method
    
    grpowned?
  grpowned?(p1)
  public
  Returns true if the named file exists and the effective group id of the calling process is the owner of the file. Returns false on Windows.
file_name can be an IO object.
  grpowned?(p1)
  public
  Returns true if the named file exists and the effective group id of the calling process is the owner of the file. Returns false on Windows.
file_name can be an IO object.