How to lookup the latest git commit hash from an ant build script

I wrote the following ant target for a project on github. Usage:

• stores version in property "repository.version"
• works if no git is installed or no .git directory is present (fallback)
• other targets must depend on this target if they need the git version
• only one git command gets executed (--always)

<available file=".git" type="dir" property="git.present"/>

<target name="git.revision" description="Store git revision in ${repository.version}" if="git.present">
    <exec executable="git" outputproperty="git.revision" failifexecutionfails="false" errorproperty="">
        <arg value="describe"/>
        <arg value="--tags"/>
        <arg value="--always"/>
        <arg value="HEAD"/>
    </exec>
    <condition property="repository.version" value="${git.revision}" else="unknown">
        <and>
            <isset property="git.revision"/>
            <length string="${git.revision}" trim="yes" length="0" when="greater"/>
        </and>
    </condition>
</target>

It e.g. be used for expanding the token @repository.version@ in a template file:

<target name="index.html" depends="git.revision" description="build index.html from template">
    <copy file="index.html.template" tofile="index.html" overwrite="yes">
        <filterchain>
            <replacetokens>
                <token key="repository.version" value="${repository.version}" />
            </replacetokens>
        </filterchain>
    </copy>
</target>

This command returns always the working folder's last commit SHA1, useful when you don't always build from HEAD. The command should run both on Windows and *nix systems

<exec executable="git" outputproperty="git.revision">
    <arg value="log" />
    <arg value="-1" />
    <arg value="--pretty=format:%H" />
</exec>