Regex - To find word startswith __ and endswith __ but does not contain __

 Regex to match words start with double underscore (__) and endswith double underscore (__), but should not contains double underscore (__)

Pattern: /\_\_[^_\n]{1}.*?([^_\n]+)\_\_/g

This will match __somekey__ ,  __some_key__,  but not __some__key__, insted it will match __some__