TerraformVariablesUsage.tf

# string variable declare
variable "region" {
    description = "The region where to provision resources"
    type = string
    default = "us-west-2"
}
# string variable usage
provider "aws" {
  region     = var.region # this will assign the value "us-west-2" to region
  access_key = var.access_key
  secret_key = var.secret_key
}
#----------------------------------------------------------------------------
# list variable declare
variable "bucket_name" {
    description = "The name of S3 bucket"
    type = list(string)
    default = ["beans", "pepper", "tomato"]
}
# list variable usage
resource "aws_s3_bucket" "aws-b1" {
  bucket = "${var.bucket_name[count.index]}-${random_integer.rand_int.result}"
  acl    = "private"
  count  = 3
  tags = {
    Name        = "My bucket"
    Environment = "Dev"
  }
}
#----------------------------------------------------------------------------
#map variable declare
variable "ami_location" {
  type = map
  default = {
    us-east-1 = "ami-0412e100c0177fb4b"
    us-east-2 = "ami-0354df7841220296c"
  }
}
#map variable usage
resource "aws_instance" "server" {
  ami = "${var.ami_location["${var.region}"]}"
  instance_type = "t2.micro"
  key_name = "terraform-key"
  security_groups = ["${aws_security_group.allow_rdp.name}"]
  tags = {
    Name = "Web-App-Prod-1"
  }
}