Linode dynamic dns on ubiquiti edge router

linode-ddns.sh

#!/bin/bash

# See https://gist.github.com/zsimic/c39dd9686c6d6b0d149a67ff23286b99 for docs on how to use

# Note: you can invoke with LOGFILE= for troubleshooting
[ -z "$LOGFILE" ] && LOGFILE=/var/log/messages
if [ -z "$1" -a -f $LOGFILE ]; then  # Pass any command line arg to avoid the logging redirect
    exec $0 run 1>> $LOGFILE 2>&1
fi

function do_log {
    echo "$(date +'%h %e %T') $(hostname) linode-ddns: $@"
}

function usage {
    do_log "Usage error: $@"
    exit 1
}

# Note: you can invoke with CFGFILE= for troubleshooting
[ -z "$CFGFILE" ] && CFGFILE=~/.ssh/linode-ddns-cfg.sh
CFGFOLDER=$(dirname $CFGFILE)
IPFILE="$CFGFOLDER/.last-ip"  # Allows to do nothing when IP didn't change, remove file to force re-run

[ ! -f $CFGFILE ] && usage "Config file $CFGFILE does not exist"
source $CFGFILE
[ -z "$TOKEN" ] && usage "TOKEN not defined in $CFGFILE"
[ -z "$RECORDS" ] && usage "RECORDS not defined in $CFGFILE"

URL="https://api.linode.com/v4"
H1="Content-type: application/json"
H2="Authorization: Bearer $TOKEN"
CURRENT_IP=$(ip address show eth0 | grep -Eo 'inet [0-9\.]+' | cut -d " " -f2)
LAST_IP=$([ -f $IPFILE ] && head -1 $IPFILE)

[[ $LAST_IP == $CURRENT_IP ]] && exit 0

DBG=""
[ ! -d /config/scripts ] && DBG="echo"  # Useful to debug, allows to perform actual REST call only on router

for record in $RECORDS; do
    OUTPUT=$($DBG curl -s -H"$H1" -H"$H2" "$@" -XPUT $URL/domains/$record -d "{\"target\": \"$CURRENT_IP\"}")
    if [ $? -ne 0 ]; then
        do_log "Updating record $record failed: $OUTPUT"
        exit 1
    fi
done

do_log "Home IP updated to $CURRENT_IP"
[ ! -f $IPFILE ] && touch $IPFILE && chmod 0600 $IPFILE  # chmod just because domainId is logged there...
echo $CURRENT_IP > $IPFILE
echo "# Updated on $(date) for $RECORDS" >> $IPFILE

Yes, like https://www.youtube.com/watch?v=nmE28_BA83w or https://www.youtube.com/watch?v=B4pnGyvj2sM or https://www.youtube.com/watch?v=Cs8yOmTJNYQ - all very good channels, Techno Tim (that last one) probably explains things more in depth