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Previously the templatefile function would permit any arbitrary string as a variable name, but due to the HCL template syntax it would be impossible to refer to one that isn't a valid HCL identifier without causing an HCL syntax error. The HCL syntax errors are correct, but don't really point to the root cause of the problem. Instead, we'll pre-verify that the variable names are valid before we even try to render the template, and given a specialized error message that refers to the vars argument expression as the problematic part, which will hopefully make the resolution path clearer for a user encountering this situation. The syntax error still remains for situations where all of the variable names are correct but e.g. the user made a typo referring to one, which makes sense because in that case the problem _is_ inside the template.
126 lines
4.3 KiB
Markdown
126 lines
4.3 KiB
Markdown
---
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layout: "functions"
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page_title: "templatefile - Functions - Configuration Language"
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sidebar_current: "docs-funcs-file-templatefile"
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description: |-
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The templatefile function reads the file at the given path and renders its
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content as a template.
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---
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# `templatefile` Function
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-> **Note:** This page is about Terraform 0.12 and later. For Terraform 0.11 and
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earlier, see
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[0.11 Configuration Language: Interpolation Syntax](../../configuration-0-11/interpolation.html).
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`templatefile` reads the file at the given path and renders its content
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as a template using a supplied set of template variables.
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```hcl
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templatefile(path, vars)
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```
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The template syntax is the same as for
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[string templates](../expressions.html#string-templates) in the main Terraform
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language, including interpolation sequences delimited with `${` ... `}`.
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This function just allows longer template sequences to be factored out
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into a separate file for readability.
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The "vars" argument must be a map. Within the template file, each of the keys
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in the map is available as a variable for interpolation. The template may
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also use any other function available in the Terraform language, except that
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recursive calls to `templatefile` are not permitted. Variable names must
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each start with a letter, followed by zero or more letters, digits, or
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underscores.
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Strings in the Terraform language are sequences of Unicode characters, so
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this function will interpret the file contents as UTF-8 encoded text and
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return the resulting Unicode characters. If the file contains invalid UTF-8
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sequences then this function will produce an error.
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This function can be used only with files that already exist on disk at the
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beginning of a Terraform run. Functions do not participate in the dependency
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graph, so this function cannot be used with files that are generated
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dynamically during a Terraform operation. We do not recommend using dynamic
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templates in Terraform configurations, but in rare situations where this is
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necessary you can use
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[the `template_file` data source](/docs/providers/template/d/file.html)
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to render templates while respecting resource dependencies.
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## Examples
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Given a template file `backends.tmpl` with the following content:
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```
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%{ for addr in ip_addrs ~}
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backend ${addr}:${port}
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%{ endfor ~}
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```
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The `templatefile` function renders the template:
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```
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> templatefile("${path.module}/backends.tmpl", { port = 8080, ip_addrs = ["10.0.0.1", "10.0.0.2"] })
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backend 10.0.0.1:8080
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backend 10.0.0.2:8080
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```
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### Generating JSON or YAML from a template
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If the string you want to generate will be in JSON or YAML syntax, it's
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often tricky and tedious to write a template that will generate valid JSON or
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YAML that will be interpreted correctly when using lots of individual
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interpolation sequences and directives.
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Instead, you can write a template that consists only of a single interpolated
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call to either [`jsonencode`](./jsonencode.html) or
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[`yamlencode`](./yamlencode.html), specifying the value to encode using
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[normal Terraform expression syntax](/docs/configuration/expressions.html)
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as in the following examples:
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```
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${jsonencode({
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"backends": [for addr in ip_addrs : "${addr}:${port}"],
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})}
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```
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```
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${yamlencode({
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"backends": [for addr in ip_addrs : "${addr}:${port}"],
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})}
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```
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Given the same input as the `backends.tmpl` example in the previous section,
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this will produce a valid JSON or YAML representation of the given data
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structure, without the need to manually handle escaping or delimiters.
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In the latest examples above, the repetition based on elements of `ip_addrs` is
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achieved by using a
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[`for` expression](/docs/configuration/expressions.html#for-expressions)
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rather than by using
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[template directives](/docs/configuration/expressions.html#directives).
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```json
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{"backends":["10.0.0.1:8080","10.0.0.2:8080"]}
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```
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If the resulting template is small, you can choose instead to write
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`jsonencode` or `yamlencode` calls inline in your main configuration files, and
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avoid creating separate template files at all:
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```hcl
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locals {
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backend_config_json = jsonencode({
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"backends": [for addr in ip_addrs : "${addr}:${port}"],
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})
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}
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```
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For more information, see the main documentation for
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[`jsonencode`](./jsonencode.html) and [`yamlencode`](./yamlencode.html).
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## Related Functions
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* [`file`](./file.html) reads a file from disk and returns its literal contents
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without any template interpretation.
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