CMake : how to use bash command in CMakeLists.txt

I'm wondering how I can use bash command in CMakeLists.txt. What I want is to get the number of processor retrieved using :

export variable=`getconf _NPROCESSORS_ONLN`

and set NB_PROCESSOR to variable using something like :

SET (NB_PROCESSOR variable)

So my question is how can I use the getconf command in CMakeLists.txt and how can I use the result (stored in variable) in CMake SET command?

From stackoverflow

• This seems to do the trick, and saves the "set" too.

  execute_process(COMMAND getconf  _NPROCESSORS_ONLN
                  OUTPUT_VARIABLE NB_PROCESSOR)
  

  claferri : with this, i see the result of the command during "cmake ." but if I have "#cmakedefine NB_PROCESSOR ${NB_PROCESSOR}" to my config.h.in, I'll get "#undef NB_PROCESSOR" instead of "#define NB_PROCESSOR value". Any clue?

  rq : I messed up - it should be OUTPUT_ not RESULT_VARIABLE. The former stores the output from the program, the latter the result ($? in bash-speak)

  claferri : already tried and seems not to work, I think the result may be considered as a string and I want a int. Still trying to find a solution :)

  claferri : oups, I was wrong about saying I tried using the output_var, it works! thanks!

• Use the EXEC_PROGRAM command and then use the CACHE option of the SET command to save the output to a variable like GTK_PKG_FLAGS. Then use the SET command to add the value. Something like this:

  IF(NOT GTK_PKG_FLAGS)
     EXEC_PROGRAM(pkg-config ARGS --cflags --libs gtkmm
                  OUTPUT_VARIABLE GTK_PKG_FLAGS)
     SET(GTK_PKG_FLAGS "${GTK_PKG_FLAGS}" CACHE STRING "GTK Flags")
  ENDIF(NOT GTK_PKG_FLAGS)
  SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${GTK_PKG_FLAGS}")
  

  Links: http://www.cmake.org/pipermail/cmake/2005-January/006051.html