AWK - Arrays

AWK has associative arrays and one of the best thing about it is – the indexes need not to be continuous set of number; you can use either string or number as an array index. Also, there is no need to declare the size of an array in advance – arrays can expand/shrink at runtime.

Its syntax is as follows −


array_name[index] = value

Where array_name is the name of array, index is the array index, and value is any value assigning to the element of the array.

Creating Array

To gain more insight on array, let us create and access the elements of an array.


[jerry]$ awk 'BEGIN {
   fruits["mango"] = "yellow";
   fruits["orange"] = "orange"
   print fruits["orange"] "\n" fruits["mango"]

On executing this code, you get the following result −



In the above example, we declare the array as fruits whose index is fruit name and the value is the color of the fruit. To access array elements, we use array_name[index] format.

Deleting Array Elements

For insertion, we used assignment operator. Similarly, we can use delete statement to remove an element from the array. The syntax of delete statement is as follows −


delete array_name[index]

The following example deletes the element orange. Hence the command does not show any output.


[jerry]$ awk 'BEGIN {
   fruits["mango"] = "yellow";
   fruits["orange"] = "orange";
   delete fruits["orange"];
   print fruits["orange"]

Multi-Dimensional arrays

AWK only supports one-dimensional arrays. But you can easily simulate a multi-dimensional array using the one-dimensional array itself.

For instance, given below is a 3x3 two-dimensional array −

100   200   300
400   500   600
700   800   900

In the above example, array[0][0] stores 100, array[0][1] stores 200, and so on. To store 100 at array location [0][0], we can use the following syntax −


array["0,0"] = 100

Though we gave 0,0 as index, these are not two indexes. In reality, it is just one index with the string 0,0.

The following example simulates a 2-D array −


[jerry]$ awk 'BEGIN {
   array["0,0"] = 100;
   array["0,1"] = 200;
   array["0,2"] = 300;
   array["1,0"] = 400;
   array["1,1"] = 500;
   array["1,2"] = 600;

   # print array elements
   print "array[0,0] = " array["0,0"];
   print "array[0,1] = " array["0,1"];
   print "array[0,2] = " array["0,2"];
   print "array[1,0] = " array["1,0"];
   print "array[1,1] = " array["1,1"];
   print "array[1,2] = " array["1,2"];

On executing this code, you get the following result −


array[0,0] = 100
array[0,1] = 200
array[0,2] = 300
array[1,0] = 400
array[1,1] = 500
array[1,2] = 600

You can also perform a variety of operations on an array such as sorting its elements/indexes. For that purpose, you can use assort and asorti functions