How to only match a single instance of a character?

Question

Not quite sure how to go about this, but basically what I want to do is match a character, say a for example. In this case all of the following would not contain ma

Answer 1

Basically what I want to do is match any single a that has any other non a character around it (except for the start and end of the string).

^[^\sa]*\Ka(?=[^\sa]*$)

DEMO

\K discards the previously matched characters and lookahead assertes whether a match is possibel or not. So the above matches only the letter a which satifies the conditions.

OR

a{2,}(*SKIP)(*F)|a

DEMO