50 lines
1.7 KiB
Markdown
50 lines
1.7 KiB
Markdown
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---
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layout: "docs"
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---
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# Configuration Templates
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Certain configuration parameters within templates are themselves a
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type of "template." These are not Packer templates, but text templates,
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where variables can be used to modify the value of a configuration parameter
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during runtime.
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For example, the `ami_name` configuration for the [AMI builder](/docs/builders/amazon-ebs.html)
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is a template. An example value may be `My Packer AMI {{.CreateTime}}`. At
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runtime, this will be turned into `My Packer AMI 1370900368`, where the
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"CreateTime" variable was replaced with the Unix timestamp of when the
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AMI was actually created.
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This sort of templating is pervasive throughout Packer. Instead of documenting
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the templating syntax in each location, it is documented once here so
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you know how to use it.
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<div class="alert alert-info">
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<strong>For advanced users:</strong> The templates are actually parsed and executed
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using Go's <a href="http://golang.org/pkg/text/template/">text/template</a>
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package. It therefore supports the complete template syntax.
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</div>
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## Syntax
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99% of the time all you'll need within configuration templates are variables.
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Variables are accessed by using `{{.VARIABLENAME}}`. The "." prefixing the
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variable name signals that you're accessing a variable on the root
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template object. All template directives go between braces. Here is a piece
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of a VMware VMX template that uses variables:
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<pre>
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.encoding = "UTF-8"
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displayName = "{{ .Name }}"
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guestOS = "{{ .GuestOS }}"
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</pre>
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In this case, the "Name" and "GuestOS" variables will be replaced, potentially
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resulting in a VMX that looks like this:
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<pre>
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.encoding = "UTF-8"
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displayName = "packer"
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guestOS = "otherlinux"
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</pre>
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