Help needed - os.exec

[R Srinivasan]

I cannot figure the error in the following.

package main

import (

"io"

"os"

"os/exec"

"strings"

)

func Run(args []string) {

lf, _ := os.Create("lf.log")

defer lf.Close()

cmd := exec.Command(args[0], strings.Join(args[1:], " "))

stderr, _ := cmd.StderrPipe()

cmd.Start()

io.Copy(lf, stderr)

cmd.Wait()

}

func main() {

args := []string{"go", "build", "./"}

Run(args)

}

I can execute go build ./ and get an executable. However when I run it I get the following in the logfile:

cat lf.log go build ./: unknown command Run 'go help build' for usage.

I exected that the "exec" will just execute go build ./

I did rename the exe to something else before running it.

Anyone can spot the error?

Thanks, srini

PS - I am not sure if it matters but I am on a Mac and use go version go1.13.6 darwin/amd64

[burak serdar]

On Sun, Apr 5, 2020 at 4:36 PM R Srinivasan <s...@srin.me> wrote:
>
> I cannot figure the error in the following.

> cmd := exec.Command(args[0], strings.Join(args[1:], " "))

Do not join the args. You're passing one arg, "build ./", instead of
two args "build" "./" to exec. Instead:

cmd := exec.Command(args[0], args[1:]...)

> stderr, _ := cmd.StderrPipe()
> cmd.Start()
> io.Copy(lf, stderr)
> cmd.Wait()
> }
>
> func main() {
> args := []string{"go", "build", "./"}
> Run(args)
> }
>
> I can execute go build ./ and get an executable. However when I run it I get the following in the logfile:
>
> cat lf.log go build ./: unknown command Run 'go help build' for usage.
>
> I exected that the "exec" will just execute go build ./
>
> I did rename the exe to something else before running it.
>
> Anyone can spot the error?
>
> Thanks, srini
>
> PS - I am not sure if it matters but I am on a Mac and use go version go1.13.6 darwin/amd64
>

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[Ian Lance Taylor]

Besides other comments, always check your error returns. Do that
before you ask for help on any program. Thanks.

Ian