old_contents: #!/usr/bin/env python
  
  import os
  
  csibe_path = os.path.dirname(os.path.realpath(__file__))
  build_directory = "build"
  
  if not os.path.isdir(build_directory):
      os.makedirs(build_directory)
  
  os.chdir(build_directory)
  
  os.system("cmake {0}".format(csibe_path))
  
  
new_contents: #!/usr/bin/env python
  
  import os
  import subprocess
  import unittest
  
  csibe_path = os.path.dirname(os.path.realpath(__file__))
  build_directory = "build"
  
  if not os.path.isdir(build_directory):
      os.makedirs(build_directory)
  
  os.chdir(build_directory)
  
  subprocess.call(["cmake", csibe_path])
  
  
subject: Switch os.system() to subprocess.call()