More and more DBMS are supporting queries with regular expressions. Eg. MySql uses 'rlike' or 'regexp' in the same syntax as 'like', and Oracle uses REGEXP as a function.
It seems that Hibernate supports this feature - at least the 'rlike' is included in the WhereParser, even though I could not find any rlikeExpression.
Since the rlike operator has the exact same syntax as the like operator, I imagine it would be relatively simple to include this feature in a future release of Grails.
I've only studied the code for the Grails project for very short time, but I think it could be doable somehow if a new Criterion class 'RlikeExpression' is created as a subclass of the 'IlikeExpression' class, and then override the toSqlString() method. Then it should be wired in to the 'HibernateCriteriaBuilder' class, and maybe a few other places that I haven't thought about.
I would like to patch it myself, but right now I think it is quite a mouthful to understand how this whole Grails project is structured.