Application auto build versioning

Use ldflags to set variables in main package:

With file main.go:

package main

import "fmt"

var (
    version string
    build   string
)

func main() {
    fmt.Println("version=", version)
    fmt.Println("build=", build)
}

Then run:

go run \
  -ldflags "-X main.version=1.0.0 -X main.build=12082019" \ 
  main.go

Build:

go build -o mybinary \
  -ldflags "-X main.version=1.0.0 -X 'main.build=$(date)'" \ 
  main.go

---

Use ldflags to set variable in a non-main package:

With file config.go:

package config

import "fmt"

var (
    Version string
)

func LogVersion() {
    fmt.Println("version=", Version)
}

You will also need file main.go:

package main

import (
    "fmt"
    "github.com/user/repo/config"
}

func main() {
    config.LogVersion()
}

Build your binary first:

go build -o mybinary main.go 

Find the full path of variable name you want to set:

go tool nm <path_to_binary> | grep Version

Run and build the binary again but with the ldflags:

go run \
  -ldflags "-X github.com/user/repo/config.Version=1.0.0" \
  main.go --version       


go build -o mybinary \
  -ldflags "-X github.com/user/repo/config.Version=1.0.0" \
  main.go     

---

Inspired by https://github.com/golang/go/wiki/GcToolchainTricks#including-build-information-in-the-executable

---

Also if you are using goreleaser then read this https://goreleaser.com/environment/#using-the-mainversion :

Default wise GoReleaser sets three ldflags:

main.version: Current Git tag
main.commit: Current git commit SHA
main.date: Date according RFC3339

---

If you want to see this in action: https://github.com/hoto/fuzzy-repo-finder/blob/master/pkg/config/config.go

The Go linker (go tool link) has an option to set the value of an uninitialised string variable:

-X importpath.name=value
  Set the value of the string variable in importpath named name to

value. Note that before Go 1.5 this option took two separate arguments. Now it takes one argument split on the first = sign.

As part of your build process, you could set a version string variable using this. You can pass this through the go tool using -ldflags. For example, given the following source file:

package main

import "fmt"

var xyz string

func main() {
    fmt.Println(xyz)
}

Then:

$ go run -ldflags "-X main.xyz=abc" main.go
abc

In order to set main.minversion to the build date and time when building:

go build -ldflags "-X main.minversion=`date -u +.%Y%m%d.%H%M%S`" service.go

If you compile without initializing main.minversion in this way, it will contain the empty string.