Go命令行標誌實例

命令行標誌是指定命令行程序選項的常用方法。 例如，在wc -l中，-l是命令行標誌。Go提供了一個支持基本命令行標誌解析的標誌包。這裏將使用這個包來實現示例命令行程序。

所有的示例代碼，都放在 F:\worksp\golang 目錄下。安裝Go編程環境請參考：http://www.yiibai.com/go/go\_environment.html

command-line-flags.go的完整代碼如下所示 -

package main

// Go provides a `flag` package supporting basic
// command-line flag parsing. We'll use this package to
// implement our example command-line program.
import "flag"
import "fmt"

func main() {

    // Basic flag declarations are available for string,
    // integer, and boolean options. Here we declare a
    // string flag `word` with a default value `"foo"`
    // and a short description. This `flag.String` function
    // returns a string pointer (not a string value);
    // we'll see how to use this pointer below.
    wordPtr := flag.String("word", "foo", "a string")

    // This declares `numb` and `fork` flags, using a
    // similar approach to the `word` flag.
    numbPtr := flag.Int("numb", 42, "an int")
    boolPtr := flag.Bool("fork", false, "a bool")

    // It's also possible to declare an option that uses an
    // existing var declared elsewhere in the program.
    // Note that we need to pass in a pointer to the flag
    // declaration function.
    var svar string
    flag.StringVar(&svar, "svar", "bar", "a string var")

    // Once all flags are declared, call `flag.Parse()`
    // to execute the command-line parsing.
    flag.Parse()

    // Here we'll just dump out the parsed options and
    // any trailing positional arguments. Note that we
    // need to dereference the pointers with e.g. `*wordPtr`
    // to get the actual option values.
    fmt.Println("word:", *wordPtr)
    fmt.Println("numb:", *numbPtr)
    fmt.Println("fork:", *boolPtr)
    fmt.Println("svar:", svar)
    fmt.Println("tail:", flag.Args())
}

執行上面代碼，將得到以下輸出結果 -

F:\worksp\golang>go build command-line-flags.go

F:\worksp\golang>command-line-flags -word=opt -numb=7 -fork -svar=flag
word: opt
numb: 7
fork: true
svar: flag
tail: []

F:\worksp\golang>command-line-flags -word=opt
word: opt
numb: 42
fork: false
svar: bar
tail: []

F:\worksp\golang>command-line-flags -word=opt a1 a2 a3
word: opt
numb: 42
fork: false
svar: bar
tail: [a1 a2 a3]

F:\worksp\golang>command-line-flags -word=opt a1 a2 a3 -numb=7
word: opt
numb: 42
fork: false
svar: bar
tail: [a1 a2 a3 -numb=7]

F:\worksp\golang>command-line-flags -h
Usage of command-line-flags:
  -fork
        a bool
  -numb int
        an int (default 42)
  -svar string
        a string var (default "bar")
  -word string
        a string (default "foo")

F:\worksp\golang>command-line-flags -wat
flag provided but not defined: -wat
Usage of command-line-flags:
  -fork
        a bool
  -numb int
        an int (default 42)
  -svar string
        a string var (default "bar")
  -word string
        a string (default "foo")