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04-variables-and-outputs/examples/README.md

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+# Variables
+
+## Variable block
+
+must define variable block
+
+```
+variable "var_name" {
+  type = string
+}
+```
+
+## Variable types
+- string
+- number
+- bool
+- list(<TYPE>)
+- set(<TYPE>)
+- map(<TYPE>)
+- object({<ATTR NAME> = <TYPE>, ... })
+- tuple([<TYPE>, ...])
+
+## Variable files
+`variables.tfvars` (or `<FILENAME>.auto.tfvars`) automatically applied 
+
+## Apply default
+`terraform apply`
+
+## Apply a different variable file
+`terraform apply -var-file=another-variable-file.tfvars`
+
+## Passing Variable via Prompt
+If value not specified, Terraform will prompt for value. (this is okay for testing... but don't depend on it since you should be automating things!)
+```
+  var.db_pass
+  password for database
+
+  Enter a value:
+```
+
+## Passing Variables via CLI
+`terraform apply -var="db_pass=$DB_PASS_ENV_VAR"`
+
+# Local Variables
+
+Allows you to store the value of expression for reuse but doesn't allow for passing in values 
+```
+locals {
+  extra_tag = "extra-tag"
+}
+```
+
+# Output Variables
+
+Allows you to output some value  (which might not be known ahead of time).
+
+For example it might be useful to know the IP address of a VM that was created:
+
+```
+output "instance_ip_addr" {
+  value = aws_instance.instance.private_ip
+}
+```
+
+Sample output:
+```
+db_instance_addr = "terraform-20210504182745335900000001.cr2ub9wmsmpg.us-east-1.rds.amazonaws.com"
+instance_ip_addr = "172.31.24.95"
+```
+
+Will be output after `terraform apply` or `terraform output`