envconf.go

package envconf

import (
	"errors"
	"os"
	"strconv"
	"strings"
)

var (
	// ErrUnsupportedType is returned if the type passed in is unsupported
	ErrUnsupportedType = errors.New("Unsupported type")
)

// FromEnvP is the same as FromEnv, but panics on error
func FromEnvP(env string, value interface{}) interface{} {
	ev, err := FromEnv(env, value)
	if err != nil {
		panic(err)
	}
	return ev
}

// FromEnv returns the environment variable specified by env
// using the type of value
func FromEnv(env string, value interface{}) (interface{}, error) {
	envs := os.Environ()
	found := false
	for _, e := range envs {
		if strings.HasPrefix(e, env+"=") {
			found = true
			break
		}
	}

	if !found {
		return value, nil
	}

	ev := os.Getenv(env)

	switch value.(type) {
	case string:
		vt := interface{}(ev)
		return vt, nil
	case int:
		i, e := strconv.ParseInt(ev, 10, 64)
		return int(i), e
	case int8:
		i, e := strconv.ParseInt(ev, 10, 8)
		return int8(i), e
	case int16:
		i, e := strconv.ParseInt(ev, 10, 16)
		return int16(i), e
	case int32:
		i, e := strconv.ParseInt(ev, 10, 32)
		return int32(i), e
	case int64:
		i, e := strconv.ParseInt(ev, 10, 64)
		return i, e
	case uint:
		i, e := strconv.ParseUint(ev, 10, 64)
		return uint(i), e
	case uint8:
		i, e := strconv.ParseUint(ev, 10, 8)
		return uint8(i), e
	case uint16:
		i, e := strconv.ParseUint(ev, 10, 16)
		return uint16(i), e
	case uint32:
		i, e := strconv.ParseUint(ev, 10, 32)
		return uint32(i), e
	case uint64:
		i, e := strconv.ParseUint(ev, 10, 64)
		return i, e
	case float32:
		i, e := strconv.ParseFloat(ev, 32)
		return float32(i), e
	case float64:
		i, e := strconv.ParseFloat(ev, 64)
		return float64(i), e
	case bool:
		i, e := strconv.ParseBool(ev)
		return i, e
	default:
		return value, ErrUnsupportedType
	}
}