flag 参数

flag包实现了命令行参数的解析。

-h=true  实现帮助文档

package main

import (

    "flag"

    "fmt"

    "os"

)

// 实际中应该用更好的变量名

var (

    h bool

    v, V bool

    t, T bool

    q    *bool

    s string

    p string

    c string

    g string

)

func init() {

    flag.BoolVar(&h, "h", false, "this help")

    flag.BoolVar(&v, "v", false, "show version and exit")

    flag.BoolVar(&V, "V", false, "show version and configure options then exit")

    flag.BoolVar(&t, "t", false, "test configuration and exit")

    flag.BoolVar(&T, "T", false, "test configuration, dump it and exit")

    // 另一种绑定方式

    q = flag.Bool("q", false, "suppress non-error messages during configuration testing")

    // 注意 `signal`。默认是 -s string，有了 `signal` 之后，变为 -s signal

    flag.StringVar(&s, "s", "", "send `signal` to a master process: stop, quit, reopen, reload")

    flag.StringVar(&p, "p", "/usr/local/nginx/", "set `prefix` path")

    flag.StringVar(&c, "c", "conf/nginx.conf", "set configuration `file`")

    flag.StringVar(&g, "g", "conf/nginx.conf", "set global `directives` out of configuration file")

    // 改变默认的 Usage，flag包中的Usage 其实是一个函数类型。这里是覆盖默认函数实现，具体见后面Usage部分的分析

    flag.Usage = usage

}

func main() {

    flag.Parse()

    if h {

        flag.Usage()

    }

}

func usage() {

    fmt.Fprintf(os.Stderr, `nginx version: nginx/1.10.0

Usage: nginx [-hvVtTq] [-s signal] [-c filename] [-p prefix] [-g directives]

Options:

`)

    flag.PrintDefaults()

}