tools.gradle

def getCheckedOutGitCommitHash() {
    def gitFolder = project.rootDir.getPath() + "/.git/"
    def takeFromHash = 12   // take the first n chars from the commit hash

    /*
     * Simple access to the current commit-hash, without having to rely on a local git installation
     *   (based on https://gist.github.com/JonasGroeger/7620911 )
     *
     *  '.git/HEAD' contains either
     *      in case of detached head: the currently checked out commit hash ("3b3fe8f99d45d48ada83596cee371b21899d97a8")
     *      otherwise: a reference to a file containing the current commit hash  ("ref: refs/heads/master")
     */
    def hash = ""
    try {
        def head = new File(gitFolder + "HEAD").text.split(":") // .git/HEAD
        def isCommit = (head.length == 1)

        if (isCommit) {
            hash = head[0].trim();
        } else {
            def refHead = new File(gitFolder + head[1].trim()) // .git/refs/heads/master
            hash = refHead.text.trim()
        }
    }catch(IOException ex){
        hash = ""
        logger.warn("Unable to detect current git commit hash: {}", ex.toString())
    }

    def version = hash.take(takeFromHash)
    logger.debug("Detected '{}' as git commit hash - using {} as version", hash, version)

    return version
}

def getGitBranch() {
    def gitFolder = project.rootDir.getPath() + "/.git/"

    /*
     * Simple access to the current branch, without having to rely on a local git installation
     *   (based on https://gist.github.com/JonasGroeger/7620911 )
     *
     *  '.git/HEAD' contains either
     *      in case of detached head: the currently checked out commit hash ("3b3fe8f99d45d48ada83596cee371b21899d97a8")
     *      otherwise: a reference to a file containing the current commit hash  ("ref: refs/heads/master")
     */
    def branch = ""
    try {
        def head = new File(gitFolder + "HEAD").text.split(":") // .git/HEAD
        def isDetached = (head.length == 1)

        if (isDetached) {
            logger.warn("Unable to detect current git branch, {}", head)
        } else {
            def refHead = new File(gitFolder + head[1].trim()) // .git/refs/heads/master
            branch = head.last().split("/").last().trim();
        }
    }catch(IOException ex){
        logger.warn("Unable to detect current git branch: {}", ex.toString())
    }

    logger.debug("Detected '{}' as git branch", branch)

    return branch
}

// export the functions
ext{
    getCheckedOutGitCommitHash = this.&getCheckedOutGitCommitHash
    getGitBranch = this.&getGitBranch
}