流os / exec.Command

Question

I want to build a benchmarking tool similar to the unix tool time. What I currently have is this:

package main

import (
    "fmt"
    "os"
    "os/exec"
    "time"
)

func main() {
    command := os.Args[1]
    args := os.Args[2:]
    cmd := exec.Command(command, args...)
    start_time := time.Now().UnixNano()
    stdout, err := cmd.Output()

    if err != nil {
        println(err.Error())
        return
    }

    print(string(stdout))
    total_time := int64(time.Nanosecond) * (time.Now().UnixNano() - start_time) / int64(time.Millisecond)
    fmt.Println(total_time)
}

My problem with this is, that the output is not streaming, instead it is printed all at once, and weirdly enough for some programs not at all.

Answer 1

The best way is to avoid touching the stream altogether. You can pass your own file descriptors for stdout and stderr directly.

package main

import (
    "fmt"
    "os"
    "os/exec"
    "time"
)

func main() {
    command := os.Args[1]
    args := os.Args[2:]
    cmd := exec.Command(command, args...)
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    start_time := time.Now()

    err := cmd.Run()
    if err != nil {
        println(err.Error())
        return
    }

    total_time := int64(time.Since(start_time) / time.Millisecond)
    fmt.Println(total_time)
}

---

Also, print() should never be used. Instead, use one of the fmt.Print* functions.

---

total_time := int64(time.Nanosecond) * (time.Now().UnixNano() - start_time) / int64(time.Millisecond)

This line is extremely confusing. int64(time.Nanosecond) * x resolves to 1 * x or just x.