Script to remove homie devices from mosquitto MQTT

#!/bin/bash
#
# Remove Homie Device from MQTT
# 
# Simple Script to remove all reatined messages for a homie device, effectively removing the device from MQTT.
# The script get all topics "below" a device e.g homie/a020a615f72c/$mac and
# send a NULL message with mosquitto_pub to the topic. This removes the retained 
# message and the topic will not show up anymore. 
#
# How? 
# mosquitto_pub -r -n --> sends an empty retained message, which clears the retained message and therefor the topic
#
# Example:
# $ ./clear-retained-messags.sh a020a615f72c
#
# Clearing for device a020a615f72c all messages, last clean will block kill with Ctrl+C when nothing happens anymore.
# 
# STARTING :: Checking for valid topics one after the other....
#  0 Checking for Topic ....
#    homie/a020a615f72c/$homie >> sending empty payload to topic with retained flag
#  1 Checking for Topic ....
#    homie/a020a615f72c/$mac >> sending empty payload to topic with retained flag
#  2 Checking for Topic ....
#    homie/a020a615f72c/$name >> sending empty payload to topic with retained flag
#  3 Checking for Topic ....
#    homie/a020a615f72c/$localip >> sending empty payload to topic with retained flag
#
echo 
echo "Clearing for device $1 all messages, last clean will block kill with Ctrl+C when nothing happens anymore."
echo 
#mosquitto_sub -v -h 10.0.2.2 -t "homie/$1/#" -C $2
echo "STARTING :: Checking for valid topics one after the other...."

# will stop after 100 topics
MAX_TOPICS_TO_CHECK=100

for c in `seq 0 $MAX_TOPICS_TO_CHECK`
    do
    echo "  $c Checking for Topic ...."
    for i in `mosquitto_sub -v -h 10.0.2.2 -t "homie/$1/#" -C 1|cut -d' ' -f1`
        do  
            # echo "mosquitto_pub -h 10.0.2.2 -r -n -t \"`echo $i | sed s#'\\$'#'\\\\\\\$'#g`\"" 
            echo "    $i >> sending empty payload to topic with retained flag"
            mosquitto_pub -h 10.0.2.2 -r -n -t "`echo $i | sed s#'\\$'#'\\\$'#g`" 
        done
done

Remove Homie Device from MQTT

Simple Script to remove all reatined messages for a homie device, effectively removing the Homie device from MQTT.
The script get all topics "below" a device e.g homie/a020a615f72c/$mac and send a NULL message with mosquitto_pub to the topic. This removes the retained message and the topic will not show up anymore.

Also works for MQTT Topic Tree not related to Homie.

How?

Subscribing with mosquitto_sub '#' to the sub topics and iterating over all sub topics up to MAX_TOPICS_TO_CHECK
mosquitto_pub -r -n --> sends an empty retained message, which clears the retained message and therefor the topic

Example:

$ ./clear-retained-messags.sh a020a615f72c
Clearing for device a020a615f72c all messages, last clean will block kill with Ctrl+C when nothing happens anymore.

STARTING :: Checking for valid topics one after the other....
0 Checking for Topic ....
   homie/a020a615f72c/$homie >> sending empty payload to topic with retained flag
1 Checking for Topic ....
   homie/a020a615f72c/$mac >> sending empty payload to topic with retained flag
 2 Checking for Topic ....
   homie/a020a615f72c/$name >> sending empty payload to topic with retained flag
3 Checking for Topic ....
   homie/a020a615f72c/$localip >> sending empty payload to topic with retained flag