code: protected function handleInput(InputInterface $input)
      {
          if ($file = $input->getArgument('file')) {
              if (!file_exists($file)) {
                  throw new \InvalidArgumentException(sprintf('The input file "%s" not found', $file));
              }
  
              return file_get_contents($file);
          } else {
              $contents = '';
  
              if ($stdin = fopen('php://stdin', 'r')) {
                  // Warning: stream_set_blocking always fails on Windows
                  if (stream_set_blocking($stdin, false)) {
                      $contents = stream_get_contents($stdin);
                  }
  
                  fclose($stdin);
              }
  
              // @codeCoverageIgnoreStart
              if ($contents) {
                  return $contents;
              }
              // @codeCoverageIgnoreEnd
          }
  
          throw new \InvalidArgumentException('No input file');
      }
docs: Get a markdown content from input
  
  __Warning: Reading from STDIN always fails on Windows__
  
  @param InputInterface $input
  
  @throws \InvalidArgumentException
  
  @return string