Matching an overlapping pattern in regex

In the following string:

7thousand3hundred54

I want to match:

7thousand3
3hundred54

I’m currently using this pattern:

(\d?[(1-9)]|[1-9]0)(hundred|thousand)(\d?[(1-9)]|[1-9]0)

Which matches just:

7thousand3

Which makes sense, but how can I modify the pattern such that the 3 in the middle overlaps in the two matches that I’m looking for in 7thousand3hundred54?

>Solution :

You’ve to use positive lookahead assertion, to get it to work. The simplest solution is:

(?=(\d+(hundred|thousand)\d+))

If you want the extra digit checks you had, you can use:

(?=((\d?[(1-9)]|[1-9]0)(hundred|thousand)(\d?[(1-9)]|[1-9]0)))

Regex101