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"
)
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
Struct Tag Support
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.
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
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"`
}
Also, envconfig will use a Set(string) error method like from the
flag.Value interface if implemented.