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

[Norbert Hartl < >]

Am 21.09.2011 um 14:27 schrieb 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

thank you guys! 

Didn't know about a string being evaluated as command. The command I need to 
evaluate is about 10 to 20 lines. I've built a library the contructs the 
proper strings and that I use. So I do basically

...
script "install seaside" do
        interpreter "bash"
        ...
        not_if GemStone.isDefinedClass("stone-default", "WASession")
end

To me it looks as nice as it has to be. Great stuff! And I like that 
libraries are visible everywhere.

Norbert