code: def grep(regex, output):
      
      lines = output.decode('utf-8').strip().splitlines()
      results = []
      for line in lines:
          if re.search(regex, line):
              results.append(line.strip())
      return results
docs: Similar to linux's `grep`, this returns the line in an output stream
      that matches a given regex pattern.
  
      It does not rely on the `grep` binary and is not sensitive to line endings,
      so it can be used cross-platform.
  
      Args:
          regex: string, a regex that matches the expected pattern.
          output: byte string, the raw output of the adb cmd.
  
      Returns:
          A list of strings, all of which are output lines that matches the
          regex pattern.