Present perfect continuous.

Affirmative: He has been writing
Negative: He has not been writing
Interrogative: Has he been writing?
Negative interrogative: Has he not been writing?
Used for unbroken action in the past which continues right up to the present. I have been writing this paper all morning (and still am).

Present Perfect Continuous is used for denoting the action which was in progress and has just finished (a) or is still going on (b). For example,

a) Why are your eyes red? – I have been crying since morning. (The action has already finished but was in progress for some time)
b) She has been working here for two years already and she is happy. (The action is still in progress).
If we have to ask a question with “How long…?” we should use the present perfect continuous. For example,

How long have you been working here?
However, with stative words (such as see, want, like, etc), or if the situation is considered permanent, we should use the present perfect simple. For example,

I have known her since childhood.
If we talk about the whole period, we use “for” and when we talk about the starting point of the action, we use “since”.

We should not use the present simple tense for denoting actions that began in the past and are still going on. For example,

I am ill since Monday. (It is not correct).
I have been ill since Monday. (It is correct).