script for updating dynamic DNS records on he.net (hurricane electric)

he-dns-update.sh

#!/bin/bash
#
# Script for updating DNS records on  Hurricane Electirc's DNS system (https://dns.he.net).
#
# The record will be updated with the IP address that originates the request.
#
# Usage
# -----
#
# Create config file `/etc/he-dns-update.conf`:
#
#  HOSTNAME=myhost.dom.tld
#  KEY=<update_key>
#
# Update IPv4 (A) record:
#
#  $ ./he-dns-update.sh 4
#
# Update IPv6 (AAAA) record:
#
#  $ ./he-dns-update.sh 6
#
# Logs / Output
# -------------
#
# Output is sent to syslog instead of stdout (unless there is an error with the config file).
#
# Examples:
#
#    Apr  1 12:00:03 gw HE-DNS: OK: ipv4 address updated: good 12.34.56.78
#    Apr  1 12:00:05 gw HE-DNS: OK: ipv4 address no change: nochg 12.34.56.78
#    Apr  1 12:00:11 gw HE-DNS: ERROR: ipv6 address not updated : curl timed out.
#
# Cron example
# ------------
# Hourly:
#
#   0 * * * * /usr/local/bin/he-dns-update.sh 4
#   0 * * * * /usr/local/bin/he-dns-update.sh 6
#
# Author
# ------
# Joe Miller / https://github.com/joemiller 2016
#

LOGGER_BIN="logger"
CURL_BIN="curl"
CURL_TIMEOUT_SECS=10


# load config file and verify required args
. "/etc/he-dns-update.conf"
if [ -z "$HOSTNAME" ] || [ -z "$KEY" ]; then
  echo "ERROR: Config file '/etc/he-dns-update.conf' is missing one or more required vars: HOSTNAME, KEY"
  exit 1
fi

proto="$1"
if [ -z "$proto" ]; then
  echo "Usage: $0 [4|6]"
  exit 1
fi

out=$("$CURL_BIN" \
  -"$proto" \
  --silent \
  -m "$CURL_TIMEOUT_SECS" \
  -k \
  https://dyn.dns.he.net/nic/update \
  -d "hostname=$HOSTNAME" \
  -d "password=$KEY" 2>&1)

# $out will be empty on timeout, so we catch curl's return code for timeout and populate
# $out with a helpful message. Could do this for other common errors from curl too.
rc=$?
if [ "$rc" == 28 ]; then
  out="curl timed out."
fi

# possible outputs from curl:
#
# on success, either:
#   good 192.168.0.1
#   nochg 192.168.0.1
#
# on error:
#  could be anything else. we log an error with the full output.

case $out in
  *good*)
    "$LOGGER_BIN" -p local0.info   -t HE-DNS "OK: ipv$proto address updated: $out" ;;
  *nochg*)
    "$LOGGER_BIN" -p local0.notice -t HE-DNS "OK: ipv$proto address no change: $out" ;;
  *)
    "$LOGGER_BIN" -p local0.err    -t HE-DNS "ERROR: ipv$proto address not updated : $out" ;;
esac