--- title: "Redis List for Dynamic Data: A Comprehensive Guide" description: "Need a powerful and flexible solution for dynamic data management? Explore Redis List and unlock new possibilities for your applications with this tutorial." canonical: "https://adamtheautomator.com/redis-list/" --- # Redis List for Dynamic Data: A Comprehensive Guide > Need a powerful and flexible solution for dynamic data management? Explore Redis List and unlock new possibilities for your applications with this tutorial. Source: https://adamtheautomator.com/redis-list/ --- ATA Learning Tap to hide [ ATA Learning ](/) * [Home](/) * [Tutorials](/tutorials/) * [Instructors](/author/) * [Advertising](/advertising/) * [Recommended Resources](/resources/) * [About Adam](/about-adam/) Search for: * [](https://twitter.com/adbertram) * [](https://github.com/Adam-the-Automator) * [](https://www.linkedin.com/company/adam-the-automator-llc) * [](/feed/) ![Redis List for Dynamic Data: A Comprehensive Guide](https://adamtheautomator.com/wp-content/uploads/2022/05/Learn-to-Manage-a-Dynamic-Redis-List.jpg) # Redis List for Dynamic Data: A Comprehensive Guide [![](https://secure.gravatar.com/avatar/2788bb1a3f735603f81eca51d68daec56a9d97e805a10268fb2c20afcc76b81b?s=192&d=mm&r=g)Nicholas Xuan Nguyen](https://adamtheautomator.com/author/nicholas-xuan-nguyen/)7 March 20248 min. read Categories: [IT Ops](/category/it-ops/) Tags:[Redis](/tag/redis/) Table of Contents * [Prerequisites](#prerequisites) * [Creating an Inventory Management Redis List](#creating-an-inventory-management-redis-list) * [Appending Elements Only if the Specified List Exists](#appending-elements-only-if-the-specified-list-exists) * [Retrieving Elements from the Redis List](#retrieving-elements-from-the-redis-list) * [Removing Old Elements](#removing-old-elements) * [Moving Elements from One List to Another](#moving-elements-from-one-list-to-another) * [Blocking Operations on a List](#blocking-operations-on-a-list) * [Conclusion](#conclusion) Are you working with collections of data in your application? If you find yourself using arrays or linked lists to store data, you’ll need to use a [Redis list](https://redis.io/docs/manual/data-types/#lists). In this tutorial, you’ll learn how to use Redis lists to build sophisticated applications. Ready? Read on and never use an array the same way again! ## Prerequisites This tutorial will be a hands-on demonstration. If you’d like to follow along, be sure you have the following. * A Linux machine – This tutorial uses Ubuntu 20.04. Related:[How to Install Ubuntu 20.04 \[Step-by-Step\]](https://adamtheautomator.com/install-ubuntu/) * Redis installed and running on your machine. Related:[How to Perform a Secure Redis Install on Linux](https://adamtheautomator.com/redis-install/) ## **Creating an Inventory Management Redis List** There are many ways to use Redis lists, but this tutorial covers examples you can use for real-world applications. You’ll create a list that can be used to manage your inventory. 1\. SSH to your server, open the terminal and run the following command to check the status of the Redis service. ```bash sudo systemctl status redis ``` You can see in the output below that the Redis service is active (running). ![Checking Redis Service Status](https://adamtheautomator.com/wp-content/uploads/2022/05/image-20.png) Checking Redis Service Status Related:[Getting Started using SSH with PowerShell](https://adamtheautomator.com/powershell-ssh/) > _If the Redis service is not running, run the systemctl command below to start the Redis service. sudo systemctl start redis_ Related:[Correct Way of Using Ubuntu systemctl to Control Systemd](https://adamtheautomator.com/ubuntu-systemctl/) 2\. Next, run the following command to open the [Redis CLI](https://redis.io/docs/manual/cli/). The Redis CLI is a command-line tool used to send commands to a Redis server and read responses from the server. ```bash redis-cli ``` As shown below, the prompt changes once you’re in the Redis CLI, indicating you’re now working in the Redis environment. ![Viewing Redis CLI](https://adamtheautomator.com/wp-content/uploads/2022/05/image-21.png) Viewing Redis CLI 3\. Now, run the following [RPUSH](https://redis.io/commands/rpush/) command to add an element named ata1 to the list named my\_member. This command inserts all specified items at the tail of the list (my\_member). If the list (my\_member) does not exist, Redis creates it as an empty list just before the append operation. > _Redis List supports both left and right pushes, which means you can add elements to the list’s head or tail. This behavior is helpful when you want to implement a queue or a stack._ ```bash RPUSH my_member ata1 ``` You can see below that the command returned an integer value of 1, which indicates that one element was added to the list. This value is the length of the list after the push operation. ![Adding One Member to the List (my\_member)](https://adamtheautomator.com/wp-content/uploads/2022/05/image-22.png) Adding One Member to the List (my\_member) Perhaps you need to add multiple elements in one go. If so, run the same RPUSH command and specify the members’ names separated by single spaces, as shown below: ```bash RPUSH my_member ata1 ata2 ata3 ata4 ``` > _Note that members are added one after another to the tail of the list from left to right._ As you can see below, five elements were added to the list (one existing and four new members). ![Adding Multiple Members to the Tail of the List](https://adamtheautomator.com/wp-content/uploads/2022/05/image-23.png) Adding Multiple Members to the Tail of the List 4\. Lastly, run the [LPUSH](https://redis.io/commands/lpush/) command below to add elements to the head of a list (my\_member2), from left to right. Like the RPUSH command, if the specified list doesn’t exist, that list is created as an empty list just before the push operation. Each member will be added to the list in the following order: * `ata4` as the first element. * `ata3` as the second element. * `ata2` as the third element. * ata1 as the fourth element. ```bash LPUSH my_member2 ata1 ata2 ata3 ata4 ``` You can see in the output that four elements (4) were added to the list since you added four new members. ![Adding members to the head of the list](https://adamtheautomator.com/wp-content/uploads/2022/05/image-24.png) Adding members to the head of the list ## Appending Elements Only if the Specified List Exists You’ve created a list and added a couple of elements. But what if the specified list doesn’t exist? You can use the [RPUSHX](https://redis.io/commands/rpushx/) command to append an element to the tail of a list, but only if the list exists. The RPUSHX command is similar to the RPUSH command. The only difference is that no operation is performed when the specified list doesn’t exist. The RPUSHX command can be helpful to avoid wasting memory by creating lists that will never be used. Run the following [RPUSHX](https://redis.io/commands/rpushx/) command to append elements to a non-existent list named my\_list\_nonexisted. ```bash RPUSHX my_list_nonexisted ata1 ata2 ata3 ``` You can see in the following output that no elements (**0**) were added to the list since the list doesn’t exist. ![Adding Members to the Head of Non-existent List](https://adamtheautomator.com/wp-content/uploads/2022/05/image-25.png) Adding Members to the Head of Non-existent List Now, run the following command to add multiple members to the head of a non-existent list named `my_list_not_existed`. Like RPUSHX, the [LPUSHX](https://redis.io/commands/lpushx/) command adds elements to the head of a list only if the specified list exists. If the specified list doesn’t exist, no operation is performed. ```bash LPUSHX my_list_not_existed ata1 ata2 ata3 ata4 ``` You can see in the output below that no elements were added (**0**) to the list since the specified list (**my\_list\_not\_existed**) doesn’t exist. ![Adding Members to the Head of Non-existent List](https://adamtheautomator.com/wp-content/uploads/2022/05/image-26.png) Adding Members to the Head of Non-existent List ## Retrieving Elements from the Redis List Adding data to your Redis list is not the only thing you need to build an application. Undoubtedly, your application needs to retrieve elements from your Redis list. To retrieve elements from your Redis list, you’ll run the [LINDEX](https://redis.io/commands/lindex/) command. This command returns elements at specified indices in a list. > _The zero-based index is used to specify the position of an element in a list. The 0 index represents the first element in the list, 1 represents the next element/second, and so on._ 1\. Run the following LINDEX commands to retrieve the first, second, and third elements from the my\_member2 list. ```bash LINDEX my_member2 0 LINDEX my_member2 1 LINDEX my_member2 2 ``` Below, only three elements were retrieved from the list by the corresponding indices: * The **ata4** element is at the first index (**0**). * The **ata3** element is at the second index (**1**). * The ata2 element is at the third index (2). As you remember, you added these elements to the my\_member2 list using the LPUSH command. This output confirms that the elements were added to the list as expected. ![Retrieving the first, second, and third elements](https://adamtheautomator.com/wp-content/uploads/2022/05/image-27.png) Retrieving the first, second, and third elements 2\. Next, run the following LRANGE command to retrieve the first five elements (0 5) from the my\_member list instead of a single element only. ```bash LRANGE my_member 0 5 ``` You can see in the output below that Redis retrieved all elements from the my\_member list. ![Retrieving All Members from a List (my\_member)](https://adamtheautomator.com/wp-content/uploads/2022/05/image-28.png) Retrieving All Members from a List (my\_member) 3\. Finally, run the command below to retrieve only the last five members from the my\_member2 list. Specify the start (-5) and stop (-1) positions for the range of elements you’re retrieving. You use negative indexes to retrieve data from the end of the list as follows: * The -1 index represents the last element in a list. * The -2 index represents the penultimate element. ```bash LRANGE my_member2 -5 -1 ``` ![Retrieving Only the Last Five Elements from a List (my\_member2)](https://adamtheautomator.com/wp-content/uploads/2022/05/image-29.png) Retrieving Only the Last Five Elements from a List (my\_member2) ## **Removing Old Elements** Adding elements to your list consumes memory, especially if you still keep unused ones. Good thing Redis lets you remove old elements with the LREM command. Make room for new ones, and save memory. The `LREM` command takes the list (`key`), the number of items (`count`) to remove, and the `element` value as arguments in the syntax below. The `count` argument can take the following values: * count = 0: removes all elements that match the element value from a list. * count > 0: removes the number of elements that match the element value from the head of a list. * count < 0: removes the number of elements that match the element value from the tail of the list. ```bash LREM key count element ``` To see how the `LREM` command removes old elements from your lists: 1\. Run the following LREM command to remove the ata1 element in the my\_member list. Since you added two ata1 elements in the previous examples, this command removes the first old ata1 element from the head of the list. ```bash LREM my_member 1 "ata1" ``` ![Removing an Old Element](https://adamtheautomator.com/wp-content/uploads/2022/05/image-30.png) Removing an Old Element 2\. Next, run the LRANGE command below to retrieve the first four elements (0 4) from the my\_member list. ```bash LRANGE my_member 0 4 ``` Below, you can confirm that the ata1 item was removed from the head of the my\_member list. ![Retrieving All Elements](https://adamtheautomator.com/wp-content/uploads/2022/05/image-31.png) Retrieving All Elements 3\. Run the below command to remove all elements with values as ata1 from the my\_member list. ```bash LREM my_member 0 "ata1" ``` ![Removing All ata1 Elements](https://adamtheautomator.com/wp-content/uploads/2022/05/image-32.png) Removing All ata1 Elements 4\. Lastly, rerun the LRANGE command to retrieve the first four elements (0 3) from the my\_member list. ```bash LRANGE my_member 0 3 ``` Below, you can confirm all elements with the ata1 value were removed from the my\_member list. ![Confirming All Elements with ata1 Value Were Removed](https://adamtheautomator.com/wp-content/uploads/2022/05/image-33.png) Confirming All Elements with ata1 Value Were Removed ## **Moving Elements from One List to Another** Suppose you migrated your website to a new hosting service, and you want to move all your users from the old list to the new one. If so, the Redis list is still up to the task with the [RPOPLPUSH](https://redis.io/commands/rpoplpush/) command. The RPOPLPUSH command lets you move elements from one list to another. Run the following `RPOPLPUSH` command to move all elements from the `my_member2` to `my_member3` list. ```bash RPOPLPUSH my_member2 my_member3 ``` The `RPOPLPUSH` command moves one element at a time. So if you have like five elements in a list, you’ll run the same command five times, as shown below. And after moving all the elements, you’ll receive a **(nil)** output. > _Running the same command to move elements one at a time can be tedious, especially if you’re moving tons of them. Of course, you might want to move all elements in one go by implementing a loop in your application code. Learning [How To Manage Redis Sorted Set](https://adamtheautomator.com/redis-sorted-set/) will also come in handy._ ![Moving Elements from One List to Another](https://adamtheautomator.com/wp-content/uploads/2022/05/image-34.png) Moving Elements from One List to Another Now, run the following `LRANGE` command to retrieve all elements in the `my_member3` list. ```bash LRANGE my_member3 0 3 ``` The output below confirms that all members are now in the destination list (my\_member3). ![Viewing Elements in the Destination List (my\_member3)](https://adamtheautomator.com/wp-content/uploads/2022/05/image-35.png) Viewing Elements in the Destination List (my\_member3) ## Blocking Operations on a List Blocking popup primitive (BLPOP) for lists is a Redis command that returns the first element in a list, if available. BLPOP also blocks the client for a specific time before executing any command. Blocking commands, like `BLPOP`, are helpful in many situations. For instance, you may want to wait for a new job from a queue or for a new notification that arrives from some other system. > _Note that blocking commands doesn’t block the server but just the connection calling the command._ When your application calls `BLPOP`, you provide one or more keys (i.e., `list1`, `list2`, and `list3`), as shown below. Redis checks if any of the keys hold a non-empty list. If so, an element is popped from the head of this list. The element is then returned to your application together with the name of the key where it was taken. ```bash BLPOP list1 list2 list3 ``` To see how the `BLPOP` command works: 1\. Run the following RPUSH command to insert some data into the list1. ```bash RPUSH list1 ata1 ata2 ata3 ``` ![Adding Data to the list1 List](https://adamtheautomator.com/wp-content/uploads/2022/05/image-36.png) Adding Data to the list1 List 2\. Now, run the BLPOP command below to block the client’s connection if at least one of the specified lists is not empty, and wait for (0) seconds for new data to arrive. ```bash BLPOP list1 list2 0 ``` > _The time limit can also be specified as -1, which means no time limit. And Redis will block the connection indefinitely if the lists are empty._ If no new data arrives after the specified time limit, Redis returns two elements if at least one list is not empty, as shown below, The first element is the list’s name from which the data was taken (from list1 since list2 doesn’t exist). The second element is the actual data from the list (list1). ![Blocking Connection Until Condition is Met](https://adamtheautomator.com/wp-content/uploads/2022/05/image-37.png) Blocking Connection Until Condition is Met > _When a new element is added to one of the lists, Redis wakes up your connection. Redis then returns the element together with the name of the key where it was taken._ ## Conclusion In this tutorial, you’ve learned how to manage a Redis list. You’ve seen commands to dynamically add, remove and fetch data in a Redis list. Moreover, you learned about blocking commands and how they can be used with Redis lists. Remember to practice all the different Redis commands to become confident using them. Why not try implementing Redis lists in your own projects? You can use [Redis list with Node.js](https://www.sitepoint.com/using-redis-node-js/) to store data like user sessions, message queues, etc. You can also use lists with other data types to create more complex data structures like graphs and [trees](https://medium.com/@chethanbandi/storing-tree-structure-in-redis-cf43c3775c99). 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