given:
       file("a/b.txt") << "\$foo"

       when:
       buildScript """
           task c(type: Copy) {
               from("a") {
                   filesMatching("b.txt") {
                       expand foo: "bar"
                   }
                   into "nested"
               }
               into "out"
           }
       """

       then:
       succeeds "c"

       and:
       file("out/nested/b.txt").text == "bar"