同时扫描stdout和stderr

Question

I'm looking for a way to process both stdout and stderr simultaneously as one stream. For a stdout I can use:

cmd := exec.Command(command, flags...)
var wg sync.WaitGroup

stdout, err := cmd.StdoutPipe()
if err != nil {
    return fmt.Errorf("RunCommand: cmd.StdoutPipe(): %v", err)
}

if err := cmd.Start(); err != nil {
    return fmt.Errorf("RunCommand: cmd.Start(): %v", err)
}

scanner := bufio.NewScanner(stdout)
scanner.Split(ScanLinesR)
wg.Add(1)
go func() {
    for scanner.Scan() {
        text := scanner.Text()
        if strings.TrimSpace(text) != "" {
            DoWhateverYouNeedWithText(text)
        }
    }
    wg.Done()
}()

wg.Wait()

But how I add stderr to the same code?

Answer 1

As above commentors suggested I added 2 more goroutines (one for stderr, one for closing channel).

var wg sync.WaitGroup

stdout, err := cmd.StdoutPipe()
if err != nil {
    return fmt.Errorf("RunCommand: cmd.StdoutPipe(): %v", err)
}
stderr, err := cmd.StderrPipe()
if err != nil {
    return fmt.Errorf("RunCommand: cmd.StderrPipe(): %v", err)
}

if err := cmd.Start(); err != nil {
    return fmt.Errorf("RunCommand: cmd.Start(): %v", err)
}

outch := make(chan string, 10)

scannerStdout := bufio.NewScanner(stdout)
scannerStdout.Split(ScanLinesR)
wg.Add(1)
go func() {
    for scannerStdout.Scan() {
        text := scannerStdout.Text()
        if strings.TrimSpace(text) != "" {
            outch <- text
        }
    }
    wg.Done()
}()
scannerStderr := bufio.NewScanner(stderr)
scannerStderr.Split(ScanLinesR)
wg.Add(1)
go func() {
    for scannerStderr.Scan() {
        text := scannerStderr.Text()
        if strings.TrimSpace(text) != "" {
            outch <- text
        }
    }
    wg.Done()
}()

go func() {
    wg.Wait()
    close(outch)
}()

for t := range outch {
    DoWhateverYouNeedWithText(t)
}