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Rewriting the documentation
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README.md
196
README.md
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@ -5,11 +5,19 @@ Go configuration with fangs
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## What is Viper?
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Viper is a complete configuration solution. Designed to work within an
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application to handle file based configuration and seamlessly marry that with
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command line flags which can also be used to control application behavior.
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Viper also supports retrieving configuration values from remote key/value stores.
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Etcd and Consul are supported.
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Viper is a complete configuration solution for go applications. It has
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been designed to work within an application to handle all types of
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configuration. It supports
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* setting defaults
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* reading from yaml, toml and json config files
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* reading from environment variables
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* reading from remote config systems (Etcd or Consul)
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* reading from command line flags
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* setting explicit values
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It can be thought of as a registry for all of your applications
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configuration needs.
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## Why Viper?
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@ -19,42 +27,66 @@ Viper is here to help with that.
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Viper does the following for you:
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1. Find, load and marshall a configuration file in YAML, TOML or JSON.
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2. Provide a mechanism to setDefault values for your different configuration options
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3. Provide a mechanism to setOverride values for options specified through command line flags.
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4. Provide an alias system to easily rename parameters without breaking existing code.
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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.
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1. Find, load and marshal a configuration file in YAML, TOML or JSON.
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2. Provide a mechanism to set default values for your different
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configuration options
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3. Provide a mechanism to set override values for options specified
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through command line flags.
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4. Provide an alias system to easily rename parameters without breaking
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existing code.
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5. Make it easy to tell the difference between when a user has provided
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a command line or config file which is the same as the default.
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Viper believes that:
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Viper uses the following precedence order. Each item takes precedence
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over the item below it:
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1. command line flags take precedence over options set in config files
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2. config files take precedence over options set in remote key/value stores
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3. remote key/value stores take precedence over defaults
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* explicit call to Set
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* flag
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* env
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* config
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* key/value store
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* default
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Viper configuration keys are case insensitive.
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## Usage
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### Initialization
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### Establishing Defaults
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A good configuration system will support default values. A default value
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is not required for a key, but can establish a default to be used in the
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event that the key hasn’t be set via config file, environment variable,
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remote configuration or flag.
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Examples:
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viper.SetDefault("ContentDir", "content")
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viper.SetDefault("LayoutDir", "layouts")
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viper.SetDefault("Indexes", map[string]string{"tag": "tags", "category": "categories"})
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### Reading Config Files
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If you want to support a config file, Viper requires a minimal
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configuration so it knows where to look for the config file. Viper
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supports yaml, toml and json files. Viper can search multiple paths, but
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currently a single viper only supports a single config file.
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viper.SetConfigName("config") // name of config file (without extension)
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viper.AddConfigPath("/etc/appname/") // path to look for the config file in
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viper.AddConfigPath("$HOME/.appname") // call multiple times to add many search paths
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viper.ReadInConfig() // Find and read the config file
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### Setting Defaults
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viper.SetDefault("ContentDir", "content")
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viper.SetDefault("LayoutDir", "layouts")
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viper.SetDefault("Indexes", map[string]string{"tag": "tags", "category": "categories"})
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### Setting Overrides
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These could be from a command line flag, or from your own application logic.
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viper.Set("Verbose", true)
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viper.Set("LogFile", LogFile)
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### Registering and Using Aliases
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Aliases permit a single value to be referenced by multiple keys
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viper.RegisterAlias("loud", "Verbose")
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viper.Set("verbose", true) // same result as next line
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@ -65,11 +97,102 @@ Viper configuration keys are case insensitive.
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### Getting Values
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In Viper there are a few ways to get a value depending on what type of value you want to retrieved.
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The following functions and methods exist:
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* Get(key string) : interface{}
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* GetBool(key string) : bool
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* GetFloat64(key string) : float64
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* GetInt(key string) : int
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* GetString(key string) : string
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* GetStringMap(key string) : map[string]interface{}
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* GetStringMapString(key string) : map[string]string
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* GetStringSlice(key string) : []string
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* GetTime(key string) : time.Time
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* IsSet(key string) : bool
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One important thing to recognize is that each Get function will return
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it’s zero value if it’s not found. To check if it’s found, the IsSet()
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method has been provided.
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Example:
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viper.GetString("logfile") // case insensitive Setting & Getting
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if viper.GetBool("verbose") {
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fmt.Println("verbose enabled")
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}
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### Marshaling
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You also have the option of Marshaling all or a specific value to a struct, map, etc.
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There are two methods to do this:
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* Marshal(rawVal interface{}) : error
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* MarshalKey(key string, rawVal interface{}) : error
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Example:
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type config struct {
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Port int
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Name string
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}
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var C config
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err := Marshal(&C)
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if err != nil {
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t.Fatalf("unable to decode into struct, %v", err)
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}
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### Working with Environment Variables
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Viper has full support for environment variables. This enables 12 factor
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applications out of the box. There are two methods that exist to aid
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with working with ENV:
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* AutomaticEnv()
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* BindEnv(input ) : error
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When working with ENV variables it’s important to recognize that Viper
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treats ENV variables as case sensitive.
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BindEnv takes one or two parameters. The first parameter is the key
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name, the second is the name of the environment variable. The name of
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the environment variable is case sensitive.
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If the ENV variable name is not provided then Viper will automatically
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assume that the key name matches the ENV variable name but the ENV
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variable is IN ALL CAPS.
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One important thing to recognize when working with ENV variables is that
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the value will be read each time it is accessed. It does not fix the
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value when the BindEnv is called.
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AutomaticEnv is intended to be a convience helper. It will look for all
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keys that have been set (via defaults, config file, flag, or remote key
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value) and call BindEnv on that key. It does
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not simply import all ENV variables. Because of this behavior it’s
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usually best to call it last.
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### Working with Flags
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Viper has the ability to bind to flags. Specifically Viper supports
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Pflags as used in the [Cobra](http://github.com/spf13/cobra) library.
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Like BindEnv the value is not set when the binding method is called, but
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when it is accessed. This means you can bind as early as you want, even
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in an init() function.
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The BindPFlag() method provides this functionality.
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Example:
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serverCmd.Flags().Int("port", 1138, "Port to run Application server on")
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viper.BindPFlag("port", serverCmd.Flags().Lookup("port"))
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### Remote Key/Value Store Support
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Viper will read a config string (as JSON, TOML, or YAML) retrieved from a
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path in a Key/Value store such as Etcd or Consul. These values take precedence
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@ -110,6 +233,35 @@ to use Consul.
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err := viper.ReadRemoteConfig()
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### Viper or Vipers?
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Viper comes ready to use out of the box. There is no configuration or
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initialization needed to begin using Viper. Since most applications will
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want to use a single central repository for their configuration the
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viper package provides this. It is similar to a singleton.
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In all of the examples above they demonstrate using viper in it’s
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singleton style approach.
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### Working with multiple vipers
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You can also create many different vipers for use in your application.
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Each will have it’s own unique set of configurations and values. Each
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can read from a different config file, key value store, etc. All of the
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functions that viper package supports are mirrored as methods on a viper.
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Example:
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x := viper.New()
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y := viper.New()
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x.SetDefault("ContentDir", "content")
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y.SetDefault("ContentDir", "foobar")
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...
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When working with multiple vipers it is up to the user to keep track of
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the different vipers.
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## Q & A
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@ -130,5 +282,3 @@ application foundation needs.
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Q: Why is it called "Cobra"?
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A: Is there a better name for a commander?
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