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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.

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.

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:

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:

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:

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.

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:

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.

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.

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

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.