# unset

Unset a variable, cache variable, or environment variable.

## Unset Normal Variable or Cache Entry

    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 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 `set()` command for further details.

## Unset Environment Variable

    unset(ENV{<variable>})

Removes `<variable>` from the currently available `Environment Variables`. 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.