awk Programming

Arrays 1

You may know what arrays are from previous programming experience - they are collections of related elements or objects.

Arrays in awk are associative. Each array is a collection of pairs - an index and the associated element. In this sense, it is similar to a Perl hash.
Arrays in awk only store values - the index is implied from the order of the values.
Indices can be either numeric or strings.
Numeric indices do not have to be contiguous.
Numeric indices do not have to be positive integers.
Array subsripts are always strings. A numeric value is converted to a string before being used.
An array cannot have the same name as a variable in the same awk program.
A reason to use arrays - the time to access an element is independent of the number of elements in the array!

As a programming language, awk can deal with arrays of data very well. So let's create an array to work with.

In a previous page on Scripting, we introduced the ability to write scripts, which can then be executed by awk. That's what we're going to do here to create our array.

Copy and paste the following code into a file and name it 'arrays1.awk':

BEGIN {
	awry["three"] = "blueberry"
	awry["four"] = "apple"
	awry["two"] = "cherry"
	awry["seven"] = "pineapple"
	awry["eight"] = "orange"
	awry["five"] = "grape"
	awry["six"] = "strawberry"
	awry[1] = "pear"
	print "\nUnsorted ...";
	for (i in awry) {
		print i " : " awry[i]
	}
}

That is an awk script, which you call when running awk:

 awk -f arrays1.awk

You will notice a few things that might seem odd. First, most of the indices are strings - there is one numeric index. How does that work?

We've also snuck in a loop construction. Not complicated but unique when dealing with an array.

When you run it in your shell, you should see something like this:

Unsorted ...
three : blueberry
seven : pineapple
two : cherry
five : grape
eight : orange
six : strawberry
four : apple
1 : pear

Another odd thing: these are not in the same order as the array!.

This shows us the difference between a loop index, and an array index.

When awk creates an array, the indices are consecutive integers beginning at 1. Note the loop is different from a regular 'for' loop - it is using the array index.

awk

Arrays 1

Sorting an array