how to check if a variable is defined (in a template)?

[Dave Alden]

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

[Blake Barnett]

Post by Dave Alden
Hi,
I'd like to include a line in a template if a facter is defined.
I've
<% 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

[Dave Alden]

Hi,

Post by Blake Barnett
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
<% 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

[Luke Kanies]

Post by Dave Alden
I'm sorry - I thought I had replied on #puppet that this too did not
<% 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
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.

[D***@barclayscapital.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-***@madstop.com
[mailto:puppet-users-***@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)?

Post by Dave Alden
I'm sorry - I thought I had replied on #puppet that this too did not
<% 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
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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[Luke Kanies]

Post by D***@barclayscapital.com
<%
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.