Automatic Versioning for gradle-based Android applications on Bitrise CI

app.gradle

// When running on the Bitrise-CI, this will return the build-number. Otherwise use 0
def buildNumber = System.getenv("BITRISE_BUILD_NUMBER") as Integer ?: 0
// Use your own current version number
def versionNumber = "1.0."

android {
    ...
    defaultConfig {
        ...
        versionCode buildNumber
        versionName versionNumber + buildNumber
        ...
    }
}