import "github.com/kelseyhightower/envconfig"

See godoc

Set some environment variables:

export MYAPP_DEBUG=false export MYAPP_PORT=8080 export MYAPP_USER=Kelsey export MYAPP_RATE="0.5" export MYAPP_TIMEOUT="3m" export MYAPP_USERS="rob,ken,robert" export MYAPP_COLORCODES="red:1,green:2,blue:3"

Write some code:

package main import ( "fmt" "log" "time" "github.com/kelseyhightower/envconfig" ) type Specification struct { Debug bool Port int User string Users []string Rate float32 Timeout time.Duration ColorCodes map[string]int } func main() { var s Specification err := envconfig.Process("myapp", &s) if err != nil { log.Fatal(err.Error()) } format := "Debug: %v\nPort: %d\nUser: %s\nRate: %f\nTimeout: %s\n" _, err = fmt.Printf(format, s.Debug, s.Port, s.User, s.Rate, s.Timeout) if err != nil { log.Fatal(err.Error()) } fmt.Println("Users:") for _, u := range s.Users { fmt.Printf(" %s\n", u) } fmt.Println("Color codes:") for k, v := range s.ColorCodes { fmt.Printf(" %s: %d\n", k, v) } }

Results:

Debug: false Port: 8080 User: Kelsey Rate: 0.500000 Timeout: 3m0s Users: rob ken robert Color codes: red: 1 green: 2 blue: 3

Envconfig supports the use of struct tags to specify alternate, default, and required environment variables.

For example, consider the following struct:

type Specification struct { ManualOverride1 string `envconfig:"manual_override_1"` DefaultVar string `default:"foobar"` RequiredVar string `required:"true"` IgnoredVar string `ignored:"true"` AutoSplitVar string `split_words:"true"` RequiredAndAutoSplitVar string `required:"true" split_words:"true"` }

Envconfig has automatic support for CamelCased struct elements when the split_words:"true" tag is supplied. Without this tag, AutoSplitVar above would look for an environment variable called MYAPP_AUTOSPLITVAR. With the setting applied it will look for MYAPP_AUTO_SPLIT_VAR. Note that numbers will get globbed into the previous word. If the setting does not do the right thing, you may use a manual override.

Envconfig will process value for ManualOverride1 by populating it with the value for MYAPP_MANUAL_OVERRIDE_1. Without this struct tag, it would have instead looked up MYAPP_MANUALOVERRIDE1. With the split_words:"true" tag it would have looked up MYAPP_MANUAL_OVERRIDE1.

export MYAPP_MANUAL_OVERRIDE_1="this will be the value" # export MYAPP_MANUALOVERRIDE1="and this will not"

If envconfig can't find an environment variable value for MYAPP_DEFAULTVAR, it will populate it with "foobar" as a default value.

If envconfig can't find an environment variable value for MYAPP_REQUIREDVAR, it will return an error when asked to process the struct. If MYAPP_REQUIREDVAR is present but empty, envconfig will not return an error.

If envconfig can't find an environment variable in the form PREFIX_MYVAR, and there is a struct tag defined, it will try to populate your variable with an environment variable that directly matches the envconfig tag in your struct definition:

export SERVICE_HOST=127.0.0.1 export MYAPP_DEBUG=true

type Specification struct { ServiceHost string `envconfig:"SERVICE_HOST"` Debug bool }

Envconfig won't process a field with the "ignored" tag set to "true", even if a corresponding environment variable is set.

envconfig supports these struct field types:

• string
• int8, int16, int32, int64
• bool
• float32, float64
• slices of any supported type
• maps (keys and values of any supported type)
• encoding.TextUnmarshaler
• encoding.BinaryUnmarshaler
• time.Duration

Embedded structs using these fields are also supported.

Any field whose type (or pointer-to-type) implements envconfig.Decoder can control its own deserialization:

export DNS_SERVER=8.8.8.8

type IPDecoder net.IP func (ipd *IPDecoder) Decode(value string) error { *ipd = IPDecoder(net.ParseIP(value)) return nil } type DNSConfig struct { Address IPDecoder `envconfig:"DNS_SERVER"` }

Example for decoding the environment variables into map[string][]structName type

export SMS_PROVIDER_WITH_WEIGHT= `IND=[{"name":"SMSProvider1","weight":70},{"name":"SMSProvider2","weight":30}];US=[{"name":"SMSProvider1","weight":100}]`

type providerDetails struct { Name string Weight int } type SMSProviderDecoder map[string][]providerDetails func (sd *SMSProviderDecoder) Decode(value string) error { smsProvider := map[string][]providerDetails{} pairs := strings.Split(value, ";") for _, pair := range pairs { providerdata := []providerDetails{} kvpair := strings.Split(pair, "=") if len(kvpair) != 2 { return fmt.Errorf("invalid map item: %q", pair)	} err := json.Unmarshal([]byte(kvpair[1]), &providerdata) if err != nil { return fmt.Errorf("invalid map json: %w", err)	} smsProvider[kvpair[0]] = providerdata	} *sd = SMSProviderDecoder(smsProvider) return nil } type SMSProviderConfig struct { ProviderWithWeight SMSProviderDecoder `envconfig:"SMS_PROVIDER_WITH_WEIGHT"` }

Also, envconfig will use a Set(string) error method like from the flag.Value interface if implemented.