go使用urfave/cli開發命令行工具

cli包為創建一個Go命令行應用程式提供了一個最小的框架。他使用簡單，最簡單的方式就是：

  func main() {    cli.NewApp().Run(os.Args)  }
實際場景中使用方式：
  func main() {    app := cli.NewApp()    app.Name = "greet"    app.Usage = "say a greeting"    app.Action = func(c *cli.Context) error {      println("Greetings")      return nil    }
    app.Run(os.Args)  }
上面定義了應用程式名稱，用法，不指定子命令時函數入口，並運行應用程式。
App結構體，我們可以根據需要來定義自己的命令行工具：
type App struct {    // The name of the program. Defaults to path.Base(os.Args[0])    Name string    // Full name of command for help, defaults to Name    HelpName string    // Description of the program.    Usage string    // Text to override the USAGE section of help    UsageText string    // Description of the program argument format.    ArgsUsage string    // Version of the program    Version string    // Description of the program    Description string    // List of commands to execute    Commands []Command    // List of flags to parse    Flags []Flag    // Boolean to enable bash completion commands    EnableBashCompletion bool    // Boolean to hide built-in help command    HideHelp bool    // Boolean to hide built-in version flag and the VERSION section of help    HideVersion bool    // Populate on app startup, only gettable through method Categories()    categories CommandCategories    // An action to execute when the bash-completion flag is set    BashComplete BashCompleteFunc    // An action to execute before any subcommands are run, but after the context is ready    // If a non-nil error is returned, no subcommands are run    Before BeforeFunc    // An action to execute after any subcommands are run, but after the subcommand has finished    // It is run even if Action() panics    After AfterFunc
    // The action to execute when no subcommands are specified    // Expects a `cli.ActionFunc` but will accept the *deprecated* signature of `func(*cli.Context) {}`    // *Note*: support for the deprecated `Action` signature will be removed in a future version    Action interface{}
    // Execute this function if the proper command cannot be found    CommandNotFound CommandNotFoundFunc    // Execute this function if an usage error occurs    OnUsageError OnUsageErrorFunc    // Compilation date    Compiled time.Time    // List of all authors who contributed    Authors []Author    // Copyright of the binary if any    Copyright string    // Name of Author (Note: Use App.Authors, this is deprecated)    Author string    // Email of Author (Note: Use App.Authors, this is deprecated)    Email string    // Writer writer to write output to    Writer io.Writer    // ErrWriter writes error output    ErrWriter io.Writer    // Execute this function to handle ExitErrors. If not provided, HandleExitCoder is provided to    // function as a default, so this is optional.    ExitErrHandler ExitErrHandlerFunc    // Other custom info    Metadata map[string]interface{}    // Carries a function which returns app specific info.    ExtraInfo func() map[string]string    // CustomAppHelpTemplate the text template for app help topic.    // cli.go uses text/template to render templates. You can    // render custom help text by setting this variable.    CustomAppHelpTemplate string    // Boolean to enable short-option handling so user can combine several    // single-character bool arguements into one    // i.e. foobar -o -v -> foobar -ov    UseShortOptionHandling bool
    didSetup bool}
下面示例一下，寫一個命令行，這個命令行定義了命令行參數，初始化應用程式日誌，之後就是從run開始實現自己的業務了。
var (    kubeConfig     string)
func main() {    var config app.Config
    app := cli.NewApp()    app.Version = "v0.1.0-20210226"    app.Usage = "Complete container management platform"    app.Flags = []cli.Flag{        cli.StringFlag{            Name:        "kubeconfig",            Usage:       "Kube config for accessing k8s cluster",            EnvVar:      "KUBECONFIG",            Destination: &kubeConfig,        },        cli.BoolFlag{            Name:        "debug",            Usage:       "Enable debug logs",            Destination: &config.Debug,        },        cli.IntFlag{            Name:        "http-listen-port",            Usage:       "HTTP listen port",            Value:       8080,            Destination: &config.HTTPListenPort,        },        cli.IntFlag{            Name:        "https-listen-port",            Usage:       "HTTPS listen port",            Value:       8443,            Destination: &config.HTTPSListenPort,        },        cli.StringFlag{            Name:        "log-path",            EnvVar:      "LOG_PATH",            Value:       "kubevision-api.log",            Usage:       "Log path for kubevision API",            Destination: &config.LogPath,        },    }
    app.Action = func(c *cli.Context) error {        initLogs(c, config)        return run(c, config)    }
    // app.ExitErrHandler = func(c *cli.Context, err error) {    //     logrus.Fatal(err)    // }
    app.Run(os.Args)}
func initLogs(c *cli.Context, cfg app.Config) {    logrus.SetFormatter(&logrus.JSONFormatter{})    if cfg.Debug {        logrus.SetLevel(logrus.DebugLevel)        logrus.Debugf("Loglevel set to [%v]", logrus.DebugLevel)    }    logrus.SetOutput(os.Stdout)}
func run(cli *cli.Context, cfg app.Config) error {    return nil}
package app
type Config struct {    HTTPListenPort    int    HTTPSListenPort   int    Debug             bool    LogPath          string}