How do I unmarshal environment variables to a slice using viper?

Question

I have the following code:

package main

import (
    "log"

    "github.com/spf13/viper"
)

func main() {
    viper.SetEnvPrefix("myprefix")
    viper.SetDefault("languages", []string{"french", "spanish"})
    viper.BindEnv("name")
    viper.BindEnv("languages")

    type config struct {
        Name      string
        Languages []string
    }

    var C config

    err := viper.Unmarshal(&C)
    if err != nil {
        log.Fatalln("unable to decode into struct, %v", err)
    }

    log.Println(C)
    log.Println(len(C.Languages))
}

When $MYPREFIX_LANGUAGES is not set the length of C.Languages is 2 (eg the default). When I set $MYPREFIX_LANGUAGES to "english spanish french russian" I get a length of 1. It is just taking the variable as 1 long string, not a slice. How do I get a slice ([]string{"english", "spanish", "french", "russian"}?

Seems like you need to do that manually after unmarshalling. — zerkms, Apr 03 '17 at 04:19
Apparently it works if you use a config file but not with environmental variables. http://stackoverflow.com/questions/38955605/reading-a-slice-of-maps-with-golang-viper — , Apr 03 '17 at 04:21
Yep, because config files are structured, and environment variables is a collection of strings. — zerkms, Apr 03 '17 at 04:21
What's the value for `viper.Get("languages")` ... ? Reason I ask is that I had a quick look at the source for viper and found this line: https://github.com/spf13/viper/blob/master/viper.go#L560 which leads me to believe that what you want can be done... just maybe not by the .`Unmarshall` func. — Charlino, Apr 04 '17 at 00:03
@Charlino Actually, that is the correct answer. Setting that to true will unmarshall it correctly. Please make an answer. — , Apr 04 '17 at 01:38

score 7 · Accepted Answer · answered Apr 05 '17 at 21:21

Thanks to @Charlino here is the answer:

package main

import (
    "log"

    "github.com/spf13/viper"
)

func main() {
    viper.SetEnvPrefix("myprefix")
    viper.SetTypeByDefaultValue(true)
    viper.SetDefault("languages", []string{"french", "spanish"})
    viper.BindEnv("name")
    viper.BindEnv("languages")

    type config struct {
        Name      string
        Languages []string
    }

    var C config

    err := viper.Unmarshal(&C)
    if err != nil {
        log.Fatalln("unable to decode into struct, %v", err)
    }

    log.Println(C)
    log.Println(len(C.Languages))
}

How do I unmarshal environment variables to a slice using viper?

1 Answers1