Question: I don't like the default behavior of this command:

```
knife node run_list add myserver '"role[THISISATEST]"'

```

It adds THIISATEST even if the role doesn't exists. Is there a switch or argument that will prevent knife from adding a role/recipe to a node if it does not exist?

Answer: 
I'm a newbie, so I can't comment. An "answer" might be overkill, but it's all I can do for now. 

My favorite thing for this is [tqdm](https://pypi.python.org/pypi/tqdm). It's minimally invasive, both code-wise and output-wise, and it gets the job done.
Using the modulus check (counter % N == 0) is almost free compared print and a great solution if you run a high frequency iteration (log a lot).
Specially if you does not need to print for each iteration but want some feedback along the way.