TerraformHow-ToBeginner · 3 min read

How to Use -var-file in Terraform for Variable Management

Use -var-file with the terraform apply or terraform plan commands to load variables from a file instead of the command line. This helps keep your variable values organized and reusable by specifying a file like terraform apply -var-file="vars.tfvars".

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Syntax

The -var-file option tells Terraform to load variables from a specified file. This file contains variable definitions in HCL or JSON format. You can use it with commands like terraform plan or terraform apply.

Syntax parts:

-var-file="filename": The path to your variable file.
terraform plan or terraform apply: Terraform commands that accept the variable file.

bash

terraform apply -var-file="variables.tfvars"

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Example

This example shows how to define variables in a file and use -var-file to apply them.

1. Create a file named variables.tfvars with variable values.

2. Use terraform apply -var-file="variables.tfvars" to apply the configuration with those values.

hcl

/* variables.tfvars */
region = "us-west-2"
instance_type = "t2.micro"

/* main.tf */
variable "region" {
  description = "AWS region"
  type        = string
}

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
  default     = "t2.small"
}

provider "aws" {
  region = var.region
}

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = var.instance_type
}

/* Command to run */
terraform init
terraform apply -var-file="variables.tfvars" -auto-approve

Output

aws_instance.example: Creating... aws_instance.example: Creation complete after 10s [id=i-0abcd1234efgh5678] Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

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Common Pitfalls

Common mistakes when using -var-file include:

Using the wrong file path or filename causes Terraform to ignore the file.
Incorrect variable names or types in the file lead to errors.
Forgetting to include -var-file means default or command-line variables are used instead.
Using multiple -var-file options can override variables; the last file has priority.

bash

/* Wrong usage example: missing quotes or wrong path */
terraform apply -var-file=variables.tfvars

/* Correct usage example: quotes and correct path */
terraform apply -var-file="variables.tfvars"

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Quick Reference

Option	Description	Example
-var-file	Load variables from a file	terraform apply -var-file="vars.tfvars"
Multiple -var-file	Use multiple files; last overrides	terraform apply -var-file="file1.tfvars" -var-file="file2.tfvars"
Variable file format	HCL or JSON format supported	region = "us-west-2"
Default variable file	Terraform automatically loads terraform.tfvars	No need to specify -var-file for terraform.tfvars

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Key Takeaways

Use -var-file to load variables from a file for cleaner Terraform commands.

Variable files must be in valid HCL or JSON format with correct variable names.

Specify the correct path and filename with quotes to avoid errors.

Multiple -var-file options can be used; later files override earlier ones.

Terraform automatically loads terraform.tfvars without needing -var-file.