CMake file in script mode inheriting variables - cmake

Question

How can I call to a cmake file in script mode (-P) from other cmake file, so this "cmake child" knows all variable of its parent? Because, if I have a lot of variables the child needs, I have to write many -D options, and I want to avoid it.
Example:
// CMakeLists.txt
cmake_minimum_required(VERSION 2.8)
set(teststr "Hello World!")
add_custom_command(test
${CMAKE_COMMAND} -Dteststr=${teststr} -P test.cmake
)
// test.cmake
message("${teststr}")
$ cmake .
$ make test
Hello world!
Built target test
Works fine!. But, without "-Dteststr":
// CMakeLists.txt
cmake_minimum_required(VERSION 2.8)
set(teststr "Hello World!")
add_custom_command(test
${CMAKE_COMMAND} -P test.cmake
)
// test.cmake
message("${teststr}")
$ cmake .
$ make test
Built target test
Of course, without -D option, the "teststr" variable, in test.cmake, is unset, and thus, the output is empty.
Any option to call test.cmake in "heritage mode", or something like that?

Answer 1

You can pass arguments to a script with cmake -P.
If you call:
cmake -P <script-file> <arg3> <arg4> <arg5> ...
then the variables CMAKE_ARGC, CMAKE_ARGV0, CMAKE_ARGV1, ... will be available for the script.
See documentation for CMAKE_ARGC and CMAKE_ARGV0.
The other way is to define variables, just like with the non-script cmake command. However there's one thing to be aware of: you need to define the variables before -P:
cmake -DVAR=VALUE -DFOO=BAR -P <script-file> <arg5> <arg6> ...
Now in the cmake VAR and FOO will be available.
Also, note that the numbering of the args after the script-file will be shifted accordingly.

Answer 2

There's no particularly easy way to do this that I know of.
You could write all the current variables in the parent CMakeLists.txt to a separate file and then include this in your test.cmake:
# CMakeLists.txt:
cmake_minimum_required(VERSION 2.8)
set(teststr "Hello World!")
set(CacheForScript ${CMAKE_BINARY_DIR}/CMakeCacheForScript.cmake)
file(WRITE ${CacheForScript} "")
get_cmake_property(Vars VARIABLES)
foreach(Var ${Vars})
if(${Var})
string(REPLACE "\\" "\\\\" ${Var} ${${Var}})
endif()
file(APPEND ${CacheForScript} "set(${Var} \"${${Var}}\")\n")
endforeach()
add_custom_target(test ${CMAKE_COMMAND} -P ${CMAKE_SOURCE_DIR}/test.cmake)
# test.cmake
include(${CMAKE_BINARY_DIR}/CMakeCacheForScript.cmake)
message("${teststr}")