package altsrc_test import ( "fmt" "log" "os" "time" "github.com/urfave/cli/v2" "github.com/urfave/cli/v2/altsrc" ) func ExampleApp_Run_yamlFileLoaderDuration() { execServe := func(c *cli.Context) error { keepaliveInterval := c.Duration("keepalive-interval") fmt.Printf("keepalive %s\n", keepaliveInterval) return nil } fileExists := func(filename string) bool { stat, _ := os.Stat(filename) return stat != nil } // initConfigFileInputSource is like altsrc.InitInputSourceWithContext and altsrc.NewYamlSourceFromFlagFunc, but checks // if the config flag is exists and only loads it if it does. If the flag is set and the file exists, it fails. initConfigFileInputSource := func(configFlag string, flags []cli.Flag) cli.BeforeFunc { return func(context *cli.Context) error { configFile := context.String(configFlag) if context.IsSet(configFlag) && !fileExists(configFile) { return fmt.Errorf("config file %s does not exist", configFile) } else if !context.IsSet(configFlag) && !fileExists(configFile) { return nil } inputSource, err := altsrc.NewYamlSourceFromFile(configFile) if err != nil { return err } return altsrc.ApplyInputSourceValues(context, inputSource, flags) } } flagsServe := []cli.Flag{ &cli.StringFlag{ Name: "config", Aliases: []string{"c"}, EnvVars: []string{"CONFIG_FILE"}, Value: "../testdata/empty.yml", DefaultText: "../testdata/empty.yml", Usage: "config file", }, altsrc.NewDurationFlag( &cli.DurationFlag{ Name: "keepalive-interval", Aliases: []string{"k"}, EnvVars: []string{"KEEPALIVE_INTERVAL"}, Value: 45 * time.Second, Usage: "interval of keepalive messages", }, ), } cmdServe := &cli.Command{ Name: "serve", Usage: "Run the server", UsageText: "serve [OPTIONS..]", Action: execServe, Flags: flagsServe, Before: initConfigFileInputSource("config", flagsServe), } c := &cli.App{ Name: "cmd", HideVersion: true, UseShortOptionHandling: true, Commands: []*cli.Command{ cmdServe, }, } if err := c.Run([]string{"cmd", "serve", "--config", "../testdata/empty.yml"}); err != nil { log.Fatal(err) } // Output: // keepalive 45s }