envconfig

import"github.com/kelseyhightower/envconfig"

Documentation

See godoc

Usage

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"
)
typeSpecificationstruct {
DebugboolPortintUserstringUsers []stringRatefloat32Timeout time.DurationColorCodesmap[string]int
}
funcmain() {
varsSpecificationerr:=envconfig.Process("myapp", &s)
iferr!=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)
iferr!=nil {
log.Fatal(err.Error())
}
fmt.Println("Users:")
for_, u:=ranges.Users {
fmt.Printf(" %s\n", u)
}
fmt.Println("Color codes:")
fork, v:=ranges.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

Struct Tag Support

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

For example, consider the following struct:

typeSpecificationstruct {
ManualOverride1string`envconfig:"manual_override_1"`DefaultVarstring`default:"foobar"`RequiredVarstring`required:"true"`IgnoredVarstring`ignored:"true"`AutoSplitVarstring`split_words:"true"`RequiredAndAutoSplitVarstring`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

typeSpecificationstruct {
ServiceHoststring`envconfig:"SERVICE_HOST"`Debugbool
}

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

Supported Struct Field Types

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.

Custom Decoders

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

export DNS_SERVER=8.8.8.8

typeIPDecoder net.IPfunc (ipd*IPDecoder) Decode(valuestring) error {
*ipd=IPDecoder(net.ParseIP(value))
returnnil
}
typeDNSConfigstruct {
AddressIPDecoder`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}]`

typeproviderDetailsstruct {
NamestringWeightint
}
typeSMSProviderDecodermap[string][]providerDetailsfunc (sd*SMSProviderDecoder) Decode(valuestring) error {
smsProvider:=map[string][]providerDetails{}
pairs:=strings.Split(value, ";")
for_, pair:=rangepairs {
providerdata:= []providerDetails{}
kvpair:=strings.Split(pair, "=")
iflen(kvpair) !=2 {
returnfmt.Errorf("invalid map item: %q", pair)
}
err:=json.Unmarshal([]byte(kvpair[1]), &providerdata)
iferr!=nil {
returnfmt.Errorf("invalid map json: %w", err)
}
smsProvider[kvpair[0]] =providerdata
}
*sd=SMSProviderDecoder(smsProvider)
returnnil
}
typeSMSProviderConfigstruct {
ProviderWithWeightSMSProviderDecoder`envconfig:"SMS_PROVIDER_WITH_WEIGHT"`
}

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