code: public static int permissions(File f) {
  		if(f == null) {
  			throw new NullPointerException("File is null.");
  		}
  		if(!f.exists()) {
  			throw new IllegalArgumentException("File " + f + " does not exist.");
  		}
  
  		return isPosix ? posixPermissions(f) : standardPermissions(f);
  	}
docs: Get file permissions in octal mode, e.g. 0755.
  
  Note: it uses `java.nio.file.attribute.PosixFilePermission` if OS supports this, otherwise reverts to
  using standard Java file operations, e.g. `java.io.File#canExecute()`. In the first case permissions will
  be precisely as reported by the OS, in the second case 'owner' and 'group' will have equal permissions and
  'others' will have no permissions, e.g. if file on Windows OS is `read-only` permissions will be `0550`.
  
  @throws NullPointerException if file is null.
  @throws IllegalArgumentException if file does not exist.