checkip.sh

#!/bin/bash
# checkip.sh
# Detect when public IP address changes
# Add the following to the crontab (i.e. crontab -e)
# */30 * * * * ~/checkip.sh
# To successfully start SubstratumNode in privileged mode this script has to run as root or as a sudoer.
# When run by cron sudo can't prompt for a password. See creating /etc/sudoers.d/<username> and adding an entry like the following: 
# %<your-user-here> ALL=(ALL) NOPASSWD:SETENV: /your/path/to/build/directory/node_ui/static/binaries/SubstratumNode
# Change paths ./recorded-ipv4 and SubstratumNode as needed for your system

currentIPv4=$(curl --silent 'https://api.ipify.org')
test -e ./recorded-ipv4 || echo $currentIPv4 > ./recorded-ipv4
previousIPv4=$(cat ./recorded-ipv4)

echo $currentIPv4 > ./recorded-ipv4

if [ "$previousIPv4" != "$currentIPv4" ]; then
	echo Detected IPv4 Address change from $previousIPv4 to $currentIPv4. Retarting SubstratumNode...
  pkill -f SubstratumNode
  sleep 10
  # the following requires sudo if not run as root
  SubstratumNode
fi