The lets block

Use the lets block in Terramate to define context-based variables local to the parent block where you declare them. Utilize these variables in surrounding attributes or blocks, such as generate_hcl, generate_file, and script blocks. The lets block achieves cleaner code by preventing global namespace clutter with locally scoped variables.

Arguments

• <variable-name>: The name of the variable to be defined.
• <expression>: The expression to be evaluated and assigned to the variable.

Syntax

lets {
  <variable-name> = <expression>
}

Contexts

You can use the lets block in the following contexts:

• generate_hcl blocks
• generate_file blocks
• script blocks

Key Differences from Global Variables

• lets variables are only available within the block they are defined in and do not carry over to child directories.
• lets variables cannot use labels.
• lets variables can be accessed using the let namespace in expressions.

Examples

Using lets in a generate_file Block

In this example, a JSON-encoded object is created using a lets variable and used within the generate_file block.

generate_file "file.json" {
  lets {
    # let.json is available in the current generate_file block only
    json = tm_jsonencode({ "hello" = "world" })
  }

  content = let.json
}

Defining Temporary Variables

Here, a temporary variable is defined within the lets block and used in other arguments within the generate_file block.

generate_file "example.txt" {
  lets {
    temp_a_plus_b = global.a + global.b
  }

  content = let.temp_a_plus_b
}

Using lets in a generate_hcl Block

In this example, a lets block is used within a generate_hcl block to define a temporary variable.

generate_hcl "file.tf" {
  lets {
    greeting = "Hello, World!"
  }

  content {
    message: let.greeting
  }
}