runtime-env

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interpolate ​

interpolate substitutes runtime values into HTML/text templates.

Command syntax ​

bash
runtime-env [top-level options] interpolate [command options] [rawInput]

Top-level options and ordering ​

Top-level options are passed before the subcommand and affect interpolation behavior:

  • --schema-file <path>: defines expected keys used during resolution.
  • --global-variable-name <name>: controls placeholder namespace (for example, runtimeEnv).
  • --watch: reruns interpolation on changes.

This command is useful for general HTML/text substitution flows, deployment/startup, and custom workflows.

interpolate command options ​

  • --input-file <path>: read template content from a file.
  • --output-file <path>: write interpolated content to a file.
  • --env-file <path>: load values from one or more env files.

Interpolation uses the global variable name in templates (for example, <%= runtimeEnv.APP_TITLE %> by default).

Default behavior ​

  • --schema-file default: .runtimeenvschema.json
  • --global-variable-name default: runtimeEnv
  • --watch default: off
  • if --env-file is omitted: values come from the current process environment
  • if --output-file is omitted: output is written to stdout
  • if --input-file is omitted: the first positional argument is treated as the raw input string, not a file path
  • if both env files and process environment are used: process environment wins

GA / third-party script example ​

Template snippet:

html
<script
  async
  src="https://www.googletagmanager.com/gtag/js?id=<%= runtimeEnv.GA_MEASUREMENT_ID %>"
></script>
<script src="<%= runtimeEnv.THIRD_PARTY_SCRIPT_URL %>"></script>

Example ​

bash
runtime-env --schema-file .runtimeenvschema.json interpolate --env-file .env.staging --input-file ./templates/index.template.html --output-file ./out/index.html