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Flagger is a library based on Viper and Pflag for structured parameter handling.

go get github.com/robotism/flagger

• Parameter Struct

  type AppConfig struct {
   Debug bool `mapstructure:"debug" short:"d" description:"debug mode" default:"false"`
   Timezone string `mapstructure:"timezone" description:"timezone" default:"UTC"`
   Server Server `mapstructure:"server" group:"server"`
   Database map[string]Database `mapstructure:"database" group:"database" mapkey:"<dbkey>"`
  }
  type Server struct {
   Port int `mapstructure:"port" description:"port" default:"8080"`
  }
  type Database struct {
   Host string `mapstructure:"host" description:"host" default:"localhost"`
   Port int `mapstructure:"port" description:"port" default:"3306"`
   User string `mapstructure:"user" description:"user" default:"root"`
   Pass string `mapstructure:"pass" description:"pass"`
  }

• Command Initialization

  package cmd
  import (
   "log"
   "os"
   "github.com/robotism/flagger"
   "github.com/robotism/flagger/example/config"
   "github.com/spf13/cobra"
  )
  var (
   f = flagger.New()
   c = &config.AppConfig{}
  )
  // rootCmd represents the base command when called without any subcommands
  var rootCmd = &cobra.Command{
   Use: "example",
   Short: "a flagger example",
   Long: `a flagger example`,
   Run: func(cmd *cobra.Command, args []string) {
   log.Printf("%+v\n", c)
   },
  }
  func Execute() {
   err := rootCmd.Execute()
   if err != nil {
   os.Exit(1)
   }
  }
  func init() {
   f.UseFlags(rootCmd.Flags())
   f.UseConfigFileArgDefault()
   f.Parse(c)
  }

• Run: Display Help

  > go run main.go -h
  a flagger example
  Usage:
  example [flags]
  Flags:
  -c, --config string config file path
   --database.<dbkey>.host string host (default "localhost")
   --database.<dbkey>.pass string pass
   --database.<dbkey>.port int port (default 3306)
   --database.<dbkey>.user string user (default "root")
  -d, --debug debug mode
  -h, --help help for example
   --server.port int port (default 8080)
   --timezone string timezone (default "UTC")
  

• Run: Use Environment Variables and Command Line Parameters

  > set SERVER_PORT=9999
  > go run main.go -d=true --timezone=Asia/Shanghai --database.default.host=127.0.0.1
  2025年02月20日 14:07:31 &{Debug:true Timezone:Asia/Shanghai Server:{Port:9999} Database:map[default:{Host:127.0.0.1 Port:3306 User:root Pass:}]}

• Run: Use Configuration File

  go run main.go -d=true --timezone=Asia/Shanghai --database.default.host=127.0.0.1 -c config.yaml
  2025年02月20日 14:07:59 &{Debug:true Timezone:Asia/Shanghai Server:{Port:9999} Database:map[default:{Host:127.0.0.1 Port:4000 User:root Pass:12345678}]}
  go run main.go -c config.yaml
  2025年02月20日 14:08:14 &{Debug:true Timezone:UTC Server:{Port:9999} Database:map[default:{Host:xxx.xxx.xxx.xxx Port:4000 User:root Pass:12345678}]}

• Command Line Flags (Flags): If a configuration option is provided via the command line, the value from the command line will take precedence.
• Environment Variables: If the configuration option is not provided via the command line, it will attempt to retrieve the value from environment variables.
• Configuration File: If the configuration option is not found in environment variables, it will load from the configuration file.
• Default Values: If none of the above methods provide the value, the default value set in the code will be used.