Ignore variable names starting with numbers

Signed-off-by: Ulysses Souza <ulyssessouza@gmail.com>

dotenv/fixtures/plain.env

@@ -3,6 +3,7 @@ OPTION_B=2
 OPTION_C= 3
 OPTION_D =4
 OPTION_E = 5
+456 = ABC
 OPTION_F = 
 OPTION_G=
 OPTION_H = my string # Inline comment

dotenv/godotenv.go

@@ -96,24 +96,27 @@ func load(overload bool, filenames ...string) (err error) {
 
 // ReadWithLookup gets all env vars from the files and/or lookup function and return values as
 // a map rather than automatically writing values into env
-func ReadWithLookup(lookupFn LookupFn, filenames ...string) (envMap map[string]string, err error) {
+func ReadWithLookup(lookupFn LookupFn, filenames ...string) (map[string]string, error) {
 	filenames = filenamesOrDefault(filenames)
-	envMap = make(map[string]string)
+	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
+			return envMap, individualErr
 		}
 
 		for key, value := range individualEnvMap {
+			r := regexp.MustCompile(`^\s*\d.*`) // Keys starting with numbers are ignored
+			if r.MatchString(key) {
+				continue
+			}
 			envMap[key] = value
 		}
 	}
 
-	return
+	return envMap, nil
 }
 
 // Read all env (with same file loading semantics as Load) but return values as
@@ -235,10 +238,9 @@ var exportRegex = regexp.MustCompile(`^\s*(?:export\s+)?(.*?)\s*$`)
 func parseLine(line string, envMap map[string]string) (key string, value string, err error) {
 	return parseLineWithLookup(line, envMap, nil)
 }
-func parseLineWithLookup(line string, envMap map[string]string, lookupFn LookupFn) (key string, value string, err error) {
+func parseLineWithLookup(line string, envMap map[string]string, lookupFn LookupFn) (string, string, error) {
 	if len(line) == 0 {
-		err = errors.New("zero length string")
-		return
+		return "", "", errors.New("zero length string")
 	}
 
 	// ditch the comments (but keep quoted hashes)
@@ -273,14 +275,13 @@ func parseLineWithLookup(line string, envMap map[string]string, lookupFn LookupF
 	}
 
 	if len(splitString) != 2 {
-		err = errors.New("can't separate key from value")
-		return
+		return "", "", errors.New("can't separate key from value")
 	}
-	key = exportRegex.ReplaceAllString(splitString[0], "$1")
+	key := exportRegex.ReplaceAllString(splitString[0], "$1")
 
 	// Parse the value
-	value = parseValue(splitString[1], envMap, lookupFn)
-	return
+	value := parseValue(splitString[1], envMap, lookupFn)
+	return key, value, nil
 }
 
 var (