Fix comments from Rob Pike

Author: tebeka

src/flag/example_flagset_test.go

@@ -1,4 +1,4 @@
-// Copyright 2020 The Go Authors. All rights reserved.
+// Copyright 2023 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -11,18 +11,25 @@ import (
 )
 
 func ExampleFlagSet() {
+
 	start := func(args []string) {
+		// A real program (not an example) would use flag.ExitOnError.
 		fs := flag.NewFlagSet("start", flag.ContinueOnError)
-		addr := fs.String("address", ":8080", "`address` to listen on")
-		fs.Parse(args)
+		addr := fs.String("addr", ":8080", "`address` to listen on")
+		if err := fs.Parse(args); err != nil {
+			fmt.Printf("error: %s", err)
+			return
+		}
 		fmt.Printf("starting server on %s\n", *addr)
 	}
 
 	stop := func(args []string) {
-		// On regular program use `flag.ExitOnError`.
 		fs := flag.NewFlagSet("stop", flag.ContinueOnError)
 		timeout := fs.Duration("timeout", time.Second, "stop timeout in `seconds`")
-		fs.Parse(args)
+		if err := fs.Parse(args); err != nil {
+			fmt.Printf("error: %s", err)
+			return
+		}
 		fmt.Printf("stopping server (timeout=%v)\n", *timeout)
 	}
 
@@ -35,16 +42,16 @@ func ExampleFlagSet() {
 			stop(subArgs)
 		default:
 			fmt.Printf("error: unknown command - %q\n", args[1])
-			// On regular main print to `os.Stderr` and exit the program with non-zero value.
+			// On a real program (not an example) print to os.Stderr and exit the program with non-zero value.
 		}
 	}
 
-	main([]string{"httpd", "start", "-address", ":9999"})
+	main([]string{"httpd", "start", "-addr", ":9999"})
 	main([]string{"httpd", "stop"})
-	main([]string{"http", "info"})
+	main([]string{"http", "start", "-log-level", "verbose"})
 
 	// Output:
 	// starting server on :9999
 	// stopping server (timeout=1s)
-	// error: unknown command - "info"
+	// error: flag provided but not defined: -log-level
 }