• unset: Unset a variable, cache variable, or environment variable.
      unset(<variable> [CACHE])

    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.

    <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.