In this article you are going to learn about placeholders, varibles and environment variables in Caddy.

Placeholders #

You can access placeholders in Caddy using curly braces { } to access dynamic values inside caddy's configuration. Some of these dynamic values are built in and some are defined by you.

For example, to get current time use time.now.

:80 {
	respond {time.now}
}
Caddyfile

This will return the current time.

Here is a complete list of some built in placeholders.

Variables #

You can you define variables using the vars keyword.

The defined variable is to use with vars.*. For example, to access a variable named root use vars.root.

:80 {
	vars root https://example.com

	handle {
		respond "{vars.root}"
	}
}
Caddyfile

To define multiple varibles use the block form of vars.

:80 {
	vars {
		root https://example.com
		message "Hello, World!"
	}

	handle {
		respond "{vars.root} {vars.message}"
	}
}
Caddyfile

You can define variable values based on route as well. Below is how you can have different value in a variable depending on the path prefix.

:80 {
	vars base "/app"
	vars /admin* base "/admin"
	vars /manage* base "/manage"

	handle {
		respond "{vars.base}"
	}
}
Caddyfile

Some examples of evaluation:

• Path: /123 -> base: /app
• Path: /admin/settings -> base: /admin
• Path /manage/users/1 -> base: /manage

Environment Variables #

Envrionment variables can be accessed from using the {env.*} placeholder.

For example, if you have an envrionment varible BASE_URL: https://example.com.

BASE_URL=https://example.com caddy run --config Caddyfile

You can access it using env.BASE_URL.

:80 {
	respond {env.BASE_URL}
}
Caddyfile

$ curl localhost
https://example.com

You can also use the {$ENV_NAME} format to access envrionment variables in Caddy.

:80 {
	respond {$BASE_URL}
}
Caddyfile

I personally prefer {$} over {env.}, keeps it separate from all other placeholders.