unset ----- Unset a variable, cache variable, or environment variable. :: unset(<variable> [CACHE | PARENT_SCOPE]) Removes the specified variable causing it to become undefined. If CACHE is present then the variable is removed from the cache instead of the current scope. If PARENT_SCOPE is present then the variable is removed from the scope above the current scope. See the same option in the set() command for further details. <variable> can be an environment variable such as: :: unset(ENV{LD_LIBRARY_PATH}) in which case the variable will be removed from the current environment.