getting tag from CVS for use in Ant

[Alison Monteith <al...@edusoft.com>]

Hi,
 
I don't know much about ant and am trying to fix a problem in our
existing build.xml file.
 
We have many branches in CVS and our normal procedue is to checkout out
a module which contains a build.xml file then run an ant package in this
directory which creates our software packages etc.  As part of the build
script a file called release.txt is created which should contain the cvs
tag and date and timestamp.  
 
Here are the relevant lines from build.xml:
 
<property name="label" value=${build_num} ${DSTAMP} ${TSTAMP}" />
 
<exec dir="www"
          executable="echo"
          output="www/release.txt"
          <arg line="${label}"/>
</exec>
 
Nowhere in build.xml is build_num set, so as expected the output is
"${build_num} <actual date> <actual time>"
 
Does anyone know how to set a variable (in this case ${build_num}) with
the cvs tag for the current module?
 
Thanks in advance for any info.
 
Alison