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https://github.com/jamiealquiza/envy

Envy automatically exposes environment variables for all of your Go flags
https://github.com/jamiealquiza/envy

cli env environment environment-variables flags go-packages golang library

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Envy automatically exposes environment variables for all of your Go flags

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# envy



Automatically exposes environment variables for all of your flags. It supports the standard flags package along with limited support for [Cobra](https://github.com/spf13/cobra) commands.



Envy takes a namespace prefix that will be used for environment variable lookups. Each flag registered in your app will be prefixed, uppercased, and hyphens exchanged for underscores; if a matching environment variable is found, it will set the respective flag value as long as the value is not otherwise explicitly set (see usage for precedence).



### Example: flag



Code:

```go

package main



import (

        "flag"

        "fmt"



        "github.com/jamiealquiza/envy"

)



func main() {

        var address = flag.String("address", "127.0.0.1", "Some random address")

        var port = flag.String("port", "8131", "Some random port")



        envy.Parse("MYAPP") // Expose environment variables.

        flag.Parse()



        fmt.Println(*address)

        fmt.Println(*port)

}

```



Output:

```sh

# Prints flag defaults

% ./example

127.0.0.1

8131



# Setting flags via env vars.

% MYAPP_ADDRESS="0.0.0.0" MYAPP_PORT="9080" ./example

0.0.0.0

9080

```



### Example: Cobra



Code:

```go



// Where to execute envy depends on the structure

// of your Cobra implementation. A common pattern

// is to define a root command and an 'Execute' function

// that's called from the application main. We can call

// envy ParseCobra here and configure it to recursively

// update all child commands. Alternatively, it can be

// scoped to child commands at some point in their

// initialization.



var rootCmd = &cobra.Command{

 Use: "myapp",

}



func Execute() {

  // Configure envy.

  cfg := CobraConfig{

    // The env var prefix.

    Prefix: "MYAPP",

    // Whether to parse persistent flags.

    Persistent: true,

    // Whether to recursively update child command FlagSets.

    Recursive: true,

  }



  // Apply.

  envy.ParseCobra(rootCmd, cfg)



  if err := rootCmd.Execute(); err != nil {

    fmt.Println(err)

    os.Exit(1)

  }

}

```



Output:

```sh

# Root command flags.

% myapp

Usage:

  myapp [command]



Available Commands:

  help        Help about any command

  doathing    This is a subcommand



Flags:

  -h, --help               help for myapp

      --some-config        A global config [MYAPP_SOME_CONFIG]



Use "myapp [command] --help" for more information about a command.



# Child command flags. Notice that the prefix

# has the subcommand name automatically appended

# while preserving global/parent env vars.

% myapp doathing

Usage:

  myapp doathing [flags]



Flags:

  -h, --help               help for myapp

      --subcmd-config      Another config [MYAPP_DOATHING_SUBCMD_CONFIG]



Global Flags:

      --some-flag          A global flag [MYAPP_SOME_FLAG]

```



### Usage



**Variable precedence:**



Envy results in the following order of precedence, each item overwriting the previous:

`flag default` -> `Envy generated env var` -> `flag set at the CLI`.



Results referencing the stdlib flag example code:

- `./example` will result in `port` being set to `8131`

- `MYAPP_PORT=5678 ./example` will result in `port` being set to `5678`

- `MYAPP_PORT=5678 ./example -port=1234` will result in `port` being set to `1234`



**Env vars in help output:**



Envy can update your app help output so that it includes the environment variable generated/referenced for each flag. This is done by calling `envy.Parse()` before `flag.Parse()`.



The above example:

```

Usage of ./example:

  -address string

        Some random address [MYAPP_ADDRESS] (default "127.0.0.1")

  -port string

        Some random port [MYAPP_PORT] (default "8131")

```



 If this isn't desired, simply call `envy.Parse()` after `flag.Parse()`:

```go

// ...

	flag.Parse()

        envy.Parse("MYAPP") // looks for MYAPP_ADDRESS & MYAPP_PORT

// ...

```



```

Usage of ./example:

  -address string

        Some random address (default "127.0.0.1")

  -port string

        Some random port (default "8131")

```



**Satisfying types:**



Environment variables should be defined using a type that satisfies the respective type in your Go application's flag. For example:

- `string` -> `APP_ASTRINGVAR="someString"`

- `int` -> `APP_ANINTVAR=42`

- `bool` -> `APP_ABOOLVAR=true`



**Side effects:**



Setting a flag through an Envy generated environment variable will have the same effects on the default `flag.CommandLine` as if the flag were set via the command line. This only affect users that may rely on `flag.CommandLine` methods that make distinctions between set and to-be set flags (such as the `Visit` method).



**Cobra compatibility:**



The extensive types in Cobra's underlying [pflag](https://github.com/spf13/pflag) have not been tested, hence the "limited support" reference.



Also, keep in mind that Cobra can change in a way that breaks support with envy. Functionality was tested as of 2018-11-19.