github.com/tarrant/terraform@v0.3.8-0.20150402012457-f68c9eee638e/website/source/docs/configuration/interpolation.html.md (about)

     1  ---
     2  layout: "docs"
     3  page_title: "Interpolation Syntax"
     4  sidebar_current: "docs-config-interpolation"
     5  description: |-
     6    Embedded within strings in Terraform, whether you're using the Terraform syntax or JSON syntax, you can interpolate other values into strings. These interpolations are wrapped in `${}`, such as `${var.foo}`.
     7  ---
     8  
     9  # Interpolation Syntax
    10  
    11  Embedded within strings in Terraform, whether you're using the
    12  Terraform syntax or JSON syntax, you can interpolate other values
    13  into strings. These interpolations are wrapped in `${}`, such as
    14  `${var.foo}`.
    15  
    16  The interpolation syntax is powerful and allows you to reference
    17  variables, attributes of resources, call functions, etc.
    18  
    19  ## Available Variables
    20  
    21  **To reference user variables**, use the `var.` prefix followed by the
    22  variable name. For example, `${var.foo}` will interpolate the
    23  `foo` variable value. If the variable is a mapping, then you
    24  can reference static keys in the map with the syntax
    25  `var.MAP.KEY`. For example, `${var.amis.us-east-1}` would
    26  get the value of the `us-east-1` key within the `amis` variable
    27  that is a mapping.
    28  
    29  **To reference attributes of your own resource**, the syntax is
    30  `self.ATTRIBUTE`. For example `${self.private_ip_address}` will
    31  interpolate that resource's private IP address. Note that this is
    32  only allowed/valid within provisioners.
    33  
    34  **To reference attributes of other resources**, the syntax is
    35  `TYPE.NAME.ATTRIBUTE`. For example, `${aws_instance.web.id}`
    36  will interpolate the ID attribute from the "aws\_instance"
    37  resource named "web". If the resource has a `count` attribute set,
    38  you can access individual attributes with a zero-based index, such
    39  as `${aws_instance.web.0.id}`. You can also use the splat syntax
    40  to get a list of all the attributes: `${aws_instance.web.*.id}`.
    41  This is documented in more detail in the
    42  [resource configuration page](/docs/configuration/resources.html).
    43  
    44  **To reference outputs from a module**, the syntax is
    45  `MODULE.NAME.OUTPUT`. For example `${module.foo.bar}` will
    46  interpolate the "bar" output from the "foo"
    47  [module](/docs/modules/index.html).
    48  
    49  **To reference count information**, the syntax is `count.FIELD`.
    50  For example, `${count.index}` will interpolate the current index
    51  in a multi-count resource. For more information on count, see the
    52  resource configuration page.
    53  
    54  **To reference path information**, the syntax is `path.TYPE`.
    55  TYPE can be `cwd`, `module`, or `root`. `cwd` will interpolate the
    56  cwd. `module` will interpolate the path to the current module. `root`
    57  will interpolate the path of the root module. In general, you probably
    58  want the `path.module` variable.
    59  
    60  ## Built-in Functions
    61  
    62  Terraform ships with built-in functions. Functions are called with
    63  the syntax `name(arg, arg2, ...)`. For example,
    64  to read a file: `${file("path.txt")}`. The built-in functions
    65  are documented below.
    66  
    67  The supported built-in functions are:
    68  
    69    * `concat(args...)` - Concatenates the values of multiple arguments into
    70        a single string.
    71  
    72    * `element(list, index)` - Returns a single element from a list
    73        at the given index. If the index is greater than the number of
    74        elements, this function will wrap using a standard mod algorithm.
    75        A list is only possible with splat variables from resources with
    76        a count greater than one.
    77        Example: `element(aws_subnet.foo.*.id, count.index)`
    78  
    79    * `file(path)` - Reads the contents of a file into the string. Variables
    80        in this file are _not_ interpolated. The contents of the file are
    81        read as-is.
    82  
    83    * `format(format, args...)` - Formats a string according to the given
    84        format. The syntax for the format is standard `sprintf` syntax.
    85        Good documentation for the syntax can be [found here](http://golang.org/pkg/fmt/).
    86        Example to zero-prefix a count, used commonly for naming servers:
    87        `format("web-%03d", count.index+1)`.
    88  
    89    * `join(delim, list)` - Joins the list with the delimiter. A list is
    90        only possible with splat variables from resources with a count
    91        greater than one. Example: `join(",", aws_instance.foo.*.id)`
    92  
    93    * `lookup(map, key)` - Performs a dynamic lookup into a mapping
    94        variable. The `map` parameter should be another variable, such
    95        as `var.amis`.
    96  
    97    * `replace(string, search, replace)` - Does a search and replace on the
    98        given string. All instances of `search` are replaced with the value
    99        of `replace`. If `search` is wrapped in forward slashes, it is treated
   100        as a regular expression. If using a regular expression, `replace`
   101        can reference subcaptures in the regular expression by using `$n` where
   102        `n` is the index or name of the subcapture. If using a regular expression,
   103        the syntax conforms to the [re2 regular expression syntax](https://code.google.com/p/re2/wiki/Syntax).
   104  
   105    * `split(delim, string)` - Splits the string previously created by `join`
   106        back into a list. This is useful for pushing lists through module
   107        outputs since they currently only support string values.
   108        Example: `split(",", module.amod.server_ids)`