Example- 1)(abc)xxx --> output-xxx
2)(abc)(xxx) --> output-xxx
3)((abc)xxx) ---> output-xxx
4)((abc) xxx + yyy)--> output-xxx+yyy
5)((abc)) ---> output-null
Example- 1)(abc)xxx --> output-xxx
2)(abc)(xxx) --> output-xxx
3)((abc)xxx) ---> output-xxx
4)((abc) xxx + yyy)--> output-xxx+yyy
5)((abc)) ---> output-null
This actually does what you ask for for all your examples, but I suspect is not what you wanted
[^\)]+\)[\(]*([^\)]*)