Regex to collect batches of substring permutations of increasing lengths

Question

I have a string e.g. HRJSHR and search for a way to find all possible permutations of A-Z with the length of 2 or more letters. For example

• HR, RJ, JS, SH, HR
• HRJ, RJS, JSH, SHR
• HRJS, RJSH, JSHR
• HRJSH, RJSHR
• HRJSHR

|[A-Z]{2,}| just returns the whole string "HRJSHR" and |[A-Z]{2}| just that ones whith a length of 2 letters. |[A-Z]{2+}| doesn't works.

Which regular expression will find all permutations of A-Z with a length of 2 ore more letters in the string?

Answer 1

Could capture inside a lookahead: (?=([A-Z]{2})) would match all substrings composed of two [A-Z] such as HR,RJ,JS,SH,HR. See test at regex101.

Combine it with a loop to get the desired result:

$str =  "HRJSHR"; $res = array();

for($i=2; preg_match_all('/(?=([A-Z]{'.$i.'}))/', $str, $out); $i++)
  $res[$i] = $out[1];

print_r($res);

See test at eval.in, outputs to:

Array
(
    [2] => Array
        (
            [0] => HR
            [1] => RJ
            [2] => JS
            [3] => SH
            [4] => HR
        )

    [3] => Array
        (
            [0] => HRJ
            [1] => RJS
            [2] => JSH
            [3] => SHR
        )

    [4] => Array
        (
            [0] => HRJS
            [1] => RJSH
            [2] => JSHR
        )

    [5] => Array
        (
            [0] => HRJSH
            [1] => RJSHR
        )

    [6] => Array
        (
            [0] => HRJSHR
        )

)

For a result without grouping by length, use:
$res = array_merge($res, $out[1]); instead of $res[$i] = $out[1];