Ant target for autogenerating changelog based on Git tags

gistfile1.xml

<!--

    Ant target for autogenerating a changelog based on Git tags

    Workflow:
    1. Do all of your checkins for a given version.
    2. When you're ready to officially create a new version, tag it using git tag, such as "git tag v0.3.0".
    3. If you don't already have a file named CHANGELOG in the root directory, make one.
    4. Run "ant changelog.update"

    Assumptions:
    1. You only use tags for version numbers, that's it.
    2. You have a file named CHANGELOG that you want to auto-update.
    3. You want today's date stamped in the CHANGELOG file/
    4. Your project name is "project". That's dumb, it should be something better.

-->
<target name="changelog.update">
    <exec executable="git" failonerror="true" outputproperty="git.tag">
        <arg line="tag"/>
    </exec>      
    <script language="javascript"><![CDATA[
        //get the two most recent tags to get the diff
        var tags = project.getProperty("git.tag").replace("\r", "").split("\n"),
            curTag = tags[tags.length-1],
            priorTag = tags[tags.length-2];
        project.setProperty("project.current", curTag);
        project.setProperty("git.log.range", priorTag + ".." + curTag);
    ]]></script>
    
    <!-- git log -pretty=format:'* %s (%an)' v0.4.0..v0.5.0-->
    <exec executable="git" failonerror="true" outputproperty="git.changelog">
        <arg line="log --pretty=format:'* %s (%an)' ${git.log.range}"/>
    </exec>      
    
    <concat destfile="CHANGELOG.tmp"  fixlastline="true">
        <header trimleading="yes">${SIMPLE_DATE} - v${project.current}
        
        ${git.changelog}
        </header>
        <fileset dir="." includes="CHANGELOG" />
    </concat>
    
    <delete file="CHANGELOG"/>
    <move file="CHANGELOG.tmp" tofile="CHANGELOG"/>
    
</target>

Sorry but, I still don't understand completely how to use it. There have to be a build.xml file right?

Yes. If you don't know how to use Ant, I'd suggest reading up on that first and creating some simple build.xml files.

Allright thank you!