Add foreach command to run a shell command in each dependency's directory

foreach.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+)
+
+var cmdForeach = &Command{
+	Name:  "foreach",
+	Short: "run a command in each dependency's path",
+	Long: `
+Foreach runs the provided command for each dependency path in GOPATH. This can
+be useful for checking out the master branch after running "godep restore" to
+avoid breaking "go get -u".
+
+`,
+	Run:          runForeach,
+	OnlyInGOPATH: true,
+}
+
+func runForeach(cmd *Command, args []string) {
+	g, err := loadDefaultGodepsFile()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	if args == nil || len(args) < 1 {
+		log.Fatalln("Must provide a command to foreach")
+	}
+
+	for _, dep := range g.Deps {
+		c := exec.Command(args[0], args[1:]...)
+		c.Dir = getRoot(dep.root, dep.ImportPath)
+
+		fmt.Fprintf(os.Stderr, "\n%s:\n", dep.ImportPath)
+		out, err := c.StdoutPipe()
+		if err != nil {
+			log.Fatalln(err)
+		}
+
+		serr, err := c.StderrPipe()
+		if err != nil {
+			log.Fatalln(err)
+		}
+
+		go io.Copy(os.Stdout, out)
+		go io.Copy(os.Stderr, serr)
+
+		err = c.Run()
+		if err != nil {
+			log.Fatalln(err)
+		}
+	}
+}

main.go

@@ -65,6 +65,7 @@ var commands = []*Command{
 	cmdGet,
 	cmdPath,
 	cmdRestore,
+	cmdForeach,
 	cmdUpdate,
 	cmdDiff,
 	cmdVersion,

restore.go

@@ -25,6 +25,13 @@ https://github.com/golang/go/commit/42206598671a44111c8f726ad33dc7b265bdf669.
 	OnlyInGOPATH: true,
 }
 
+func getRoot(root, path string) string {
+	if root == "" {
+		return filepath.Join(filepath.SplitList(build.Default.GOPATH)[0], "src", path)
+	}
+	return root
+}
+
 // Three phases:
 // 1. Download all deps
 // 2. Restore all deps (checkout the recorded rev)
@@ -104,15 +111,12 @@ func download(dep *Dependency) error {
 			continue
 		}
 		if fi.IsDir() {
-			dep.root = t
+			// If none found, just pick the first GOPATH entry (AFAICT that's what go get does)
+			dep.root = getRoot(t, rr.Root)
 			break
 		}
 	}
 
-	// If none found, just pick the first GOPATH entry (AFAICT that's what go get does)
-	if dep.root == "" {
-		dep.root = filepath.Join(filepath.SplitList(build.Default.GOPATH)[0], "src", rr.Root)
-	}
 	ppln("dep", dep)
 
 	if downloaded[rr.Repo] {