| 42 | ) |
| 43 | |
| 44 | func main() { |
| 45 | // Configure logging for a command-line program. |
| 46 | log.SetFlags(0) |
| 47 | log.SetPrefix("hello: ") |
| 48 | |
| 49 | // Parse flags. |
| 50 | flag.Usage = usage |
| 51 | flag.Parse() |
| 52 | |
| 53 | // Parse and validate arguments. |
| 54 | name := "world" |
| 55 | args := flag.Args() |
| 56 | if len(args) >= 2 { |
| 57 | usage() |
| 58 | } |
| 59 | if len(args) >= 1 { |
| 60 | name = args[0] |
| 61 | } |
| 62 | if name == "" { // hello '' is an error |
| 63 | log.Fatalf("invalid name %q", name) |
| 64 | } |
| 65 | |
| 66 | // Run actual logic. |
| 67 | if *reverseFlag { |
| 68 | fmt.Printf("%s, %s!\n", reverse.String(*greeting), reverse.String(name)) |
| 69 | return |
| 70 | } |
| 71 | fmt.Printf("%s, %s!\n", *greeting, name) |
| 72 | } |