README.md - third_party/spf13/viper - Git at Google

 viper [![Build Status](https://travis-ci.org/spf13/viper.svg)](https://travis-ci.org/spf13/viper)
 =====

 [![Join the chat at https://gitter.im/spf13/viper](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/spf13/viper?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)

 Go configuration with fangs

 ## What is Viper?

 Viper is a complete configuration solution for go applications. It has
 been designed to work within an application to handle all types of
 configuration. It supports

 * setting defaults
 * reading from json, toml and yaml config files
 * reading from environment variables
 * reading from remote config systems (Etcd or Consul), watching changes
 * reading from command line flags
 * reading from buffer
 * setting explicit values

 It can be thought of as a registry for all of your applications
 configuration needs.

 ## Why Viper?

 When building a modern application, you don’t want to have to worry about
 configuration file formats; you want to focus on building awesome software.
 Viper is here to help with that.

 Viper does the following for you:

 1. Find, load and marshal a configuration file in JSON, TOML or YAML.
 2. Provide a mechanism to set default values for your different
    configuration options.
 3. Provide a mechanism to set override values for options specified
    through command line flags.
 4. Provide an alias system to easily rename parameters without breaking
    existing code.
 5. Make it easy to tell the difference between when a user has provided
    a command line or config file which is the same as the default.

 Viper uses the following precedence order. Each item takes precedence
 over the item below it:

  * explicit call to Set
  * flag
  * env
  * config
  * key/value store
  * default

 Viper configuration keys are case insensitive.

 ## Putting Values into Viper

 ### Establishing Defaults

 A good configuration system will support default values. A default value
 is not required for a key, but can establish a default to be used in the
 event that the key hasn’t be set via config file, environment variable,
 remote configuration or flag.

 Examples:

 	viper.SetDefault("ContentDir", "content")
 	viper.SetDefault("LayoutDir", "layouts")
 	viper.SetDefault("Taxonomies", map[string]string{"tag": "tags", "category": "categories"})

 ### Reading Config Files

 If you want to support a config file, Viper requires a minimal
 configuration so it knows where to look for the config file. Viper
 supports json, toml and yaml files. Viper can search multiple paths, but
 currently a single viper only supports a single config file.

 	viper.SetConfigName("config") // name of config file (without extension)
 	viper.AddConfigPath("/etc/appname/")   // path to look for the config file in
 	viper.AddConfigPath("$HOME/.appname")  // call multiple times to add many search paths
 	err := viper.ReadInConfig() // Find and read the config file
     if err != nil { // Handle errors reading the config file
         panic(fmt.Errorf("Fatal error config file: %s \n", err))
     }

 ### Reading Config from io.Reader

 Viper predefined many configuration sources, such as files, environment variables, flags and
 remote K/V store. But you are not bound to them. You can also implement your own way to
 require configuration and feed it to viper.

 ````go
 viper.SetConfigType("yaml") // or viper.SetConfigType("YAML")

 // any approach to require this configuration into your program.
 var yamlExample = []byte(`
 Hacker: true
 name: steve
 hobbies:
 - skateboarding
 - snowboarding
 - go
 clothing:
   jacket: leather
   trousers: denim
 age: 35
 eyes : brown
 beard: true
 `)

 viper.ReadConfig(bytes.NewBuffer(yamlExample))

 viper.Get("name") // this would be "steve"
 ````

 ### Setting Overrides

 These could be from a command line flag, or from your own application logic.

     viper.Set("Verbose", true)
     viper.Set("LogFile", LogFile)

 ### Registering and Using Aliases

 Aliases permit a single value to be referenced by multiple keys

     viper.RegisterAlias("loud", "Verbose")

     viper.Set("verbose", true) // same result as next line
     viper.Set("loud", true)   // same result as prior line

     viper.GetBool("loud") // true
     viper.GetBool("verbose") // true

 ### Working with Environment Variables

 Viper has full support for environment variables. This enables 12 factor
 applications out of the box. There are four methods that exist to aid
 with working with ENV:

  * AutomaticEnv()
  * BindEnv(string...) : error
  * SetEnvPrefix(string)
  * SetEnvReplacer(string...) *strings.Replacer

 _When working with ENV variables, it’s important to recognize that Viper
 treats ENV variables as case sensitive._

 Viper provides a mechanism to try to ensure that ENV variables are
 unique. By using SetEnvPrefix, you can tell Viper to use add a prefix
 while reading from the environment variables. Both BindEnv and
 AutomaticEnv will use this prefix.

 BindEnv takes one or two parameters. The first parameter is the key
 name, the second is the name of the environment variable. The name of
 the environment variable is case sensitive. If the ENV variable name is
 not provided, then Viper will automatically assume that the key name
 matches the ENV variable name but the ENV variable is IN ALL CAPS. When
 you explicitly provide the ENV variable name, it **does not**
 automatically add the prefix.

 One important thing to recognize when working with ENV variables is that
 the value will be read each time it is accessed. It does not fix the
 value when the BindEnv is called.

 AutomaticEnv is a powerful helper especially when combined with
 SetEnvPrefix. When called, Viper will check for an environment variable
 any time a viper.Get request is made. It will apply the following rules.
 It will check for a environment variable with a name matching the key
 uppercased and prefixed with the EnvPrefix if set.

 SetEnvReplacer allows you to use a `strings.Replacer` object to rewrite Env keys
 to an extent. This is useful if you want to use `-` or something in your Get()
 calls, but want your environmental variables to use `_` delimiters. An example
 of using it can be found in `viper_test.go`.

 #### Env example

 	SetEnvPrefix("spf") // will be uppercased automatically
 	BindEnv("id")

 	os.Setenv("SPF_ID", "13") // typically done outside of the app

 	id := Get("id") // 13


 ### Working with Flags

 Viper has the ability to bind to flags. Specifically, Viper supports
 Pflags as used in the [Cobra](https://github.com/spf13/cobra) library.

 Like BindEnv, the value is not set when the binding method is called, but
 when it is accessed. This means you can bind as early as you want, even
 in an init() function.

 The BindPFlag() method provides this functionality.

 Example:

     serverCmd.Flags().Int("port", 1138, "Port to run Application server on")
     viper.BindPFlag("port", serverCmd.Flags().Lookup("port"))


 ### Remote Key/Value Store Support
 Viper will read a config string (as JSON, TOML, or YAML) retrieved from a
 path in a Key/Value store such as Etcd or Consul.  These values take precedence
 over default values, but are overriden by configuration values retrieved from disk,
 flags, or environment variables.

 Viper uses [crypt](https://github.com/xordataexchange/crypt) to retrieve configuration
 from the K/V store, which means that you can store your configuration values
 encrypted and have them automatically decrypted if you have the correct
 gpg keyring.  Encryption is optional.

 You can use remote configuration in conjunction with local configuration, or
 independently of it.

 `crypt` has a command-line helper that you can use to put configurations
 in your K/V store. `crypt` defaults to etcd on http://127.0.0.1:4001.

 	go get github.com/xordataexchange/crypt/bin/crypt
 	crypt set -plaintext /config/hugo.json /Users/hugo/settings/config.json

 Confirm that your value was set:

 	crypt get -plaintext /config/hugo.json

 See the `crypt` documentation for examples of how to set encrypted values, or how
 to use Consul.

 ### Remote Key/Value Store Example - Unencrypted

 	viper.AddRemoteProvider("etcd", "http://127.0.0.1:4001","/config/hugo.json")
 	viper.SetConfigType("json") // because there is no file extension in a stream of bytes
 	err := viper.ReadRemoteConfig()

 ### Remote Key/Value Store Example - Encrypted

 	viper.AddSecureRemoteProvider("etcd","http://127.0.0.1:4001","/config/hugo.json","/etc/secrets/mykeyring.gpg")
 	viper.SetConfigType("json") // because there is no file extension in a stream of bytes
 	err := viper.ReadRemoteConfig()

 ### Watching Changes in Etcd - Unencrypted

     // alternatively, you can create a new viper instance.
     var runtime_viper = viper.New()

     runtime_viper.AddRemoteProvider("etcd", "http://127.0.0.1:4001", "/config/hugo.yml")
     runtime_viper.SetConfigType("yaml") // because there is no file extension in a stream of bytes

     // read from remote config the first time.
     err := runtime_viper.ReadRemoteConfig()

     // marshal config
     runtime_viper.Marshal(&runtime_conf)

     // open a goroutine to wath remote changes forever
     go func(){
         for {
             time.Sleep(time.Second * 5) // delay after each request

             // currenlty, only tested with etcd support
             err := runtime_viper.WatchRemoteConfig()
             if err != nil {
                 log.Errorf("unable to read remote config: %v", err)
                 continue
             }

             // marshal new config into our runtime config struct. you can also use channel
             // to implement a signal to notify the system of the changes
             runtime_viper.Marshal(&runtime_conf)
         }
     }()


 ## Getting Values From Viper

 In Viper, there are a few ways to get a value depending on what type of value you want to retrieved.
 The following functions and methods exist:

  * Get(key string) : interface{}
  * GetBool(key string) : bool
  * GetFloat64(key string) : float64
  * GetInt(key string) : int
  * GetString(key string) : string
  * GetStringMap(key string) : map[string]interface{}
  * GetStringMapString(key string) : map[string]string
  * GetStringSlice(key string) : []string
  * GetTime(key string) : time.Time
  * GetDuration(key string) : time.Duration
  * IsSet(key string) : bool

 One important thing to recognize is that each Get function will return
 its zero value if it’s not found. To check if a given key exists, the IsSet()
 method has been provided.

 Example:

     viper.GetString("logfile") // case-insensitive Setting & Getting
     if viper.GetBool("verbose") {
         fmt.Println("verbose enabled")
     }

 ### Accessing nested keys

 The accessor methods also accept formatted paths to deeply nested keys.
 For example, if the following JSON file is loaded:

 ```
 {
     "host": {
         "address": "localhost",
         "port": 5799
     },
     "datastore": {
         "metric": {
             "host": "127.0.0.1",
             "port": 3099
         },
         "warehouse": {
             "host": "198.0.0.1",
             "port": 2112
         }
     }
 }

 ```

 Viper can access a nested field by passing a `.` delimited path of keys:
 ```
 GetString("datastore.metric.host") // (returns "127.0.0.1")
 ```

 This obeys the precendense rules established above; the search for the root key
 (in this examole, `datastore`) will cascade through the remaining configuration registries
 until found. The search for the subkeys (`metric` and `host`), however, will not.

 For example, if the `metric` key was not defined in the configuration loaded
 from file, but was defined in the defaults, Viper would return the zero value.

 On the other hand, if the primary key was not defined, Viper would go through the
 remaining registries looking for it.

 Lastly, if there exists a key that matches the delimited key path, its value will
 be returned instead. E.g.

 ```
 {
     "datastore.metric.host": "0.0.0.0",
     "host": {
         "address": "localhost",
         "port": 5799
     },
     "datastore": {
         "metric": {
             "host": "127.0.0.1",
             "port": 3099
         },
         "warehouse": {
             "host": "198.0.0.1",
             "port": 2112
         }
     }
 }

 GetString("datastore.metric.host") //returns "0.0.0.0"
 ```

 ### Marshaling

 You also have the option of Marshaling all or a specific value to a struct, map, etc.

 There are two methods to do this:

  * Marshal(rawVal interface{}) : error
  * MarshalKey(key string, rawVal interface{}) : error

 Example:

 	type config struct {
 		Port int
 		Name string
 	}

 	var C config

 	err := Marshal(&C)
 	if err != nil {
 		t.Fatalf("unable to decode into struct, %v", err)
 	}


 ## Viper or Vipers?

 Viper comes ready to use out of the box. There is no configuration or
 initialization needed to begin using Viper. Since most applications will
 want to use a single central repository for their configuration, the
 viper package provides this. It is similar to a singleton.

 In all of the examples above, they demonstrate using viper in its
 singleton style approach.

 ### Working with multiple vipers

 You can also create many different vipers for use in your application.
 Each will have it’s own unique set of configurations and values. Each
 can read from a different config file, key value store, etc. All of the
 functions that viper package supports are mirrored as methods on a viper.

 Example:

     x := viper.New()
     y := viper.New()

 	x.SetDefault("ContentDir", "content")
 	y.SetDefault("ContentDir", "foobar")

     ...

 When working with multiple vipers, it is up to the user to keep track of
 the different vipers.

 ## Q & A

 Q: Why not INI files?

 A: Ini files are pretty awful. There’s no standard format, and they are hard to
 validate. Viper is designed to work with JSON, TOML or YAML files. If someone
 really wants to add this feature, I’d be happy to merge it. It’s easy to
 specify which formats your application will permit.

 Q: Why is it called “Viper”?

 A: Viper is designed to be a [companion](http://en.wikipedia.org/wiki/Viper_(G.I._Joe)) to
 [Cobra](https://github.com/spf13/cobra). While both can operate completely
 independently, together they make a powerful pair to handle much of your
 application foundation needs.

 Q: Why is it called “Cobra”?

 A: Is there a better name for a [commander](http://en.wikipedia.org/wiki/Cobra_Commander)?
	viper [![Build Status](https://travis-ci.org/spf13/viper.svg)](https://travis-ci.org/spf13/viper)
	=====

	[![Join the chat at https://gitter.im/spf13/viper](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/spf13/viper?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)

	Go configuration with fangs

	## What is Viper?

	Viper is a complete configuration solution for go applications. It has
	been designed to work within an application to handle all types of
	configuration. It supports

	* setting defaults
	* reading from json, toml and yaml config files
	* reading from environment variables
	* reading from remote config systems (Etcd or Consul), watching changes
	* reading from command line flags
	* reading from buffer
	* setting explicit values

	It can be thought of as a registry for all of your applications
	configuration needs.

	## Why Viper?

	When building a modern application, you don’t want to have to worry about
	configuration file formats; you want to focus on building awesome software.
	Viper is here to help with that.

	Viper does the following for you:

	1. Find, load and marshal a configuration file in JSON, TOML or YAML.
	2. Provide a mechanism to set default values for your different
	configuration options.
	3. Provide a mechanism to set override values for options specified
	through command line flags.
	4. Provide an alias system to easily rename parameters without breaking
	existing code.
	5. Make it easy to tell the difference between when a user has provided
	a command line or config file which is the same as the default.

	Viper uses the following precedence order. Each item takes precedence
	over the item below it:

	* explicit call to Set
	* flag
	* env
	* config
	* key/value store
	* default

	Viper configuration keys are case insensitive.

	## Putting Values into Viper

	### Establishing Defaults

	A good configuration system will support default values. A default value
	is not required for a key, but can establish a default to be used in the
	event that the key hasn’t be set via config file, environment variable,
	remote configuration or flag.

	Examples:

	viper.SetDefault("ContentDir", "content")
	viper.SetDefault("LayoutDir", "layouts")
	viper.SetDefault("Taxonomies", map[string]string{"tag": "tags", "category": "categories"})

	### Reading Config Files

	If you want to support a config file, Viper requires a minimal
	configuration so it knows where to look for the config file. Viper
	supports json, toml and yaml files. Viper can search multiple paths, but
	currently a single viper only supports a single config file.

	viper.SetConfigName("config") // name of config file (without extension)
	viper.AddConfigPath("/etc/appname/") // path to look for the config file in
	viper.AddConfigPath("$HOME/.appname") // call multiple times to add many search paths
	err := viper.ReadInConfig() // Find and read the config file
	if err != nil { // Handle errors reading the config file
	panic(fmt.Errorf("Fatal error config file: %s \n", err))
	}

	### Reading Config from io.Reader

	Viper predefined many configuration sources, such as files, environment variables, flags and
	remote K/V store. But you are not bound to them. You can also implement your own way to
	require configuration and feed it to viper.

	````go
	viper.SetConfigType("yaml") // or viper.SetConfigType("YAML")

	// any approach to require this configuration into your program.
	var yamlExample = []byte(`
	Hacker: true
	name: steve
	hobbies:
	- skateboarding
	- snowboarding
	- go
	clothing:
	jacket: leather
	trousers: denim
	age: 35
	eyes : brown
	beard: true
	`)

	viper.ReadConfig(bytes.NewBuffer(yamlExample))

	viper.Get("name") // this would be "steve"
	````

	### Setting Overrides

	These could be from a command line flag, or from your own application logic.

	viper.Set("Verbose", true)
	viper.Set("LogFile", LogFile)

	### Registering and Using Aliases

	Aliases permit a single value to be referenced by multiple keys

	viper.RegisterAlias("loud", "Verbose")

	viper.Set("verbose", true) // same result as next line
	viper.Set("loud", true) // same result as prior line

	viper.GetBool("loud") // true
	viper.GetBool("verbose") // true

	### Working with Environment Variables

	Viper has full support for environment variables. This enables 12 factor
	applications out of the box. There are four methods that exist to aid
	with working with ENV:

	* AutomaticEnv()
	* BindEnv(string...) : error
	* SetEnvPrefix(string)
	* SetEnvReplacer(string...) *strings.Replacer

	_When working with ENV variables, it’s important to recognize that Viper
	treats ENV variables as case sensitive._

	Viper provides a mechanism to try to ensure that ENV variables are
	unique. By using SetEnvPrefix, you can tell Viper to use add a prefix
	while reading from the environment variables. Both BindEnv and
	AutomaticEnv will use this prefix.

	BindEnv takes one or two parameters. The first parameter is the key
	name, the second is the name of the environment variable. The name of
	the environment variable is case sensitive. If the ENV variable name is
	not provided, then Viper will automatically assume that the key name
	matches the ENV variable name but the ENV variable is IN ALL CAPS. When
	you explicitly provide the ENV variable name, it does not
	automatically add the prefix.

	One important thing to recognize when working with ENV variables is that
	the value will be read each time it is accessed. It does not fix the
	value when the BindEnv is called.

	AutomaticEnv is a powerful helper especially when combined with
	SetEnvPrefix. When called, Viper will check for an environment variable
	any time a viper.Get request is made. It will apply the following rules.
	It will check for a environment variable with a name matching the key
	uppercased and prefixed with the EnvPrefix if set.

	SetEnvReplacer allows you to use a `strings.Replacer` object to rewrite Env keys
	to an extent. This is useful if you want to use `-` or something in your Get()
	calls, but want your environmental variables to use `_` delimiters. An example
	of using it can be found in `viper_test.go`.

	#### Env example

	SetEnvPrefix("spf") // will be uppercased automatically
	BindEnv("id")

	os.Setenv("SPF_ID", "13") // typically done outside of the app

	id := Get("id") // 13


	### Working with Flags

	Viper has the ability to bind to flags. Specifically, Viper supports
	Pflags as used in the [Cobra](https://github.com/spf13/cobra) library.

	Like BindEnv, the value is not set when the binding method is called, but
	when it is accessed. This means you can bind as early as you want, even
	in an init() function.

	The BindPFlag() method provides this functionality.

	Example:

	serverCmd.Flags().Int("port", 1138, "Port to run Application server on")
	viper.BindPFlag("port", serverCmd.Flags().Lookup("port"))


	### Remote Key/Value Store Support
	Viper will read a config string (as JSON, TOML, or YAML) retrieved from a
	path in a Key/Value store such as Etcd or Consul. These values take precedence
	over default values, but are overriden by configuration values retrieved from disk,
	flags, or environment variables.

	Viper uses [crypt](https://github.com/xordataexchange/crypt) to retrieve configuration
	from the K/V store, which means that you can store your configuration values
	encrypted and have them automatically decrypted if you have the correct
	gpg keyring. Encryption is optional.

	You can use remote configuration in conjunction with local configuration, or
	independently of it.

	`crypt` has a command-line helper that you can use to put configurations
	in your K/V store. `crypt` defaults to etcd on http://127.0.0.1:4001.

	go get github.com/xordataexchange/crypt/bin/crypt
	crypt set -plaintext /config/hugo.json /Users/hugo/settings/config.json

	Confirm that your value was set:

	crypt get -plaintext /config/hugo.json

	See the `crypt` documentation for examples of how to set encrypted values, or how
	to use Consul.

	### Remote Key/Value Store Example - Unencrypted

	viper.AddRemoteProvider("etcd", "http://127.0.0.1:4001","/config/hugo.json")
	viper.SetConfigType("json") // because there is no file extension in a stream of bytes
	err := viper.ReadRemoteConfig()

	### Remote Key/Value Store Example - Encrypted

	viper.AddSecureRemoteProvider("etcd","http://127.0.0.1:4001","/config/hugo.json","/etc/secrets/mykeyring.gpg")
	viper.SetConfigType("json") // because there is no file extension in a stream of bytes
	err := viper.ReadRemoteConfig()

	### Watching Changes in Etcd - Unencrypted

	// alternatively, you can create a new viper instance.
	var runtime_viper = viper.New()

	runtime_viper.AddRemoteProvider("etcd", "http://127.0.0.1:4001", "/config/hugo.yml")
	runtime_viper.SetConfigType("yaml") // because there is no file extension in a stream of bytes

	// read from remote config the first time.
	err := runtime_viper.ReadRemoteConfig()

	// marshal config
	runtime_viper.Marshal(&runtime_conf)

	// open a goroutine to wath remote changes forever
	go func(){
	for {
	time.Sleep(time.Second * 5) // delay after each request

	// currenlty, only tested with etcd support
	err := runtime_viper.WatchRemoteConfig()
	if err != nil {
	log.Errorf("unable to read remote config: %v", err)
	continue
	}

	// marshal new config into our runtime config struct. you can also use channel
	// to implement a signal to notify the system of the changes
	runtime_viper.Marshal(&runtime_conf)
	}
	}()


	## Getting Values From Viper

	In Viper, there are a few ways to get a value depending on what type of value you want to retrieved.
	The following functions and methods exist:

	* Get(key string) : interface{}
	* GetBool(key string) : bool
	* GetFloat64(key string) : float64
	* GetInt(key string) : int
	* GetString(key string) : string
	* GetStringMap(key string) : map[string]interface{}
	* GetStringMapString(key string) : map[string]string
	* GetStringSlice(key string) : []string
	* GetTime(key string) : time.Time
	* GetDuration(key string) : time.Duration
	* IsSet(key string) : bool

	One important thing to recognize is that each Get function will return
	its zero value if it’s not found. To check if a given key exists, the IsSet()
	method has been provided.

	Example:

	viper.GetString("logfile") // case-insensitive Setting & Getting
	if viper.GetBool("verbose") {
	fmt.Println("verbose enabled")
	}

	### Accessing nested keys

	The accessor methods also accept formatted paths to deeply nested keys.
	For example, if the following JSON file is loaded:

	```
	{
	"host": {
	"address": "localhost",
	"port": 5799
	},
	"datastore": {
	"metric": {
	"host": "127.0.0.1",
	"port": 3099
	},
	"warehouse": {
	"host": "198.0.0.1",
	"port": 2112
	}
	}
	}

	```

	Viper can access a nested field by passing a `.` delimited path of keys:
	```
	GetString("datastore.metric.host") // (returns "127.0.0.1")
	```

	This obeys the precendense rules established above; the search for the root key
	(in this examole, `datastore`) will cascade through the remaining configuration registries
	until found. The search for the subkeys (`metric` and `host`), however, will not.

	For example, if the `metric` key was not defined in the configuration loaded
	from file, but was defined in the defaults, Viper would return the zero value.

	On the other hand, if the primary key was not defined, Viper would go through the
	remaining registries looking for it.

	Lastly, if there exists a key that matches the delimited key path, its value will
	be returned instead. E.g.

	```
	{
	"datastore.metric.host": "0.0.0.0",
	"host": {
	"address": "localhost",
	"port": 5799
	},
	"datastore": {
	"metric": {
	"host": "127.0.0.1",
	"port": 3099
	},
	"warehouse": {
	"host": "198.0.0.1",
	"port": 2112
	}
	}
	}

	GetString("datastore.metric.host") //returns "0.0.0.0"
	```

	### Marshaling

	You also have the option of Marshaling all or a specific value to a struct, map, etc.

	There are two methods to do this:

	* Marshal(rawVal interface{}) : error
	* MarshalKey(key string, rawVal interface{}) : error

	Example:

	type config struct {
	Port int
	Name string
	}

	var C config

	err := Marshal(&C)
	if err != nil {
	t.Fatalf("unable to decode into struct, %v", err)
	}


	## Viper or Vipers?

	Viper comes ready to use out of the box. There is no configuration or
	initialization needed to begin using Viper. Since most applications will
	want to use a single central repository for their configuration, the
	viper package provides this. It is similar to a singleton.

	In all of the examples above, they demonstrate using viper in its
	singleton style approach.

	### Working with multiple vipers

	You can also create many different vipers for use in your application.
	Each will have it’s own unique set of configurations and values. Each
	can read from a different config file, key value store, etc. All of the
	functions that viper package supports are mirrored as methods on a viper.

	Example:

	x := viper.New()
	y := viper.New()

	x.SetDefault("ContentDir", "content")
	y.SetDefault("ContentDir", "foobar")

	...

	When working with multiple vipers, it is up to the user to keep track of
	the different vipers.

	## Q & A

	Q: Why not INI files?

	A: Ini files are pretty awful. There’s no standard format, and they are hard to
	validate. Viper is designed to work with JSON, TOML or YAML files. If someone
	really wants to add this feature, I’d be happy to merge it. It’s easy to
	specify which formats your application will permit.

	Q: Why is it called “Viper”?

	A: Viper is designed to be a [companion](http://en.wikipedia.org/wiki/Viper_(G.I._Joe)) to
	[Cobra](https://github.com/spf13/cobra). While both can operate completely
	independently, together they make a powerful pair to handle much of your
	application foundation needs.

	Q: Why is it called “Cobra”?

	A: Is there a better name for a [commander](http://en.wikipedia.org/wiki/Cobra_Commander)?