How to Stream Command Output in Real-time Instead of Waiting for Execution Completion?

Running a Command and Streaming Its Output

Problem: Delayed Output Display

Currently, your code processes a command and only displays its output once the execution is complete. You seek a solution to stream the output live instead of waiting for the process to finish.

Solution: Command Output Streaming

Employ the following approach to stream command output:

cmdParams := [][]string{
    {filepath.Join(dir, path), "npm", "install"},
    {filepath.Join(pdir, n.path), "gulp"},
}
for _, cp := range cmdParams {
    log.Printf("Starting %s in folder %s...", cp[1:], cp[0])
    cmd := exec.Command(cp[1], cp[2:]...)
    cmd.Dir = cp[0]

    stdout, err := cmd.StdoutPipe()
    if err != nil {
        log.Printf("%s cmd.StdoutPipe() error: %v\n", cp[1:], err)
        return
    }
    // Start command:
    if err = cmd.Start(); err != nil {
        log.Printf("%s start error: %v\n", cp[1:], err)
        return
    }

    // Stream command output:
    scanner := bufio.NewScanner(stdout)
    scanner.Split(bufio.ScanRunes)
    for scanner.Scan() {
        fmt.Print(scanner.Text())
    }
    if scanner.Err() != nil {
        log.Printf("Reading %s stdout error: %v\n", cp[1:], err)
        return
    }

    // Get execution success or failure:
    if err = cmd.Wait(); err != nil {
        log.Printf("Error running %s: %v\n", cp[1:], err)
        return
    }
    log.Printf("Finished %s", cp[1:])
}

Explanation

• cmd.StdoutPipe() creates a pipe that will supply any output written by the command.
• scanner := bufio.NewScanner(stdout) initializes a scanner that will read the output from the pipe.
• scanner.Split(bufio.ScanRunes) ensures that scanner reads and processes each character (rune) of the output.
• The for loop continuously reads characters from the stdout pipe and prints them to the screen.
• After the command execution finishes, cmd.Wait() checks its success or failure and logs the result.

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