Environment Substitution

The envsubst function replaces environment variable placeholders in strings.

Usage

import { envsubst } from "rhdh-e2e-test-utils/utils";

Basic Substitution

// Simple variable
process.env.API_URL = "https://api.example.com";
const result = envsubst("URL: $API_URL");
// Result: "URL: https://api.example.com"

// With braces
const result2 = envsubst("URL: ${API_URL}");
// Result: "URL: https://api.example.com"

Default Values

Use :- syntax for default values:

// If PORT is not set, use 8080
const result = envsubst("Port: ${PORT:-8080}");
// Result: "Port: 8080"

// If PORT is set
process.env.PORT = "3000";
const result2 = envsubst("Port: ${PORT:-8080}");
// Result: "Port: 3000"

YAML Configuration

Common use case is processing YAML configuration files:

# config-template.yaml
app:
  title: ${APP_TITLE:-My App}
  baseUrl: https://${HOST}.${DOMAIN}

backend:
  cors:
    origin: ${CORS_ORIGIN:-*}

import { envsubst } from "rhdh-e2e-test-utils/utils";
import * as fs from "fs";

const template = fs.readFileSync("config-template.yaml", "utf-8");
const config = envsubst(template);
fs.writeFileSync("config.yaml", config);

Secrets Processing

The package uses envsubst internally for secrets:

# rhdh-secrets.yaml
apiVersion: v1
kind: Secret
metadata:
  name: rhdh-secrets
type: Opaque
stringData:
  GITHUB_TOKEN: ${GITHUB_TOKEN}
  API_KEY: ${API_KEY:-default-key}

When deployed, environment variables are substituted automatically.

If you are writing tests in the overlay repository, see Overlay Configuration Files for how secrets and substitution are applied in CI.

Complete Example

import { test } from "rhdh-e2e-test-utils/test";
import { envsubst } from "rhdh-e2e-test-utils/utils";

test.beforeAll(async ({ rhdh }) => {
  // Set environment variables
  process.env.CUSTOM_API_URL = "https://custom.example.com";
  process.env.NAMESPACE = rhdh.deploymentConfig.namespace;

  // Template with variables
  const template = `
    backend:
      baseUrl: https://backstage-\${NAMESPACE}.\${K8S_CLUSTER_ROUTER_BASE}
    custom:
      apiUrl: \${CUSTOM_API_URL}
  `;

  // Substitute variables
  const config = envsubst(template);
  console.log(config);

  await rhdh.configure({ auth: "keycloak" });
  await rhdh.deploy();
});

Supported Syntax

Syntax	Description
$VAR	Simple substitution
${VAR}	Braced substitution
${VAR:-default}	Default if unset or empty