Publish and subscribe to MQTT messages on the command line

thin-edge.io cli provides a convenient way to debug and aid development process.

Publish

Command tedge mqtt pub can be used to publish MQTT messages on a topic to the local mosquitto server.

Example:

tedge

tedge mqtt pub 'te/device/main///m/env_sensor' '{
  "temperature": 21.3
}'

mosquitto

mosquitto_pub -t 'te/device/main///m/env_sensor' -m '{
  "temperature": 21.3
}'

mqtt

Publish topic

te/device/main///m/env_sensor

Payload

{
  "temperature": 21.3
}

Messages can also be published with a different Quality of Service (QoS).

tedge

tedge mqtt pub -q 2 'te/device/main///m/env_sensor' '{
  "temperature": 21.3
}'

mosquitto

mosquitto_pub -q 2 -t 'te/device/main///m/env_sensor' -m '{
  "temperature": 21.3
}'

mqtt

Publish topic: qos=2

te/device/main///m/env_sensor

Payload

{
  "temperature": 21.3
}

MQTT messages can also be published using the retained option which means that the message will be received by new MQTT clients connecting to the broker after the message was published.

Below shows an example of publishing a retained MQTT message:

tedge

tedge mqtt pub -r -q 1 'te/device/main///a/high_temperature' '{
  "text": "Temperature is critical",
  "severity": "critical"
}'

mosquitto

mosquitto_pub -r -q 1 -t 'te/device/main///a/high_temperature' -m '{
  "text": "Temperature is critical",
  "severity": "critical"
}'

mqtt

Publish topic: retain=true, qos=1

te/device/main///a/high_temperature

Payload

{
  "text": "Temperature is critical",
  "severity": "critical"
}

note

By default the mqtt message will be published with retain flag set to false.

Subscribe

Command tedge mqtt sub can be used to ease debugging of of MQTT communication on local bridge. You can subscribe to topic of your choosing:

tedge

tedge mqtt sub 'te/errors'

mosquitto

mosquitto_sub -t 'te/errors'

mqtt

Subscribe: topic

te/errors

Or you can subscribe to any topic on the server using wildcard (#) topic:

tedge

tedge mqtt sub '#'

mosquitto

mosquitto_sub -t '#'

mqtt

Subscribe: topic

#

Now using a different console/shell, publish the following measurement so that the previous subscription will receive it:

tedge

tedge mqtt pub -r -q 1 'te/device/main///m/env_sensor' '{
  "temperature": 21.3
}'

mosquitto

mosquitto_pub -r -q 1 -t 'te/device/main///m/env_sensor' -m '{
  "temperature": 21.3
}'

mqtt

Publish topic: retain=true, qos=1

te/device/main///m/env_sensor

Payload

{
  "temperature": 21.3
}

All messages from sub command are printed to stdout and can be captured to a file if you need to:

tedge

tedge mqtt sub '#' > filename.mqtt

mosquitto

mosquitto_sub -t '#' > filename.mqtt

mqtt

Subscribe: topic

#

Wildcard (#) topic is used by MQTT protocol as a wildcard and will listen on all topics