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Primer on HCL Terminology

HCL is an extensible configuration language developed by HashiCorp. See this for the full specification.

Example:

environment "an_environment" {
  filter {
    paths = ["an-environment/*"]
  }
}

The main terminology you need to know to understand the documentation below includes:

Blocks​

A block is a collection of nested configurations that are defined within curly braces {}, immediately after the identifier of the block.

A filter block is nested in the environment block in the example above.

Blocks come in three variants: bare, labeled or fully qualified.

  • The filter block in the above example is bare - it has no additional qualification or labelling beyond the name `filter.
  • The environment block is a labeled block, and its label is an_environment.
  • Most terraform you've seen uses fully qualified blocks that have both a type and a label. For example, resource "aws_instance" "my_instance" { ... } - in this case the type is aws_instance and the label is my_instance.

Attributes​

An attribute is a key-value pair separated by an = that is defined within a block.

The paths attribute is defined within the filter block in the example above.

Labels​

A label is one or more strings that are used to qualify a block.

The an_environment label is used to qualify the environment block in the example above.