Is it grammatically correct to say has been being?

"has been being" - no matter how awkward it may sound is actually grammatically correct.

It is a very old-fashioned way or manner of writing or talking.

It can be used to describe a state which began in the past, is continuous to the present and

may continue into the future (past-continuous action / state)

But most people will debate on that as it sounds awkward so it is still best to rephrase the thought using present perfect and still mean the same.

The only correct ,though rare or even unusual , usage of such a construction which I can think of right now is the so called " perfective progressive  passive" :

- The Conservatives have not been winning seats lately. (Active Voice)

- Seats have not been being won by the Conservatives lately. (Passive Voice but Rare)

Even though  it may be a true usage in the present progressive  I believe that such a verb "to be" is a static verb that can never be used in the contunious form in the given example.

Hello ,

it appear that the sentence is not really easy to pronounce, but grammatically, it's correct.

We use the format "be being" to express that someone is acting or behaving in a way that he/she is not usually. e.g.

He is being selfish. (He is acting selfish now, he is not selfish)

Now, by sayin "have been being something" can mean that someone has been acting in a manner recently that is not / was not his character.

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This question has been answered and so please refer to the previous questions and answers.  I would like to get new questions and I will be greatly interested in answering unanswered/new questions

It's valid in the sense that it follows the rules. It is the present perfect progressive conjugation of "to be", describing an action (or in this case, a state) which began in the past, is continuous to the present, and may continue into the future.For example: "I have been being sad" makes perfect sense to me.  It differs slightly from "I have been sad", which isn't continuous, or "I am being sad", which doesn't call attention to the fact that it started in the past. 

i don't know but first time to see or hear this sentence