AWK - Loops

This chapter explains AWK's loops with suitable example. Loops are used to execute a set of actions in a repeated manner. The loop execution continues as long as the loop condition is true.
The syntax of for loop is −
for (initialization; condition; increment/decrement)
   action

Initially, the for statement performs initialization action, then it checks the condition. If the condition is true, it executes actions, thereafter it performs increment or decrement operation. The loop execution continues as long as the condition is true. For instance, the following example prints 1 to 5 using for loop −
[jerry]$ awk 'BEGIN { for (i = 1; i <= 5; ++i) print i }'
On executing this code, you get the following result −
1
2
3
4
5

The while loop keeps executing the action until a particular logical condition evaluates to true. Here is the syntax of while loop −
while (condition)
   action

AWK first checks the condition; if the condition is true, it executes the action. This process repeats as long as the loop condition evaluates to true. For instance, the following example prints 1 to 5 using while loop −
[jerry]$ awk 'BEGIN {i = 1; while (i < 6) { print i; ++i } }'
On executing this code, you get the following result −
1
2
3
4
5

The do-while loop is similar to the while loop, except that the test condition is evaluated at the end of the loop. Here is the syntax of do-whileloop −
do
   action
while (condition)

In a do-while loop, the action statement gets executed at least once even when the condition statement evaluates to false. For instance, the following example prints 1 to 5 numbers using do-while loop −
[jerry]$ awk 'BEGIN {i = 1; do { print i; ++i } while (i < 6) }'
On executing this code, you get the following result −
1
2
3
4
5

As its name suggests, it is used to end the loop execution. Here is an example which ends the loop when the sum becomes greater than 50.
[jerry]$ awk 'BEGIN {
   sum = 0; for (i = 0; i < 20; ++i) { 
      sum += i; if (sum > 50) break; else print "Sum =", sum 
   } 
}'
On executing this code, you get the following result −
Sum = 0
Sum = 1
Sum = 3
Sum = 6
Sum = 10
Sum = 15
Sum = 21
Sum = 28
Sum = 36
Sum = 45

The continue statement is used inside a loop to skip to the next iteration of the loop. It is useful when you wish to skip the processing of some data inside the loop. For instance, the following example uses continue statement to print the even numbers between 1 to 20.
[jerry]$ awk 'BEGIN {
   for (i = 1; i <= 20; ++i) {
      if (i % 2 == 0) print i ; else continue
   } 
}'
On executing this code, you get the following result −
2
4
6
8
10
12
14
16
18
20

It is used to stop the execution of the script. It accepts an integer as an argument which is the exit status code for AWK process. If no argument is supplied, exit returns status zero. Here is an example that stops the execution when the sum becomes greater than 50.
[jerry]$ awk 'BEGIN {
   sum = 0; for (i = 0; i < 20; ++i) {
      sum += i; if (sum > 50) exit(10); else print "Sum =", sum 
   } 
}'
On executing this code, you get the following result −
Sum = 0
Sum = 1
Sum = 3
Sum = 6
Sum = 10
Sum = 15
Sum = 21
Sum = 28
Sum = 36
Sum = 45

Let us check the return status of the script.
[jerry]$ echo $?
On executing this code, you get the following result −
10

 Print
 Add Notes
 Bookmark this page