Script to update DDNS IP for DynuDNS domain

dynuddnsupdate.sh

#!/usr/bin/env bash

#### OPTIONS

set -o errexit -o pipefail

#### DEFINITIONS

PROG=$(basename "${0}")
DDNS_USERNAME="${DDNS_USERNAME:-}"
DDNS_PASSWORD="${DDNS_PASSWORD:-}"
DDNS_HOSTNAME="${DDNS_HOSTNAME:-}"
DDNS_ALIAS="${DDNS_ALIAS:-}"
UPDATE_ALL="${DDNS_UPDATE_ALL:-false}"
IPV4="${DDNS_IPV4:-auto}"
IPV6="${DDNS_IPV6:-no}"
DRY_RUN=false

#### FUNCTIONS

## Function to throw an error
function throw_error() {
  local error_input="${1}"
  printf "[ERROR]: %s\n" "${error_input}" >&2
  exit 1
}

function is_installed(){
  local input="${1}"
  if ! command -v "${input}" >/dev/null 2>&1; then
    throw_error "Cannot find '${input}' in PATH. Please make sure '${input}' is installed and is in your PATH"
  fi
}

function usage() {
  cat << EOF
Usage: ${PROG} [options]

Options:
  -u, --username <username>    Dynu username (required if not updating single hostname)
  -p, --password <password>    Dynu password (required)
  -h, --hostname <hostname>    Hostname to update (required if not updating all domains)
  -a, --alias <alias>          Subdomain alias to update
  -A, --all                    Update all domains in account (requires username)
  -4, --ipv4 <ip|no|auto>      IPv4 address, 'no' to skip, or 'auto' to auto-detect (default: auto)
  -6, --ipv6 <ip|no|auto>      IPv6 address, 'no' to skip, or 'auto' to auto-detect (default: auto)
  -d, --dry-run                Print the curl command without executing it
  -?, --help                   Show this help message

Environment Variables:
  DDNS_USERNAME                Dynu username
  DDNS_PASSWORD                Dynu password
  DDNS_HOSTNAME                Hostname to update
  DDNS_ALIAS                   Subdomain alias
  DDNS_UPDATE_ALL              Set to 'true' to update all domains (default: false)
  DDNS_IPV4                    IPv4 address, 'no', or 'auto' (default: auto)
  DDNS_IPV6                    IPv6 address, 'no', or 'auto' (default: auto)
EOF
  exit 0
}

function parse_args() {
  while [[ $# -gt 0 ]]; do
    case "${1}" in
      -u|--username)
        DDNS_USERNAME="${2}"
        shift 2
        ;;
      -p|--password)
        DDNS_PASSWORD="${2}"
        shift 2
        ;;
      -h|--hostname)
        DDNS_HOSTNAME="${2}"
        shift 2
        ;;
      -a|--alias)
        DDNS_ALIAS="${2}"
        shift 2
        ;;
      -A|--all)
        UPDATE_ALL=true
        shift
        ;;
      -4|--ipv4)
        IPV4="${2}"
        shift 2
        ;;
      -6|--ipv6)
        IPV6="${2}"
        shift 2
        ;;
      -d|--dry-run)
        DRY_RUN=true
        shift
        ;;
      -\?|--help)
        usage
        ;;
      *)
        throw_error "Unknown option: ${1}"
        ;;
    esac
  done
}

function validate_args() {
  if [[ -z "${DDNS_PASSWORD}" ]]; then
    throw_error "Password is required (set DDNS_PASSWORD or use --password)"
  fi
  if [[ "${UPDATE_ALL}" == true && -z "${DDNS_USERNAME}" ]]; then
    throw_error "Username is required when updating all domains (set DDNS_USERNAME or use --username)"
  fi
  if [[ "${UPDATE_ALL}" == false && -z "${DDNS_HOSTNAME}" ]]; then
    throw_error "Hostname is required when not updating all domains (set DDNS_HOSTNAME or use --hostname)"
  fi
}

function build_url() {
  local base_url="https://api.dynu.com/nic/update"
  local params=()

  if [[ "${UPDATE_ALL}" == true ]]; then
    params+=("username=${DDNS_USERNAME}")
  fi
  params+=("password=${DDNS_PASSWORD}")

  if [[ -n "${DDNS_HOSTNAME}" ]]; then
    params+=("hostname=${DDNS_HOSTNAME}")
  fi
  if [[ -n "${DDNS_ALIAS}" ]]; then
    params+=("alias=${DDNS_ALIAS}")
  fi
  if [[ "${IPV4}" != "auto" ]]; then
    params+=("myip=${IPV4}")
  fi
  if [[ "${IPV6}" != "auto" ]]; then
    params+=("myipv6=${IPV6}")
  fi

  query_string=$(IFS='&'; echo "${params[*]}")
  local query_string
  echo "${base_url}?${query_string}"
}

#### MAIN

is_installed "curl"

parse_args "$@"
validate_args
url=$(build_url)

if [[ "${DRY_RUN}" == true ]]; then
  echo "Dry run: curl -s \"${url}\""
  exit 0
fi

response=$(curl -s "${url}")
if [[ "${response}" == "good"* || "${response}" == "nochg"* ]]; then
  echo "DDNS update successful: ${response}"
else
  throw_error "DDNS update failed: ${response}"
fi