Inherit variables from environment

fixtures/inherited-not-found.env

@@ -0,0 +1 @@
+VARIABLE_NOT_FOUND

fixtures/inherited.env

@@ -0,0 +1 @@
+PATH

godotenv.go

@@ -28,7 +28,9 @@ import (
 
 const doubleQuoteSpecialChars = "\\\n\r\"!$`"
 
-// Load will read your env file(s) and load them into ENV for this process.
+// LoadWithLookupFn will read your env file(s), lookup the inherited variables with `lookupFn`
+//
+// and load them into ENV for this process.
 //
 // Call this function as close as possible to the start of your program (ideally in main)
 //
@@ -39,18 +41,35 @@ const doubleQuoteSpecialChars = "\\\n\r\"!$`"
 //		godotenv.Load("fileone", "filetwo")
 //
 // It's important to note that it WILL NOT OVERRIDE an env variable that already exists - consider the .env file to set dev vars or sensible defaults
-func Load(filenames ...string) (err error) {
+func LoadWithLookupFn(lookupFn func(string) (string, bool), filenames ...string) (err error) {
 	filenames = filenamesOrDefault(filenames)
 
 	for _, filename := range filenames {
-		err = loadFile(filename, false)
+		err = loadFile(filename, false, lookupFn)
 		if err != nil {
 			return // return early on a spazout
 		}
 	}
 	return
 }
 
+// Load 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 Load 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.Load("fileone", "filetwo")
+//
+// It's important to note that it WILL NOT OVERRIDE an env variable that already exists - consider the .env file to set dev vars or sensible defaults
+func Load(filenames ...string) (err error) {
+	return LoadWithLookupFn(func(string) (string, bool){
+		return "", true
+	}, filenames...)
+}
+
 // 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)
@@ -66,7 +85,9 @@ func Overload(filenames ...string) (err error) {
 	filenames = filenamesOrDefault(filenames)
 
 	for _, filename := range filenames {
-		err = loadFile(filename, true)
+		err = loadFile(filename, true, func(string) (string, bool) {
+			return "", true
+		})
 		if err != nil {
 			return // return early on a spazout
 		}
@@ -81,7 +102,7 @@ func Read(filenames ...string) (envMap map[string]string, err error) {
 	envMap = make(map[string]string)
 
 	for _, filename := range filenames {
-		individualEnvMap, individualErr := readFile(filename)
+		individualEnvMap, individualErr := readFile(filename, noLookupFn)
 
 		if individualErr != nil {
 			err = individualErr
@@ -96,32 +117,61 @@ func Read(filenames ...string) (envMap map[string]string, err error) {
 	return
 }
 
-// Parse reads an env file from io.Reader, returning a map of keys and values.
-func Parse(r io.Reader) (envMap map[string]string, err error) {
+// ReadWithLookup all env (with same file loading semantics as Load) but return values as
+// a map rather than automatically writing values into env
+func ReadWithLookup(lookupFn func(string)(string, bool), filenames ...string) (envMap map[string]string, err error) {
+	filenames = filenamesOrDefault(filenames)
 	envMap = make(map[string]string)
 
+	for _, filename := range filenames {
+		individualEnvMap, individualErr := readFile(filename, lookupFn)
+
+		if individualErr != nil {
+			err = individualErr
+			return // return early on a spazout
+		}
+
+		for key, value := range individualEnvMap {
+			envMap[key] = value
+		}
+	}
+
+	return
+}
+
+// ParseWithLookup reads an env file from io.Reader resolving variables with lookupFn, returning a map of keys and values.
+func ParseWithLookup(r io.Reader, lookupFn func(string)(string, bool)) (map[string]string, error) {
+	envMap := make(map[string]string)
+
 	var lines []string
 	scanner := bufio.NewScanner(r)
 	for scanner.Scan() {
 		lines = append(lines, scanner.Text())
 	}
 
-	if err = scanner.Err(); err != nil {
-		return
+	if err := scanner.Err(); err != nil {
+		return envMap, err
 	}
 
 	for _, fullLine := range lines {
 		if !isIgnoredLine(fullLine) {
 			var key, value string
-			key, value, err = parseLine(fullLine, envMap)
-
+			key, value, err := parseLine(fullLine, envMap, lookupFn)
 			if err != nil {
-				return
+				return envMap, err
+			}
+			if key == "" {
+				continue
 			}
 			envMap[key] = value
 		}
 	}
-	return
+	return envMap, nil
+}
+
+// Parse reads an env file from io.Reader, returning a map of keys and values.
+func Parse(r io.Reader) (map[string]string, error) {
+	return ParseWithLookup(r, noLookupFn)
 }
 
 //Unmarshal reads an env file from a string, returning a map of keys and values.
@@ -187,8 +237,8 @@ func filenamesOrDefault(filenames []string) []string {
 	return filenames
 }
 
-func loadFile(filename string, overload bool) error {
-	envMap, err := readFile(filename)
+func loadFile(filename string, overload bool, lookupFn func(string)(string, bool)) error {
+	envMap, err := readFile(filename, lookupFn)
 	if err != nil {
 		return err
 	}
@@ -209,19 +259,19 @@ func loadFile(filename string, overload bool) error {
 	return nil
 }
 
-func readFile(filename string) (envMap map[string]string, err error) {
+func readFile(filename string, lookupFn func(string)(string, bool)) (envMap map[string]string, err error) {
 	file, err := os.Open(filename)
 	if err != nil {
 		return
 	}
 	defer file.Close()
 
-	return Parse(file)
+	return ParseWithLookup(file, lookupFn)
 }
 
 var exportRegex = regexp.MustCompile(`^\s*(?:export\s+)?(.*?)\s*$`)
 
-func parseLine(line string, envMap map[string]string) (key string, value string, err error) {
+func parseLine(line string, envMap map[string]string, lookupFn func(string)(string, bool)) (key string, value string, err error) {
 	if len(line) == 0 {
 		err = errors.New("zero length string")
 		return
@@ -258,30 +308,49 @@ func parseLine(line string, envMap map[string]string) (key string, value string,
 		splitString = strings.SplitN(line, ":", 2)
 	}
 
-	if len(splitString) != 2 {
-		err = errors.New("Can't separate key from value")
+	// Parse the key
+	key = strings.TrimSpace(strings.TrimPrefix(splitString[0], "export "))
+	key = exportRegex.ReplaceAllString(key, "$1")
+	if err = validateVariableName(key); err != nil {
 		return
 	}
 
-	// Parse the key
-	key = splitString[0]
-	if strings.HasPrefix(key, "export") {
-		key = strings.TrimPrefix(key, "export")
+	// Environment inherited variable
+	if firstEquals < 0 && firstColon < 0 {
+		value = ""
+		v, ok := lookupFn(strings.TrimSpace(key))
+		if ok {
+			value = v
+		}
+		return
 	}
-	key = strings.TrimSpace(key)
 
-	key = exportRegex.ReplaceAllString(splitString[0], "$1")
+	if len(splitString) != 2 {
+		err = errors.New("Can't separate key from value")
+		return
+	}
 
 	// Parse the value
 	value = parseValue(splitString[1], envMap)
 	return
 }
 
+func validateVariableName(key string) error {
+	key = strings.TrimSpace(strings.TrimPrefix(key, "export "))
+	if !variableNameRegex.MatchString(key) {
+		return fmt.Errorf("invalid variable name %q", key)
+	}
+	return nil
+}
+
 var (
 	singleQuotesRegex  = regexp.MustCompile(`\A'(.*)'\z`)
 	doubleQuotesRegex  = regexp.MustCompile(`\A"(.*)"\z`)
 	escapeRegex        = regexp.MustCompile(`\\.`)
 	unescapeCharsRegex = regexp.MustCompile(`\\([^$])`)
+	variableNameRegex  = regexp.MustCompile(`^[_\\.a-zA-Z0-9]+$`)
+
+	noLookupFn = func(string)(string, bool) {return "", true}
 )
 
 func parseValue(value string, envMap map[string]string) string {

godotenv_test.go

@@ -12,7 +12,7 @@ import (
 var noopPresets = make(map[string]string)
 
 func parseAndCompare(t *testing.T, rawEnvLine string, expectedKey string, expectedValue string) {
-	key, value, _ := parseLine(rawEnvLine, noopPresets)
+	key, value, _ := parseLine(rawEnvLine, noopPresets, noLookupFn)
 	if key != expectedKey || value != expectedValue {
 		t.Errorf("Expected '%v' to parse as '%v' => '%v', got '%v' => '%v' instead", rawEnvLine, expectedKey, expectedValue, key, value)
 	}
@@ -83,6 +83,33 @@ func TestReadPlainEnv(t *testing.T) {
 	}
 
 	envMap, err := Read(envFileName)
+	if err != nil {
+		t.Errorf("Error reading file: %q", err)
+	}
+
+	if len(envMap) != len(expectedValues) {
+		t.Error("Didn't get the right size map back")
+	}
+
+	for key, value := range expectedValues {
+		if envMap[key] != value {
+			t.Error("Read got one of the keys wrong")
+		}
+	}
+}
+
+func TestInheritedEnvVariable(t *testing.T) {
+	pathVariable, ok := os.LookupEnv("PATH")
+	if !ok {
+		t.Error("Error getting path variable")
+	}
+
+	envFileName := "fixtures/inherited.env"
+	expectedValues := map[string]string{
+		"PATH": pathVariable,
+	}
+
+	envMap, err := ReadWithLookup(os.LookupEnv, envFileName)
 	if err != nil {
 		t.Error("Error reading file")
 	}
@@ -98,6 +125,31 @@ func TestReadPlainEnv(t *testing.T) {
 	}
 }
 
+func TestInheritedEnvVariableNotFound(t *testing.T) {
+	envMap, err := Read("fixtures/inherited-not-found.env")
+	if envMap["VARIABLE_NOT_FOUND"] != "" || err != nil {
+		t.Errorf("Expected 'VARIABLE_NOT_FOUND' to be '' with no errors")
+	}
+}
+
+func TestInheritedEnvVariableNotFoundWithLookup(t *testing.T) {
+	notFoundMap := make(map[string]interface{})
+	envMap, err := ReadWithLookup(func(v string)(string, bool){
+		envVar, ok := os.LookupEnv(v)
+		if !ok {
+			notFoundMap[v] = nil
+		}
+		return envVar, ok
+	}, "fixtures/inherited-not-found.env")
+	if envMap["VARIABLE_NOT_FOUND"] != "" || err != nil {
+		t.Errorf("Expected 'VARIABLE_NOT_FOUND' to be '' with no errors")
+	}
+	_, ok := notFoundMap["VARIABLE_NOT_FOUND"]
+	if !ok {
+		t.Errorf("Expected 'VARIABLE_NOT_FOUND' to be in the set of not found variables")
+	}
+}
+
 func TestParse(t *testing.T) {
 	envMap, err := Parse(bytes.NewReader([]byte("ONE=1\nTWO='2'\nTHREE = \"3\"")))
 	expectedValues := map[string]string{
@@ -358,7 +410,6 @@ func TestParsing(t *testing.T) {
 	parseAndCompare(t, `FOO="bar\\\n\ b\az"`, "FOO", "bar\\\n baz")
 	parseAndCompare(t, `FOO="bar\\r\ b\az"`, "FOO", "bar\\r baz")
 
-	parseAndCompare(t, `="value"`, "", "value")
 	parseAndCompare(t, `KEY="`, "KEY", "\"")
 	parseAndCompare(t, `KEY="value`, "KEY", "\"value")
 
@@ -370,9 +421,9 @@ func TestParsing(t *testing.T) {
 	// it 'throws an error if line format is incorrect' do
 	// expect{env('lol$wut')}.to raise_error(Dotenv::FormatError)
 	badlyFormattedLine := "lol$wut"
-	_, _, err := parseLine(badlyFormattedLine, noopPresets)
+	k, v, err := parseLine(badlyFormattedLine, noopPresets, noLookupFn)
 	if err == nil {
-		t.Errorf("Expected \"%v\" to return error, but it didn't", badlyFormattedLine)
+		t.Errorf("Expected \"%v\" to return error, but it didn't. key=%q, value=%q", badlyFormattedLine, k, v)
 	}
 }
 
@@ -454,7 +505,7 @@ func TestRoundtrip(t *testing.T) {
 	fixtures := []string{"equals.env", "exported.env", "plain.env", "quoted.env"}
 	for _, fixture := range fixtures {
 		fixtureFilename := fmt.Sprintf("fixtures/%s", fixture)
-		env, err := readFile(fixtureFilename)
+		env, err := readFile(fixtureFilename, noLookupFn)
 		if err != nil {
 			t.Errorf("Expected '%s' to read without error (%v)", fixtureFilename, err)
 		}