Git revision in Android build config using Gradle

build.gradle

def exec(String cmdline) {
    def os = new ByteArrayOutputStream()
    exec {
        commandLine cmdline.split(" ")
        standardOutput = os;
    }
    return os.toString().replaceAll('\\s', '')
}

def getGitSha() {
    return exec('git rev-parse --short HEAD')
}

android {
    buildTypes {
        debug {
            # Make sure debug builds aren't being rebuild each time you do a commit.
            buildConfigField "String", "GIT_SHA", "\"\""
        }
        release {
            buildConfigField "String", "GIT_SHA", "\"" + getGitSha() + "\""
        }
    }
}