CODEWITHSUNDEEP
goenvironment-variables
Ryan Clair
Ryan Clair

Reputation: 1421

How to assign default value if env var is empty?

How do you assign a default value if an environment variable isn't set in Go?

In Python I could do mongo_password = os.getenv('MONGO_PASS', 'pass') where pass is the default value if MONGO_PASS env var isn't set.

I tried an if statement based on os.Getenv being empty, but that doesn't seem to work due to the scope of variable assignment within an if statement. And I'm checking for multiple env var's, so I can't act on this information within the if statement.

Upvotes: 131

Views: 144752

Answers (8)

Eddy Hernandez
Eddy Hernandez

Reputation: 5856

To have a clean code I do this:

myVar := getEnv("MONGO_PASS", "default-pass")

I defined a function that is used in the whole app

// getEnv get key environment variable if exist, otherwise return defaultValue
func getEnv(key, defaultValue string) string {
    value := os.Getenv(key)
    if len(value) == 0 {
        return defaultValue
    }
    return value
}

Upvotes: 22

AVarf
AVarf

Reputation: 5169

I also had the same problem and I just created a small package called getenvs exactly to answer this problem.

Getenvs supports string, bool, int and float and it can be used like below:

package main

import (
    "fmt"

    "gitlab.com/avarf/getenvs"
)

func main() {
    value := getenvs.GetEnvString("STRING_GETENV", "default-string-value")
    bvalue, _ := getenvs.GetEnvBool("BOOL_GETENV", false)
    ivalue, _ := getenvs.GetEnvInt("INT_GETENV", 10)

    fmt.Println(value)
    fmt.Println(bvalue)
    fmt.Println(ivalue)
}

Upvotes: 3

Stanislav
Stanislav

Reputation: 2677

For more complex application you can use tooling such as viper, which allows you to set global custom default values, parse configuration files, set a prefix for your app's env var keys (to ensure consistency and name spacing of env var configurations) and many other cool features.

Sample code:

package main

import (
    "fmt"

    "github.com/spf13/viper"
)

func main() {
    viper.AutomaticEnv() // read value ENV variable
    // Set default value
    viper.SetEnvPrefix("app")
    viper.SetDefault("linetoken", "DefaultLineTokenValue")

    // Declare var
    linetoken := viper.GetString("linetoken")

    fmt.Println("---------- Example ----------")
    fmt.Println("linetoken :", linetoken)
}

Upvotes: 2

Jaime Gago
Jaime Gago

Reputation: 342

Had the same question as the OP and found someone encapsulated the answers from this thread into a nifty library that is fairly simple to use, hope this help others!

https://github.com/caarlos0/env

Upvotes: 3

puradox
puradox

Reputation: 1468

What you're looking for is os.LookupEnv combined with an if statement.

Here is janos's answer updated to use LookupEnv:

func getEnv(key, fallback string) string {
    value, exists := os.LookupEnv(key)
    if !exists {
        value = fallback
    }
    return value
}

Upvotes: 60

janos
janos

Reputation: 124656

There's no built-in to fall back to a default value, so you have to do a good old-fashioned if-else.

But you can always create a helper function to make that easier:

func getenv(key, fallback string) string {
    value := os.Getenv(key)
    if len(value) == 0 {
        return fallback
    }
    return value
}

Note that as @michael-hausenblas pointed out in a comment, keep in mind that if the value of the environment variable is really empty, you will get the fallback value instead.

Even better as @ŁukaszWojciechowski pointed out, using os.LookupEnv:

func getEnv(key, fallback string) string {
    if value, ok := os.LookupEnv(key); ok {
        return value
    }
    return fallback
}

Upvotes: 190

Michael Hausenblas
Michael Hausenblas

Reputation: 13951

Go doesn't have the exact same functionality as Python here; the most idiomatic way to do it though, I can think of, is:

mongo_password := "pass"
if mp := os.Getenv("MONGO_PASS"); mp != "" {
    mongo_password = mp
}

Upvotes: 25

Oleg Neumyvakin
Oleg Neumyvakin

Reputation: 10282

In case you are OK with adding little dependency you can use something like https://github.com/urfave/cli

package main

import (
  "os"

  "github.com/urfave/cli"
)

func main() {
  app := cli.NewApp()

  app.Flags = []cli.Flag {
    cli.StringFlag{
      Name: "lang, l",
      Value: "english",
      Usage: "language for the greeting",
      EnvVar: "APP_LANG",
    },
  }

  app.Run(os.Args)
}

Upvotes: 1

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