Golang flag

flag 是 go 標準庫提供的解析命令行參數的包。

1. flag use style

   • flag.Type(name, defvalue, usage)

       其中 Type: [String, Int, Bool ...], 并返回一個相應類型的指針。
     

   • 將 flag 綁定到一個變量上 : flag.TypeVar(&flagvar, name, defvalue, usage)

       其中 Type: [String, Int, Bool ...]
     

2. Custom flag

   只要實現 flag.Value interface:

    type Value interface {
        String() string
        Set(string) error        
    }
   

   以 flag.Var(&flagvar, name, usage) 方式定義此 flag

3. Example

    package main 
    
    import (
        "flag"
        "fmt"
        "strconv"
    )
    
    const APP_VERSION = "0.1"
    
    type percentage float32
    func (p *percentage) Set(s string) error {
        v, err := strconv.ParseFloat(s, 32)
        *p = percentage(v)
        return err
    }
    func (p *percentage) String() string {
        return fmt.Sprintf("%f", *p)
    }
    
    func main() {
        // *T
        namePtr := flag.String("name", "hl", "user`s name")
        agePtr := flag.Int("age", 22, "user`s age")
        vipPtr := flag.Bool("vip", true, "is a vip user")
    
        var email string
        flag.StringVar(&email, "email", "hlGopen@doingsbook.com", "user`s email")
    //    p := &email
    //    fmt.Println(p)
    //    fmt.Println(*p)
        
        var pop percentage
        flag.Var(&pop, "pop", "popularity")
        
        flag.Parse() // Scan the arguments list 
        others := flag.Args()
        
        if *vipPtr {
            fmt.Println("Version:", APP_VERSION)
        }
        
        fmt.Println("name: ", *namePtr)
        fmt.Println("age: ", *agePtr)
        fmt.Println("pop: ", pop)
        fmt.Println("email: ", email)
        fmt.Println("others: ", others)
        
    }     
   

• $ ./command-line-flags   
  Version: 0.1
  name:  hl
  age:  22
  pop:  0
  email:  hlGopen@doingsbook.com
  others:  []
  

•  $ ./command-line-flags -name golang -age 20 -vip=false -pop 99 簡潔 高并發 等等
   name:  golang
   age:  20
   pop:  99
   email:  hlGopen@doingsbook.com
   others:  [簡潔 高并發 等等]
  

•   $ ./command-line-flags -h
    Usage of command-line-flags:
      -age=22: user`s age
      -email="hlGopen@doingsbook.com": user`s email
      -name="hl": user`s name
      -pop=0.000000: popularity
      -vip=true: is a vip user