github.com/phobos182/packer@v0.2.3-0.20130819023704-c84d2aeffc68/website/source/docs/templates/configuration-templates.html.markdown (about)

     1  ---
     2  layout: "docs"
     3  page_title: "Configuration Templates"
     4  ---
     5  
     6  # Configuration Templates
     7  
     8  All strings within templates are processed by a common Packer templating
     9  engine, where variables and functions can be used to modify the value of
    10  a configuration parameter at runtime.
    11  
    12  For example, the `{{timestamp}}` function can be used in any string to
    13  generate the current timestamp. This is useful for configurations that require
    14  unique keys, such as AMI names. By setting the AMI name to something like
    15  `My Packer AMI {{timestamp}}`, the AMI name will be unique down to the second.
    16  
    17  In addition to globally available functions like timestamp shown before,
    18  some configurations have special local variables that are available only
    19  for that configuration. These are recognizable because they're prefixed by
    20  a period, such as `{{.Name}}`.
    21  
    22  The complete syntax is covered in the next section, followed by a reference
    23  of globally available functions.
    24  
    25  ## Syntax
    26  
    27  The syntax of templates is extremely simple. Anything template related
    28  happens within double-braces: `{{ }}`. Variables are prefixed with a period
    29  and capitalized, such as `{{.Variable}}` and functions are just directly
    30  within the braces, such as `{{timestamp}}`.
    31  
    32  Here is an example from the VMware VMX template that shows configuration
    33  templates in action:
    34  
    35  <pre>
    36  .encoding = "UTF-8"
    37  displayName = "{{ .Name }}"
    38  guestOS = "{{ .GuestOS }}"
    39  </pre>
    40  
    41  In this case, the "Name" and "GuestOS" variables will be replaced, potentially
    42  resulting in a VMX that looks like this:
    43  
    44  <pre>
    45  .encoding = "UTF-8"
    46  displayName = "packer"
    47  guestOS = "otherlinux"
    48  </pre>
    49  
    50  ## Global Functions
    51  
    52  While some configuration settings have local variables specific to only that
    53  configuration, a set of functions are available globally for use in _any string_
    54  in Packer templates. These are listed below for reference.
    55  
    56  * ``timestamp`` - The current Unix timestamp in UTC.