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website: new config template docs

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Mitchell Hashimoto 2013-08-08 16:56:09 -07:00
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website/source/docs/templates/configuration-templates.html.markdown vendored
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# Configuration Templates # Configuration Templates
Certain configuration parameters within templates are themselves a All strings within templates are processed by a common Packer templating
type of "template." These are not Packer templates, but text templates, engine, where variables and functions can be used to modify the value of
where variables can be used to modify the value of a configuration parameter a configuration parameter at runtime.
during runtime.
For example, the `ami_name` configuration for the [AMI builder](/docs/builders/amazon-ebs.html) For example, the `{{timestamp}}` function can be used in any string to
is a template. An example value may be `My Packer AMI {{.CreateTime}}`. At generate the current timestamp. This is useful for configurations that require
runtime, this will be turned into `My Packer AMI 1370900368`, where the unique keys, such as AMI names. By setting the AMI name to something like
"CreateTime" variable was replaced with the Unix timestamp of when the `My Packer AMI {{timestamp}}`, the AMI name will be unique down to the second.
AMI was actually created.
This sort of templating is pervasive throughout Packer. Instead of documenting In addition to globally available functions like timestamp shown before,
the templating syntax in each location, it is documented once here so some configurations have special local variables that are available only
you know how to use it. for that configuration. These are recognizable because they're prefixed by
a period, such as `{{.Name}}`.
<div class="alert alert-info"> The complete syntax is covered in the next section, followed by a reference
<strong>For advanced users:</strong> The templates are actually parsed and executed of globally available functions.
using Go's <a href="http://golang.org/pkg/text/template/">text/template</a>
package. It therefore supports the complete template syntax.
</div>
## Syntax ## Syntax
99% of the time all you'll need within configuration templates are variables. The syntax of templates is extremely simple. Anything template related
Variables are accessed by using `{{.VARIABLENAME}}`. The "." prefixing the happens within double-braces: `{{ }}`. Variables are prefixed with a period
variable name signals that you're accessing a variable on the root and capitalized, such as `{{.Variable}}` and functions are just directly
template object. All template directives go between braces. Here is a piece within the braces, such as `{{timestamp}}`.
of a VMware VMX template that uses variables:
Here is an example from the VMware VMX template that shows configuration
templates in action:
<pre> <pre>
.encoding = "UTF-8" .encoding = "UTF-8"
@ -47,3 +45,11 @@ resulting in a VMX that looks like this:
displayName = "packer" displayName = "packer"
guestOS = "otherlinux" guestOS = "otherlinux"
</pre> </pre>
## Global Functions
While some configuration settings have local variables specific to only that
configuration, a set of functions are available globally for use in _any string_
in Packer templates. These are listed below for reference.
* ``timestamp`` - The current Unix timestamp in UTC.