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README.md
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@ -5,11 +5,19 @@ Go configuration with fangs
## What is Viper?
Viper is a complete configuration solution. Designed to work within an
application to handle file based configuration and seamlessly marry that with
command line flags which can also be used to control application behavior.
Viper also supports retrieving configuration values from remote key/value stores.
Etcd and Consul are supported.
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 yaml, toml and json config files
* reading from environment variables
* reading from remote config systems (Etcd or Consul)
* reading from command line flags
* setting explicit values
It can be thought of as a registry for all of your applications
configuration needs.
## Why Viper?
@ -19,42 +27,66 @@ Viper is here to help with that.
Viper does the following for you:
1. Find, load and marshall a configuration file in YAML, TOML or JSON.
2. Provide a mechanism to setDefault values for your different configuration options
3. Provide a mechanism to setOverride 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.
1. Find, load and marshal a configuration file in YAML, TOML or JSON.
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 believes that:
Viper uses the following precedence order. Each item takes precedence
over the item below it:
1. command line flags take precedence over options set in config files
2. config files take precedence over options set in remote key/value stores
3. remote key/value stores take precedence over defaults
* explicit call to Set
* flag
* env
* config
* key/value store
* default
Viper configuration keys are case insensitive.
## Usage
### Initialization
### 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("Indexes", 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 yaml, toml and json 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
viper.ReadInConfig() // Find and read the config file
### Setting Defaults
viper.SetDefault("ContentDir", "content")
viper.SetDefault("LayoutDir", "layouts")
viper.SetDefault("Indexes", map[string]string{"tag": "tags", "category": "categories"})
### 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
@ -65,11 +97,102 @@ Viper configuration keys are case insensitive.
### Getting Values
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
* IsSet(key string) : bool
One important thing to recognize is that each Get function will return
it’s zero value if it’s not found. To check if it’s found, the IsSet()
method has been provided.
Example:
viper.GetString("logfile") // case insensitive Setting & Getting
if viper.GetBool("verbose") {
fmt.Println("verbose enabled")
}
### 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)
}
### Working with Environment Variables
Viper has full support for environment variables. This enables 12 factor
applications out of the box. There are two methods that exist to aid
with working with ENV:
* AutomaticEnv()
* BindEnv(input ) : error
When working with ENV variables it’s important to recognize that Viper
treats ENV variables as case sensitive.
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.
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 intended to be a convience helper. It will look for all
keys that have been set (via defaults, config file, flag, or remote key
value) and call BindEnv on that key. It does
not simply import all ENV variables. Because of this behavior it’s
usually best to call it last.
### Working with Flags
Viper has the ability to bind to flags. Specifically Viper supports
Pflags as used in the [Cobra](http://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
@ -110,6 +233,35 @@ to use Consul.
err := viper.ReadRemoteConfig()
### 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 it’s
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
@ -130,5 +282,3 @@ application foundation needs.
Q: Why is it called "Cobra"?
A: Is there a better name for a commander?