1. I kept a diary last night.

Question

2. I wrote a diary last night.
3. I wrote up a diary last night.
4. I wrote in a diary last night.
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Which expressions are right? Are they the same in meaning?

Answer 1

Only #4 is correct.

Here are some variations that would make the others correct:
I kept a diary during my teenage years.
I wrote in my diary last night.
I wrote three diary entries last week.