### Command Line Interface
```
terraform init
terraform plan
terraform plan -destroy
terraform plan -var 'access_key=foo' -var 'secret_key=bar'
terraform plan -var-file="secret.tfvars" -var-file="production.tfvars"
terraform plan -var 'amis={ us-east-1 = "foo", us-west-2 = "bar" }'
terraform apply
terraform output <output-variable-named>
terraform show
terraform get
terraform destroy
```

### Provider eg. digitalocean, aws (write on <filename>.tf file eg. main.tf)
```
provider "digitalocean" {
  token = "${var.token}"
}
provider "aws" {
  access_key   = "${var.access_key}"
  secret_key   = "${var.secret_key}"
  region       = "${var.region}"
}
```

### Variable Defined (write on <filename>.tf file eg. variables.tf)
```
variable "token" {}

# implicitly by using brackets [...]
variable "cidrs" { default = [] }

# explicitly
variable "cidrs" { type = "list" }
```

### Maps
```
# Maps are a way to create variables that are lookup tables.
variable "amis" {
  type = "map"
  default = {
    "us-east-1" = "ami-b374d5a5"
    "us-west-2" = "ami-4b32be2b"
  }
}

# Using Maps Lookup
ami = "${lookup(var.amis, var.region)}"
```

### terraform.tfvars
```
token = ""
cidrs = ["10.0.0.0/16", "10.1.0.0/16"]
amis = {
  "us-east-1" = "ami-abc123"
  "us-west-2" = "ami-def456"
}
```

### Output Variables (write on .tf file eg. output.tf)
```
output "ip" {
  value = "${aws_eip.ip.public_ip}"
}
output "consul_address" {
  value = "${module.consul.server_address}"
}
```

### Provisioner
```
provisioner "local-exec" {
  command = "echo ${aws_instance.web.ipv4_address} > ip_address.txt"
}
provisioner "remote-exec" {
  scripts = [
    "${path.module}/../shared/scripts/install.sh",
  ]
}
```