Is there a way to compare regular expression backreferences?

I have the following sample expr开发者_JAVA技巧ession that I'm passing to egrep over a word list:

^([a-z])lu([a-z])\2er$

I'd like to further stipulate that the content of \1 and \2 must be different, e.g. this would match "bluffer" but not "blubber". Is there a way to build this into the expression itself (so I can get my results right from egrep or something like it), or am I stuck doing this in some real language with regular expression support and manually checking that none of my groups are the same?

---

You could add the negative lookahead (?!\1) in front of the 2nd match group. The following regex:

([a-z])lu(?!\1)([a-z])\2er

matches "bluffer" but not "blubber". This only works properly if both the groups match the same amount of characters.

---

You need something more powerful. Regular expressions can't track state. Sed could probably do what you need.