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SUBSCRIBE

Subscribes the client to one or more channels.

Syntax​

SUBSCRIBE channel [channel ...]

Parameters​

  • channel: One or more channel names to subscribe to. Each channel is specified separately.

Details​

  • Available since: 1.0.0
  • Time complexity: O(1) for each subscription. The time complexity depends on the number of channels subscribed to.
  • ACL categories: @pubsub, @read

The SUBSCRIBE command allows a client to subscribe to one or more channels. Once subscribed, the client will receive messages sent to those channels. This command is used for direct channel-based message distribution, where each message is sent to the channels specified.

Examples​

Basic Usage​

To subscribe to a single channel:

SUBSCRIBE news

After running this command, the client will start receiving messages published to the news channel.

Subscribing to Multiple Channels​

To subscribe to multiple channels simultaneously:

SUBSCRIBE news sports weather

The client will receive messages from all specified channels: news, sports, and weather.

Receiving Messages​

When a message is published to a subscribed channel, the client will receive a message formatted as follows:

1) "message"
2) "channel"
3) "message content"

For example, if a message "Hello world!" is published to the news channel:

1) "message"
2) "news"
3) "Hello world!"

Unsubscribing​

To stop receiving messages from a channel, use the UNSUBSCRIBE command:

UNSUBSCRIBE news

Edge Cases​

  • If a channel does not exist or has no subscribers, the client will still be subscribed to it, but no messages will be received until a message is published.
  • If the client is already subscribed to the specified channels, the command has no effect on those existing subscriptions.

RESP2/RESP3 Reply​

  • Array reply: The command returns an array containing the following elements:
    1. The message type subscribe.
    2. The channel that was subscribed to.
    3. The number of channels the client is currently subscribed to.

Example reply for SUBSCRIBE news:

1) "subscribe"
2) "news"
3) (integer) 1

This indicates that the client has been subscribed to the news channel and is currently subscribed to 1 channel.

Notes​

  • The SUBSCRIBE command is used for direct channel-based messaging in Redis.
  • For pattern-based subscriptions, use the PSUBSCRIBE command.
  • To unsubscribe from channels, use the UNSUBSCRIBE command.