github.com/ezbercih/terraform@v0.1.1-0.20140729011846-3c33865e0839/website/source/docs/configuration/interpolation.html.md (about)

     1  ---
     2  layout: "docs"
     3  page_title: "Interpolation Syntax"
     4  sidebar_current: "docs-config-interpolation"
     5  ---
     6  
     7  # Interpolation Syntax
     8  
     9  Embedded within strings in Terraform, whether you're using the
    10  Terraform syntax or JSON syntax, you can interpolate other values
    11  into strings. These interpolations are wrapped in `${}`, such as
    12  `${var.foo}`.
    13  
    14  The interpolation syntax is powerful and allows you to reference
    15  variables, attributes of resources, call functions, etc.
    16  
    17  To reference variables, use the `var.` prefix followed by the
    18  variable name. For example, `${var.foo}` will interpolate the
    19  `foo` variable value. If the variable is a mapping, then you
    20  can reference static keys in the map with the syntax
    21  `var.MAP.KEY`. For example, `${var.amis.us-east-1}` would
    22  get the value of the `us-east-1` key within the `amis` variable
    23  that is a mapping.
    24  
    25  To reference attributes of other resources, the syntax is
    26  `TYPE.NAME.ATTRIBUTE`. For example, `${aws_instance.web.id}`
    27  will interpolate the ID attribute from the "aws\_instance"
    28  resource named "web".
    29  
    30  Finally, Terraform ships with built-in functions. Functions
    31  are called with the syntax `name(arg, arg2, ...)`. For example,
    32  to read a file: `${file("path.txt")}`. The built-in functions
    33  are documented below.
    34  
    35  ## Built-in Functions
    36  
    37  The supported built-in functions are:
    38  
    39    * `file(path)` - Reads the contents of a file into the string.
    40  
    41    * `lookup(map, key)` - Performs a dynamic lookup into a mapping
    42        variable.