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Primer on HCL Terminology

HCL is an extensible configuration language created by HashiCorp. For the full specification, see this document.

Example:

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

The key terminology to understand the documentation below includes:

Blocks​

A block is a collection of nested configurations defined within curly braces {}, immediately following the block's identifier.

For example, a filter block is nested within the environment block in the example above.

Blocks can be one of three types: bare, labeled, or fully qualified.

  • The filter block in the example is a bare block, as it lacks additional qualification or labeling beyond its name, filter.

  • The environment block is a labeled block, with an_environment as its label.

  • Most OpenTofu/Terraform configurations use fully qualified blocks, which include both a type and a label. For instance, resource "aws_instance" "my_instance" { ... } has a type of aws_instance and a label of my_instance.

Attributes​

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

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

Labels​

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

For example, the an_environment label qualifies the environment block in the example above.