In this example, we will use three files:

.
├── cmake
│   ├── custom.cmake
│   └── include_guard.cmake
└── CMakeLists.txt

The custom custom.cmake module contains the following code:

include_guard(GLOBAL)
  
message(STATUS "custom.cmake is included and processed")

We will discuss cmake/include_guard.cmake and CMakeLists.txt later.