A function to validate whether an input is a valid ipv4 address

ipv4::validate_addr

ipv4::validate_addr() {
  # Disable SC2086 for 'set -- ${*%/*}' as we require this to be word split
  # shellcheck disable=SC2086
  (
    IFS=.; set -f; set -- ${*//\"/}; set -- ${*%/*}
    local octet; local count=0; local errcount=0
    if (( "${#}" == 4 )); then
      for octet in "${@}"; do
        (( ++count ))
        case "${octet}" in
          (""|*[!0-9]*)
            printf -- '%s\n' "Octet ${count} appears to be empty or non-numeric" >&2
            (( ++errcount ))
          ;;
          (*)
            if (( octet > 255 )); then
              printf -- '%s\n' "Octet ${count} appears to be invalid (>255)" >&2
              (( ++errcount ))
            fi
          ;;
        esac
      done
      (( errcount > 0 )) && return 1
    else
      printf -- '%s\n' "Input does not appear to be a valid IPv4 address" >&2
      return 1
    fi
    # If we get to this point, then all should be ok
    return 0
  )
}