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.yiibai.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")
