Adding Version Info to Your Go App at Build Time

Intro #

Want app to show its version? Here's how.

Git tags are like labels for code versions. ldflags are special instructions for Go builder.

I like git tags as a single source of version the app. Based on them I run builds and releases. To add same version to Go app in automated way we can use ldflags.

Add one variable on build time #

Create file main.go with content

package main
import "fmt"

var version = "dev"

func main() {
    fmt.Println("Version:\t", version)
}

To your build script add -ldflags where main.version is package and var from code above.

go build -ldflags "-X main.version=$(git describe --abbrev=0 --tags)"

Add multiple variables on build time #

Adding multiple variables on build time is as simple as follow.

Edit main.go and add buildTime variable

package main
import "fmt"

var (
    version = "dev"
    buildTime = "devTime"
)

func main() {
    fmt.Println("Version:\t", version)
    fmt.Println("Build time:\t", buildTime)
}

Edit -ldfalgs by adding another -X block

go build -ldflags "-X main.version=$(git describe --abbrev=0 --tags) -X main.buildTime=$(date)"

Encapsulate variables in different package than main #

If you want to import those variables to different package than main it's good practice to encapsulate it in different package.
Let's keep them in package build in separate directory.

Create directory build and file build/build.go

mkdir build
touch build/build.go
vim build/build.go

package build

var (
	// These variables are replaced by ldflags at build time
	GitVersion = "v0.0.0-main"
	GitCommit  = ""
	BuildTime  = "1970-01-01T00:00:00Z" // build date in ISO8601 format
)

And we can print in in main.go as an example

package main

import (
	"fmt"

	"github.com/me/my-app/build"
)

func main() {
	fmt.Println("GitCommit:\t", build.GitCommit)
}

This time you need to know your module name. It's in first line of go.mod file

$> head -1 go.mod
module github.com/me/my-app

Finally we can compose command where github.com/me/my-app is our main module, github.com/me/my-app/build is full path to build package and GitCommit is variable dynamically linked on build time

go build -ldflags="-X 'github.com/me/my-app/build.GitCommit=$(shell git rev-parse --short=7 HEAD)'" -o=/tmp/bin/my-app .

Conclusion #

Adding version to your app is useful for 'About' page, startup info or --version command line flag. It's like putting a sticker on a product after it's made. This info is essential for debugging app that is already on production. Now users always know which version they're using!

Published 05 Oct 2024