How to Redirect Command Output to a Log in Real-Time in Golang?

Redirecting Command Output to Log in Golang

When executing a command using the exec.Command function, it is often desirable to redirect the output to a log for real-time monitoring. While CombinedOutput can capture the entire output once the command finishes, it is not suitable for long-running or unfinished processes.

A common solution for real-time output redirection is to directly assign stdout and stderr to system output streams (os.Stdout and os.Stderr). However, this may not be practical for applications that do not write to a terminal.

Solution Using Pipes

To redirect command output to a log, you can utilize pipes. Here is an example:

stdout, err := cmd.StdoutPipe()
if err != nil {
    return nil, err
}

// Start the command with the pipe in place
if err := cmd.Start(); err != nil {
    return nil, err
}

// Real-time monitoring of stdout
in := bufio.NewScanner(stdout)

for in.Scan() {
    log.Printf(in.Text()) // Write line to log or perform other operations
}
if err := in.Err(); err != nil {
    log.Printf("Error: %s", err)
}

Considerations

This method handles stdout, but you can also manage stderr by creating a separate pipe and goroutine. Additionally, you may need to handle context cancellation or other edge cases to ensure proper cleanup and resource management.

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