php - 正则表达式匹配组不是由字母数字(\w)的前面忽略空格

Question

我正在尝试匹配一个组，该组仅在匹配之前的第一个非空格字符不是字母数字字符时才匹配。
RegExp 我试过，先用\s* 消耗空格，然后回头检查\w:

(?<!\w)\s*\({\w+}\)

成功

Input:  this will = ({match})
Expected: ({match})
Actual: ({match})

失败，仍然匹配，前面是字母数字(忽略空格)

Input:  this should = not ({match})
Expected: -
Actual: ({match})

使用\s+ 而不是\s* 部分解决了它，但现在它至少需要一个不需要的空间!

(?<!\w)\s+\({\w+}\)

我一直在浏览互联网，但无法解决问题。任何人？

Answer 1

使用此解决方案(@horcrux 和 @Wiktor Stribizew 建议的混合):

<?php

$regex = '/(?<![\w\s])\s*(\({\w+}\))/';
$string = 'this will = ({match})
this should = not ({match})';
preg_match_all($regex, $string, $matches);
var_dump($matches[1]);

?>

见 regex proof .
结果 :

array(1) {
  [0]=>
  string(9) "({match})"
}

见 PHP proof .
说明

--------------------------------------------------------------------------------
  (?<!                     look behind to see if there is not:
--------------------------------------------------------------------------------
    [\w\s]                   any character of: word characters (a-z,
                             A-Z, 0-9, _), whitespace (\n, \r, \t,
                             \f, and " ")
--------------------------------------------------------------------------------
  )                        end of look-behind
--------------------------------------------------------------------------------
  \s*                      whitespace (\n, \r, \t, \f, and " ") (0 or
                           more times (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    \(                       '('
--------------------------------------------------------------------------------
    {                        '{'
--------------------------------------------------------------------------------
    \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                             more times (matching the most amount
                             possible))
--------------------------------------------------------------------------------
    }                        '}'
--------------------------------------------------------------------------------
    \)                       ')'
--------------------------------------------------------------------------------
  )                        end of \1