Category: Golang

Hi all,
this is day 1 of 100 days I am coding one go program a day. Wish me good luck!

In this example I will show how to parse command line arguments with flag module and os.Args array.

Flag module is very powerful and can be as simple as this:

//...
import "flag"
//...
name := flag.String("user", "", "user name")
flag.Parse()
fmt.Printf("user name is %s\n", *name)

To have the “same” functionality with os.Args you have to do some work. In following example I added support for –user, -user and user=<value> arguments.

//...
import "os"
//...
var userArg string
for index, arg := range os.Args {
	pattern := "-user="
	x := strings.Index(arg, pattern)
	if x > -1 {
		userArg = arg[x+len(pattern):]
		continue
	}
	if arg == "-user" || arg == "--user" {
		userArg = os.Args[index+1]
		continue
	}
}
fmt.Printf("user name is %s", userArg)

Full code:

package main

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

func main() {
	name := flag.String("user", "", "user name")
	flag.Parse()
	fmt.Printf("user name is %s\n", *name)

	var userArg string
	for index, arg := range os.Args {
		pattern := "-user="
		x := strings.Index(arg, pattern)
		if x > -1 {
			userArg = arg[x+len(pattern):]
			continue
		}
		if arg == "-user" || arg == "--user" {
			userArg = os.Args[index+1]
			continue
		}
	}
	fmt.Printf("user name is %s", userArg)
}

Latest code examples see on GitHub