Awk from getting started to digging in (9) circular statement

In addition to the conditional statements introduced above ,AWK Circular statements are also provided . The function of this statement is to repeat a series of commands when the condition is true . This chapter will cover AWK How to use circular statements in .

For

For The syntax of the loop is as follows ：

for (initialisation; condition; increment/decrement)
    action

for Statement first performs the initialization action ( initialisation ), Then check the conditions ( condition ). If the condition is true , Then perform the action ( action ), Then perform incremental ( increment ) Or decreasing ( decrement ) operation . As long as the condition is true, the loop will always execute . Condition check will be carried out at the end of each cycle , If the condition is false, it ends 　 loop . The following example uses For Loop out numbers 1 to 5：

$ awk 'BEGIN { for (i = 1; i <= 5; ++i) print i }'

You can get the following result by executing the above command ：

1
2
3
4
5

While

While The loop will execute the action until the logical condition is false . Its usage is as follows ：

while (condition)
    action

AWK First, check whether the condition is true , If the condition is true, execute the action . This process is repeated until the condition is false , Then stop . Here's how to use While Loop out numbers 1 To 5 Example ：

$ awk 'BEGIN {i = 1; while (i < 6) { print i; ++i } }'

Execute the above command to get the following result ：

1
2
3
4
5

Do-While

Do-While Circulation and While Cyclic similarity , however Do-While The conditional test of is placed at the end of the loop . Here is do-while The grammar of ：

do
    action
while (condition)

stay do-while In circulation , Whether the condition is true or false , The loop statement is executed at least once , Check whether the conditions are true or false after execution . Here's how to use do-While Loop out numbers 1 To 5 Example ：

$ awk 'BEGIN {i = 1; do { print i; ++i } while (i < 6) }'

Execute the above command to get the following result ：

1
2
3
4
5

Break

seeing the name of a thing one thinks of its function ,break To end the cycle . In the example shown below , When the calculated sum is greater than 50 When you use break End the cycle process ：

$ awk 'BEGIN {
    sum = 0; 
    for (i = 0; i < 20; ++i) { 
         sum += i; 
         if (sum > 50) break; 
         else 
         	print "Sum =", sum 
          } 
}'

Execute the above command to get the following result ：

Sum = 0
Sum = 1
Sum = 3
Sum = 6
Sum = 10
Sum = 15
Sum = 21
Sum = 28
Sum = 36
Sum = 45

Continue

Continue Statement is used to end the loop inside the loop body , So as to directly enter the next cycle iteration . It is used when we want to skip data processing somewhere in the loop Continue. The following example outputs 1 To 20 Even number between ：

$ awk 'BEGIN {for (i = 1; i <= 20; ++i) {if (i % 2 == 0) print i ; else continue} }'

Execute the above command to get the following result ：

2
4
6
8
10
12
14
16
18
20

Exit

Exit Used to end the execution of a script program . This function takes an integer as an argument AWK Process end state . If the parameter is not provided , Its default state is 0 . In the following example, when and are greater than 50 End of time AWK Program .

$ awk 'BEGIN {
    sum = 0; 
    for (i = 0; i < 20; ++i) {
        sum += i; 
        if (sum > 50) 
        	exit(10); 
        else print "Sum =", sum;
    } 
}'

Execute the above command to 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's check the return status of the script after execution ：

$ echo $?

Execute the above command to get the following result ：

19