Terraform external data source

check.sh

if [ -f "dontdoit" ]; then
  RESULT="true"
else 
  RESULT="false"
fi
echo "{ \"check\": \"$RESULT\" }"

main.tf

data "external" "check_for_file" {
  program = [ "bash", "check.sh" ]
}

resource "null_resource" "helloworld" {
  count = data.external.check_for_file.result.check == "true" ? 0:1
}

terminal.sh

$ terraform plan
data.external.check_for_file: Reading...
data.external.check_for_file: Read complete after 0s [id=-]

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # null_resource.helloworld[0] will be created
  + resource "null_resource" "helloworld" {
      + id = (known after apply)
    }

Plan: 1 to add, 0 to change, 0 to destroy.

────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

Note: You didn't use the -out option to save this plan, so Terraform can't guarantee to take exactly these actions if you run "terraform apply" now.
$ touch dontdoit
$ terraform plan
data.external.check_for_file: Reading...
data.external.check_for_file: Read complete after 0s [id=-]

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration and found no differences, so no changes are needed.
$