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+unset
+-----
+
+Unset a variable, cache variable, or environment variable.
+
+Unset Normal Variable or Cache Entry
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: cmake
+
+  unset(<variable> [CACHE | PARENT_SCOPE])
+
+Removes a normal variable from the current scope, causing it
+to become undefined.  If ``CACHE`` is present, then a cache variable
+is removed instead of a normal variable.  Note that when evaluating
+:ref:`Variable References` of the form ``${VAR}``, CMake first searches
+for a normal variable with that name.  If no such normal variable exists,
+CMake will then search for a cache entry with that name.  Because of this
+unsetting a normal variable can expose a cache variable that was previously
+hidden.  To force a variable reference of the form ``${VAR}`` to return an
+empty string, use ``set(<variable> "")``, which clears the normal variable
+but leaves it defined.
+
+If ``PARENT_SCOPE`` is present then the variable is removed from the scope
+above the current scope.  See the same option in the :command:`set` command
+for further details.
+
+Unset Environment Variable
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: cmake
+
+  unset(ENV{<variable>})
+
+Removes ``<variable>`` from the currently available
+:manual:`Environment Variables <cmake-env-variables(7)>`.
+Subsequent calls of ``$ENV{<variable>}`` will return the empty string.
+
+This command affects only the current CMake process, not the process
+from which CMake was called, nor the system environment at large,
+nor the environment of subsequent build or test processes.