title: Terraform CIDR block for VPC not valid when using a variable
body: <p>I am trying to create a vpc as following:</p>
  
  <pre><code>resource "aws_vpc" "vpc" {
    cidr_block = "{$var.network_cidr}"
    tags {
      Name = "ECS_VPC"
    }
  }
  </code></pre>
  
  <p>where <code>network_cidr</code> is defined in variables.tf file as </p>
  
  <pre><code>variable "network_cidr" {
    description = "IP addressing for the network"
  }
  </code></pre>
  
  <p>and populated in terraform.tfvars as</p>
  
  <pre><code>network_cidr = "10.0.0.0/16"
  </code></pre>
  
  <p>When I try to run terraform apply <code>-var-file="terraform.tfvars"</code></p>
  
  <p>I get the following error :</p>
  
  <pre><code>Error: aws_vpc.vpc: "cidr_block" must contain a valid CIDR, got error
  parsing: invalid CIDR address: {$var.network_cidr}
  </code></pre>
  
  <p>However if I hardcode the <code>cider_block = "10.0.0.0/16"</code> directly it works fine</p>
  
  <p>Does anybody know what might be causing this?</p>