regex - regexp: FirstName.LastName or FirstName.Letter.LastName -

I want to make a regular expression, but unfortunately my thoughts do not work. Regular expressions should only allow entry A string consisting of parts:

Part one: letter (az) and dot

part two: only one letter and dot (this part is not required but tolerant)

Part two: Dot and letters (az)

Valid example:

• john.shmith
• john.a.smith
• harry.x.doe
• test.y.acme

E matches Example:

• John. Smith
• John Smith
• John. Esith
• John. X.Smith
• John.y.smith
• Jen.Ismith.
• Mary-Kate.

A potential solution:

  ^ [ Az] + \. ([Az] \.)? [Az] + $  

In more detail:

  ^ ---> Match starts [a-z] + \. --- & gt; The first part (the letters [a-z] and one dot) ([a-z] \.)? --- & gt; Optional part (only one letter and one point) [a-z] + --- & gt; Second part (letter [a-z]) $ --- & gt; Match end