Variable containing hyphens can not be set using environment variable

[colllijo]

Terraform Version

Terraform v1.13.5
on linux_amd64
+ provider registry.terraform.io/hashicorp/null v3.2.4

Terraform Configuration Files

terraform {
  required_version = ">= 1.13.5"
}

variable "works" {
  type = string
}

variable "does-not-work" {
  type = string
}

resource "null_resource" "dummy" {
  provisioner "local-exec" {
    command = "echo 'This works: ${var.works}, but this doesn't: ${var.does-not-work}"
  }
}

Debug Output

debug.log

Expected Behavior

Terraform should have seen that the environment variable (TF_VAR_does__not__work) was set and used the value from this environment variable as value for var.does-not-work.

This would be the same behavior as with TF_TOKEN where hyphens in the hostname are also replaced by two underscores.

Actual Behavior

Terraform does not find the environment variable and terraform prompts for it / errors, because it hasn't been set.

Steps to Reproduce

1. terraform init
2. export TF_VAR_works="works"
3. export TF_VAR_does__not__work="doesn't work"
4. terraform apply

Additional Context

No response

References

• fix(creds): allow periods in TF_TOKEN_... credentials vars #30878

Generative AI / LLM assisted development?

No response

[jbardin]

Hi @colllijo,

Thanks for filing the issue. I don't recall seeing where Terraform would implicitly convert _ to -, so I don't think the behavior you are expecting here was ever supported. Terraform will actually use a matching environment variable, like TF_VAR_does-not-work, however most shells don't support assigning that variable name directly on the CLI.

Thanks!

[colllijo]

Hi @jbardin

I belife you are correct in saying that terraform has not yet done that implicit conversion for the TF_VARs. But I would assume/hope that it should be possible to use that feature also for variables containing hyphens.

With the TF_TOKEN where the same problem arises with hostnames containing hyphens it is solved by converting them to two underscores for the environment variable.
See:

terraform/internal/command/cliconfig/credentials.go

Line 141 in 4048233

rawHost = strings.ReplaceAll(rawHost, "__", "-")