43 lines
1.5 KiB
Markdown
43 lines
1.5 KiB
Markdown
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---
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layout: "docs"
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page_title: "Interpolation Syntax"
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sidebar_current: "docs-config-interpolation"
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---
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# Interpolation Syntax
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Embedded within strings in Terraform, whether you're using the
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Terraform syntax or JSON syntax, you can interpolate other values
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into strings. These interpolations are wrapped in `${}`, such as
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`${var.foo}`.
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The interpolation syntax is powerful and allows you to reference
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variables, attributes of resources, call functions, etc.
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To reference variables, use the `var.` prefix followed by the
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variable name. For example, `${var.foo}` will interpolate the
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`foo` variable value. If the variable is a mapping, then you
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can reference static keys in the map with the syntax
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`var.MAP.KEY`. For example, `${var.amis.us-east-1}` would
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get the value of the `us-east-1` key within the `amis` variable
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that is a mapping.
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To reference attributes of other resources, the syntax is
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`TYPE.NAME.ATTRIBUTE`. For example, `${aws_instance.web.id}`
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will interpolate the ID attribute from the "aws\_instance"
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resource named "web".
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Finally, Terraform ships with built-in functions. Functions
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are called with the syntax `name(arg, arg2, ...)`. For example,
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to read a file: `${file("path.txt")}`. The built-in functions
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are documented below.
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## Built-in Functions
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The supported built-in functions are:
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* `file(path)` - Reads the contents of a file into the string.
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* `lookup(map, key)` - Performs a dynamic lookup into a mapping
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variable.
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