Here also, newlines are optional after the keyword do and after action statements. If while appears on the same line as statement, then the only statement should be terminated by a semicolon.

Let's understand the working of the while loop with some examples. In the following example the print statement is executed only once because we ensure that the conditional-expression evaluates to false. If this were a while statement, with the same initialization of counter to 1 and conditional-expression, the body of the loop containing action statements would not be executed once:

$ vi dowhile1.awk

BEGIN    {
    counter = 1;
    do 
    print "Print this line one time"
    while ( counter != 1 )
}

$ awk -f dowhile1.awk

The output on execution of the preceding code is as follows:

Print this line one time

In the following example, we will use the marks.txt sample file to calculate the total of marks obtained by the student in different subjects. For each line, the program has to add the values of field 2 through the to last field. So, we first initialize i=2 before entering the loop. Then it execute the loop body followed by a test using conditional-expression if it has reached last field in record (I <= NF). NF represents the total number of fields in each record. The output of this program is the same as the while3.awk program, but it uses the do...while loop construct as follows:

$ vi dowhile2.awk

{
    i=2; total=0;
    do 
    {
    total = total + $i;
    i++;
    }
    while ( i <= NF )
    print "Student Name : ", $1, "	", "Total Marks :", total;

}

$ awk -f dowhile2.awk marks.txt

The output on execution of the preceding code is as follows:

Student Name :  ram         Total Marks : 375
Student Name :  amit        Total Marks : 323
Student Name :  vijay       Total Marks : 473
Student Name :  satvik      Total Marks : 386
Student Name :  akshat      Total Marks : 353
Student Name :  rishi       Total Marks : 407
Student Name :  tushar      Total Marks : 359 

In the following example, we will print four fields of each record, one field per line from /etc/passwd file to user info from the user database. The body of the loop is a compound statement containing an action statement and the other conditional if...else...if statement. First, the value of i is initialized to 1. Then the while statement tests whether i is less than or equal to 7. If this is true, statements given inside the while body are executed. Then as last action statement in the while body, i is incremented using i++ and the loop repeats. The loop terminates when i attains the value of 8:

$ vi dowhile3.awk

BEGIN    {
    FS=":"
    }
{
    
    i=1
    while ( i<=7 )
    {
    if ( i == 1 )
    { printf "User Name 	: %s
", $i }
    else if ( i == 3 )
    { printf "UID 		: %s
", $i }
    else if ( i == 6 )
    { printf "Home Directory 	: %s
", $i }
    else if ( i == 7 )
    { printf "Default Shell 	: %s
", $i 
      printf "************************************
"
    }
    i++
    }

}

$ awk -f dowhile3.awk /etc/passwd