Skip to main content
Redis Basics
CHAPTER 04 Intermediate

Redis Strings Tutorial | SET, GET, INCR Commands

Updated: May 16, 2026
15 min read

# CHAPTER 4

Redis Strings and Basic Operations

1. Introduction

Welcome to the terminal. It is time to start caching data. The most foundational, essential building block of Redis is the String. Despite the name, a Redis String can hold text, serialized JSON, binary files, or integers. If you only ever learn how to use Redis Strings, you can still architect incredibly powerful caching layers. In this chapter, we will master the basic CLI commands required to insert, read, and manipulate string data.

2. Learning Objectives

By the end of this chapter, you will be able to:
  • Connect to the redis-cli.
  • Execute the SET and GET commands.
  • Check if a key exists using EXISTS.
  • Delete keys using DEL.
  • Perform atomic integer math using INCR and DECR.

3. The Holy Grail: SET and GET

The entire Key-Value paradigm is built on these two words. Open your terminal and type redis-cli.

To insert data, use SET:

bash
1 
SET username "alice_smith"

*(Redis responds: OK)*

To retrieve data, use GET:

bash
1 
GET username

*(Redis responds: "alice_smith")*

If you try to GET a key that hasn't been created yet, Redis returns (nil). (Nil is the Redis equivalent of Null).

4. Overwriting and Appending

What happens if you run SET on a key that already exists?
bash
1 
SET username "bob_jones"

It instantly overwrites the old data. GET username will now return "bob_jones".

What if you want to add to the end of a string without destroying the original? Use APPEND:

bash
123 
SET greeting "Hello"
APPEND greeting " World!"
GET greeting

*(Redis responds: "Hello World!")*

5. Managing Keys (EXISTS and DEL)

Before your application tries to fetch a massive block of data, it is good practice to check if the key even exists in RAM.
bash
1 
EXISTS username

*(Redis responds with an integer: 1 if it exists, 0 if it does not).*

To remove data from RAM and free up memory, use the Delete command:

bash
1 
DEL username

*(Redis responds: 1 to confirm it deleted one key).*

6. Atomic Counters (INCR and DECR)

This is where Strings become magical. If a String contains a number, Redis can perform math on it natively.
bash
123 
SET page_views 100
INCR page_views
GET page_views

*(Redis responds: "101").*

To decrease a number, use DECR:

bash
1 
DECR page_views

*(Redis responds: "100").*

To add a specific amount (like 50 points), use INCRBY:

bash
1 
INCRBY page_views 50

7. Why INCR is "Atomic" (Real-World Use Case)

Imagine 10,000 users visit your website at the exact same millisecond. If you use MySQL to track page views, 10,000 users will run SELECT views, see the number 100, add 1, and run UPDATE views SET views = 101. The final total will be 101, which is mathematically disastrous. 10,000 hits were lost due to a "Race Condition."

INCR is an Atomic Operation. Because Redis is single-threaded, if 10,000 users trigger the INCR command at the same time, Redis queues them up in a single file line and executes them perfectly one-by-one in microseconds. The final result will be a mathematically perfect 10,100.

8. Mini Project: The Live Counter

Let's build the logic for a "Likes" button on a social media app.
  1. 1. redis-cli
  1. 2. Initialize the post's like count:
SET post:5499:likes 0
  1. 3. Three users click "Like" simultaneously:
INCR post:5499:likes INCR post:5499:likes INCR post:5499:likes
  1. 4. Fetch the final score to display on the frontend:
GET post:5499:likes *(Returns 3)*.

9. Common Mistakes

  • Spacing in values: If you type SET mykey Hello World, Redis will throw a syntax error. Because there is a space, Redis thinks "World" is a separate command parameter. If your value contains spaces, you MUST wrap it in double quotes: SET mykey "Hello World".

10. Best Practices

  • MSET and MGET: If you need to set or get 5 keys at the same time, do not run SET 5 separate times. This creates "Network Latency" (the time it takes data to travel from the app to the database). Use MSET (Multiple Set) and MGET to do it all in one single round-trip connection.
MSET user1 "Alice" user2 "Bob" MGET user1 user2

11. Exercises

  1. 1. What command do you use to retrieve the value associated with a specific key?
  1. 2. If the key score currently holds the value "10", what command will instantly change the value to "15" using mathematical addition?

12. Redis Challenges

You run the command INCR activeusers. However, you forgot to create the activeusers key first with the SET command. What will Redis do? Will it crash? *(Answer: It will not crash. In Redis, if you call INCR on a key that does not exist, Redis is smart enough to assume the starting value is 0. It will automatically create the key and instantly increment it to 1).*

13. MCQ Quiz with Answers

Question 1

A web application tracks product inventory using Redis. 50 users attempt to buy the last remaining laptop at the exact same millisecond. Why is utilizing the Redis DECR command mathematically safer than pulling the inventory count into the backend application, subtracting 1, and saving it back?

Question 2

When utilizing the redis-cli, what is the correct syntax to store a string containing spaces?

14. Interview Questions

  • Q: Define an "Atomic Operation" in the context of Redis. Why is the INCR command heavily favored by system architects for implementing rate-limiters and global counters?
  • Q: Explain the purpose of the MGET command. How does fetching multiple keys simultaneously improve application performance compared to executing GET multiple times?

15. FAQs

Q: Can I store a massive PDF file in a Redis String? A: Technically, yes. A Redis String can hold up to 512MB of binary data. However, storing large files in RAM is an incredibly expensive waste of server resources. Files should be stored on AWS S3, and you should only store the *URL link* to the file in Redis.

16. Summary

You are now manipulating data in memory. By mastering SET, GET, and the atomic power of INCR, you possess the foundational skills required to build blazing-fast caching layers, API rate-limiters, and high-concurrency tracking systems.

17. Next Chapter Recommendation

Strings are perfect for single values. But what if you need to manage a massive line of people waiting to buy tickets? In Chapter 5: Redis Lists and Queue Systems, we will learn how to build high-performance data pipelines using linked lists.

Finish this Chapter

Save your progress on your learning path and prepare for coding interview challenges.

Previous Chapter Redis Data Structures Explained | Strings, Lists, Sets & Hashes
Next Chapter Redis Lists Tutorial | Building Queues with LPUSH & RPOP

Discussion

Join the discussion

Log in or create a free account to participate.

Sort: ·

Explore More

📖 Related Tutorials 6

❓ Related Quizzes 6