How do I extact the first element in a list using replaceregex in an Ant file?

Question

Working with Ant's regular expressions system seems to give me no end of trouble. With enough work I can usually get it to work (and understand what I was doing wrong earlier). But not this time. I have a simple target wherein I want to extract the first element out of a property that contains one or more comma separated words, like this:

tgt.list.full=word1,word2,word3,word4

(Edit: tgt.list.full is actually populated by another property: tgt.list.basic, so the actual cfg.list.file looks like this:

tgt.list.basic=word1,word2,word3,word4
tgt.list.full=${tgt.list.basic}

)

I want the first word: "word1" to replace the ${target} property. This is what my task looks like:

 <target name="load-configuration-list">
     <loadproperties srcfile="${cfg.list.file}">
         <filterchain>
             <containsregex pattern="^tgt.list.full=(.*),?.*" replace="target=\1" />
             <concatfilter prepend="${cfg.list.file}" />
         </filterchain>
     </loadproperties>
     <echo message="TGT: ${target}, FULL: ${tgt.list.full}"/>
     <fail unless="target" message="A target cannot be determined"/>
 </target>

With the current version I have listed under the "containsregex" task, ${target} gets populated with the full list ("word1,word2,word3,word4") and not simply "word1." I have tried a large number of variations o the them. Here's an example:

<containsregex pattern="^tgt.list.full=(word1),?.*" replace="target=\1" />

I would expect that this would at least FORCE the target property to be populated, but in this case, ${target} remains undefined (not even the full list is put into it).

Perhaps there is a flaw in my filterchain logic. I know I could probably write task of my own, but Ant seems to have the components already that I need, if I can understand them better.

To rephrase my original question: given a comma separated list in an Ant property, how might I use an Ant task (not necessarily even using containsregex or replaceregex) to extract the first element?

Answer 1

Would this regex be better suited to what you need ?

^tgt.list.full=([^,]+),?.*
^tgt.list.full=([^,]+),?[^\r\n]*$

Since '.' (dot) represents any character, '(.*),?.*' does select word1,word2,... because of the greediness of the * quantifier.
May be '(.*?),?.*' would have been better, but at least with [^,]+, we know a greedy operator will not capture any ','.

The second form may be needed to be sure to capture only what is on one line, and not "everything that follows a ," (including the next lines, since '.' in a 'dotall' mode, can include crlf characters).

---

As mentioned by Adam in the comments:

The "target" prop was actually being populated by "${tgt.list.basic}," not "full".
So after everything resolved, the target was now populated by the basic list.
I moved the full list out of the cfg file to be populated by the basic list later (instead of immediately)