Hi, It looks like I have stumbled upon a bug in substitution of evaluated expressions. A test case: String result = org.apache.nifi.attribute.expression.language.Query.prepare("${foo}$${foo}").evaluateExpressions(Collections.singletonMap("foo", "bar"), null); Expected result: "bar${foo}"Observed result: "barbar" The issue exists in 1.5.0 and, as far as I can tell, in the master branch.The cause is quite simple: Query.prepare(...) splits the input string into pieces to be evaluated and substituted or to be copied literally, but it doesn't keep track of which is which.That couldn't possibly work. If a piece to be copied literally happens to be equal to one of the pieces to be substituted, the things go wrong, as the test case demonstrates.
Regards,Sergei.