命令行标志是指定命令行程序选项的常用方法。 例如，在wc -l中，-l是命令行标志。go提供了一个支持基本命令行标志解析的标志包。这里将使用这个包来实现示例命令行程序。

所有的示例代码，都放在 f:\worksp\golang 目录下。安装go编程环境请参考：http://www.h3.com/go/go_environment.html

command-line-flags.go的完整代码如下所示 -

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())
}

执行上面代码，将得到以下输出结果 -

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")