[#config-envs]
= Environment Variables in the Config File

You can pull configuration values from environment variables like this:

.`config.yaml`
[source,yaml]
----
logLevel: ${{ LOG_LEVEL }}

pageTitle: Olivetin - ${{ DEPLOY_ENV }}

actions:
    ...
----

While loading the config file, Olivetin will substitute the value of the named environment variable for the token.
If the variable is unset, Olivetin will use an empty string as the value and log a warning. This syntax works even for
configuration values that aren't strings, as long as the final string value can be converted to the proper type.

== Notes

. These variables are read while loading the config file. Changes in the environment won't be reflected until the config
file is reloaded. If you want to read environment variables at execution time in your action's `shell` line, make sure
to use regular shell syntax, i.e., `$FOO` rather than `${{ FOO }}`. See xref:args/env.adoc[environment variables]
for info on using environment variables in your actions.

[#using-env-in-template-replacements]
== Using .Env in template replacements

In addition to config-file substitution, OliveTin supports using the process environment inside *action templates* (e.g. `shell`, `shellAfterCompleted`, entity directory titles, and other fields that use Go template syntax). Use `{{ .Env.VAR_NAME }}` to substitute an environment variable at the time the action is executed.

This is useful when you want a command to depend on the runtime environment (e.g. container or system env) rather than config-load time, or when you need env values in template fields that are not the raw `shell` command (where you could use `$VAR`).

.Example: use `.Env` in a shell command
[source,yaml]
----
actions:
  - title: Run with deploy env
    shell: /opt/deploy.sh --env {{ .Env.DEPLOY_ENV }} --host {{ .Env.HOSTNAME }}
----

.Example: use `.Env` in a completion notification
[source,yaml]
----
actions:
  - title: Backup
    shell: /opt/backup.sh
    shellAfterCompleted: "apprise -t 'Backup on {{ .Env.HOSTNAME }}' -b '{{ output }}'"
----

`.Env` uses the same Go template context as other action variables (e.g. `.Arguments`, `.CurrentEntity`, `.OliveTin`). The map is built from the process environment when OliveTin starts; values are read at template execution time. If a variable is missing, the template engine will report a missing-key error (with `missingkey=error`), so use defaulting when a variable might be unset, e.g. `{{ or .Env.OPTIONAL_VAR "default" }}`. For template functions such as JSON encoding, see xref:args/templates.adoc#json-encoding[JSON encoding with Json].

This feature addresses the need to use environment variables in templates without changing the config loader (see link:https://github.com/OliveTin/OliveTin/issues/840[GitHub issue #840]).
