正则表达式始终匹配第一个组“ first”（在其他组之前）

Question

Sorry for the stupid question, I'm pretty sure the regex needs lookahead / lookbehind and \\G anchor, but I'm not able to find a solution. Thanks in advance for the help.

I have this string:

(:xyz:) word word [match1] word word [match2] word [match...] word ...

I need this result:

Match 1:
Group 1 = xyz
Group 2 = match1
Match 2:
Group 1 = xyz
Group 2 = match2
Match 3:
Group 1 = xyz
Group 2 = match...

Answer 1

You can use lookbehind:

(?<=\(:(xyz):\).*)\[(.*?)\]

But you can do this only in a few languages, like the C# or VB.NET. Or in Java, if you specify a max limit for the chars in the lookbehind (eg .{0,100} instead of .* ).

Answer 2

You can use this regex with \\G boundary matcher:

(?:\(:([^:]+):\)|\G(?!^)).*?\[([^\]]+)\]

RegEx Demo

• (?:\\(:([^:]+):\\)|\\G(?!^)) will match our first capturing group or end of previous match using \\G anchor.
• .*?\\[([^\\]]+)\\] will match & capture text from 2nd group that is between [...] .

---

Code:

$re = '/(?:\(:([^:]+):\)|\G(?!^)).*?\[([^\]]+)\]/';
$str = '(:xyz:) word word [match1] word word [match2] word [match...] word ...';

preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);

// Print the entire match result

$match1 = "";
foreach($matches as $val) {
  //print_r($val);
  if (!empty($val[1])) {
    $match1 = $val[1];
  }
  echo "Match " . (++$i) . ":\n";
  echo "Group 1 = " . $match1 . "\n";
  echo "Group 2 = " . $val[2] . "\n";
}

Code Demo

Answer 3

Lookahead is not limited to fixed string lengths, and in some cases (this included) we can abuse this fact.

function find($str) {
  $n = preg_match_all("/\](.*?)\[(?=.*\):(.*?):\()/", strrev($str), $matches);
  $result = Array();
  for ($i = 0; $i < $n; $i++) {
    $result[] = [strrev($matches[2][$i]), strrev($matches[1][$i])];
  }
  return $result;
}

$str = "(:xyz:) word word [match1] word word [match2] word [match...] word ...";
print_r(find($str));

# =>
Array
(
    [0] => Array
        (
            [0] => xyz
            [1] => match...
        )

    [1] => Array
        (
            [0] => xyz
            [1] => match2
        )

    [2] => Array
        (
            [0] => xyz
            [1] => match1
        )

)