April 16, 2024

Associative Arrays in Bash – How to Use Them

Associative Arrays in Bash - How to Use Them

While Bash doesn’t support associative arrays natively, there are several ways to get the same functionality using command line tools and other Bash utilities. In this tutorial, I’ll go over some of the methods you can use to create and interact with associative arrays in Bash as well as give examples of how you can use them in your scripts and terminal sessions. But first, let’s talk about what these things actually are!

 What are they?

The associative arrays that Bash provides are a little more powerful than regular arrays because they give you access to keys as well as values. An associative array is an indexed data structure where both the index (or key) and the data are strings. These arrays can contain anything, but usually include strings or numbers. Associative arrays are often used as name-value pairs with one or more associated names or identifiers being assigned a value. For example, here’s how we could represent the collection of fruits:

fruits=(apple mango banana)

Declaring an array

The first step to working with associative arrays is to declare them. This can be done with the declare builtin command, which requires that the name of the array and its contents are separated by a space:

# Declare an associative array called languages

declare -A languages

As seen here, these two commands would make up a syntax for declaring an associative array called languages. Next, we will assign values for each key. To do this, use subscripts which correspond with each key’s position. For example:

# Assign a value for the ‘en’ key

Counting elements

Bash arrays are implemented as an associative array data structure, which is a list that uses an arbitrary string to index the member of the list. In bash, arrays can be created by running the following command:

This will create two empty arrays called cars and colors. To populate these arrays with content, you need to access them using indices instead of indexes (i.e., $cars

Creating an array with lines from a file

Arrays are a useful data structure that can be used to hold a list of information. A key feature of arrays is the use of a unique identifier as its index, which is known as an associative index. Let’s look at an example of assigning values to different keys inside an array:

ARRAY=(cheese kiwi strawberry)

Appending to an array

You can also append arrays by using the following command:

myArray+=(value1 value2 …)

To update or delete entries, use these commands: myArray

Deleting an element from an array

To delete an element from an array, you can use the unset command. When deleting one or more elements at a time, it is important to remember that the order matters and you need to change all instances of the element(s) you are trying to delete. For example, if I had this array:

Adding all values together from an array

You can also use a formula. Add all the values together with this command: (( $(unset ARRAY) + $1 ) * 2) Remember that it may take time for the result to update because it has to go through each element of the array first before taking the sum. That is why the above solution using set is better than a simple calculation like adding values on line by line because Bash will execute those commands at once instead of one by one. For example, if you wanted to add up all the numbers from 1-10 and then output Sum: 50 you could use this command

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