How To Manage Strings in Redis
Redis is an open-source, in-memory key-value data store. In Redis, strings are the most basic type of value you can create and manage. This tutorial provides an overview of how to create and retrieve strings, as well as how to manipulate the values held by string keys.
How To Use This Guide
This guide is written as a cheat sheet with self-contained examples. We encourage you to jump to any section that is relevant to the task you’re trying to complete.
The commands shown in this guide were tested on an Ubuntu 18.04 server running Redis version 4.0.9. To set up a similar environment, you can follow Step 1 of our guide on How To Install and Secure Redis on Ubuntu 18.04. We will demonstrate how these commands behave by running them with
redis-cli, the Redis command line interface. Note that if you’re using a different Redis interface — Redli, for example — the exact output of certain commands may differ.
Alternatively, you could provision a managed Redis database instance to test these commands, but note that depending on the level of control allowed by your database provider, some commands in this guide may not work as described. To provision a DigitalOcean Managed Database, follow our Managed Databases product documentation. Then, you must either install Redli or set up a TLS tunnel in order to connect to the Managed Database over TLS.
Creating and Managing Strings
Keys that hold strings can only hold one value; you cannot store more than one string in a single key. However, strings in Redis are binary-safe, meaning a Redis string can hold any kind of data, from alphanumeric characters to JPEG images. The only limit is that strings must be 512 MB long or less.
To create a string, use the
set command. For example, the following
set command creates a key named
key_Welcome1 that holds the string
- set key_Welcome1 "Howdy"
To set multiple strings in one command, use
- mset key_Welcome2 "there" key_Welcome3 "partners,"
You can also use the
append command to create strings:
- append key_Welcome4 "welcome to Texas"
If the string was created successfully,
append will output an integer equal to how many characters the string includes:
append can also be used to change the contents of strings. See the section on manipulating strings for details on this.
To retrieve a string, use the
- get key_Welcome1
To retrieve multiple strings with one command, use
- mget key_Welcome1 key_Welcome2 key_Welcome3 key_Welcome4
Output1) "Howdy" 2) "there" 3) "partners," 4) "welcome to Texas"
For every key passed to
mget that doesn’t hold a string value or doesn’t exist at all, the command will return
If a string is made up of an integer, you can run the
incr command to increase it by one:
- set key_1 3
- incr key_1
Similarly, you can use the
incrby command to increase a numeric string’s value by a specific increment:
- incrby key_1 16
decrby commands work the same way, but they decrease the integer stored in a numeric string:
- decr key_1
- decrby key_1 16
If an alphabetic string already exists,
append will append the value onto the end of the existing value and return the new length of the string. To illustrate, the following command appends
", y'all" to the string held by the key
key_Welcome4, so now the string will read
"welcome to Texas, y'all":
- append key_Welcome4 ", y'all"
You can also append integers to a string holding a numeric value. The following example appends
3, the integer held in
key_1, so it will then hold
345. In this case,
append will also return the new length of the string, rather than its new value:
- append key_1 45
Because this key still only holds a numeric value, you can perform the
decr operations on it. You can also append alphabetic characters to an integer string, but if you do this then running
decr on the string will produce an error as the string value is no longer an integer.
This guide details a number of commands used to create and manage strings in Redis. If there are other related commands, arguments, or procedures you’d like to see outlined in this guide, please ask or make suggestions in the comments below.
For more information on Redis commands, see our tutorial series on How to Manage a Redis Database.