Redis Caching & Messaging (Pub/Sub, Streams) · Lesson

Pattern Matching Subscriptions

Utilize `PSUBSCRIBE` to subscribe to multiple channels based on patterns, enhancing flexibility.

Pattern Matching Subscriptions is a free Redis Caching & Messaging (Pub/Sub, Streams) lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Redis Caching & Messaging (Pub/Sub, Streams) learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Flexible Subscriptions with Patterns

Welcome to a powerful feature of Redis Pub/Sub: Pattern Matching Subscriptions. Instead of subscribing to a single, exact channel name, you can subscribe to multiple channels using flexible patterns.

This allows your application to listen for a wider range of related messages with a single subscription, making your message handling more dynamic.

Why Use Pattern Matching?

Imagine you have many services, each publishing events to channels like service.auth.login, service.orders.created, or service.inventory.updated.

Centralized Logging: A single logger service can subscribe to service.* to catch all events.
Dynamic Event Handling: Easily react to new event types without changing subscription code.
Microservices: Decouple services further by allowing them to publish to specific sub-channels within a pattern.

PSUBSCRIBE in the Redis CLI

The command for pattern matching is PSUBSCRIBE. Let's see how it works in the Redis CLI.

First, open a Redis CLI client and run:

PSUBSCRIBE log.*

The Asterisk (*) Wildcard

The * (asterisk) wildcard is used to match any sequence of characters (including an empty sequence) within a single part of a channel name.

For example, log.* will match log.app, log.system, but not log.web.server because * only matches up to the next . (dot).

If you then publish a message:

PUBLISH log.app "User logged in"

The Question Mark (?) Wildcard

The ? (question mark) wildcard matches exactly one character at a specific position.

This is useful when you expect a fixed number of characters, like an ID or a specific status code.

Try this pattern in your CLI:

PSUBSCRIBE device.temp.??

Combining Wildcards for Power

You can combine * and ? for even more granular control over your subscriptions. This allows for highly flexible and specific pattern matching.

Consider a pattern like chat.room.*.user.???. This pattern would match channels like chat.room.general.user.001 or chat.room.private.user.abc, but not chat.room.main.user.1 (too few chars for ???).

If a message is published to chat.room.general.user.007, it would be received by the above pattern.

Python `psubscribe` Example

Let's see how to implement pattern subscriptions using a Python client library (redis-py). This subscriber will listen for any message on channels matching events.*.

Run this code first, then the publisher in the next scene:

import redis
import time

r = redis.Redis(decode_responses=True)
pubsub = r.pubsub()

pubsub.psubscribe('events.*')

print("Subscribed to 'events.*'. Listening for 5 seconds...")

start_time = time.time()
for message in pubsub.listen():
    if message['type'] == 'pmessage':
        print(f"Pattern: {message['pattern']}")
        print(f"Channel: {message['channel']}")
        print(f"Data: {message['data']}")
    
    if time.time() - start_time > 5: # Listen for 5 seconds
        pubsub.punsubscribe('events.*')
        break
    time.sleep(0.01)

print("Subscriber stopped.")

Python Publisher Interaction

Now, run this Python publisher. The messages it sends will be caught by the pattern subscriber you just ran, demonstrating the power of pattern matching.

import redis
import time

r = redis.Redis(decode_responses=True)

print("Publishing messages...")

r.publish('events.user.signup', 'New user: Alice')
time.sleep(0.5)
r.publish('events.product.view', 'Product ID: 12345')
time.sleep(0.5)
r.publish('events.order.placed', 'Order ID: 98765')
time.sleep(0.5)
r.publish('metrics.cpu', 'CPU usage: 85%') # This won't match 'events.*'

print("Messages published.")

Real-World Use Cases

Pattern matching subscriptions are incredibly versatile for building real-time applications:

Monitoring & Analytics: Collect data from various services (e.g., metrics.cpu.*, metrics.memory.*).
Notifications: Send alerts for different event types (e.g., alert.high_priority.*).
Multi-tenant Systems: Isolate messages for different tenants (e.g., tenant.123.events.*).
Dynamic Routing: Route messages to different handlers based on their channel patterns.

Test Your Pattern Skills

A client uses PSUBSCRIBE with the pattern device.*.status.?. Which of these published channel names would it receive messages from?

Recap: Dynamic Pub/Sub

You've learned how Redis PSUBSCRIBE allows for incredibly flexible and dynamic message routing in your applications. By using the * and ? wildcards, you can listen to broad categories of events or very specific sub-channels.

This capability is fundamental for building scalable and decoupled real-time systems, enabling powerful event-driven architectures.

Frequently asked questions

Is the “Pattern Matching Subscriptions” lesson free?

Yes — the full text of “Pattern Matching Subscriptions” is free to read here on the web, and the Redis Caching & Messaging (Pub/Sub, Streams) course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Redis Caching & Messaging (Pub/Sub, Streams) course, upgrade to CoddyKit PRO.

What will I learn in “Pattern Matching Subscriptions”?

Utilize `PSUBSCRIBE` to subscribe to multiple channels based on patterns, enhancing flexibility. You practise Redis Caching & Messaging (Pub/Sub, Streams) with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Redis Caching & Messaging (Pub/Sub, Streams)?

No prior experience is required. Redis Caching & Messaging (Pub/Sub, Streams) on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Pattern Matching Subscriptions” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Redis Caching & Messaging (Pub/Sub, Streams) lesson?

Yes. Every Redis Caching & Messaging (Pub/Sub, Streams) lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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