How to combine cobra and klog

I have a project that needs to use cobra and klog to generate executable and print logs and keep.

Firstly, I tested that using the following klog can output the log to the terminal and file at the same time.

package main
import (
	"flag"
	"k8s.io/klog"
)
func init() {
	var fs flag.FlagSet
	klog.InitFlags(&fs)
	fs.Set("logtostderr", "false")
	fs.Set("log_file_max_size", "100")
	fs.Set("log_file", "/home/test/workspace/klogfile/test.log")
	fs.Set("alsologtostderr", "true")
}
func main() {
	defer klog.Flush()
	klog.Info("info")
	klog.Warning("warning")
	klog.Error("error")
}

The content of file /home/test/workspace/klogfile/test.log is as follow

Log file created at: 2023/04/06 16:46:07
Running on machine: s52
Binary: Built with gc go1.16.12 for linux/amd64
Log line format: [IWEF]mmdd hh:mm:ss.uuuuuu threadid file:line] msg
I0406 16:46:07.751183   13512 main.go:20] info
W0406 16:46:07.751594   13512 main.go:21] warning
E0406 16:46:07.751629   13512 main.go:22] error

Then I try to add it to cobra based on k8s style

package main
import (
	"flag"
	"github.com/spf13/cobra"
	"k8s.io/klog"
)
var (
	str = "hello world"
)
func NewCommand() *cobra.Command {
	cmd := &cobra.Command{
		Use:   "echo",
		Short: "use klog with cobra",
		Long:  "Use klog together with cobra.",
		Run: func(cmd *cobra.Command, args []string) {
			Run()
		},
	}
	klog.InitFlags(flag.CommandLine)
	cmd.Flags().AddGoFlagSet(flag.CommandLine)
	cmd.Flags().SortFlags = false
	cmd.Flags().StringVar(&str, "str", str, "string to print")
	return cmd
}
func Run() {
	defer klog.Flush()
	klog.Infof("Running, str:%s", str)
}

func main() {
	if err := NewCommand().Execute(); err != nil {
		klog.Fatalf("root cmd execute failed, err=%v", err)
	}
}

I can print out the required log options through --help, but when I override them to achieve the save to file in the above example, only the output is output to the terminal and not to the file

# go run main2.go --logtostderr false --log_file_max_size "100" --alsologtostderr true --log_file "/home/test/workspace/klogfile/test2.log"
I0406 16:52:57.479455   15217 cobra_klog.go:34] Running, str:hello world

May I ask where I am missing the necessary code, if so, please let me know how to modify it, thank you!

There is nothing wrong in your code. The only issue is that you must use the -flag=false form to turn off a boolean flag (see Command line flag syntax).

Try this command (repalce --logtostderr false with --logtostderr=false):

go run main2.go --logtostderr=false --log_file_max_size "100" --alsologtostderr true --log_file "/home/test/workspace/klogfile/test2.log"

BTW, I think --log_file_max_size "100" could be simplified to --log_file_max_size 100.

Update:

To reduce the exposed flags of klog:

 package main
 
 import (
    "flag"
    "github.com/spf13/cobra"
    "k8s.io/klog"
 )
 
 var (
    str     = "hello world"
+   logFile string
 )
 
 func NewCommand() *cobra.Command {
+   var fs flag.FlagSet
+   klog.InitFlags(&fs)

    cmd := &cobra.Command{
        Use:   "echo",
        Short: "use klog with cobra",
        Long:  "Use klog together with cobra.",
        Run: func(cmd *cobra.Command, args []string) {
+           fs.Set("logtostderr", "false")
+           fs.Set("log_file", logFile)

            Run()
        },
    }
-   klog.InitFlags(flag.CommandLine)
-   cmd.Flags().AddGoFlagSet(flag.CommandLine)
    cmd.Flags().SortFlags = false
    cmd.Flags().StringVar(&str, "str", str, "string to print")
+   cmd.Flags().StringVar(&logFile, "log_file", "", "If non-empty, use this log file")
    return cmd
 }
 func Run() {
    defer klog.Flush()
    klog.Infof("Running, str:%s", str)
 }
 
 func main() {
    if err := NewCommand().Execute(); err != nil {
        klog.Fatalf("root cmd execute failed, err=%v", err)
    }
 }