System.File.Process

  Force a write of all user-space buffered data for the given `File`.
  
  @ h the file handle to flush

  Wait for the process associated with the pipe to terminate.
  
  @ fh the file handle to the stream to close/wait on

  Create a new unidirectional pipe by invoking the shell, which is passed the
  given command-string using the '-c' flag, in a new process. The pipe is
  opened with the given mode.
  
  @ cmd the command to pass to the shell
  @ m the mode the pipe should have