CloudAMQP with MQTT from the command line

The Mosquitto clients, mosquitto_pub and mosquitto_sub, publish and subscribe from a terminal: a quick way to try MQTT, check your connection details or watch a topic.

sudo apt-get install mosquitto-clients   # Debian and Ubuntu
brew install mosquitto                   # macOS

Set MQTT_HOST, MQTT_PORT, MQTT_USERNAME and MQTT_PASSWORD to the MQTT details on your instance’s details page in the CloudAMQP console. Port 8883 uses TLS. Without them, the scripts connect to a local broker.

Save the publisher as publisher.sh:

#!/bin/sh
set -eu

port=${MQTT_PORT:-1883}
# Port 8883 uses TLS, verified against the system's certificates
[ "$port" = 8883 ] && set -- --tls-use-os-certs

# QoS 1 waits for the broker's PUBACK
mosquitto_pub "$@" -h "${MQTT_HOST:-localhost}" -p "$port" \
  -u "${MQTT_USERNAME:-guest}" -P "${MQTT_PASSWORD:-guest}" \
  -q 1 -t hello -m "Hello world!"
echo " [x] Sent 'Hello world!'"

Save the subscriber as worker.sh:

#!/bin/sh
set -eu

port=${MQTT_PORT:-1883}
# Port 8883 uses TLS, verified against the system's certificates
[ "$port" = 8883 ] && set -- --tls-use-os-certs

# Subscribes with QoS 1, and prints each message until you press CTRL+C
exec mosquitto_sub "$@" -h "${MQTT_HOST:-localhost}" -p "$port" \
  -u "${MQTT_USERNAME:-guest}" -P "${MQTT_PASSWORD:-guest}" \
  -q 1 -t hello -F " [x] Received '%p'"

Make them executable with chmod +x publisher.sh worker.sh, then run ./worker.sh in one terminal and ./publisher.sh in another.

A runnable example is in shell/mosquitto in cloudamqp/examples.

Good to know

Put the vhost in the username, as vhost:user. MQTT has no vhost of its own, and the console shows the username that way.
Use --tls-use-os-certs for TLS on port 8883. It verifies the server certificate against the system’s certificates; don’t add --insecure.
Use QoS 1 with -q 1, so mosquitto_pub waits for the broker’s PUBACK.
Add -d to see each packet, which helps when a connection fails.

← Rust