/usr/share/cmake-3.10/Help/variable/UNIX.rst is in cmake-data 3.10.2-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | UNIX
----
Set to ``True`` when the target system is UNIX or UNIX-like
(e.g. :variable:`APPLE` and :variable:`CYGWIN`). The
:variable:`CMAKE_SYSTEM_NAME` variable should be queried if
a more specific understanding of the target system is required.
|