piping exec.Cmd in golang (example finds most recently modified file that is not directory or executable)

piping.go

package main
import (
    "os"
    "exec"
)

func pipe_commands(commands ...*exec.Cmd) ([]byte, os.Error) {
    for i, command := range commands[:len(commands) - 1] {
        out, err := command.StdoutPipe()
        if err != nil {
            return nil, err
        }
        command.Start()
        commands[i + 1].Stdin = out
    }
    final, err := commands[len(commands) - 1].Output()
    if err != nil {
        return nil, err
    }
    return final, nil
}

func main() {
    var dirs []string
    if len(os.Args) > 1 {
        dirs = os.Args[1:]
    } else {
        dirs = []string{"."}
    }
    for _, dir := range dirs {
        ls := exec.Command("ls", "-Ft", dir)
        grep_dir := exec.Command("grep", "-v", "/$")
        grep_exe := exec.Command("grep", "-v", "\\*$")
        head := exec.Command("head", "-n", "1")
        output, err := pipe_commands(ls, grep_dir, grep_exe, head)
        if err != nil {
            println(err.String())
        } else {
            print(string(output))
        }
    }
}

There is a problem, defunct process will be left before main process quit.

!!NOTICE, please use this code >> https://gist.github.com/kylelemons/1525278