add "g env" subcomment for better debug

cli/commands.go

@@ -47,6 +47,12 @@ var (
 			UsageText: "g clean",
 			Action:    clean,
 		},
+		{
+			Name:      "env",
+			Usage:     "Show env variables of g",
+			UsageText: "g env",
+			Action:    showEnv,
+		},
 		{
 			Name:  "self",
 			Usage: "Modify g itself",

cli/env.go

+package cli
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/urfave/cli/v2"
+)
+
+func showEnv(ctx *cli.Context) (err error) {
+	var envVars = []string{experimentalEnv, homeEnv, mirrorEnv}
+
+	for _, v := range envVars {
+		fmt.Printf("%s = %s\n", v, os.Getenv(v))
+	}
+	return nil
+}