RegEx standards across languages

Question

I am asking this question because I notice there are some slight differences in the syntax of RegEx between different languages.

I am wondering if there is a RegEx

Answer 1

No there isn't such a standard. Of course there is PCRE, POSIX BRE, POSIX ERE, ...

But in fact there will be "small" differences in any language. You can relay on very basic things for most flavours, like the . for any character or the quantifiers +*?, character classes are also common, but it already starts at predefined classes like \w, is it supported at all? or ASCII based or Unicode?

A good help here is the flavor comparison on regular-expressions.info by Jan Goyvaerts.