CMake script for using as cross-platform scripting language

script.cmake

# to execute: "cmake -P ./script.cmake"
# *****************************************************************************
if(CMAKE_SCRIPT_MODE_FILE AND NOT CMAKE_PARENT_LIST_FILE) # if it is dirrectly launched in a script mode
    execute_process(
        # vvv
        COMMAND "python" "--version"
        # ^^^
        RESULT_VARIABLE RES # result of the cmd
        OUTPUT_VARIABLE OUT # output var
        ERROR_VARIABLE ERR) # error var

    if(${RES} STREQUAL "0") # if no errors
        message("The python version is : ${OUT}")
    else()
        message(FATAL_ERROR "Not executed! \n${ERR}")
    endif()
else()
    message(FATAL_ERROR "Should be run directly with `-P`-key, not included. E.g. cmake -P ./script.cmake")
endif()