Demo Making the Most of the Terraform CLI

This lesson walks through practical Terraform CLI features you’ll use every day: the built-in help system, command-specific help (for validate, plan, etc.), variable usage, and passing values with environment variables — including credentials used by providers.

Getting general help

To see Terraform’s built-in usage and global options, run:

terraform --help

This prints usage, primary subcommands, and global options. Example output (trimmed):

Usage: terraform [global options] <subcommand> [args]

Main commands:
    init           Prepare your working directory for other commands
    validate       Check whether the configuration is valid
    plan           Show changes required by the current configuration
    apply          Create or update infrastructure
    destroy        Destroy previously-created infrastructure

Other commands:
    output        Show output values from your root module
    providers     Show the providers required for this configuration
    refresh       Update the state to match remote systems
    show          Show the current state or a saved plan
    state         Advanced state management
    test          Execute integration tests for Terraform modules
    version       Show the current Terraform version
    workspace     Workspace management

Global options (use these before the subcommand, if any):
  -chdir=DIR    Switch to a different working directory before executing the given subcommand.
  -help         Show this help output, or the help for a specified subcommand.
  -version      An alias for the "version" subcommand.

Note: Some legacy commands (for example taint/untaint) may still appear for backward compatibility; they are deprecated in favor of modern flags such as -replace on plan/apply.

Command-specific help

You can request help for any subcommand to see flags and usage details:

terraform validate --help
terraform plan --help

Example validate options:

Options:
  -json       Produce output in machine-readable JSON format (disables color).
  -no-color   Suppress colored output.

terraform validate checks configuration syntax and internal references in the module. It does not contact providers or create resources; use it to catch common errors before planning or applying. terraform plan --help lists many plan customization options. Example (trimmed):

Plan Customization Options:
  -destroy            Create a plan to destroy all resources.
  -refresh=true|false
                      Control whether Terraform refreshes state prior to planning.
  -replace=ADDRESS   Mark the resource at ADDRESS for replacement.
  -target=RESOURCE   Limit planning to the given module, resource, or resource instance (for exceptional use).
  -var 'foo=bar'     Set a variable value from the command line (can be used multiple times).
  -var-file=FILE     Load variable values from the given file (can be used multiple times).
  -no-color          Disable colored output.

These built-in help pages are an authoritative and quick way to recall flags and behavior while you work.

Using Terraform variables and environment variables

Below is an example Terraform configuration that uses a numeric variable to control the length argument of two random_pet resources. The root output publishes the random_pet.name.id.

provider "random" {}

variable "num_of_pets" {
  type        = number
  description = "How many pets do we want"
}

resource "random_pet" "name" {
  length = var.num_of_pets
}

resource "random_pet" "bryans_pet" {
  length = var.num_of_pets
}

output "random_pet_name" {
  value = random_pet.name.id
}

If you run terraform plan without setting num_of_pets, Terraform will prompt you:

$ terraform plan
var.num_of_pets
  How many pets do we want

Enter a value:

To avoid interactive prompts, provide variables using one of Terraform’s supported methods. Common approaches:

Method	Use case	Example
Command-line `-var`	Quick, one-off overrides	`terraform plan -var 'num_of_pets=3'`
Variable file	Reusable sets of values	`terraform plan -var-file="ci.tfvars"`
Environment variable	CI/CD or ephemeral shell values	`export TF_VAR_num_of_pets=3`
`terraform.tfvars` file	Default values checked into working directory (not for secrets)	`num_of_pets = 3`

Environment variables prefixed with TF_VAR_ map directly to input variables in the root module. For example, to set num_of_pets:

export TF_VAR_num_of_pets=3

Now running terraform plan uses that value and will not prompt:

$ terraform plan
Plan: 2 to add, 0 to change, 0 to destroy.

Changes to Outputs:
  + random_pet_name = (known after apply)

Note: You didn't use the -out option to save this plan...

Apply the plan (confirm with yes when prompted):

terraform apply
# confirm with "yes" when prompted

Sample apply output (trimmed):

random_pet.name: Creation complete after 0s [id=specially-centrally-locally-separately-credible-camel]
random_pet.bryans_pet: Creation complete after 0s [id=aptly-upbeat-wise-...-friendly]

Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

Outputs:
random_pet_name = "specially-centrally-locally-separately-credible-camel"

If you change TF_VAR_num_of_pets (for example to 6) and re-run terraform apply, the length values will reflect that updated variable value.

Environment variables prefixed with TF_VAR_ map directly to input variables in your root module. This is a convenient way to provide non-sensitive values or CI/CD overrides without modifying configuration files.

Provider credentials and environment variables

Providers (AWS, Azure, GCP, Vault, and others) typically support environment variables as one of their authentication methods. Terraform provider plugins read those variables to authenticate and perform actions on the target platform. Example: AWS provider in your configuration:

provider "aws" {
  region = "us-east-1"
}

Then in your shell set credentials:

export AWS_ACCESS_KEY_ID=AKIAxxxxxxxxxxxx
export AWS_SECRET_ACCESS_KEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

For Vault you might set a token:

export VAULT_TOKEN=hvs.abcdef1234567890

Terraform and the provider plugins will pick up these environment variables during operations. Each provider documents its supported environment variables and priority rules (see links below).

Do not store sensitive credentials in source-controlled files or expose them in logs. Use secure secret management (Vault, cloud secret stores, CI/CD secrets) and ephemeral credentials where possible.

Quick reference: common CLI flags and options

Topic	Flag / Example	Notes
Disable color	`-no-color`	Useful for CI logs and machine parsing.
Export variable	`export TF_VAR_name=value`	Maps to `var.name` in the root module.
One-off var	`-var 'name=value'`	Safe for quick overrides; careful with shell quoting.
Load var file	`-var-file=FILE`	`terraform plan -var-file="secrets.tfvars"`
Replace resource	`-replace=ADDRESS`	Force replacement of specific resource during apply/plan.
Destroy plan	`-destroy`	Generate a plan which destroys all resources.

Summary

Use terraform --help and terraform <subcommand> --help to discover commands and flags quickly.
Variables can be supplied interactively, via -var/-var-file, or via environment variables (TF_VAR_<name>).
Provider credentials (AWS, Vault, etc.) are commonly supplied via environment variables; handle secrets securely.
The CLI help pages are authoritative and the fastest reference when working with Terraform.

Links and references

Terraform: https://www.terraform.io/
Terraform CLI documentation: https://www.terraform.io/cli
AWS provider docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs
Vault provider docs: https://registry.terraform.io/providers/hashicorp/vault/latest/docs

Course Introduction

Preparing Your Environment

Terraform Foundations

The Core Terraform Workflow

Terraform CLI

Terraform File Structure and Organization

Terraform Configuration - Fundamentals

Understading and Managing Terraform State

Marking Code Reusable

Refactoring Terraform State

Terraform Modules

Managing Resource Behavior and Dependencies

Securing Terraform Configurations

Terraform Troubleshooting

HCP Terraform

Demo Making the Most of the Terraform CLI

Getting general help

Command-specific help

Using Terraform variables and environment variables

Provider credentials and environment variables

Quick reference: common CLI flags and options

Summary

Links and references

Watch Video

​Getting general help

​Command-specific help

​Using Terraform variables and environment variables

​Provider credentials and environment variables

​Quick reference: common CLI flags and options

​Summary

​Links and references

Watch Video

Getting general help

Command-specific help

Using Terraform variables and environment variables

Provider credentials and environment variables

Quick reference: common CLI flags and options

Summary

Links and references