This script is on each Raspberry Pi and activated through a CRON Task (CRONTAB).
It sends the CPU temperature via MQTT (mosquitto)
#!/bin/bash -e
# This routine is meant to sent at regular intervalthe CPU temperature via MQTT message
topic='cpu_temp'
HOSTNAME=`hostname`
MQTT_BROKER='192.168.86.225'
TOPIC="$topic"/"$HOSTNAME"
last_temp=0.0
TEMP=`vcgencmd measure_temp | egrep -o '[0-9]*\.[0-9]*'`
mosquitto_pub -h $MQTT_BROKER -t $TOPIC -m $TEMP
exit