Regexp to capture overlapping matches

Question

I am looking for a regexp option or trick to capture all possible strings in a regexp when matches can overlap.

Example : /A.A/ in string "ABACADA"

It finds : ABA, ADA and not ACA !!

I would like : ABA, ACA, ADA

I am working in PHP, but it can be applied to other languages

preg_match_all('/A.A/',"ABACADA",$matches);
var_dump($matches[0]);
// output : array (size=2)
// 0 => string 'ABA' (length=3)
// 1 => string 'ADA' (length=3)

Can you help me? Thanks

just use a lookahead `(?=(A.A))` see http://regex101.com/r/wU8uM7/18 — Avinash Raj, Sep 19 '14 at 07:57
IMO lookahead is common factor but this is a PHP problem not a Python one. — anubhava, Feb 23 '22 at 15:19

anubhava · Accepted Answer · 2022-02-23T15:18:51.750

5

You can use a positive lookahead assertion to get all 3 matches:

(?=(A.A))

RegEx Demo

For your input it finds 3 matches in captured group #1:

ABA
ACA
ADA

PHP Code:

if (preg_match_all('/(?=(A.A))/', "ABACADA", $m))
   print_r($m[1]); // printing index 1

Output:

Array
(
    [0] => ABA
    [1] => ACA
    [2] => ADA
)

edited Feb 23 '22 at 15:18

answered Sep 19 '14 at 08:03

anubhava

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Regexp to capture overlapping matches

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