Usage of -ldflags:

go build -ldflags "-X main.varName=from_build" -o mycli

Inside your code:

var varName string

func main() {
  fmt.Println(varName) // prints "from_build"
}

Here's what I'm using for StaticBackend -v flag:

go build -ldflags \ 
"-X github.com/staticbackendhq/core/config.BuildTime=$(shell date +'%Y-%m-%d.%H:%M:%S') \
-X github.com/staticbackendhq/core/config.CommitHash=$(shell git log --pretty=format:'%h' -n 1) \
-X github.com/staticbackendhq/core/config.Version=$(shell git describe --tags)" \
-o staticbackend

Links:

• StaticBackend website
• StaticBackend GitHub repo
• Build SaaS apps in Go (my online course and book)