The spelling of the name Sean,Shaun,Shawn which is the correct spelling is it a matter of performance at the time?

Shaun and Shawn are the way Sean is pronounced in different parts of Ireland. The name is adapted from the Anglo-Norman name John.

https://en.wikipedia.org/wiki/Seán

As is often the case, the Wikipedia article is full of it! No one should ever believe what Wikipedia says without additional corroboration. Sean is the Gaelic form of the name John, which is, of course, found in the Bible, and was known in Ireland long before the Norman invasion.

The first couple of posts on here:

http://www.reddit.com/r/explainlikeimfive/comments/2fn69p/eli5_why_is_the_name_sean_pronounced_like_shawn/

explain this. There should be an accent on the letter a, which changes the pronunciation to the 'sh' sound. I believe that Sean is the 'correct' spelling and that the other versions are because non Irish people would pronounce the name as 'seen'. The same applies to the Welsh variation, Sion, which is also pronounced Shaun.