Go - pflag and viper

pflag is a drop-in replacement of Go's native flag package. If you import pflag under the name "flag" then all code should continue to function with no changes.

import flag "github.com/spf13/pflag"

There is one exception to this: if you directly instantiate the Flag struct there is one more field "Shorthand" that you will need to set. Most code never instantiates this struct directly, and instead uses functions such as String(), BoolVar(), and Var(), and is therefore unaffected.

package main

import (
    "fmt"

    "github.com/spf13/pflag"
    "github.com/spf13/viper"
)

func aliasNormalizeFunc(f *pflag.FlagSet, n string) pflag.NormalizedName {
    switch n {
    case "pass", "ps":
        n = "password"
    }
    return pflag.NormalizedName(n)
}

func main() {
    pflag.StringP("name", "n", "Frank", "Name parameter")
    pflag.StringP("password", "p", "hardToGuess", "Password")
    pflag.CommandLine.SetNormalizeFunc(aliasNormalizeFunc)
    pflag.Parse()

    viper.BindPFlags(pflag.CommandLine)

    name := viper.GetString("name")
    password := viper.GetString("password")
    fmt.Println(name, password)

    // Reading an environment variable
    viper.BindEnv("GOMAXPROCS")
    val := viper.Get("GOMAXPROCS")
    if val != nil {
        fmt.Println("GOMAXPROCS:", val)
    } else {
        // Setting an environment variable
        viper.Set("GOMAXPROCS", 8)
        val = viper.Get("GOMAXPROCS")
        fmt.Println("GOMAXPROCS:", val)
    }
}

zzh@ZZHPC:/zdata/Github/ztest$ go run main.go --help
Usage of /tmp/go-build3847677257/b001/exe/main:
  -n, --name string       Name parameter (default "Frank")
  -p, --password string   Password (default "hardToGuess")
pflag: help requested
exit status 2
zzh@ZZHPC:/zdata/Github/ztest$ go run main.go -n ZhangZhihui -p ZZZ
ZhangZhihui ZZZ
GOMAXPROCS: 8
zzh@ZZHPC:/zdata/Github/ztest$ go run main.go
Frank hardToGuess
GOMAXPROCS: 8