Puppet users - Feb 2008 - how to check if a variable is defined (in a template)?

Hi,
  I''d like to include a line in a template if a facter is defined. 
I''ve
tried (along with a few variations):

<% if defined?(foo) %>
foo is defined
<% else %>
foo is undefined
<% end %>

I always get ''foo is undefined'' (whether the facter foo is
defined or not).
Help?

...thnx,
...dave

-- 
Dave Alden
The Ohio State University
Department of Mathematics

On Feb 18, 2008, at 2:16 PM, Dave Alden wrote:
>
> Hi,
>  I''d like to include a line in a template if a facter is defined.
> I''ve
> tried (along with a few variations):
>
> <% if defined?(foo) %>
> foo is defined
> <% else %>
> foo is undefined
> <% end %>
>
> I always get ''foo is undefined'' (whether the facter foo
is defined
> or not).
> Help?
I guess you didn''t see my message on IRC:  defined? doesn''t
return
true if the object is defined, it returns the value of the object.  So  
to follow closely what you have... you will probably want something  
more like:

<% if !defined? foo %>
foo is undefined
<% else %>
foo is defined
<% end %>

-Blake

Hi,

On Mon, Feb 18, 2008 at 02:25:29PM -0800, Blake Barnett
wrote:
> I guess you didn''t see my message on IRC:  defined?
doesn''t return
> true if the object is defined, it returns the value of the object.  So  
> to follow closely what you have... you will probably want something  
> more like:
> 
> <% if !defined? foo %>
> foo is undefined
> <% else %>
> foo is defined
> <% end %>
I''m sorry - I thought I had replied on #puppet that this too did not
work.  I have the following in a template:

<% if !defined? foo %>
foo is undefined, although its value is set to "<%= foo %>"
<% else %>
foo is defined
<% end %>

I have the environment variable "FACTER_FOO" defined to be
"bob".  I then
run puppet and I get:

foo is undefined, although its value is set to "bob"

So even though it thinks it is undefined, it puts the value into the output.
Of course if it truly isn''t defined, I get the error "Could not
find value
for ''foo'' at ..." (which I would expect due to the <%=
foo %> line).  I''m
confused...:(

...dave
-- 
Dave Alden
The Ohio State University
Department of Mathematics

On Feb 19, 2008, at 8:42 AM, Dave Alden wrote:
>
> I''m sorry - I thought I had replied on #puppet that this too did
not
> work.  I have the following in a template:
>
> <% if !defined? foo %>
> foo is undefined, although its value is set to "<%= foo %>"
> <% else %>
> foo is defined
> <% end %>
>
> I have the environment variable "FACTER_FOO" defined to be
"bob".  I
> then
> run puppet and I get:
>
> foo is undefined, although its value is set to "bob"
>
> So even though it thinks it is undefined, it puts the value into the  
> output.
> Of course if it truly isn''t defined, I get the error "Could
not find
> value
> for ''foo'' at ..." (which I would expect due to the
<%= foo %>
> line).  I''m
> confused...:(
Puppet''s templating support uses a ruby hack -- variables are actually
methods, not variables.

That is, Puppet uses Ruby''s method_missing to notice when you call a  
variable, and then it looks up variables with the same name as the  
method you''re using.

Thus, defined? will never actually work.

The only real way to do this is to get the variable''s value, and see  
if it''s set to an empty string.

Enterprising individuals could add methods to the TemplateWrapper to  
do this kind of test, if it were really needed.

-- 
Seize opportunity by the beard, for it is bald behind.
     -- Bulgarian Proverb
---------------------------------------------------------------------
Luke Kanies | http://reductivelabs.com | http://madstop.com

I use Ruby''s exception handling to deal with this:

<%
begin
    c_buildtype = buildtype
rescue
    c_buildtype = "Unknown"
end
-%>
Buildtype = <%= c_buildtype %>


If sensible (Luke?) I can put this in the FAQ.

Regards,
Derek
 

-----Original Message-----
From: puppet-users-bounces@madstop.com
[mailto:puppet-users-bounces@madstop.com] On Behalf Of Luke Kanies
Sent: 19 February 2008 14:55
To: Puppet User Discussion
Subject: Re: [Puppet-users] how to check if a variable is defined (ina
template)?

On Feb 19, 2008, at 8:42 AM, Dave Alden wrote:
>
> I''m sorry - I thought I had replied on #puppet that this too did
not
> work.  I have the following in a template:
>
> <% if !defined? foo %>
> foo is undefined, although its value is set to "<%= foo %>"
> <% else %>
> foo is defined
> <% end %>
>
> I have the environment variable "FACTER_FOO" defined to be
"bob".  I
> then run puppet and I get:
>
> foo is undefined, although its value is set to "bob"
>
> So even though it thinks it is undefined, it puts the value into the 
> output.
> Of course if it truly isn''t defined, I get the error "Could
not find
> value for ''foo'' at ..." (which I would expect due to
the <%= foo %>
> line).  I''m confused...:(
Puppet''s templating support uses a ruby hack -- variables are actually
methods, not variables.

That is, Puppet uses Ruby''s method_missing to notice when you call a
variable, and then it looks up variables with the same name as the
method you''re using.

Thus, defined? will never actually work.

The only real way to do this is to get the variable''s value, and see if
it''s set to an empty string.

Enterprising individuals could add methods to the TemplateWrapper to do
this kind of test, if it were really needed.

--
Seize opportunity by the beard, for it is bald behind.
     -- Bulgarian Proverb
---------------------------------------------------------------------
Luke Kanies | http://reductivelabs.com | http://madstop.com

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On Feb 22, 2008, at 5:32 AM, <Derek.Whayman@barclayscapital.com>
<Derek.Whayman@barclayscapital.com
 > wrote:
> I use Ruby''s exception handling to deal with this:
>
> <%
> begin
>    c_buildtype = buildtype
> rescue
>    c_buildtype = "Unknown"
> end
> -%>
> Buildtype = <%= c_buildtype %>
>
>
> If sensible (Luke?) I can put this in the FAQ.

Looks like this is the only thing you can do, at this point.

Anyone feel like adding a ''defined?'' method to the
TemplateWrapper
class, so they can just be tested directly?  It should be pretty  
obvious how to do from lib/puppet/parser/templatewrapper.rb.

-- 
The great aim of education is not knowledge but action.
     -- Herbert Spencer
---------------------------------------------------------------------
Luke Kanies | http://reductivelabs.com | http://madstop.com