code: def run_command(cmd, root, dst, input, params):
      
      use_stdout = '{output}' not in cmd
      if not use_stdout:
          params['output'] = dst
      parsed_cmd = parse_command(cmd, input=input, params=params)
  
      ensure_dirs(os.path.join(root, dst))
  
      logger.info("Running [%s] from [%s]", parsed_cmd, root)
  
      proc = subprocess.Popen(
          args=parsed_cmd,
          stdout=subprocess.PIPE,
          stderr=subprocess.PIPE,
          shell=True,
          cwd=root,
      )
      (stdout, stderr) = proc.communicate()
  
      assert not proc.returncode, stderr
  
      if use_stdout:
          # TODO: this should probably change dest to be a temp file
          with open(os.path.join(root, dst), 'w') as fp:
              fp.write(stdout)
docs: Execute a command, and if successful write it's stdout to ``root``/``dst``.