If I have the set(CPACK_PACKAGE_VERSION_MAJOR "2024-02-15") in my CMakeLists.txt that does INCLUDE(CPack), then after I create the Makefile with cmake ../, I can call make package, and the resulting .deb file will have the specified version string in its filename.

I can also do execute_process( COMMAND date +'%Y-%m-%d' OUTPUT_VARIABLE CPACK_PACKAGE_VERSION) and have the output of the date +'%Y-%m-%d' written into the CMake CPACK_PACKAGE_VERSION variable; however the command is only called once, at configure time, when cmake ../ is called – and the resulting output is hardcoded in CPackConfig.cmake and CPackSourceConfig.cmake.

What can I do, to have a Cmake variable – or even, a Makefile variable – be updated from the results of calling some external program, every time make with some specific target (like make package) is called?