set Terraform variable from environment if available

linter/terraform.go

@@ -9,6 +9,7 @@ import (
 	"github.com/hashicorp/hcl/hcl/parser"
 	"github.com/stelligent/config-lint/assertion"
 	"io/ioutil"
+	"os"
 	"path/filepath"
 	"regexp"
 )
@@ -85,15 +86,27 @@ func loadVariables(data interface{}) []Variable {
 	list := data.([]interface{})
 	for _, entry := range list {
 		m := entry.(map[string]interface{})
-		for key, value := range m {
-			variables = append(variables, Variable{Name: key, Value: extractDefault(value)})
+		for key, resource := range m {
+			variables = append(variables, Variable{Name: key, Value: getVariableValue(key, resource)})
 		}
 	}
 	return variables
 }
 
-func extractDefault(value interface{}) interface{} {
-	list := value.([]interface{})
+func getVariableValue(key string, resource interface{}) interface{} {
+	value := getVariableFromEnvironment(key)
+	if value != "" {
+		return value
+	}
+	return getVariableDefault(resource)
+}
+
+func getVariableFromEnvironment(key string) interface{} {
+	return os.Getenv("TF_VAR_" + key)
+}
+
+func getVariableDefault(resource interface{}) interface{} {
+	list := resource.([]interface{})
 	var defaultValue interface{}
 	for _, entry := range list {
 		m := entry.(map[string]interface{})

linter/terraform_test.go

@@ -2,6 +2,7 @@ package linter
 
 import (
 	"github.com/stelligent/config-lint/assertion"
+	"os"
 	"testing"
 )
 
@@ -34,7 +35,7 @@ func TestTerraformVariables(t *testing.T) {
 	}
 	resources, err := loader.PostLoad(loaded)
 	if err != nil {
-		t.Error("Expecting TestTerraformLinter.ReplaceVariables to not return an error")
+		t.Error("Expecting TestTerraformLinter.PostLoad to not return an error")
 	}
 	if len(resources) != 1 {
 		t.Errorf("Expecting to load 1 resources, not %d", len(loaded.Resources))
@@ -52,6 +53,27 @@ func TestTerraformVariables(t *testing.T) {
 	}
 }
 
+func TestTerraformVariablesFromEnvironment(t *testing.T) {
+	os.Setenv("TF_VAR_instance_type", "c4.large")
+	loader := TerraformResourceLoader{}
+	loaded, err := loader.Load("./testdata/resources/uses_variables.tf")
+	if err != nil {
+		t.Error("Expecting TestTerraformLinter.Load to not return an error")
+	}
+	resources, err := loader.PostLoad(loaded)
+	if err != nil {
+		t.Error("Expecting TestTerraformLinter.PostLoad to not return an error")
+	}
+	if len(resources) != 1 {
+		t.Errorf("Expecting to load 1 resources, not %d", len(loaded.Resources))
+	}
+	properties := resources[0].Properties.(map[string]interface{})
+	if properties["instance_type"] != "c4.large" {
+		t.Errorf("Unexpected value for variable: %s", properties["instance_type"])
+	}
+	os.Setenv("TF_VAR_instance_type", "")
+}
+
 func TestTerraformVariablesInDifferentFile(t *testing.T) {
 	options := Options{
 		Tags:    []string{},