Obtain Android versionCode from git commit count

build.gradle

def loadVersionCode() {
    def code = 1
    new ByteArrayOutputStream().withStream { os ->
        exec {
            commandLine 'git', 'rev-list', 'HEAD', '--count'
            standardOutput = os
        }
        code = os.toString().toInteger()
    }
    println "Version Code: $code"
    return code
}

android {
    defaultConfig {
        ...
        versionCode loadVersionCode()
    }
}