问题
Is it possible to detect if a given string is valid regular expression, using just regular expressions?
Say I have some strings, that may or may not be a valid regular expressions. I'd like to have a regular expression matches those string that correspond to valid regular expression. Is that possible? Or do I have use some higher level grammar (i.e. context free language) to detect this? Does it affect if I am using some extended version of regexps like Perl regexps?
If that is possible, what the regexp matching regexp is?
回答1:
No, it is not possible. This is because valid regular expressions involve grouping, which requires balanced parentheses.
Balanced delimiters cannot be matched by a regular expression; they must instead be matched with a context-free grammar. (The first example on that article deals with balanced parentheses.)
回答2:
See an excellent write-up here:
Regular expression for regular expressions?
The answer is that regexes are NOT written using a regular grammar, but a context-free one.
回答3:
If your question had been "match all valid regular expressions", the answer is (perhaps surprisingly) 'yes'. The regular expression .* match all valid (and non-valid) regular expressions, but is pretty useless for determining if you're looking at a valid one.
However, as the question is "match all and only valid regular expressions", the answer is (as DVK and Platinum Azure" have said 'no'.
来源：https://stackoverflow.com/questions/2906848/is-it-possible-to-have-regexp-that-matches-all-valid-regular-expressions