cmake(1) . -DVARIABLE=VALUE
Cross-Platform Makefile Generator
-D <var>:<type>=<value>
       Create a cmake cache entry.

       When cmake is first run in an empty build tree, it creates a CMakeCache.txt file and populates  it
       with  customizable  settings  for  the project.  This option may be used to specify a setting that
       takes priority over the project's default value.  The option may be repeated  for  as  many  cache
       entries as desired.
-E     CMake command mode.

       For true platform independence, CMake provides a list of commands that can be used on all systems.
       Run with -E help for the usage information. Commands available are:  chdir,  compare_files,  copy,
       copy_directory, copy_if_different, echo, echo_append, environment, make_directory, md5sum, remove,
       remove_directory, rename, tar, time, touch, touch_nocreate. In addition,  some  platform  specific
       commands are available. On Windows: comspec, delete_regv, write_regv. On UNIX: create_symlink.
-U <globbing_expr>
       Remove matching entries from CMake cache.

       This  option  may  be  used to remove one or more variables from the CMakeCache.txt file, globbing
       expressions using * and ? are supported. The option may be repeated for as many cache  entries  as
       desired.

       Use with care, you can make your CMakeCache.txt non-working.
source manpages: cmake