Don't override env vars user has already set

README.md

@@ -1199,6 +1199,9 @@ TF_VAR_tags='{"Name":"example-app"}' \
 terraform apply
 ```
 
+Note that Terragrunt will respect any `TF_VAR_xxx` variables you've manually set in your environment, ensuring that 
+anything in `inputs` will NOT be override anything you've already set in your environment.  
+
 
 ### AWS credentials
 

cli/cli_app.go

@@ -418,7 +418,10 @@ func setTerragruntInputsAsEnvVars(terragruntOptions *options.TerragruntOptions,
 	}
 
 	for key, value := range asEnvVars {
-		terragruntOptions.Env[key] = value
+		// Don't override any env vars the user has already set
+		if _, envVarAlreadySet := terragruntOptions.Env[key]; !envVarAlreadySet {
+			terragruntOptions.Env[key] = value
+		}
 	}
 
 	return nil