The (known as array expansion) syntax is used to represent all elements of the array. Then, we use a for loop to iterate over each value in the array. In this script, we first define an array named countries with three values. Next, insert the following script: #!/bin/bashĬountries=("India" "France" "United Kingdom") You should see the "nano" text editor in your terminal, as shown below: Run the following command to create the demo.sh file in the /usr/local/bin directory (or any other location you prefer) and open it in the "nano" text editor: nano /usr/local/bin/demo.sh Let’s start by creating a new script file. Bash Script for Looping Through Indexed Arrays With a For Loop Best of all, you won't need to go through the hassle of installing any additional software- everything you need is already set up and ready to use. You also need a text editor, such as "nano" or "vim", which come pre-installed by default in many Unix-like operating systems.įor the purpose of this blog post, I'll be using KodeKloud’s Ubuntu playground, which lets you access a pre-installed Ubuntu operating system in just one click. To try out the scripts in this blog post, you need access to a Bash shell. Now that we've covered the basics of different Bash array types and for loop syntax, let's dive in and write some Bash scripts to loop through array values. The commands within the loop are executed for each iteration.įor instance, when iterating over an array using a C-style for loop, you'd typically initialize an index variable to 0, continue the loop while the index is less than the array length, and increment the index at the end of each iteration. ![]() The increment is executed at the end of each loop iteration. The condition is evaluated before each iteration of the loop, and if it evaluates to true, the loop continues if not, the loop ends. In the C-style for loop, initialization is executed once before the loop begins. The C-style syntax looks like this: for (( initialization condition increment )) ![]() ![]() This syntax is particularly useful when you need to perform an action a specific number of times. C-style Syntaxīash also supports a C programming language style syntax for the for loop. The commands are the actions to be performed on each item. In this syntax, item is a variable that represents the current item in the item_list for each iteration of the loop. Here's what the Bash syntax looks like: for item in item_list The list of items can be a series of strings, numbers, or elements of an array. It loops through a list of items and performs a set of commands for each item. The traditional Bash for loop syntax is a simple and commonly used form. The for loop in Bash has two syntax forms: the traditional Bash syntax and a C-style syntax. To define an associative array in Bash, you use the declare command (declare -A), followed by the array name and its key-value pairs: declare -A array_name=(="value1" ="value2". ) Associative ArrayĪn associative array is an array that uses keys instead of numerical indices to store and access data. To define an indexed array, you use the following syntax: array_name=("element1" "element2" "element3". The first element in an array has an index of 0, the second has an index of 1, and so forth. Indexed ArrayĪn indexed array is a type of array where each element is assigned an automatic index based on its position. In Bash, there are two types of arrays: indexed arrays and associative arrays. Additionally, we'll also revisit the two common syntaxes of for loops - the traditional Bash syntax and the C-style syntax. ![]() Why? For loops offer a more streamlined syntax, leading to less verbose code compared to their while loop counterparts.īefore we jump into scripting, let’s refresh our understanding of the two types of arrays in Bash - indexed and associative. While for and while loops are often interchangeable in Bash, we'll be focusing solely on for loops. In this blog post, you’ll learn how to write bash scripts that utilize for loops to iterate through array values. For instance, you might want to loop through an array of filenames and execute specific commands on each one. Looping through array values is a common task in Bash scripting.
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