packer/website/content/docs/templates/hcl_templates/functions/index.mdx

---
page_title: Functions - Configuration Language
description: |-
  The HCL language has a number of built-in functions that can be called
  from within expressions to transform and combine values.
---

# Built-in Functions

`@include 'from-1.5/beta-hcl2-note.mdx'`

The HCL 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:

```hcl
max(5, 12, 9)
```

For information on invoking functions in string literals, refer to the
[String Literals](https://developer.hashicorp.com/packer/docs/templates/hcl_templates/expressions#string-literals) section
in the HCL2 expressions documentation.

The HCL language does not support user-defined functions, and so only
the functions built in to the language are available for use. The documentation includes all of the available built-in functions.