How to create one variable from another variable in terraform variable.tf file?

Question

For example, In variable.tf file we have a code like below

variable "variable1" {
    type    = string
    default = "ABC"
}

variable "variable2" {
    type    = string
    default = "DEF"
}

variable "variable3" {
    type    = string
    default = "$var.variable1-$var.variable2"
}

Expected output :

variable3 = ABC-DEF

Answer 1

you can use local instead

locals {
  variable3 = var.variable1+"-"+var.variable2
}

and then to call it instead of using var. use local. like this!

resource "example" "example" {

   example = local.variable3

}

ref : https://www.terraform.io/docs/configuration/locals.html

Answer 2

Yes, I agree with @Montassar, you can use the local block to create a new expression from the existing resources or the variables. But it should combine the variables like this:

locals {
  variable3 = "${var.variable1}-${var.variable2}"
}

And it will look like this: