title: How to know variable such as 'OpenCV' in CMake
body: <p>I am using OpenCV with gcc and cmake. And I found a tutorial <a href="https://docs.opencv.org/3.4.0/db/df5/tutorial_linux_gcc_cmake.html" rel="nofollow noreferrer">https://docs.opencv.org/3.4.0/db/df5/tutorial_linux_gcc_cmake.html</a> .In the file <code>CMakeLists.txt</code>, there are some variables such as <code>OpenCV</code> and <code>OpenCV_INCLUDE_DIRS</code>.</p>
  
  <pre><code>cmake_minimum_required(VERSION 3.9)
  project(VideoRecord)
  
  set(CMAKE_CXX_STANDARD 11)
  find_package(OpenCV REQUIRED)
  
  include_directories(${OpenCV_INCLUDE_DIRS})
  
  add_executable(VideoRecord main.cpp)
  target_link_libraries(VideoRecord ${OpenCV_LIBS})
  </code></pre>
  
  <p><strong>I want to know where to find these variables definition.</strong></p>
  
  <h1>EDIT</h1>
  
  <p>Thanks @qbranchmaster's answer. I tried to search <code>FindOpenCV.cmake</code> but failed.</p>
  
  <p>First try.</p>
  
  <pre><code>➜  ~ cmake --help-module-list | grep "FindOpen"
  FindOpenACC
  FindOpenAL
  FindOpenCL
  FindOpenGL
  FindOpenMP
  FindOpenSSL
  FindOpenSceneGraph
  FindOpenThreads
  </code></pre>
  
  <p>Another try.</p>
  
  <pre><code>➜  / find . "FindOpenCV.cmake"
  </code></pre>
  
  <p><strong>In addition, my os is osx and I install <code>cmake</code> with <code>brew</code>. I comiple and install <code>OpenCV</code> manually.</strong></p>