[golang learning notes] simple use of flag package, command line parsing

flag The package implements the parsing of command line parameters

This article is just a simple introduction , Details please see Official documents

func String

func String(name string, value string, usage string) *string
String Use the specified name 、 The default value is 、 Use the information to register a string type flag. Return a saved flag Pointer to the value of .

package main

import (
   "flag"
   "fmt"
)

// The first parameter is zero name  The second parameter is the default value   The third parameter is description 
// Note that the accepted variable is a pointer 
var mode = flag.String("mode", "", "process mode")

func main() {
    

   // To analyze 
   flag.Parse()

   // Output 
   fmt.Println(*mode)
}

Use... When executing --name=value To pass

Command line flag grammar ：

-flag
-flag=x
-flag x  //  Only non bool Type of flag Sure  bool Type used = assignment 

One - And two - It's the same

for example ：

go run main.go --mode=hello

func StringVar

func StringVar(p *string, name string, value string, usage string)
StringVar Use the specified name 、 The default value is 、 Use the information to register a string type flag, And will flag The value of is saved to p Variable pointed to .

Code ：

package main

import (
  "flag"
  "fmt"
)

func main() {
    

  var str string

  fmt.Println(" Start parsing ")

  flag.StringVar(&str, "str", "", "parse string")

  // Analytical parameters 
  flag.Parse()
  // Output 
  fmt.Println(str)

Command line input ：

 go run test1.go -str="hello go"

result ：

 Start parsing 
hello go

flag The command line parameter types supported by the package are bool、int、int64、uint、uint64、float float64、string、duration.

flag Parameters	Valid values
character string flag	Legal string
Integers flag	1234、0664、0x1234 Other types , It can also be negative .
Floating point numbers flag	Legal floating point number
bool type flag	1, 0, t, f, T, F, true, false, TRUE, FALSE, True, False.
Period of time flag	Any legal time period string . Such as ”300ms”、”-1.5h”、”2h45m”. Legal units include ”ns”、”us” /“µs”、”ms”、”s”、”m”、”h”.