1 files changed, 85 insertions, 0 deletions
diff --git a/_examples/checkout-branch/main.go b/_examples/checkout-branch/main.go
new file mode 100644
index 0000000..c7e1333
--- /dev/null
+++ b/_examples/checkout-branch/main.go
@@ -0,0 +1,85 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/go-git/go-git/v5"
+	. "github.com/go-git/go-git/v5/_examples"
+	"github.com/go-git/go-git/v5/config"
+	"github.com/go-git/go-git/v5/plumbing"
+)
+
+// Checkout a branch
+func main() {
+	CheckArgs("<url>", "<directory>", "<branch>")
+	url, directory, branch := os.Args[1], os.Args[2], os.Args[3]
+
+	// Clone the given repository to the given directory
+	Info("git clone %s %s", url, directory)
+	r, err := git.PlainClone(directory, false, &git.CloneOptions{
+		URL: url,
+	})
+	CheckIfError(err)
+
+	// ... retrieving the commit being pointed by HEAD
+	Info("git show-ref --head HEAD")
+	ref, err := r.Head()
+	CheckIfError(err)
+
+	fmt.Println(ref.Hash())
+
+	w, err := r.Worktree()
+	CheckIfError(err)
+
+	// ... checking out branch
+	Info("git checkout %s", branch)
+
+	branchRefName := fmt.Sprintf("refs/heads/%s", branch)
+	branchCoOpts := git.CheckoutOptions{
+		Branch: plumbing.ReferenceName(branchRefName),
+		Force:  true,
+	}
+	if err := w.Checkout(&branchCoOpts); err != nil {
+		Warning("local checkout of branch '%s' failed, will attempt to fetch remote branch of same name.", branch)
+		Warning("like `git checkout <branch>` defaulting to `git checkout -b <branch> --track <remote>/<branch>`")
+
+		mirrorRemoteBranchRefSpec := fmt.Sprintf("refs/heads/%s:refs/heads/%s", branch, branch)
+		err = fetchOrigin(r, mirrorRemoteBranchRefSpec)
+		CheckIfError(err)
+
+		err = w.Checkout(&branchCoOpts)
+		CheckIfError(err)
+	}
+	CheckIfError(err)
+
+	Info("checked out branch: %s", branch)
+
+	// ... retrieving the commit being pointed by HEAD (branch now)
+	Info("git show-ref --head HEAD")
+	ref, err = r.Head()
+	CheckIfError(err)
+	fmt.Println(ref.Hash())
+}
+
+func fetchOrigin(repo *git.Repository, refSpecStr string) error {
+	remote, err := repo.Remote("origin")
+	CheckIfError(err)
+
+	var refSpecs []config.RefSpec
+	if refSpecStr != "" {
+		refSpecs = []config.RefSpec{config.RefSpec(refSpecStr)}
+	}
+
+	if err = remote.Fetch(&git.FetchOptions{
+		RefSpecs: refSpecs,
+	}); err != nil {
+		if err == git.NoErrAlreadyUpToDate {
+			fmt.Print("refs already up to date")
+		} else {
+			return fmt.Errorf("fetch origin failed: %v", err)
+		}
+	}
+
+	return nil
+}