Script to update a file on a remote server with the external IP address of your local computer. This is handy for semi-automated DDNS

home-external-ip.sh

#!/usr/bin/env bash

### VARIABLES
VERBOSE=1
DEBUG=0
REMOTE_USER="your_remote_user"                           # Set your remote server username
REMOTE_HOST="your.remote.server.com"                     # Set your remote server's IP or domain
REMOTE_FILE_PATH="/home/${REMOTE_USER}/home-external-ip" # Set the path to the file on the remote server
SSH_KEY_PATH="${HOME}/.ssh/id_rsa"                       # Path to your SSH private key
EXTERNAL_IP_SERVICE="https://ifconfig.me"                # External IP address service

### SETUP
set -e
[[ ${DEBUG} == 1 ]] && set -x

### FUNCTIONS
function write_error(){
  local input error_msg
  input="${1}"
  error_msg="[ERROR]"
  printf "\x1B[0;48;5;196;38;5;255m%s\x1b[0m: \x1B[0;38;5;196m%s\x1B[0m\n" "${error_msg}" "${input}" >&2
  return 1
}

function write_verbose(){
  local input verbose_msg
  input="${1}"
  verbose_msg="[VERBOSE]"
  if [[ "${VERBOSE}" == 1 ]]; then
    printf "\x1B[0;48;5;4;38;5;226m%s\x1b[0m: \x1B[0;38;5;226m%s\x1B[0m\n" "${verbose_msg}" "${input}"
  fi
}

function is_installed(){
  local input
  input="${1}"
  if command -v "${input}" >/dev/null 2>&1; then
    write_verbose "Package: '${input}' is installed :)"
  else
    write_error "Package: '${input}' is NOT installed :("
    exit 1
  fi
}

function file_exists(){
  local input
  input="${1}"
  if [[ -e "${input}" ]]; then
    write_verbose "File: '${input}' exists :)"
  else
    write_error "File: '${input}' does NOT exist :("
    exit 1
  fi
}

function get_external_ip(){
  write_verbose "Fetching external IP address..."
  IP_ADDRESS=$(curl -s "${EXTERNAL_IP_SERVICE}")
  if [[ -z "${IP_ADDRESS}" ]]; then
    write_error "Failed to fetch external IP address."
    exit 1
  fi
  write_verbose "External IP Address: ${IP_ADDRESS}"
}

function update_remote_file(){
  write_verbose "Updating remote file with external IP: ${IP_ADDRESS} ..."
  if ssh -i "${SSH_KEY_PATH}" "${REMOTE_USER}@${REMOTE_HOST}" "echo '${IP_ADDRESS}' >! ${REMOTE_FILE_PATH}"; then # NOTE: Replace '>!' with just '>' if you do not have prevent overwrite files enabled in your shell (e.g. zsh)
    write_verbose "Remote file updated successfully."
  else
    write_error "Failed to update remote file on ${REMOTE_HOST}:${REMOTE_FILE_PATH}"
    exit 1
  fi
}

### MAIN
is_installed "curl"
is_installed "ssh"
file_exists "${SSH_KEY_PATH}"
get_external_ip
update_remote_file