强制对管道中的 stdout 进行行缓冲 [英] Force line-buffering of stdout in a pipeline

问题描述

通常，stdout 是行缓冲的.换句话说，只要您的 printf 参数以换行符结尾，您就可以期望立即打印该行.使用管道重定向到 tee 时，这似乎不成立.

Usually, stdout is line-buffered. In other words, as long as your printf argument ends with a newline, you can expect the line to be printed instantly. This does not appear to hold when using a pipe to redirect to tee.

我有一个 C++ 程序，a，它输出字符串，总是 \n 终止，到 stdout.

I have a C++ program, a, that outputs strings, always \n-terminated, to stdout.

当它自己运行时 (./a)，一切都会如预期的那样在正确的时间正确打印.但是，如果我将它通过管道传输到 tee (./a | tee output.txt)，它在退出之前不会打印任何内容，这违背了使用 <代码>三通.

When it is run by itself (./a), everything prints correctly and at the right time, as expected. However, if I pipe it to tee (./a | tee output.txt), it doesn't print anything until it quits, which defeats the purpose of using tee.

我知道我可以通过在 C++ 程序中的每个打印操作之后添加一个 fflush(stdout) 来修复它.但是有没有更干净、更简单的方法呢?例如，是否有我可以运行的命令，即使在使用管道时，它也会强制 stdout 进行行缓冲?

I know that I could fix it by adding a fflush(stdout) after each printing operation in the C++ program. But is there a cleaner, easier way? Is there a command I can run, for example, that would force stdout to be line-buffered, even when using a pipe?

推荐答案

试试 unbuffer 是 expect 包的一部分.您的系统中可能已经有了它.

Try unbuffer which is part of the expect package. You may already have it on your system.

在你的情况下，你会像这样使用它:

In your case you would use it like this:

<代码>./a |unbuffer -p tee output.txt

(-p 用于管道模式，其中 unbuffer 从 stdin 读取并将其传递给其余参数中的命令)

(-p is for pipeline mode where unbuffer reads from stdin and passes it to the command in the rest of the arguments)

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