README.md

Golang Binary Versioning Trick

To use, adapt the code in main.go for use in your project.

In addition to main.go, there's an example Makefile that includes the secret sauce for making this trick work. If you're already using package main for everything, the code should work as-is, but you'll have to adapt it for more complex (read: sane) code layouts.

Enjoy!

P.S. Special thanks to @meatballhat by way of @syscomet for showing me this trick!

main.go

package main

import (
	"flag"
	"fmt"
	"os"
	"path"
)

var (
	// VersionString is the variable set via -ldflags that contains the
	// string produced by `git describe`
	VersionString string
	// RevString is the variable set via -ldflags that contains the
	// current git revision
	RevString   string
	versionFlag = false
	revFlag     = false
)

func init() {
	flag.BoolVar(&versionFlag, "version", false, "Print version and exit")
	flag.BoolVar(&revFlag, "rev", false, "Print git revision and exit")
}

func main() {
	flag.Parse()

	if versionFlag {
		progName := path.Base(os.Args[0])
		if VersionString == "" {
			VersionString = "<unknown>"
		}
		fmt.Printf("%s %s\n", progName, VersionString)
		os.Exit(0)
	}

	if revFlag {
		if RevString == "" {
			RevString = "<unknown>"
		}
		fmt.Println(RevString)
		os.Exit(0)
	}
}

Makefile

REV_VAR := main.RevString
VERSION_VAR := main.VersionString
REPO_VERSION := $(shell git describe --always --dirty --tags)
REPO_REV := $(shell git rev-parse --sq HEAD)
GOBUILD_VERSION_ARGS := -ldflags "-X $(REV_VAR) $(REPO_REV) -X $(VERSION_VAR) $(REPO_VERSION)"

build:
	go build -x $(GOBUILD_VERSION_ARGS) -o version-trick .

Have you been able to get main.VersionString to work in a namespaced project (i.e. github.com/modcloth-labs/mithril/main.VersionString)? If so, what's the magical incantation?