assign output of exec-maven-plugin to variable - maven

Question

I want to use exec-maven-plugin to get git 'revision', so I'm using following configuration:
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<executions>
<execution>
<id>gitVersion</id>
<phase>validate</phase>
<goals>
<goal>exec</goal>
</goals>
</execution>
</executions>
<configuration>
<executable>git</executable>
<workingDirectory>./</workingDirectory>
<arguments>
<argument>rev-list</argument>
<argument>master</argument>
<argument>--count</argument>
</arguments>
</configuration>
</plugin>
but I hit a problem - how do I assign output to any variable available in other plugins/livecycles?
(I was able to get it done using gmaven-plugin and executing groovy script, but I find it a bit of overkill/less elegant)
EDIT:
for reference, working solution in groovy:
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>gmaven-plugin</artifactId>
<version>1.5</version>
<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>execute</goal>
</goals>
<configuration>
<providerSelection>2.0</providerSelection>
<properties>
<script>git rev-list master --count</script>
</properties>
<source>
def command = project.properties.script
def process = command.execute()
process.waitFor()
def describe = process.in.text.trim()
println "setting revision to: " + describe
project.properties.setProperty('gitVersion',describe)
</source>
</configuration>
</execution>
</executions>
</plugin>

Answer 1

Just for clarity, here's the solution using groovy:
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>gmaven-plugin</artifactId>
<version>1.5</version>
<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>execute</goal>
</goals>
<configuration>
<providerSelection>2.0</providerSelection>
<properties>
<script>git rev-list master --count</script>
</properties>
<source>
def command = project.properties.script
def process = command.execute()
process.waitFor()
def describe = process.in.text.trim()
println "setting revision to: " + describe
project.properties.setProperty('gitVersion',describe)
</source>
</configuration>
</execution>
</executions>
</plugin>