templatefile Function

templatefile reads the file at the given path and renders its content as a template using a supplied set of template variables.

templatefile(path, vars)

The template syntax is the same as for string templates in the main HCL2 language, including interpolation sequences delimited with ${ ... }. This function just allows longer template sequences to be factored out into a separate file for readability.

The "vars" argument must be a map. Within the template file, each of the keys in the map is available as a variable for interpolation. The template may also use any other function available in Packer, except that recursive calls to templatefile are not permitted. Variable names must each start with a letter, followed by zero or more letters, digits, or underscores.

Strings in HCL2 are sequences of Unicode characters, so this function will interpret the file contents as UTF-8 encoded text and return the resulting Unicode characters. If the file contains invalid UTF-8 sequences then this function will produce an error.

This function can be used only with files that already exist on disk at the beginning of a run.

Examples

Lists

Given a template file backends.tpl with the following content:

%{ for addr in ip_addrs ~}
backend ${addr}:${port}
%{ endfor ~}

The templatefile function renders the template:

> templatefile("${path.root}/backends.tmpl", { port = 8080, ip_addrs = ["10.0.0.1", "10.0.0.2"] })
backend 10.0.0.1:8080
backend 10.0.0.2:8080

Maps

Given a template file config.tmpl with the following content:

%{ for config_key, config_value in config }
set ${config_key} = ${config_value}
%{ endfor ~}

The templatefile function renders the template:

> templatefile(
               "${path.root}/config.tmpl",
               {
                 config = {
                   "x"   = "y"
                   "foo" = "bar"
                   "key" = "value"
                 }
               }
              )
set foo = bar
set key = value
set x = y

Generating JSON or YAML from a template

If the string you want to generate will be in JSON or YAML syntax, it's often tricky and tedious to write a template that will generate valid JSON or YAML that will be interpreted correctly when using lots of individual interpolation sequences and directives.

Instead, you can write a template that consists only of a single interpolated call to either jsonencode or yamlencode, specifying the value to encode using normal expression syntax as in the following examples:

${jsonencode({
  "backends": [for addr in ip_addrs : "${addr}:${port}"],
})}
${yamlencode({
  "backends": [for addr in ip_addrs : "${addr}:${port}"],
})}

Given the same input as the backends.tmpl example in the previous section, this will produce a valid JSON or YAML representation of the given data structure, without the need to manually handle escaping or delimiters. In the latest examples above, the repetition based on elements of ip_addrs is achieved by using a for expression rather than by using template directives.

{"backends":["10.0.0.1:8080","10.0.0.2:8080"]}

If the resulting template is small, you can choose instead to write jsonencode or yamlencode calls inline in your main configuration files, and avoid creating separate template files at all:

locals {
  backend_config_json = jsonencode({
    "backends": [for addr in ip_addrs : "${addr}:${port}"],
  })
}

For more information, see the main documentation for jsonencode and yamlencode.

Related Functions

• file reads the contents of a file at a given path.
• fileexists determines whether a file exists at a given path.