Overlapping matches in Regex

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Update 2016:

To get nn, nn, nn, SDJMcHattie proposes in the comments (?=(nn)) (see regex101).

(?=(nn))

Original answer (2008)

A possible solution could be to use a positive look behind:

(?<=n)n

It would give you the end position of:

  1. nnnn
     
  2. nnnn
     
  3. nnnn

As mentioned by Timothy Khouri, a positive lookahead is more intuitive (see example)

I would prefer to his proposition (?=nn)n the simpler form:

(n)(?=(n))

That would reference the first position of the strings you want and would capture the second n in group(2).

That is so because:

  • Any valid regular expression can be used inside the lookahead.
  • If it contains capturing parentheses, the backreferences will be saved.

So group(1) and group(2) will capture whatever ‘n’ represents (even if it is a complicated regex).

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