How to Retrieve Realtime Output from Shell Commands in Go?

Retrieve Realtime Output from Shell Commands in Go

Problem:

You want to execute shell commands in Go that may take time and retrieve their real-time output to process and display as progress information.

Solution:

1. Use os/exec for Shell Command Execution:

Create a Command using exec.Command to execute the desired shell command.

2. Capture Standard Error (stderr) Output:

By default, diagnostic messages from shell commands are sent to stderr instead of stdout. Use cmd.StderrPipe() to capture the stderr stream.

3. Create a Scanner to Read Output:

Use bufio.NewScanner to create a scanner that reads the stderr stream. Split the scan into words using bufio.ScanWords to obtain individual output lines.

4. Process and Display Output:

Inside a loop, use the scanner.Scan() method to retrieve each output line. Process it to extract the desired information, such as the progress ratio. Then, display the processed output.

5. Example Code:

Here's an example code that demonstrates how to do this:

package main

import (
    "bufio"
    "fmt"
    "os/exec"
    "strings"
)

func main() {
    args := "-i test.mp4 -acodec copy -vcodec copy -f flv rtmp://aaa/bbb"
    cmd := exec.Command("ffmpeg", strings.Split(args, " ")...)

    stderr, _ := cmd.StderrPipe()
    cmd.Start()

    scanner := bufio.NewScanner(stderr)
    scanner.Split(bufio.ScanWords)
    for scanner.Scan() {
        m := scanner.Text()
        fmt.Println(m)
    }
    cmd.Wait()
}

By following these steps, you can retrieve the real-time output from shell commands and process it to display progress information or any other desired information.

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