How to unset a variable in cmake using command line?

Question

I know that in order to set a variable, we do -DVARIABLE=VALUE , but what if I need to unset it?

I tried -DVARIABLE=FALSE but it didn't work, the compiler complains about what does FALSE means

Answer 1

The magic flag is -U . Trimmed output:

$ grep DOCS CMakeCache.txt 
HOUSEGUEST_BUILD_DOCS:BOOL=OFF
$ cmake -UHOUSEGUEST_BUILD_DOCS .
-- Configuring done
-- Generating done
-- Build files have been written to: /my/build/folder
$ !grep
grep DOCS CMakeCache.txt 
HOUSEGUEST_BUILD_DOCS:BOOL=ON

From cmake --help :

-U <globbing_expr>           = Remove matching entries from CMake cache.