golang编译时通过ldflags给包内变量赋值，实现打印版本号及commit

很多命令行程序都可以通过version参数输出版本信息，commit，操作系统等信息。下面介绍一种方法实现golang编译的命令行程序打印版本号。

docker打印的版本信息：

$ ~ docker version
Client: Docker Engine - Community
 Version:           18.09.2
 API version:       1.39
 Go version:        go1.10.8
 Git commit:        6247962
 Built:             Sun Feb 10 04:12:39 2019
 OS/Arch:           darwin/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          18.09.2
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.6
  Git commit:       6247962
  Built:            Sun Feb 10 04:13:06 2019
  OS/Arch:          linux/amd64
  Experimental:     false

-ldflags

-ldflags 'flag list' arguments to pass on each go tool link invocation.

go tool link --help

-Xversion

main.go：

package main

import (
    "flag"
    "log"
    "os"
)

var (
    Version   string
    Branch    string
    Commit    string
    BuildTime string
    lowercase string // 小写也可以
)

func main() {
    versionFlag := flag.Bool("version", false, "print the version")
    flag.Parse()

    if *versionFlag {
        log.Printf("Version: %s\n", Version)
        log.Printf("Branch: %s\n", Branch)
        log.Printf("Commit: %s\n", Commit)
        log.Printf("BuildTime: %s\n", BuildTime)
        log.Printf("lowercase: %s\n", lowercase)
        os.Exit(0)
    }

    log.Println("run main.go")
}

打包脚本：

#!/usr/bin/env bash

prog=xxx
version=1.1.0
lowercase=ok

# 交叉编译
# CGO_ENABLED=0 GOOS=linux GOARCH=amd64
go build -ldflags "\
-X main.Version=$version \
-X main.Branch=`git rev-parse --abbrev-ref HEAD` \
-X main.Commit=`git rev-parse HEAD` \
-X main.BuildTime=`date -u '+%Y-%m-%d_%H:%M:%S'` \
-X main.lowercase=$lowercase \
" -v -o $prog main.go

最终效果：

$ ./xxx -version
2019/04/11 00:59:08 Version: 1.1.0
2019/04/11 00:59:08 Branch: master
2019/04/11 00:59:08 Commit: 29921d9df18543693321e2109ea36462dbb346d3
2019/04/11 00:59:08 BuildTime: 2019-04-10_16:59:07
2019/04/11 00:59:08 lowercase: ok