Re: Using "if" to test for existence of properties

Same strategy here; ensure the property exists and then use the if attribute
to test its value. One place where you can use the if / unless attributes to
test existence is in setting the property itself, so giving it a default
value. We use the following to ensure that required properties are at least
set to a default value:

<property name="ernex.core.build" value="Latest"
unless="${property::exists('ernex.core.build')}" />

Hope that helps
---
Chris.

Continuous improvement is better than delayed perfection. - Mark Twain


On Tue, Apr 13, 2010 at 7:51 AM, Bob Archer <[email protected]> wrote:

>  I think I have run into this before. I think the easiest fix is to make
> sure the property always exists. Then you can check to see if it is not
> empty.
>
>
>
> BOb
>
>
>
>
>
> *From:* Durand Van Arnem [mailto:[email protected]]
> *Sent:* Tuesday, April 13, 2010 10:33 AM
> *To:* NAnt Users
> *Subject:* [NAnt-users] Using "if" to test for existence of properties
>
>
>
> Hello,
>
> I could use some advice about how to handle this situation:
>
> I have a property, MyProperty, that may or may not be set.  I want a task
> to execute if the property is set, e.g.
> <echo messsage="Hello ${MyProperty}!" if="${property::exists('MyProperty')"
> />
>
> If MyProperty is not set, this task fails because NAnt appears to evaluate
> the message portion regardless of the result of the IF evaluation.  I could
> rewrite like this:
>
> <if test="${property::exists('MyProperty')}">
>     <echo message="Hello ${MyProperty}!" />
> </if>
>
> However, I run into the same issue with filterchains:
>
> <!-- FAILS if MyProperty is not set, because NAnt evaluates the tokens
> regardless of the IF result -->
> <copy failonerror="true" verbose="true" todir="C:\Temp">
>     <fileset refid="Deploy-FileSet" />
>     <filterchain>
>         <replacetokens begintoken="[" endtoken="]" ignorecase="true"
> if="${property::exists('MyProperty')}">
>             <token key="ABC" value="${MyProperty}" />
>         </replacetokens>
>     </filterchain>
> </copy>
>
> I'd rather not enclose the whole definition of the copy in an IF, with a
> nearly identical "else" version for the case when MyProperty is not set.
>
> How have you handled this situation?
>
> Thanks,
> Durand
>
>
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