зеркало из https://github.com/golang/example.git
73 строки
1.4 KiB
Go
73 строки
1.4 KiB
Go
// Copyright 2023 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Hello is a hello, world program, demonstrating
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// how to write a simple command-line program.
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//
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// Usage:
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//
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// hello [options] [name]
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//
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// The options are:
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//
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// -g greeting
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// Greet with the given greeting, instead of "Hello".
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//
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// -r
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// Greet in reverse.
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//
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// By default, hello greets the world.
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// If a name is specified, hello greets that name instead.
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package main
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import (
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"flag"
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"fmt"
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"log"
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"os"
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"golang.org/x/example/hello/reverse"
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)
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func usage() {
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fmt.Fprintf(os.Stderr, "usage: hello [options] [name]\n")
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flag.PrintDefaults()
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os.Exit(2)
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}
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var (
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greeting = flag.String("g", "Hello", "Greet with `greeting`")
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reverseFlag = flag.Bool("r", false, "Greet in reverse")
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)
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func main() {
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// Configure logging for a command-line program.
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log.SetFlags(0)
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log.SetPrefix("hello: ")
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// Parse flags.
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flag.Usage = usage
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flag.Parse()
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// Parse and validate arguments.
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name := "world"
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args := flag.Args()
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if len(args) >= 2 {
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usage()
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}
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if len(args) >= 1 {
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name = args[0]
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}
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if name == "" { // hello '' is an error
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log.Fatalf("invalid name %q", name)
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}
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// Run actual logic.
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if *reverseFlag {
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fmt.Printf("%s, %s!\n", reverse.String(*greeting), reverse.String(name))
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return
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}
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fmt.Printf("%s, %s!\n", *greeting, name)
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}
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