Go package for populating structs from environment variables using struct tags
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example added real world example program Jun 27, 2014
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LICENSE initial commit Mar 28, 2014
README.md Explain struct tags and a `Decoder` interface Mar 12, 2018
envdecode_test.go check CanInterface before calling Interface Jan 29, 2018


envdecode Travis-CI GoDoc

envdecode is a Go package for populating structs from environment variables.

envdecode uses struct tags to map environment variables to fields, allowing you you use any names you want for environment variables. envdecode will recurse into nested structs, including pointers to nested structs, but it will not allocate new pointers to structs.


Full API docs are available on godoc.org.

Define a struct with env struct tags:

type Config struct {
    Hostname  string `env:"SERVER_HOSTNAME,default=localhost"`
    Port      uint16 `env:"SERVER_PORT,default=8080"`

    AWS struct {
        ID        string   `env:"AWS_ACCESS_KEY_ID"`
        Secret    string   `env:"AWS_SECRET_ACCESS_KEY,required"`
        SnsTopics []string `env:"AWS_SNS_TOPICS"`

    Timeout time.Duration `env:"TIMEOUT,default=1m,strict"`

Fields must be exported (i.e. begin with a capital letter) in order for envdecode to work with them. An error will be returned if a struct with no exported fields is decoded (including one that contains no env tags at all). Default values may be provided by appending ",default=value" to the struct tag. Required values may be marked by appending ",required" to the struct tag. Strict values may be marked by appending ",strict" which will return an error on Decode if there is an error while parsing.

Then call envdecode.Decode:

var cfg Config
err := envdecode.Decode(&cfg)

If you want all fields to act strict, you may use envdecode.StrictDecode:

var cfg Config
err := envdecode.StrictDecode(&cfg)

All parse errors will fail fast and return an error in this mode.

Supported types

  • Structs (and pointer to structs)
  • Slices of below defined types, separated by semicolon
  • bool
  • float32, float64
  • int, int8, int16, int32, int64
  • uint, uint8, uint16, uint32, uint64
  • string
  • time.Duration, using the time.ParseDuration() format
  • *url.URL, using url.Parse()
  • Types those implement a Decoder interface

Custom Decoder

If you want a field to be decoded with custom behavior, you may implement the interface Decoder for the filed type.

type Config struct {
  IPAddr IP `env:"IP_ADDR"`

type IP net.IP

// Decode implements the interface `envdecode.Decoder`
func (i *IP) Decode(repl string) error {
  *i = net.ParseIP(repl)
  return nil

Decoder is the interface implemented by an object that can decode an environment variable string representation of itself.