Match at every second occurrence

Question

Is there a way to specify a regular expression to match every 2nd occurrence of a pattern in a string?

Examples

• searching for a agains

Answer 1

Back references can find interesting solutions here. This regex:

([a-z]+).*(\1)

will find the longest repeated sequence.

This one will find a sequence of 3 letters that is repeated:

([a-z]{3}).*(\1)