Unity3D Build Script, environment variables

BuildScript.cs

public class BuildScript
{
    private static readonly string _versionNumber;
    private static readonly string _buildNumber;

    static BuildScript()
    {
        _versionNumber = Environment.GetEnvironmentVariable("VERSION_NUMBER");
        if (string.IsNullOrEmpty(_versionNumber))
            _versionNumber = "1.0.0.0";

        _buildNumber = Environment.GetEnvironmentVariable("BUILD_NUMBER");
        if (string.IsNullOrEmpty(_buildNumber))
            _buildNumber = "1";

        PlayerSettings.productName = "Your game name";
        PlayerSettings.bundleVersion = 
            PlayerSettings.shortBundleVersion = _versionNumber;
    }
}