var (
    // GOPATH environment variable
    // nolint: golint
    GOPATH Variable = "GOPATH"

    // TOP environment variable
    // nolint: golint
    TOP Variable = "TOP"

    // ISTIO_GO environment variable
    // nolint: golint
    ISTIO_GO Variable = "ISTIO_GO"

    // ISTIO_BIN environment variable
    // nolint: golint
    ISTIO_BIN Variable = "ISTIO_BIN"

    // ISTIO_OUT environment variable
    // nolint: golint
    ISTIO_OUT Variable = "ISTIO_OUT"

    // HUB is the Docker hub to be used for images.
    // nolint: golint
    HUB Variable = "HUB"

    // TAG is the Docker tag to be used for images.
    // nolint: golint
    TAG Variable = "TAG"

    // PULL_POLICY is the image pull policy to use when rendering templates.
    // nolint: golint
    PULL_POLICY Variable = "PULL_POLICY"

    // ISTIO_TEST_KUBE_CONFIG is the Kubernetes configuration file to use for testing. If a configuration file
    // is specified on the command-line, that takes precedence.
    // nolint: golint
    ISTIO_TEST_KUBE_CONFIG Variable = "ISTIO_TEST_KUBE_CONFIG"

    // IstioTop has the top of the istio tree, matches the env variable from make.
    IstioTop = TOP.ValueOrDefaultFunc(getDefaultIstioTop)

    // IstioSrc is the location if istio source ($TOP/src/istio.io/istio
    IstioSrc = path.Join(IstioTop, "src/istio.io/istio")

    // IstioBin is the location of the binary output directory
    IstioBin = verifyFile(ISTIO_BIN, ISTIO_BIN.ValueOrDefaultFunc(getDefaultIstioBin))

    // IstioOut is the location of the output directory ($TOP/out)
    IstioOut = verifyFile(ISTIO_OUT, ISTIO_OUT.ValueOrDefaultFunc(getDefaultIstioOut))

    // IstioRoot is the root of the Istio source repository.
    IstioRoot = path.Join(GOPATH.ValueOrDefault(build.Default.GOPATH), "/src/istio.io/istio")

    // ChartsDir is the Kubernetes Helm chart directory in the repository
    ChartsDir = path.Join(IstioRoot, "install/kubernetes/helm")

    // IstioChartDir is the Kubernetes Helm chart directory in the repository
    IstioChartDir = path.Join(ChartsDir, "istio")

    CrdsFilesDir = path.Join(ChartsDir, "istio-init/files")

    // BookInfoRoot is the root folder for the bookinfo samples
    BookInfoRoot = path.Join(IstioRoot, "samples/bookinfo")

    // BookInfoKube is the book info folder that contains Yaml deployment files.
    BookInfoKube = path.Join(BookInfoRoot, "platform/kube")

    // ServiceAccountFilePath is the helm service account file.
    ServiceAccountFilePath = path.Join(ChartsDir, "helm-service-account.yaml")

    // RedisInstallFilePath is the redis installation file.
    RedisInstallFilePath = path.Join(IstioRoot, "pkg/test/framework/components/redis/redis.yaml")
)

type Variable string