Build custom target by default in CMake

I'd like to run a custom command with cmake. That sounds like an incredibly simple task/question, but it's frustrating how difficult it is to find an example. Here's what I'm attempting to do: ``` $ cmake . $ make > Hello World! (Output) ``` In Gnu Make that's very easy: ``` bar: echo Hello World! ``` But I'm trying to do this in cmake. Based on what I've been reading, I should be able to do that with the `CMakeLists.txt` file below: ``` cmake_minimum_required(VERSION 3.6) project(foo) add_custom_target(bar) add_custom_command( TARGET bar COMMAND "echo Hello World!" ) ``` Currently there is no work to do if I just call `make`. I need to explicitly call `make bar`. How can I add `bar` to the `all` recipe? I've tried adding `add_dependency(foo bar)`, but `foo` is a non-existent target. If there is some super-target that I'm unaware of that would be perfect. Then I could just use that as the TARGET for my custom command and not bother with `bar`.