Check external IP and alert on change

checkextip.sh

#!/bin/bash
#set debug value to "true" to output debug code
debug=false
SlackURL_key="https://hooks.slack.com/services/KEYDATA01/KEYDATA02/KEYDATA03"
SlackUsername="icanhazip"

#obtain current IP from icanhazip
myip=`curl -4 -s icanhazip.com`
if [ $debug == "true" ]; then echo "current IP = " $myip; fi 

#check for existing temp file to compare last known IP
if [ -e /tmp/myip.txt ]
then
	tmpip=`cat /tmp/myip.txt`
	echo "temp IP = " $tmpip
	if [ $myip == $tmpip ]
	then
		if [ $debug == "true" ]; then echo "good"; fi
	else
		#if the IP does not match, sent a Slack alert!
		Slackjson="{\"text\":\"External IP Changed!\nOld IP = ${tmpip}\nCurrent IP = ${myip}\", \"username\":\"${SlackUsername}\"}"
		if [ $debug == "true" ]; then echo "nogood"; fi
	fi
#if no current temp file, create a new one with the current IP
else
	echo $myip > /tmp/myip.txt
	#if no temp file, send notice that there was nothing to compare against
	Slackjson="{\"text\":\"No temp file to compare against!\nCurrent IP = ${myip}\", \"username\":\"${SlackUsername}\"}"
	if [ $debug == "true" ]; then echo "temp file did not exist, creating a new one"; fi
fi

#check if the Slackjson variable has been set and if so, send to Slack
if [ -n "${Slackjson}" ]
then
	curl --silent --request POST --header "Content-Type: application/json" --data "${Slackjson}" ${SlackURL_key} > /dev/null
	if [ $debug == "true" ]; then echo "sending to Slack"; fi
else
	if [ $debug == "true" ]; then echo "no Slack json variable set"; fi
fi