feat: multiple config filepath support.

README.md

@@ -25,6 +25,7 @@ This is a simple configuration reading tool. It just does the following:
 - [Installation](#installation)
 - [Usage](#usage)
     - [Read Configuration](#read-configuration)
+    - [Read Configuration From List Of Paths](#read-configuration-from-list-of-paths)
     - [Read Environment Variables Only](#read-environment-variables-only)
     - [Update Environment Variables](#update-environment-variables)
     - [Description](#description)
@@ -89,6 +90,40 @@ This will do the following:
 1. reads environment variables and overwrites values from the file with the values which was found in the environment (`env` tag);
 1. if no value was found on the first two steps, the field will be filled with the default value (`env-default` tag) if it is set.
 
+### Read Configuration From List Of Paths
+
+If you have a usecase of having different config path based on environment or whatsoever, all the paths can be configured and last valid path will be used to read the configuration.
+
+```go
+import "github.com/ilyakaznacheev/cleanenv"
+
+type ConfigDatabase struct {
+    Port     string `yaml:"port" env:"PORT" env-default:"5432"`
+    Host     string `yaml:"host" env:"HOST" env-default:"localhost"`
+    Name     string `yaml:"name" env:"NAME" env-default:"postgres"`
+    User     string `yaml:"user" env:"USER" env-default:"user"`
+    Password string `yaml:"password" env:"PASSWORD"`
+}
+
+var cfg ConfigDatabase
+
+cleanenv.AddConfigPath("config.yml")
+cleanenv.AddConfigPath("/dev/config.yml")
+cleanenv.AddConfigPath("/prod/config.yml")
+
+err := cleanenv.Read(&cfg)
+if err != nil {
+    ...
+}
+```
+
+This will do the following:
+
+1. reads last valid path among added paths.
+2. parse configuration file according to YAML format (`yaml` tag in this case);
+3. reads environment variables and overwrites values from the file with the values which was found in the environment (`env` tag);
+4. if no value was found on the first two steps, the field will be filled with the default value (`env-default` tag) if it is set.
+
 ### Read Environment Variables Only
 
 Sometimes you don't want to use configuration files at all, or you may want to use `.env` file format instead. Thus, you can limit yourself with only reading environment variables:

cleanenv.go

@@ -75,6 +75,40 @@ type Updater interface {
 	Update() error
 }
 
+// paths holds user provided path.
+var paths = make([]string, 0, 4)
+
+// AddConfigPath gives ability to add miltiple paths based on environment or use cases.
+func AddConfigPath(path string) {
+	paths = append(paths, path)
+}
+
+// getValidConfigPath returns one valid path from list of paths.
+// If multiple valid paths exist, last one will be returned.
+func getValidConfigPath() (string, error) {
+	var valid string
+
+	for _, path := range paths {
+		if _, err := os.Stat(path); err == nil {
+			valid = path
+		}
+	}
+	if valid == "" {
+		return "", fmt.Errorf("%w: no valid config file found in configured path", os.ErrNotExist)
+	}
+
+	return valid, nil
+}
+
+// Read reads the config based on path set by AddConfigPaths.
+func Read(cfg interface{}) error {
+	path, err := getValidConfigPath()
+	if err != nil {
+		return err
+	}
+	return ReadConfig(path, cfg)
+}
+
 // ReadConfig reads configuration file and parses it depending on tags in structure provided.
 // Then it reads and parses
 //