MQTT

A plain GET subscribes to the topic and prints all published messages. Doing a POST publishes the post data to the topic and exits.

Subscribe to the temperature in the home/bedroom subject published by example.com:

curl mqtt://example.com/home/bedroom/temp

Send the value 75 to the home/bedroom/dimmer subject hosted by the example.com server:

curl -d 75 mqtt://example.com/home/bedroom/dimmer

What does curl deliver as a response to a subscribe

It outputs two bytes topic length (MSB | LSB), the topic followed by the payload.

Caveats

Remaining limitations in curl's MQTT support as of September 2022:

• Only QoS level 0 is implemented for publish
• No way to set retain flag for publish
• No TLS (mqtts) support