[chef] Re: What can be used in not_if / how to build something that can be used?

[Bryan McLellan < >]

On Wed, Sep 21, 2011 at 8:11 AM, Norbert Hartl 
<
 >
 wrote:
> Now I try to integrate the stuff a little bit more and make it more 
> reliable. One of the things I do is to check condition that decide if a 
> action needs to take place or not. In the tutorials/examples this almost 
> all the time done using something like "unless File.exists....". I need to 
> do something similar but for another running component. The task is to load 
> some code into server. In order not to load the code every single 
> provisioning time I like to check if it has been loaded already. I know how 
> to do it with execute/script/bash... but then I have to write the specific 
> action it has to do (that follows the condition) within the action. But I 
> need the capabiltiy of checking things in the server quite often. So I'm 
> looking for slightly more generic way of achieving it.
> I don't know if it is possible to create a definition function, an action 
> or anything that returns a value and therefor can be used in not_if, 
> only_if, etc. I had the impression LWRP could help but know I don't know 
> how. My last ressort seems to be writing a library that I include in a 
> recipe. But I wanted to ask if there is a better possibility to achieve the 
> same.

only_if and not_if either run a ruby block, or execute a command,
depending on if their argument is a block or a string. Since you know
how to perform your test in bash, you could put that in a string:

# store our shell command in a string
test_conditional = "test 1 -lt 5"

# echo run only if our previously set shell command exits with 0
execute "test" do
  command "echo run"
  only_if test_conditional
end