From Get docs


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


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.

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