$ go env
GO111MODULE="on"
GOARCH="amd64"
GOHOSTOS="darwin"
GOMODCACHE="/Users/larry/go/pkg/mod"
GOPATH="/Users/larry/go"
GOPROXY="https://mirrors.aliyun.com/goproxy/"
GOROOT="/Users/larry/Software/go"
GOTOOLDIR="/Users/larry/Software/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"

# 1. 七牛 CDN
export GOPROXY=https://goproxy.cn,direct

# 2. 阿里云
export GOPROXY=https://mirrors.aliyun.com/goproxy/,direct

# 3. 官方
export GOPROXY=https://goproxy.io,direct

# 创建project的目录
$ mkdir pkslow_test
# 进入目录
$ cd pkslow_test/
# 初始化
$ go mod init pkslow.com/pkslow_test
go: creating new go.mod: module pkslow.com/pkslow_test

$ l
-rw-r--r-- 1 larry staff 39 Dec 13 21:07 go.mod
#查看文件内容
$ cat go.mod 
module pkslow.com/pkslow_test

go 1.15

package main
import "fmt"
func main() {
 fmt.Println("hello pkslow")
}

# 直接run
$ go run main.go 
hello pkslow

# 编译成二进制文件
$ go build
t$ l
-rw-r--r-- 1 larry staff 39 Dec 13 21:07 go.mod
-rw-r--r-- 1 larry staff 74 Dec 13 21:12 main.go
-rwxr-xr-x 1 larry staff 2146904 Dec 13 21:12 pkslow_test
# 执行二进制文件
$ ./pkslow_test 
hello pkslow

$ tree
├── go.mod
├── main.go
└── mylog
 └── pkslow_log.go

package mylog
import "fmt"

func PkslowLog(str string) {
 fmt.Println(str)
}

package main
import (
	"fmt"
	"pkslow.com/pkslow_test/mylog"
)

func main() {
 fmt.Println("hello pkslow")
 mylog.PkslowLog("www.pkslow.com")
}

$ go run main.go 
hello pkslow
www.pkslow.com