如何匹配内部（可能是嵌套）括号中的换行符？ （正则表达式）

Question

I am using PHP regex. Consider a text like this:

Lorem ipsum (dolor sit 
amet (consectetur adipiscing
 elit) sed do eiusmod) tempor 
(incididunt) ut 
labore.

I need to match the newlines inside the brackets, but not the ones outside brackets (like the last two). My current regex looks like this: /\([^)]*([ ]+)[^(]*\)/s, however it doesn't capture the newline between "sit" and "amet" because of the nested brace. Can I make it work with regex only, or do I have to parse the text manually?

Answer 1

You may match all the nested parentheses with a recursive regex and then remove all CRLF sequences in the match values inside preg_replace_callback.

Use this regex to match nested parentheses:

'~\((?>[^()]++|(?R))*\)~'

And here is a PHP demo:

$re = '~\((?>[^()]++|(?R))*\)~'; 
$str = "Lorem ipsum (dolor sit 
amet (consectetur adipiscing
 elit) sed do eiusmod) tempor 
(incididunt) ut 
labore."; 
$output = preg_replace_callback($re, function($m) {
    return str_replace("
", "", $m[0]);
}, $str);
echo $output;

Output:

Lorem ipsum (dolor sit amet (consectetur adipiscing elit) sed do eiusmod) tempor 
(incididunt) ut 
labore.

Additionally, see Recursive patterns at php.net.