如何自定义处理Golang Cmd的日志输出

Golang 版本：1.22.2

为了更好的处理 Golang Cmd 的日志输出，我们可以先查看exce.Cmd 结构体的定义。在代码中可以 Stdout io.Writer 和 Stderr io.Writer 两个字段，一个进程的标准输出和标准错误输出可以通过这两个字段来指定。 简而言之我们只需要实现一个 io.Writer 接口的结构体，然后将这个结构体赋值给 Cmd 结构体的 Stdout 和 Stderr 字段即可。

type Cmd struct {
    // Path is the path of the command to run.
    //
    // This is the only field that must be set to a non-zero
    // value. If Path is relative, it is evaluated relative
    // to Dir.
    Path string

    // Args holds command line arguments, including the command as Args[0].
    // If the Args field is empty or nil, Run uses {Path}.
    //
    // In typical use, both Path and Args are set by calling Command.
    Args []string

    ......

    // Stdout and Stderr specify the process's standard output and error.
    //
    // If either is nil, Run connects the corresponding file descriptor
    // to the null device (os.DevNull).
    //
    // If either is an *os.File, the corresponding output from the process
    // is connected directly to that file.
    //
    // Otherwise, during the execution of the command a separate goroutine
    // reads from the process over a pipe and delivers that data to the
    // corresponding Writer. In this case, Wait does not complete until the
    // goroutine reaches EOF or encounters an error or a nonzero WaitDelay
    // expires.
    //
    // If Stdout and Stderr are the same writer, and have a type that can
    // be compared with ==, at most one goroutine at a time will call Write.
    Stdout io.Writer
    Stderr io.Writer

    .....
}

下面是一个简单的实现，将 Cmd 的标准输出和标准错误输出写入到文件中。

type LogWriter struct {
    file       *os.File
}

func NewLogWriter(filename string) (*LogWriter, error) {
    // 打开文件，如果文件不存在则创建
    file, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
    if err != nil {
        return nil, err
    }

    return &LogWriter{
        file:       file,
    }, nil
}

func (lw *LogWriter) Write(p []byte) (n int, err error) {
    message := string(p)
    go func() {
        // 这里可以对日志进行处理，比如sse推送等
    }()
    // 将日志写入到文件中
    if _, err := lw.file.Write(p); err != nil {
        return 0, err
    }

    return len(p), nil
}
// 关闭日志文件
func (lw *LogWriter) Close() error {
    return lw.file.Close()
}

然后在启动cmd的时候将这个结构体赋值给 Cmd 结构体的 Stdout 和 Stderr 字段即可。例如：

// 创建一个日志文件
logWriter, e := NewLogWriter("log.txt")
if e != nil {
    log.Log.Errorf("StartTask wirte log error:%s", e.Error())
}

ctx, _ := context.WithCancel(context.Background())
cmd := exec.CommandContext(ctx, "sh", "run.sh")
cmd.Stdout = logWriter
cmd.Stderr = logWriter
cmd.Start()

启动完成后查看log.txt文件是否自动创建并且驶入写入了日志信息。