php - 替换所有未包含在 OPEN 和 CLOSE 单词中的特定单词？

Question

我有以下字符串:

OPEN someone said hello CLOSE im saying hello people OPEN some said hello OPEN they said hello again CLOSE i have to go now though CLOSE hello again!

我正在尝试匹配所有出现的hello(未包含在OPEN 和CLOSE 词中)并将它们替换为换句话说，可能使用正则表达式和 PHP 的 preg_replace 函数(尽管我对其他方法持开放态度，因为我想不出任何方法)。

所以根据上面的字符串，下面的字符串将匹配(我用斜体将它们放在括号中以帮助您区分):

OPEN someone said hello CLOSE im saying (hello) people OPEN some said hello OPEN they said hello again CLOSE i have to go now though CLOSE (hello) again!

不太确定如何进行此操作。

编辑也许这会更好地阐明嵌套结构:

OPEN
text
CLOSE

OPEN 
text
  OPEN
   text
  CLOSE
text
CLOSE

正如您从上面看到的，hello 没有被注意到，因为它在 OPEN...CLOSE 中(因此它们被忽略)，而其他不会被替换。

Answer 1

Alan 的回答很有效。但是，由于我已经花时间编写它，这里是使用回调函数和 PHP (?R) 递归表达式的另一种方法:

function highlightNonNestedHello($str) {
    $re = '/# Two global alternatives. Either...
          (                          # $1: Non-O..C stuff.
            (?:                      # Step through non-O..C chars.
              (?!\b(?:OPEN|CLOSE)\b) # If not start of OPEN or CLOSE,
              .                      # then match next char.
            )+                       # One or more non-O..C chars.
          )                          # End $1:
        |                            # Or...
          (                          # $2: O..C stuff.
            \bOPEN\b                 # Open literal delimiter.
            (?R)+                    # Recurse overall regex.
            \bCLOSE\b                # Close literal delimiter.
          )                          # End $1:
    /sx';
    return preg_replace_callback($re, '_highlightNonNestedHello_cb', $str);
}
function _highlightNonNestedHello_cb($matches) {
    // Case 1: Non-O...C stuff. Highlight all "hello".
    if ($matches[1]) {
        return preg_replace('/\bhello\b/', '(HELLO)', $matches[1]);
    }
    // Case 2: O...C stuff. Preserve as-is.
    return $matches[2];
}