How to Use String Variables in Terraform: Simple Guide

In Terraform, you declare a string variable using the variable block with type = string. You assign a value to it in a terraform.tfvars file or via command line, then reference it in your configuration using var.variable_name.

Syntax

To use a string variable in Terraform, you first declare it with a variable block specifying the type as string. Then you assign a value either in a .tfvars file or directly in the command line. Finally, you reference the variable in your Terraform configuration using var.variable_name.

• variable block: declares the variable and its type.
• default: optional default value if none is provided.
• var.variable_name: how to use the variable in resources.

terraform

variable "example_string" {
  type    = string
  default = "Hello, Terraform!"
}

# Usage in resource
output "greeting" {
  value = var.example_string
}

Example

This example shows how to declare a string variable, assign a value in a terraform.tfvars file, and output the value. It demonstrates how Terraform reads and uses string variables in configuration.

terraform

variable "region" {
  type = string
}

output "selected_region" {
  value = var.region
}

# terraform.tfvars file content:
# region = "us-west-2"

Output

selected_region = "us-west-2"

Common Pitfalls

Common mistakes include forgetting to assign a value to a variable without a default, which causes errors, or using incorrect syntax when referencing variables. Also, mixing quotes or not using var. prefix leads to issues.

terraform

/* Wrong: missing var prefix */
output "wrong_usage" {
  value = example_string
}

/* Right: correct variable reference */
output "correct_usage" {
  value = var.example_string
}

Quick Reference

Concept	Syntax	Description
Declare string variable	variable "name" { type = string }	Defines a string variable
Assign value	name = "value" (in .tfvars)	Sets variable value externally
Use variable	var.name	References variable in config
Default value	default = "value"	Optional fallback value

Key Takeaways

Declare string variables with a variable block and type string.

Assign values in terraform.tfvars or via command line to avoid errors.

Reference variables using var.variable_name syntax in your config.

Always provide a default or assign a value to prevent missing variable errors.

Use consistent quotes and the var prefix to avoid syntax mistakes.