terraform. list all variables in a tf file

To effectively list all variables defined in a Terraform (.tf) file, it's essential to understand how Terraform manages variables and what best practices you can use to extract this information. Below, we explore the methods for listing variables, including the use of commands and best practices for variable management.

Understanding Terraform Variables

Terraform variables are used to parameterize and customize configuration files. They allow users to define variables within their .tf files or external files (like .tfvars files) to avoid hardcoding values in the configuration, thus promoting reusability and maintainability.

Common Variable Formats

• Simple Variables: Defined using the variable keyword.
• Inputs and Outputs: Variables can serve as inputs to modules or outputs from modules.

Example of a simple variable definition in a .tf file:

variable "instance_type" {
  description = "The type of instance"
  default     = "t2.micro"
}

How to List All Variables

1. Using Terraform Commands

You can utilize the terraform show command, which provides an insight into your Terraform state, including the values of variables and resources. However, to specifically list defined variables in your configuration files, there are a few methods you can employ:

• Terraform Console: The terraform console command allows you to interactively query Terraform variables and outputs. You can run:

  terraform console
  

  And then enter:

  var
  

• Manual Inspection: Search through your .tf files for the variable blocks. You can do this quickly by running a command like:

  grep -R "variable" .
  

  This will list all instances of variable definitions within the current directory and subdirectories.

2. Using Scripts or Modules

If you require a programmatic method to extract variable names and descriptions, you can write a script (e.g., in Python or Bash) that parses .tf files. A basic Python example using regex would look like this:

import re
import os

def list_variables(directory):
    for filename in os.listdir(directory):
        if filename.endswith('.tf'):
            with open(os.path.join(directory, filename), 'r') as file:
                content = file.read()
                variables = re.findall(r'variable "(.*?)"', content)
                print(f'Variables in {filename}: {variables}')

list_variables('.')

3. Terraform Plan Output

When you execute a terraform plan, it will output the variables being used along with their values, which can also give you a practical view of what is configured.

Best Practices for Managing Variables

• Use .tfvars files: Store variable values in .tfvars files, which Terraform automatically loads. This keeps your configurations cleaner and separates variable definitions from their values.
• Documentation: Always document your variables using the description field in the variable blocks to maintain clarity for future reference.
• Environment-Specific Variables: Differentiate variables based on environments (e.g., development, staging, production) using separate variable files or different variable sets.

Conclusion

Listing variables in a Terraform configuration file can be done using built-in commands, manual checks, or custom scripts for automation. Understanding and managing these variables through best practices not only simplifies your Terraform experience but also enhances collaboration and maintainability of your infrastructure as code.

For deeper insights on handling Terraform variables, consider exploring guides from trusted sources such as HashiCorp and practical tips from Spacelift on user management and configurations.