This is a basic example on how to use the local-exec provisioner in terraform, and I will use it to write a environment variable’s value to disk.

Installing Terraform

Get the latest version of terraform, for this post, I will be using the latest version of the time of writing:

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$ wget https://releases.hashicorp.com/terraform/0.13.3/terraform_0.13.3_linux_amd64.zip
$ unzip terraform_0.13.3_linux_amd64.zip
$ sudo mv terraform /usr/local/bin/terraform

Ensure that it’s working:

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$ terraform -version
Terraform v0.13.3

Terraform local-exec

The local-exec provisioner allows us to run a command locally, so to test that we will write the environment variable owner=ruan to disk.

First setup our main.tf:

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resource "null_resource" "this" {
  provisioner "local-exec" {
    command = "echo ${var.owner} > file_${null_resource.this.id}.txt"
  }
}

As you can see our local-exec provisioner is issuing the command echo to write the environment variable owner’s value to a file on disk, and the file name is file_ + the null resource’s id.

As we are referencing a variable, we need to define the variable, I will define it in variables.tf:

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variable "owner" {}

As you can see, I am not defining the value, as I will define the value at runtime.

Initialize

When we initialize terraform, terraform builds up a dependency tree from all the .tf files and downloads any dependencies it requires:

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$ terraform init

Apply

Run our deployment and pass our variable at runtime:

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$ terraform apply -var 'owner=ruan' -auto-approve

null_resource.this: Creating...
null_resource.this: Provisioning with 'local-exec'...
null_resource.this (local-exec): Executing: ["/bin/sh" "-c" "echo ruan > file_4397943546484635522.txt"]
null_resource.this: Creation complete after 0s [id=4397943546484635522]

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

View the written file:

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$ cat file_4397943546484635522.txt
ruan

If we wanted to define the environment variable in the variables.tf file, it will look like this:

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variable "owner" {
  description = "the owner of this project"
  default     = "ruan"
}

The github repository for this code is located at:

• https://github.com/ruanbekker/terraformfiles/tree/master/variable-via-cli