title: How can I redirect the output of the CMake "execute_process" command to STDOUT in real-time?
body: <p>I am working on a project that needs to execute a system process from a CMake script that may take a while to run. The problem is the entire time the process is running I get no feedback about whether it is succeeding or not. Since the process may take a few minutes to run it may appear as though it froze even though it is still silently working.</p>
  
  <p>At the end of the process I can get the output in a CMake variable and print all of the things that happened during that time:</p>
  
  <pre><code>execute_process(COMMAND some system command
      OUTPUT_VARIABLE command_output
  )
  
  # ... nothing happens for a few minutes while the process executes
  
  # All of the output from the past few minutes is printed all at once.
  message(STATUS ${command_output})
  </code></pre>
  
  <p>It would be much nicer if I could just redirect the process output directly to STDOUT so I could see output of the process while it is executing... Is there any way to do this?</p>