adding Overload method

godotenv.go

@@ -36,7 +36,30 @@ func Load(filenames ...string) (err error) {
 	filenames = filenamesOrDefault(filenames)
 
 	for _, filename := range filenames {
-		err = loadFile(filename)
+		err = loadFile(filename, false)
+		if err != nil {
+			return // return early on a spazout
+		}
+	}
+	return
+}
+
+// Overload will read your env file(s) and load them into ENV for this process.
+//
+// Call this function as close as possible to the start of your program (ideally in main)
+//
+// If you call Overload without any args it will default to loading .env in the current path
+//
+// You can otherwise tell it which files to load (there can be more than one) like
+//
+//		godotenv.Overload("fileone", "filetwo")
+//
+// It's important to note this WILL OVERRIDE an env variable that already exists - consider the .env file to forcefilly set all vars.
+func Overload(filenames ...string) (err error) {
+	filenames = filenamesOrDefault(filenames)
+
+	for _, filename := range filenames {
+		err = loadFile(filename, true)
 		if err != nil {
 			return // return early on a spazout
 		}
@@ -90,14 +113,14 @@ func filenamesOrDefault(filenames []string) []string {
 	return filenames
 }
 
-func loadFile(filename string) error {
+func loadFile(filename string, overload bool) error {
 	envMap, err := readFile(filename)
 	if err != nil {
 		return err
 	}
 
 	for key, value := range envMap {
-		if os.Getenv(key) == "" {
+		if os.Getenv(key) == "" || overload {
 			os.Setenv(key, value)
 		}
 	}

godotenv_test.go

@@ -5,6 +5,8 @@ import (
 	"testing"
 )
 
+var noopPresets = make(map[string]string)
+
 func parseAndCompare(t *testing.T, rawEnvLine string, expectedKey string, expectedValue string) {
 	key, value, _ := parseLine(rawEnvLine)
 	if key != expectedKey || value != expectedValue {
@@ -12,11 +14,15 @@ func parseAndCompare(t *testing.T, rawEnvLine string, expectedKey string, expect
 	}
 }
 
-func loadEnvAndCompareValues(t *testing.T, envFileName string, expectedValues map[string]string) {
+func loadEnvAndCompareValues(t *testing.T, loader func(files ...string) error, envFileName string, expectedValues map[string]string, presets map[string]string) {
 	// first up, clear the env
 	os.Clearenv()
 
-	err := Load(envFileName)
+	for k, v := range presets {
+		os.Setenv(k, v)
+	}
+
+	err := loader(envFileName)
 	if err != nil {
 		t.Fatalf("Error loading %v", envFileName)
 	}
@@ -38,6 +44,14 @@ func TestLoadWithNoArgsLoadsDotEnv(t *testing.T) {
 	}
 }
 
+func TestOverloadWithNoArgsOverloadsDotEnv(t *testing.T) {
+	err := Overload()
+	pathError := err.(*os.PathError)
+	if pathError == nil || pathError.Op != "open" || pathError.Path != ".env" {
+		t.Errorf("Didn't try and open .env by default")
+	}
+}
+
 func TestLoadFileNotFound(t *testing.T) {
 	err := Load("somefilethatwillneverexistever.env")
 	if err == nil {
@@ -45,6 +59,13 @@ func TestLoadFileNotFound(t *testing.T) {
 	}
 }
 
+func TestOverloadFileNotFound(t *testing.T) {
+	err := Overload("somefilethatwillneverexistever.env")
+	if err == nil {
+		t.Error("File wasn't found but Overload didn't return an error")
+	}
+}
+
 func TestReadPlainEnv(t *testing.T) {
 	envFileName := "fixtures/plain.env"
 	expectedValues := map[string]string{
@@ -71,6 +92,34 @@ func TestReadPlainEnv(t *testing.T) {
 	}
 }
 
+func TestLoadDoesNotOverride(t *testing.T) {
+	envFileName := "fixtures/plain.env"
+
+	// ensure NO overload
+	presets := map[string]string{
+		"OPTION_A": "do_not_override",
+	}
+
+	expectedValues := map[string]string{
+		"OPTION_A": "do_not_override",
+	}
+	loadEnvAndCompareValues(t, Load, envFileName, expectedValues, presets)
+}
+
+func TestOveroadDoesOverride(t *testing.T) {
+	envFileName := "fixtures/plain.env"
+
+	// ensure NO overload
+	presets := map[string]string{
+		"OPTION_A": "do_not_override",
+	}
+
+	expectedValues := map[string]string{
+		"OPTION_A": "1",
+	}
+	loadEnvAndCompareValues(t, Overload, envFileName, expectedValues, presets)
+}
+
 func TestLoadPlainEnv(t *testing.T) {
 	envFileName := "fixtures/plain.env"
 	expectedValues := map[string]string{
@@ -81,7 +130,7 @@ func TestLoadPlainEnv(t *testing.T) {
 		"OPTION_E": "5",
 	}
 
-	loadEnvAndCompareValues(t, envFileName, expectedValues)
+	loadEnvAndCompareValues(t, Load, envFileName, expectedValues, noopPresets)
 }
 
 func TestLoadExportedEnv(t *testing.T) {
@@ -91,7 +140,7 @@ func TestLoadExportedEnv(t *testing.T) {
 		"OPTION_B": "\n",
 	}
 
-	loadEnvAndCompareValues(t, envFileName, expectedValues)
+	loadEnvAndCompareValues(t, Load, envFileName, expectedValues, noopPresets)
 }
 
 func TestLoadEqualsEnv(t *testing.T) {
@@ -100,7 +149,7 @@ func TestLoadEqualsEnv(t *testing.T) {
 		"OPTION_A": "postgres://localhost:5432/database?sslmode=disable",
 	}
 
-	loadEnvAndCompareValues(t, envFileName, expectedValues)
+	loadEnvAndCompareValues(t, Load, envFileName, expectedValues, noopPresets)
 }
 
 func TestLoadQuotedEnv(t *testing.T) {
@@ -116,7 +165,7 @@ func TestLoadQuotedEnv(t *testing.T) {
 		"OPTION_H": "\n",
 	}
 
-	loadEnvAndCompareValues(t, envFileName, expectedValues)
+	loadEnvAndCompareValues(t, Load, envFileName, expectedValues, noopPresets)
 }
 
 func TestActualEnvVarsAreLeftAlone(t *testing.T) {