diff --git a/content/posts/build-time-vars-golang.md b/content/posts/build-time-vars-golang.md new file mode 100644 index 0000000..f28420c --- /dev/null +++ b/content/posts/build-time-vars-golang.md @@ -0,0 +1,53 @@ +--- +title: "Set Variables at Build Time in Golang" +date: 2020-01-05T21:00:00Z +tags: [golang, programming] +draft: false +--- + +For some CLI tools I use regularly I noticed that when I run the `version` flag get some version info that includes a +git commit hash or a git tag to the command line: + +```shell +> kubectl version +Client Version: version.Info{Major:"1", Minor:"16", GitVersion:"v1.16.3", GitCommit:"b3cbbae08ec52a7fc73d334838e18d17e8512749", GitTreeState:"clean", BuildDate:"2019-11-13T11:23:11Z", GoVersion:"go1.12.12", Compiler:"gc", Platform:"linux/amd64"} +Server Version: version.Info{Major:"1", Minor:"16", GitVersion:"v1.16.2", GitCommit:"c97fe5036ef3df2967d086711e6c0c405941e14b", GitTreeState:"clean", BuildDate:"2019-10-15T19:09:08Z", GoVersion:"go1.12.10", Compiler:"gc", Platform:"linux/amd64"} +``` + +I discovered a nice way to do this for go programs. You can specify a value for a global variable at build time using +the `-ldflags "-X"` flag. + +For this program: + +```go +package main + +import "fmt" + +var Version = "dev" + +func main(){ + fmt.Printf("I'm version <%s>", Version) +} +``` +You can use this one liner that builds your go program while setting the *Version* variable to the *sha* hash of the latest +commit. + +```shell +> go build -ldflags "-X main.Version=$(git rev-parse HEAD)" -o hello_app main.go +> hello_app +I'm version ba83f7c418c669f705a3cce0c58a1f9129a3de14 +``` + +Note that you have to specify the full path of the package in your project, for example: + +```bash +# You project looks like +# - main.go <- module `github.com/myrepo/test` +# - version <- `github.com/myrepo/test/version` +# - sha.go <- has `var Version = "dev"` +> go build -ldflags "-X github.com/myrepo/test/version.Version=$(git rev-parse HEAD)" -o hello_app main.go +> hello_app +I'm version ba83f7c418c669f705a3cce0c58a1f9129a3de14 +``` +