title: CMake : how to use bash command in CMakeLists.txt
body: <p>I'm wondering how I can use bash command in CMakeLists.txt. What I want is to get the number of processor retrieved using :</p>
  
  <pre><code>export variable=`getconf _NPROCESSORS_ONLN`
  </code></pre>
  
  <p>and set NB_PROCESSOR to variable using something like : </p>
  
  <pre><code>SET (NB_PROCESSOR variable)
  </code></pre>
  
  <p>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?</p>