Hands-on: Try the Perform Dynamic Operations with Functions tutorial.

The Terraform language includes a number of built-in functions that you can call from within expressions to transform and combine values. The general syntax for function calls is a function name followed by comma-separated arguments in parentheses:

max(5, 12, 9)

For more details on syntax, see Function Calls in the Expressions section.

Provider-defined Functions

You cannot define your own functions in the Terraform configuration language, but you can develop your own providers that expose functions. Refer to Provider-defined functions for information about defining functions in custom providers.

When using a provider-specific function, add the provider::<local-name>:: where <local-name> corresponds with an entry in the required_providers block. The following example calls the encoode_tvfars function in the terraform provider:

provider::terraform::encode_tfvars({
  example = "Hello!"
})

The documentation covers the built-in functions and built-in provider-defined functions only.

Functions defined by external providers are documented by those providers in the Terraform Registry.

Experimenting with Functions

You can experiment with the behavior of Terraform's built-in functions from the Terraform expression console, by running the terraform console command:

> max(5, 12, 9)
12

The examples in the documentation for each function use console output to illustrate the result of calling the function with different parameters.