源码分析 weedfs 的command.go

command包是主要是用于分析传入的参数， 并且根据传入的参数，执行特定的命令。 
Command 结构中最重要的run 成员和 UsageLine， 这个一个函数类型，每个参数对应一个特定的函数进行处理。  

package command

import (
    "flag"
    "fmt"
    "os"
    "strings"
)

/************************************
  command 目录下定义了全局变量制指针，分别是 cmdBenchmark
  Backup 等文件 每个文件都是一个 Command 的初始化，以及run函数
**********************************/
var Commands = []*Command{
    cmdBenchmark,
    cmdBackup,
    cmdCompact,
    cmdCopy,
    cmdFix,
    cmdServer,
    cmdMaster,
    cmdFiler,
    cmdUpload,
    cmdDownload,
    cmdShell,
    cmdVersion,
    cmdVolume,
    cmdExport,
    cmdMount,
}

/**********************************************
 一个Command 类型， 一个run函数，
  几个字符串是用法，
**********************************************/
type Command struct {
    // Run runs the command.
    // The args are the arguments after the command name.
    Run func(cmd *Command, args []string) bool

    // UsageLine is the one-line usage message.
    // The first word in the line is taken to be the command name.
    UsageLine string

    // Short is the short description shown in the 'go help' output.
    Short string

    // Long is the long message shown in the 'go help <this-command>' output.
    Long string

    // Flag is a set of flags specific to this command.
    Flag flag.FlagSet

    IsDebug *bool
}

// Name returns the command's name: the first word in the usage line.
/**********************************************
 返回的是  UsageLine 空格前的内容 UsageLine: "backup -dir=. -volumeId=234 -server=localhost:9333",

**********************************************/
func (c *Command) Name() string {
    name := c.UsageLine
    i := strings.Index(name, " ")
    if i >= 0 {
        name = name[:i]
    }
    return name
}

/*******************************************
   打印一下这些信息
*******************************************/
func (c *Command) Usage() {
    fmt.Fprintf(os.Stderr, "Example: weed %s\n", c.UsageLine)
    fmt.Fprintf(os.Stderr, "Default Usage:\n")
    c.Flag.PrintDefaults() // 没细看
    fmt.Fprintf(os.Stderr, "Description:\n")
    fmt.Fprintf(os.Stderr, "  %s\n", strings.TrimSpace(c.Long)) //用 strings.TrimSpace(s) 来剔除字符串开头和结尾的空白符号;
    os.Exit(2)
}

// Runnable reports whether the command can be run; otherwise
// it is a documentation pseudo-command such as importpath.
func (c *Command) Runnable() bool {
    return c.Run != nil
}