[Golang] Parse Command Line Arguments - String Variable

# cannot use relative path in GOROOT, otherwise 6g not found. For example,
#   export GOROOT=../go  (=> 6g not found)
# it is also not allowed to use relative path in GOPATH
export GOROOT=$(realpath ../go)
export GOPATH=$(realpath .)
export PATH := $(GOROOT)/bin:$(GOPATH)/bin:$(PATH)


INPUT=abc

default: fmt
	@go run demo.go -input=$(INPUT)

fmt:
	@go fmt demo.go

package main

import (
	"flag"
	"fmt"
)

func main() {
	arg := flag.String("input", "defaultValue", "Command line argument")
	flag.Parse()
	fmt.Println(*arg)
}