谢谢你的评论。我自己想出来的。

package main
import (
    "bufio"
    "fmt"
    "io"
    "os/exec"
    "time"
)
func main() {
    ch := make(chan []byte)
    cmd := exec.Command("/path/to/executable")
    stdoutReader, stdoutWriter := io.Pipe()
    cmd.Stdout = stdoutWriter
    if err := cmd.Start(); err != nil {
        return
    }
    in := bufio.NewReader(stdoutReader)
    go func() {
        b, _, _ := in.ReadLine()
        ch <- b
    }()
    complete := false
    for !complete {
        select {
        case s := <-ch:
            fmt.Println(string(s))
            complete = true
        case <-time.After(time.Second * 5):
            fmt.Println("timeout")
            complete = true
        }
    }
}