正则表达式：里面有一个正则表达式

Question

I'm falling deeper into the regex's dark side. I need to parse this:

{{word(a|b|c)|word$1}}
{{word(s?)|word$1}}
{{w(a|b|c)ord(s?)|w$1ord$2}}

As you may have noticed, it is a search & replace scheme, containing regular expressions. The wikimedia engine does it very well, but I couldn't find how it does: right here.

I just need to get the first part, and the second part into two seperated variables. For instance:

preg_match(REGEX, "{{word(a|b|c)|word$1}}", $result) // Applying REGEX on this
echo $result[1] // word(a|b|c)
echo $result[2] // word$1

How would you do ? It's like regex in regex, I'm completely lost...

Answer 1

You could match the parts using something like:

{{((?:(?!}}).)+)\|([^|]+?)}}

Note that if you are allowing arbitrary PCRE regex then some very complex and slow patterns can be constructed, possibly allowing simple DoS attacks on your site.