test scores for each student. The awk variables test1, test2, and test3 have the total score for each corresponding test.
So, in the Awk END section, dividing each test total by the total number of records (i.e. students) will give us the average score. NR is an Awk inbuilt variable which gives the total number of records in the input.

awk example 3. HTML report of student details

In above two examples, we have seen awk variables whose values are numbers. This example shows awk script to generate html report for student names and their roll numbers.

string.awk

BEGIN{
title="AWK";
print "<html>\n<title>"title"</title><body bgcolor="#ffffff">\n<table border=1><th  colspan=2 align=centre>Student Details</th>";

}
{
name=$1;
rollno=$2;
print "<tr><td>"name"</td><td>"rollno"</td></tr>";
   
}
END {
    print "</table></body>\n</html>";
}

Use the same student-marks.txt input file that we created in the example above .

$ awk -f string.awk student-marks.txt

awk example 3 generate html report

We can store the above output which gives the following html table. In the above script, the variables named name and rollno are string variables as it is used in string context.

Student	Details
Jones	2143
Gondrol	2321
RinRao	2122
Edwin	2537
Dayan	2415

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