How do you make a regex to select a pattern of X, Y or Z length

Question

If I need to find a regex that matches any positive number of lower case characters, an N, and then either 6 integers, 8 integers or 15 integers. But not match any other number of intagers

e.g. "abcN123456" or "abcdN12345678" or "abN123456789012345" or "abcdefgN123456"

How would you make a regex that finds this?

It starts with [a-z]+N but don't know how to do the variable number of integers

Answer 1

Here's a possible solution

^[a-z]+N(?:\d{6}|\d{8}|\d{15})$

Debuggex Demo

or try this "crazier" variant ;)

^[a-z]+N(?:\d{6}|(?:(?:\d{7}){1,2}\d))$

Debuggex Demo

Answer 2

This is how I would do it:

[a-z]+N(\d{6}|\d{8}|\d{15})