Using a variable in another variable name

[Ti Leggett]

In a template, is there a way to use a variable to reference another variable name? For instance, let's say I have a variable 'interface', and in my template I want to reference @ipaddress_$interface so that when interface = 'eth0' I get the value of @ipaddress_eth0, but when interface = 'eth1' I get the value of @ipaddress_eth1.

[windowsrefund]

<%= eval "macaddress_" + my_lan1 %>

That will return the appropriate fact based on the value of my_lan1

[Ti Leggett]

Many thanks!

On Feb 21, 2013, at 10:51 AM, windowsrefund <window...@gmail.com> wrote:

>
> <%= eval "macaddress_" + my_lan1 %>
>
> That will return the appropriate fact based on the value of my_lan1
>

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[Nick Fagerlund]

Other options:

<%= scope.lookupvar("macaddress_#{my_lan1}") %>

Also, the stdlib module has a function useful for doing this outside of templates:

https://github.com/puppetlabs/puppetlabs-stdlib/blob/master/lib/puppet/parser/functions/getvar.rb

[Ti Leggett]

Is there a good way to check that the fact in question actually exists prior to doing an eval? Doing the below when there is no 'my_lan1' fact produces an error.

On Feb 21, 2013, at 10:51 AM, windowsrefund <window...@gmail.com> wrote:

>

> <%= eval "macaddress_" + my_lan1 %>
>
> That will return the appropriate fact based on the value of my_lan1
>

[Ti Leggett]

Nevermind. Figured this out:

<% if defined?( eval "macaddress_" + my_lan1 -%>
...
<% end -%>

[Adrien Thebo]

Using the scope.lookupvar or getvar functions would be greatly preferable; using `eval` in this context is Really Bad (TM) and could produce some extremely bad behavior depending on the value of my_lan1.

--

Adrien Thebo | Puppet Labs

[Ti Leggett]

Can you provide an example of using those safer functions in this case?